AudioCircle
Audio/Video Gear and Systems => Open Baffle Speakers => Topic started by: Browntrout on 11 Aug 2009, 05:30 pm
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Has anyone implimented multiple Lowther full range drivers in an open baffle array? Say four or five drivers per side. With the idea being to generate good bass without losing speed and a boomy cabinet. Very interested to hear the results if someone has been brave enough.
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I like fullranges and linearrays, and with OB capacity this speakers is perfect to me.
A problem: Lowthers are expensive drivers.
I think the definitive speaker is fullrange driver + linearray + OB + 16 ohms to be driven by a tube amp.
Regards.
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Super 8 Alnico - Audio Nirvana drivers would be cheaper and might be a better choice for DIY.
(2 super 12s AN per side might be even better)
My 2 cents
Mariusz :thumb:
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While the beaming of larger drivers should help avoid comb filtering, you're still going to have a large c2c distance if you do this....
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I've got a fair grip on the pulse of the Lowther guys out there and nobody that I'm aware of has tried that. I do know several people that are doing Lowthers on top and 15"s on an OB bottom. In fact, I've got in house a prototype active crossover (from a well know mfgr) who within the XO has switches to provide not only notch filtering for the (mostly) FR driver but also a bit of EQing and boost for the OB woofer. Its a very cool concept that works quite well. All of this is done with JFets rather than opamps and digital conversion.
As FRM mentioned, a line array of Lowthers, even the cheap ones, would be really freakin' expensive. I would seriously suggest if you are thinking of going that route, do like me and a few of the other local GAS guys are doing an invest in a PM6A, or better yet the PM2A (what I personally use) then do a vintage 15" (Altec 416 please) in a vented enclosure. Cross it at 150Hz (actively), SET on top, SS on the woofer. The sound quality is phenomenal and integration between the two drivers is seamless. Oh, and no notch, shelving or baffle step compensation is needed...at all.
Here are a few pics of my Lowther OB setup
(http://www.audiocircle.com/image.php?id=19782) (http://www.audiocircle.com/image.php?id=19784)
(http://www.audiocircle.com/image.php?id=19783)
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If you are going to try a relatively full range line, a 4" is probably as big as you want to go. 3-5 drivers should get you down to 150-200 Hz. or so. Right now I am using 7 drivers and getting down to 100Hz. (4th order crossover) with no problems. My line using 40 drivers is in construction. aa
Chris H.
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Scott, beautiful set up! Do you have problems with phase? If I'm seeing this correctly the woofers are a fair distance back from the OBs. Can you share any more info on the electronic cross over manufactur / model? Thanks!
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Hiya,
Thanks for the compliment :green:
When it comes to phase I had a couple of minor issues that were easily solved by placement of the open baffles. Basically I moved the speakers further out away from the walls until everything snapped into place and the crossover point hole (cancellation due to phase) was gone. Right now they are about 6' out from the wall. One thing that is so impressive about the sound is when you listen to full orchestral pieces that have been recorded with a simple pair of stereo mics, placement of the different sections of the orchestra is like no other speakers I've heard. They have tremendous depth, placement and a monstrous soundstage. Regarding the XO, I probably shouldn't talk too much about it since it isn't in production yet and may not be for a little while, sorry. When the design does become finalized, I'll be happy to get into all of the gory details :thumb:
Scott, beautiful set up! Do you have problems with phase? If I'm seeing this correctly the woofers are a fair distance back from the OBs. Can you share any more info on the electronic cross over manufactur / model? Thanks!
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Thanks for all the replies, Scott your setup is beautifull I especially like the see through baffles very in keeping with the sound I imagine. :thumb:
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There's a technical problem with an array of full range drivers. The CTC spacing would result in a very audible comb filter effect starting at a relatively low frequency. See Jim Griffin's line array white paper for an explanation of the effects of CTC driver separation. It' on page 11:
http://www.audioroundtable.com/misc/nflawp.pdf
For a graphical example of comb filtering see the unsmoothed graph of the Kuze 3201 full range driver line array. Even with 2" drivers having relatively close CTC spacing, the comb filter effect is clearly visible:
http://www.parts-express.com/projectshowcase/kuze3201/kuze3201weqnosmooth.jpg
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Very usefull indeed Fred, thanks. It would seem that the effect of having centre to centre distances that are greater than 2 Lambda coould be countered by focusing each driver at the point of listening.
Would this create sweet spot (altering the sound of a line array from wide spacious to concentrated and focused like a single driver) whilst retainind the increase in dynamics and lower end frequency capability? I could handle that.
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While the beaming of larger drivers should help avoid comb filtering, you're still going to have a large c2c distance if you do this....
I wouldn't think it would actually help much against comb filtering. The c-t-c is just too far away. I don't know the wavelengths off the top of my head but I don't think you can get away with much larger than 2" drivers without using a tweeter unless you want a roller coaster for the FR of top octave.
That is a lot of money in drivers to be dissapointed in the results. If you are sure you want to do it, try cheaper drivers first as proof of concept and save yourself a lot of money if it doesn't work out.
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Fred is right. The response would be a real mess.
The guys over on the AV123 forum were discussing stacking speakers on top of each other.
So I did that and showed the measured results so they would understand how sever the cancellation would be. The same thing applies to stacking multiple full range drivers.
See link: http://forums.av123.com/showthread.php?t=15154&highlight=cancellation&page=2
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Hello Browntrout,
I have built open baffle line arrays using eight Visaton B200 full range drive units per line. These are nominally eight inch drive units and so this would be a theoretical no-no regarding comb effects. However, in practice they sound great and I am not finding any audible problems with combing effects at a listening distance of around twelve feet although you may find problems if your listening position is very close to the speakers.
I decided to go for it with the B200 because I recalled using 10? and 12? drive units, in line arrays, as vocal PA speakers, when playing in a band as a youngster in the 60?s and 70?s. I cannot remember suffering any audible combing effects from these line arrays. I do remember they were excellent as PA speakers and that they were very articulate and coherent with voice.
Out of interest, I wired my drive units in such a way that I could program series parallel/wiring or parallel wiring of the drive units, using 4mm plugs and sockets. It is very audibly obvious that wiring any drive units in series/parallel causes drive unit interaction that diffuses the image and makes it dynamically unstable. This problem does not occur if you wire the drive units in parallel as each drive unit sees the same drive signal from the amplifier. The whole line then behaves as one drive unit electrically. The image is very stable under all dynamic conditions. It does, however, present an awkward load to the amplifier, so I designed a power amplifier specifically to work into these low impedances. It may be that some of the audible problems attributed to combing effects are caused by series/parallel wiring of the drive units as line arrays tend to be wired in series/parallel to give an impedance that standard amplifiers can drive.
Regards
Paul
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One solution that will get you a single driver continuous 6' line down to 300hz (150Hz. if you don't listen at high volume) is the BG planar. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-700 (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-700)
Chris H.
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Hello Browntrout,
I have built open baffle line arrays using eight Visaton B200 full range drive units per line. These are nominally eight inch drive units and so this would be a theoretical no-no regarding comb effects. However, in practice they sound great and I am not finding any audible problems with combing effects at a listening distance of around twelve feet although you may find problems if your listening position is very close to the speakers.
I decided to go for it with the B200 because I recalled using 10? and 12? drive units, in line arrays, as vocal PA speakers, when playing in a band as a youngster in the 60?s and 70?s. I cannot remember suffering any audible combing effects from these line arrays. I do remember they were excellent as PA speakers and that they were very articulate and coherent with voice.
Out of interest, I wired my drive units in such a way that I could program series parallel/wiring or parallel wiring of the drive units, using 4mm plugs and sockets. It is very audibly obvious that wiring any drive units in series/parallel causes drive unit interaction that diffuses the image and makes it dynamically unstable. This problem does not occur if you wire the drive units in parallel as each drive unit sees the same drive signal from the amplifier. The whole line then behaves as one drive unit electrically. The image is very stable under all dynamic conditions. It does, however, present an awkward load to the amplifier, so I designed a power amplifier specifically to work into these low impedances. It may be that some of the audible problems attributed to combing effects are caused by series/parallel wiring of the drive units as line arrays tend to be wired in series/parallel to give an impedance that standard amplifiers can drive.
Regards
Paul
I agree with Paul Hynes above. This comb filter effect seems exist only very close to the speakers,
I built a LA of four 10 inches fullranges, sealed box and there was no problem, even close the speaker, the space between the Aluminium round frames is 45mm.
This IDS25 picture of Engineer Roger Russel use 25 cheap 4inches fullranges per sealed box and the sound is very beautiful according the reviews.
www.ids25.com (http://www.ids25.com)
Regards.
(http://www.audiocircle.com/image.php?id=21190)
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I am afraid that you (fullrangeman) and Paul are getting cancellation effects that will result in +/-15db swings (or more) from any measuring (or listening point). Keep in mind that the wave lengths in the top octave are only 1 to 2 inches long so a time delay of only 1 or 2 inches is all that it will take to create a good 15db hole in the response.
Also due to the length of those lines you guys will get comb filtering effects well down into the ranges of 2 and 3kHz.
And BTW, I heard a speaker like the one pictured below a few years ago at RMAF.
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And BTW, I heard a speaker like the one pictured below a few years ago at RMAF.
Do you listen this same IDS25 at RMAF?
What are your opinion about this LineArray do you listen?
Regards.
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I am afraid that you (fullrangeman) and Paul are getting cancellation effects that will result in +/-15db swings (or more) from any measuring (or listening point). Keep in mind that the wave lengths in the top octave are only 1 to 2 inches long so a time delay of only 1 or 2 inches is all that it will take to create a good 15db hole in the response.
I think it's worth clarifying, though, that the measurements you linked were for two drivers (in the same freq range), not an array of them.
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You are correct John.
The two speakers I measured were stacked tweeter to tweeter and the center to center distance of the tweeters was about 7".
For an array of drivers, like the one pictured, the center to center spacing is much greater and the cancellation is much worse, and much lower in the range that it cancels.
What are your opinion about this LineArray do you listen?
Do you really want to know?
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Do you really want to know?
Yes I do, cause I have no chance to listen a LA like this. And this IDS25 is very well quoted in the manufacturer Site.
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When I went into the room to see these I was the only one in there (besides the guy running the room). So I handed him a familiar disc and gave them a listen.
Having no crossover they had no baffle step compensation. So from about 1000Hz and down they got a little lean. To compensate for the lack of bass the speakers were pushed right up to the wall.
They were positioned on the long wall and the rooms are 13 feet wide so I was about 10 to 11 feet away from the front of the speakers.
I also quickly noted that the top end was not there. I'd say everything from about 3kHz and up was really rolled off. All the air and space that went along with the piano that I was listening to was gone. Imaging was 2D and sound like it was all playing from the wall forward.
They remind me of the old saying about Bose. No highs, no lows.
To make matters worse, not only did they sound badly but they were very expensive.
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Thankyou, as I live in Brazil any first hand info about a big LA is valuable to me.
Regards, Gustavo
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Thanks very much indeed for your advice Paul Hynes. :wink:
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Hello Danny,
I appreciate your concerns regarding measured comb effects when using drive units in an uncompensated vertical drive unit array and understand that your comments are based on your experiences as a loudspeaker designer and from personal experience with line design.
I can actually hear the comb effect close up to the B200 array, but the further away I listen, the less obvious it becomes and, at my usual listening position at around twelve feet away, it is not obvious at all. In fact, at the listening position, the musical program is very coherent and I value this parameter above all else.
In my opinion, more damage is done to the musical coherence, and the image dimension and stability, by wiring line drivers in series parallel. This essentially places a highly reactive element in series with each drive unit. The waveform corruption caused by this is not trivial and affects time as well as space.
Hello Browntrout,
My line source was not designed for commercial reasons. I was involved with loudspeaker design a lot in the 1980s and 1990s so have a general understanding of the main principals involved, although I would not consider myself an expert in this field. Measurement systems were pretty basic in those days and we did not have access to the test equipment available today, so we relied a lot on our ears and I still do this. Test equipment and simulation systems are useful tools but the final arbiter is how does it sound. I did learn that some parameters are important and some are not. Sometimes you can go against theory and get a good result if that parameter is not important.
Regards
Paul
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When I went into the room to see these I was the only one in there (besides the guy running the room). So I handed him a familiar disc and gave them a listen.
Having no crossover they had no baffle step compensation. So from about 1000Hz and down they got a little lean. To compensate for the lack of bass the speakers were pushed right up to the wall.
They were positioned on the long wall and the rooms are 13 feet wide so I was about 10 to 11 feet away from the front of the speakers.
I also quickly noted that the top end was not there. I'd say everything from about 3kHz and up was really rolled off. All the air and space that went along with the piano that I was listening to was gone. Imaging was 2D and sound like it was all playing from the wall forward.
They remind me of the old saying about Bose. No highs, no lows.
To make matters worse, not only did they sound badly but they were very expensive.
+1
I couldn't believe they were actually letting people in the room to listen to the things. :duh:
Lin
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Has anyone implimented multiple Lowther full range drivers in an open baffle array? Say four or five drivers per side. With the idea being to generate good bass without losing speed and a boomy cabinet. Very interested to hear the results if someone has been brave enough.
Using a single fr driver with multiple ob bass only drivers will accomplish this quite well.
Lin
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I can actually hear the comb effect close up to the B200 array, but the further away I listen, the less obvious it becomes and, at my usual listening position at around twelve feet away, it is not obvious at all.
It should be very apparent as the peaks and dips will be very sever even twelve feet away.
For instance, let's say that you draw a line from your ear level to the center of the array and get 12' exactly. Then from your ear level to the top of the array you get 12' and 5".
The differential is 5".
A 5" wavelength is about 2.6kHz.
So you will have cancellation down to 2.6kHz and the effect will be seen (with a dip at that fundamental) carrying over in each direction covering that full octave.
The dip will be in the 15db range.
Likewise where they actually couple and are in phase then there will be at least a 6db peak.
And that is from 12 feet away.
Looking at the response of a single B200, it looks like it would be hard to listen to a single unit.
(http://www.visaton.com/bilder/frequenz/gross/b200_6_fs.gif)
From only 100Hz to 8kHz it rises 15db. Wow, talk about your hot top ends. Then from there to 20kHz it drops 20db. Boy do those drivers need a corrective filter.
At lease running a group of them will elevate the bottom end (where they all couple) enough to even it out with the top end. At least it would be close if you averaged out the peaks and dips.
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Danny and anyone else interested in open baffle line arrays,
I am not disputing that there is a comb effect, but stating that from my listening position, with the B200 line, it is not obvious.
Danny, your mathematical analysis is incomplete as it only considers two vertical points on the line so the cancellation at 2.6 KHz will not be in the 15 db range. Assuming one were to sit with ones ears level with the dead centre on the line, the output at the centre would display cancellation effects with the top and bottom drive units at, for example, your stated 2.6 KHz. This would leave a dip at 2.6 KHz as you say. However that would leave the equivalent of five drive units outputting their normal level at this frequency as no other pairs of drive units suffers the 5 inch distance discrepancy between the drive unit position and the listening position. The net drop in overall line array output level at 2.6 KHz would be around 6 db. As I do not listen with my ears aligned with the dead centre of the array this is actually still not representative of real life in my listening position.
I had heavy-duty brass spikes turned to fit the aluminium frame of the line array to provide three-point rigid coupling to the floor and these together with the seating height in the listening position place my ears slightly above centre of the third drive unit from the bottom of the array. Now only two points on the array show the 5 inch discrepancy instead of the three points if I were to raise my ears to dead centre of the array. Now the output from six of the drive units are giving full output at 2.6 KHz and the output level drop, from the whole line, at this frequency, will be closer to 3 db. This picture is repeated with different pairs of drive units showing different alignment distances, and therefore different frequencies, all along the line. The net effect is a level variation of around +/- 3 db at any given frequency, due to comb effects, along the line.
Regarding the B200, I think you are underestimating the performance based on what you see from the published response curve, which I suspect was recorded using a brand new drive unit. Before I bought drive units for the full line arrays, I tested a pair on open baffles for around a month of use, for approximately 5 hours each evening, to see how they behaved. Initially they did sound somewhat ragged at the top end and light in the bass/upper bass areas as you would expect from the published response curve. After a month the top end was much better as the presentation was noticeably smoother and the lower frequencies filled out more. A run-in period is essential before judgement. The most important factor during this period was the improvement in overall coherence. After the month was over I new instinctively that the drive unit was going to work well in an open baffle line source array, and this has proved to be the case. Using eight drive units has, as Danny stated, filled out the bottom/midrange giving a well-balanced frequency response through the operating bandwidth. The high end is no longer sounds ragged now that the drive units are well broken in. Whilst the HF is not as well extended as would be provided by adding a tweeter array, I am not prepared to sacrifice the coherency of the line by adding tweeters and having to use a crossover. The reproduction of instruments with lots of high frequency energy is very good. Cymbals sound like cymbals, not someone thrashing a dustbin lid. This is extended enough for me. The bass end goes very low with low distortion and, of course no cabinet effects. Eight 8 inch drive units can easily reproduce the weight of a bass transient from a large drum and I feel no need for a subwoofer.
There are now a lot of B200 drive unit users around the world, and, whilst we users would not claim that the B200 is the best drive unit on the planet, it is damn good at what it does. It is designed to work on an open baffle and it plays music well, once run in, irrespective of any theoretical issues with respect to the published data.
I must reiterate how important it is to wire line source drive units in parallel to get the best performance from the drive units. If you wire the drive units in series/parallel this will cause electrical interaction between the drive units that will impede their correct operation as a line. If anyone wants to experiment with parallel wiring I can provide circuit information for amplification that can drive the resultant low impedance load and I will be happy to help with any technical issues like matching the amplifier to your line. I posted information about the self-biased depletion mosfet output stages, that I use in my system, a while back in the Lab thread. I have recently resurrected my older design using diode biased lateral mosfets, as depletion power mosfets are relatively expensive and difficult to obtain through normal supply chains. When I have found time to finish the drawing I will publish it in the Lab for general reference.
Regards
Paul
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Paul - apologies if I missed it, but what is the size of baffle you used?
JohnR
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Hello JohnR,
The baffles are 78.75 inches tall and 15.75 inches wide. The drive units are offset from the centre to avoid symetrical diffraction from the edges and the baffle edge is rounded to reduce diffraction effects. The drive units are also rebated to avoid diffraction from the edge of the drive unit baskets.
Regards
Paul
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Yes Paul, you will get some fill in from the other drivers in that range. Overall room response (room reflections) will fill in some areas as well. But as frequency increases and wavelengths are shorter you will still wind up with some large dips and peaks.
It will be a choppy ride, but if that ride is for you, then enjoy the ride.
I would have personally only allowed one driver to play full range and brought the others in at the lower ranges. This would give you a smoother response and sensitivity would have still been the same.
If you want to add a bit of upper end air without causing cancellation effects in the top couple of octaves, then you can try adding a rear facing tweeter.
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I would have personally only allowed one driver to play full range and brought the others in at the lower ranges. This would give you a smoother response and sensitivity would have still been the same.
I can attest to this working quite well as I have five B200s, one running full range and the other four being used for bass.
When I first tried them together with the four drivers playing up into the lower midrange everything sounded strange and the soundstage especially was very bad.
Lin
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Danny,
At the risk of repeating myself I am not getting a choppy ride at the listening position with the B200 drive units. I really would be interested to know why you think I should be suffering large peaks and dips in the upper ranges.
How do you get a smoother response and maintain sensitivity in the upper frequencies using one drive unit running full range and the rest only running in the lower ranges? I?m getting 105 db for 1 watt at present and I would be reluctant to reduce the sensitivity back down to the sensitivity of 96 db for one drive unit.
This is an open baffle design. There is plenty of air from the rear reflection. Fortunately the time delay from this rear reflection is long enough not to interfere with the initial wave-front from the front of the speakers and the image is not destroyed by it. It just sounds like hall ambience.
Opnlybafld,
Did you wire your B200s in series parallel or in parallel? If you wired them in series parallel I am not surprised they sounded strange and gave a poor soundstage. I can compare both wiring systems on my lines very easily by changing a few 4mm plug positions and the difference is not subtle. Series parallel wiring looses all coherence and this is what Danny thinks I should be hearing from my line source. This begs the question how can you appraise the performance of a line array under the conditions imposed by series parallel wiring. You may be attributing audible problems to the wrong cause.
Regards
Paul
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Opnlybafld,
Did you wire your B200s in series parallel or in parallel? If you wired them in series parallel I am not surprised they sounded strange and gave a poor soundstage. I can compare both wiring systems on my lines very easily by changing a few 4mm plug positions and the difference is not subtle. Series parallel wiring looses all coherence and this is what Danny thinks I should be hearing from my line source. This begs the question how can you appraise the performance of a line array under the conditions imposed by series parallel wiring. You may be attributing audible problems to the wrong cause.
Regards
Paul
Hi Paul,
I had them series/parallel for the easy 6 ohm load, but since I have an amp that can handle the 1.5 ohm load resulting from four in parallel I will try this. The way I'm using them now works fine for me because they get loud enough to satisfy my listening habits.
Lin
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A good discussion indeed. Thanks especially to you Paul for sharing your first hand experiences with this sort of speaker. :thumb:
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Paul,
Regardless of how many you put in a line, you will not increase the output levels in the top octave. You will still have the same output as a single unit. So if one unit will output 80db with a 1 watt input (as seen in the measured responses) and you are getting 106db in the lower ranges then you already have a variance of 36db.
And whether you wire them all in parallel or series/parallel it will not change the comb filtering behavior.
And Paul, do you have any measurements of this speaker of yours?
And there is no way that you can't get peaks and dips in the response, especially in the top octaves. It is the simple physics of it.
And the reason I suggested the rear firing tweeter is that the output level in the top end goes away. From 7kHz to 20kHz it looses 20db. That is going away.
To me, and this is just me, it is too choppy to listen to a single unit much less what the response will look like with multiples. I am used to +/-1 to 2db over the whole range.
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We all have different approaches to hifi and perhaps speakers more than any other section show this due to their very characterful nature.
One of the most important parts of discussing anything is to be able to understand each others approach and accept that what one person likes very much another might not like or think is going to work.
I personaly will take experience over simulated ideal world calculations and this is why I asked the original question in the first place. My limited experience of speakers is one of a very small but focused window into an event and I look forward very much to a more encompassing experience where I am in the music rather than looking into it, if it is possible. :D
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Just to illustrate Dennis' point:
(http://www.audiocircle.com/image.php?id=21235)
This is a simulation of an Visaton FRS8 line array, showing the vertical response at 0, 30 and 60 degree. First diagram is for two drivers spaced 20 cm with ear height just between them. For the second diagram (to the right) I added one driver above and one below (each at 20 cm distance too). Third diagram is for 6 drivers and the last (bottom right) for 8.
IMHO it shows how adding drivers will smooth the response at lower frequencies somehow, but the peaks at (in this case) 3.5 kHz and multiples of it stand out all the time.
Listening distance is assumed at infinity.
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Paul,
Tried 4 drivers in parallel, bottom driver at the floor and top driver at about ear level, the lower 2 drivers are facing backward (this probably helped since there would be fewer mids/highs), no filters, baffle tilted back a few degrees. Works surprisingly well, soundstage was good if a little lower than normal (this could likely be improved with some tweaking). Sounds much better than it has a right to.
Also tried basically same set up, but moved up one driver since there are 5 on the baffle. Top 3 drivers facing forward with bottom driver facing back, top driver @ one foot above ear level and bottom driver one foot off the floor. Soundstage was good, a little higher, but not quite as focused, also bass was thin because of loss of floor gain.
Went for a triple play and used the top 2 drivers with the bottom 2, so not really a line array because as mentioned the bottom drivers face backwards and there is a foot gap between the 2 pairs of drivers. This arrangement sounded the best to my ears with a good soundstage and good bass.
All of these configurations sounded much better than I expected them to since there were no filters (other than mechanical- provided by the driver magnets).
I used 3 drivers for quite a while with the top full range driver near ear level and the bottom 2 bass drivers as close to the floor as possible, with a single amp all drivers in parallel, biamped with the bass drivers in parallel, and inductors inline with the bass drivers in both cases.
I have benefited from the experiments, from now on I will always wire the bass only drivers in parallel (will probably triamp for a 6-3-3 ohm load), but I still plan on using only one driver full range. :D
Lin
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Opnlybafld,
Good man. It is fortuitous that you have an amplifier that can drive the resulting load. If you are using new wire give the wire a week or so to burn in before appraisal and please post your findings so we can all benefit from your experience.
Browntrout,
I am keen to ensure people do not discount ideas because theory suggests that the idea will not work. In some instances the theory is incomplete. If we all end up designing by textbooks there will be no new innovation.
Danny,
I am always keen to learn so please educate me as to why you have made the following statement :-
Regardless of how many you put in a line, you will not increase the output levels in the top octave. You will still have the same output as a single unit. So if one unit will output 80db with a 1 watt input (as seen in the measured responses) and you are getting 106db in the lower ranges then you already have a variance of 36db.
I am sorry to say that the above statement does not make much sense to me as I am not sure where you get the 80 db and 106 db figures from, although I have to say that I have had a couple of glasses of wine with my evening meal.
Wiring in series parallel will not change any comb filter behaviour. However the disruptive effects of series parallel wiring on the signal integrity will make it very difficult to hear the effects of any comb filter behaviour.
I have not measured the frequency response of the line array. I do not possess the required equipment and, as I am not marketing the design, I am certainly not going to invest thousands of pounds in test equipment just to see what the arrays are doing in areas that are not relevant to the listening position. I think you are missing the point here. With well-recorded program there is a credible image of real musicians, playing real instruments, with a real dynamic range in an acoustic space. Under these circumstances I do not really care how the array measures. I do not use other audio products as a reference, only live acoustic music, and these line arrays tick the boxes in this area. If there are any response anomalies of the magnitude you are suggesting, they are certainly not detracting from the musical performance and certainly not obvious in my listening position. Therefore I must suggest that if the peaks and troughs that you insist are in the frequency response, of a line source array that you have no experience of, are factual, they have little importance in the real world.
I am a little concerned that you keep plucking statements out of thin air, without qualifying the circumstances that allow you to arrive at these conclusions. It would be more helpful if you could give us some information about how you have arrived at these conclusions. After all, you do appear to be playing the devils advocate. As I have said before I am open to education. Let us know what the physics are.
Please also explain why the rear-firing tweeter is required to compensate for a top end that goes away and also where the top end goes away to.
Having a response within +/- 1 to 2 db would be nice as long as you do not kill the life in the performance with too much manipulation using electronic compensation whether passive or active.
Browntrout,
I have to agree with you from my long experience in the audio field for nearly 40 years. Text books, measurements and simulations do not tell the whole story and a lot potential progress is halted by an inability of the mainstream to think laterally. It is the lateral thinkers that are not constrained by currently accepted practice that often move things forward.
Rudolf,
No offence but simulations are not my scene.
Opnlybafld,
I am very pleased that you have taken the time to try my parallel wiring suggestion and found some positive results from it. Praise is due to you for doing it so quickly. It sounds like you are a keen experimenter. Keep posting your experimental results with this wiring arrangement so others can benefit for your experiences.
Regards
Paul
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Paul,
I think Danny was referring to the Visaton published graph and the spl between @3k to 10k vs. spl at 20k.
I would guess most of the regulars around here can't hear much over 15k (if that) anyway. :(
I totally agree with the flatness of the frequency response, I'm all for it except.....what do I give up?
Pick your poison. Some things I can live with and others..........well.
Lin
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I am always keen to learn so please educate me as to why you have made the following statement :-
Regardless of how many you put in a line, you will not increase the output levels in the top octave. You will still have the same output as a single unit. So if one unit will output 80db with a 1 watt input (as seen in the measured responses) and you are getting 106db in the lower ranges then you already have a variance of 36db.
I am sorry to say that the above statement does not make much sense to me as I am not sure where you get the 80 db and 106 db figures from, although I have to say that I have had a couple of glasses of wine with my evening meal.
Okay, I'll try to explain.
Go to the first post that I made and follow the link. Read what I did there and check out the graphs.
I'll re-post this one here:
(http://www.gr-research.com/images/av1test4.jpg)
The lines that are Red, Orange, Yellow, and Grey are the vertical off axis measurements of a single speaker.
Purple, Blue, Green, and lighter Blue are of the two speakers stacked one on top of the other as a MTTM arrangement.
Now note the Purple line.
Both tweeters are playing and the mic is dead center between the two of them but I got less output than with a single tweeter. It is about 6db down at 20kHz. If I moved the mic up a millimeter at a time (or down) I might get that 20kHz range to come up a few db's and if I am real lucky, then I could get it close to the output of a single tweeter.
Even if I could get perfectly dead center between them so that they are not out of phase, I am still slightly off axis from each of them. The higher you go in frequency the more narrow the dispersion. And if it makes this much difference with a 1" dome tweeter, then imagine how much the off axis energy would fall off with a 8" full range woofer.
Any time a driver is producing a wavelength that is shorter than the width of the diaphragm then it will be beaming that range. Move off axis and it drops off dramatically. This is a given with any driver and any size. This is why larger drivers have horrible off axis response compared to smaller ones.
So with a line of 8" full range drivers lined up, and even if you get dead center on one of them, there will be no off axis energy from the others at 20kHz to add anything to the overall output level, and if there was still any energy left there it would certainly not be in phase so it still would add no gain.
Check out these line sources that I designed:
http://www.av123.com//index.php?option=com_virtuemart&page=shop.browse&category_id=36&Itemid=37&vmcchk=1&Itemid=37
And the LS-6 has already won several industry awards.
One has a line of 6 tweeters and the other a line of 9 tweeters. The sensitivity of a single tweeter is 91db. Note also that each speaker only has a total sensitivity of 91db despite the long line of them. They simply do not couple and add output in the top octave.
Note these line source speakers that I designed many years ago:
http://www.epiphanyaudio.com/EALEGENDARYV3.htm
They won an Editors Choice award and a Golden Ear award...
Specifically check out this one: http://www.epiphanyaudio.com/20-21.html
21 Neo 3 tweeters and each one with a sensitivity of 96db. Note the total sensitivity of the whole speaker is only 96db.
So since the B200 only outputs 80db at 1 watt/1 meter (according to the measured response) then adding more of them in a line will never increase that, but you will get gain in the lower end.
So if you are getting 106db of output in the lower ranges (where they couple, and that is normal) then you have a 36db disparity.
Make sense?
And what you may be noticing different about the all series wiring verses all parallel wiring is likely do to the change in inductance. Putting them all in series raises the inductance quite a bit (8 times as much) and as you know a high inductance is like putting an inductor in the signal path. It rolls off the highs.
Running them all in parallel lowers the inductance to 1/8th of a single driver.
So while this is working better for you, because they are all running full range, It's not going to be the same as a line of woofers that are only playing to 1kHz or so.
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I think adding a horn in front of each driver would be a good solution.
and it's not too complicated to build if rectangular horns are used.
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I think adding a horn in front of each driver would be a good solution.
and it's not too complicated to build if rectangular horns are used.
I am sorry, but that would spread the acoustic centers even further apart, make the line even longer, and compound the problem.
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Lin,
I guess a couple of glasses of wine and a late night don?t make for lucid thinking.
I agree that the output at 20 KHz will not be magically augmented, by using 8 drive units in parallel. As I am part of your sub 15 KHz hearing club it is not a big issue to me.
Some will require the output maintained to 20 KHz, and it may be possible to integrate a super-tweeter into the design to achieve this, without damaging the musical integrity.
Regards
Paul
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Danny, if horn loads each driver to say 1khz, how can it create problems above that frequency?
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Iam not a expert like many of you guys. But I feel this test Mr. Danny made are valid only to this loudspeaker type/brand, seems it have a xover and tweeter, it is not a FR as the B200. Certainly this test is a good example of what can happen.
Over the years I learn the treble extension is not important, but the musical integrity of the fullrange is paramount. I have a sole FR sealed box with a 100mm cone, the driver is the Beyma 5MP60/N specified 50hz to 12khz and I do not fell lack of treble. (I do some tuning on this Beyma).
If I said silly please excuse-me.
Gustavo
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Guys I must be a total amateur because I can't even get my sub matched to my speakers without a mic, graph paper, and test tones. Even then I struggle.
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Danny, if horn loads each driver to say 1khz, how can it create problems above that frequency?
Because the diameter of the horn will make the distance between each driver greater and cause the cancellation of the comb filtering effects to be even lower in frequency.
But I feel this test Mr. Danny made are valid only to this loudspeaker type/brand, seems it have a xover and tweeter, it is not a FR as the B200. Certainly this test is a good example of what can happen.
It is the same result with full range drivers.
When I get time (near the end of the day, or maybe tomorrow) I will set up some full range drivers and show the results of playing them together.
Will FR125 full range drivers be okay? If not I have various 3" full range drivers as well.
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Danny,
Thank you for the physics tutorial also backed up by actual measurement information. It is very useful for those enthusiasts working on their own line arrays.
I was aware that you had been involved with the design of the line arrays you have linked to and that they had been well received by many.
Considering the latest information you have presented I think the rising response of the B200 through the midrange and lower treble, before the inevitable drop off in the upper octave, and the LF reinforcement of the array, is enabling the overall response to around 10 Khz to be reasonably well balanced. You did suggest this might be the case. Drive unit burn-in has certainly smoothed out the top end and in practice the line array does not sound ragged as the manufacturers curves would suggest. It also does not appear to lack treble output compared to the live acoustic performances I have attended. That said, at my age, my hearing is no longer what it was above 15 KHz.
When I get some spare time I think I may try and graft some HF transducers onto the arrays but they will only stay if this can be achieved seamlessly. One thing is certain, I would find it difficult to go back to other types of loudspeaker, having experienced the capabilities of the line arrays.
I was aware of the electrical issues regarding series/parallel wiring and as you suggest parallel wiring could also be working in the favour of the B200 drivers.
Regards
Paul
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FULLRANGEMAN,
Over the years I learn the treble extension is not important, but the musical integrity of the fullrange is paramount.
I have to agree with this statement.
Regards
Paul
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I thought lower frequencies don't cancel each other that easily. plus horn provides directivity.
so, Danny, why did you design arrays with multiple tweeters then?
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If all LAs have this CTC problem, what is the Filter Corretive suited ??
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I thought lower frequencies don't cancel each other that easily. plus horn provides directivity.
so, Danny, why did you design arrays with multiple tweeters then?
I'll take a stab at this question. The tweeters used in Danny's Line Arrays are ribbons and thus the spacing of them is very close together. Basically the CTC of the ribbon tweeter becomes a non issue because they start to act like one giant tweeter. The woofers are crossed low enough that the size of the wave means you are basically sitting in near field to them and combfiltering is not an issue.
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If all LAs have this CTC problem, what is the Filter Corretive suited ??
Use ribbon tweeters and cross low enough to the woofers so that they will not comb in the listening area????
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I thought lower frequencies don't cancel each other that easily. plus horn provides directivity. so, Danny, why did you design arrays with multiple tweeters then?
The lower waves will couple, but the higher ones will cancel out.
Try this: Take your center to center spacing and get the distance. Then go here and see what wavelength that distance is: http://www.soundoctor.com/freq.htm
Now if the delay in time is equal to this distance then your cancellation will be at this given frequency.
And on the long line of planar magnetics, the voice coil area of those drivers are space less than an inch apart. So cancellation is minimized.
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So, how do I know what frequencies will couple and what frequencies will cancel each other out?
I may just build horns for appropriate coupling frequency...
so, do those stacked planars actually increase high frequency sensitivity?
sorry to bug you Danny. you are just providing some very useful information, which is not easy to find.
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Use ribbon tweeters and cross low enough to the woofers so that they will not comb in the listening area????
Sorry HTCOZ, I was talking of corretive filters for fullranges as the B200. I hate tweeters, the guy that invented it must be shoted at the paredon. The tweters sound do not spread in throughout the room.
Instead of various ribbons tweeters I would prefer the Carver Amazing 60 inches ribbons and a half dozen of subs like the Gilmore Audio Model1, now with a SPL of 91,5dB. Anyone know if this Carver 60'' is sell as raw driver??
Regards.
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So, how do I know what frequencies will couple and what frequencies will cancel each other out?
I may just build horns for appropriate coupling frequency...
so, do those stacked planars actually increase high frequency sensitivity?
sorry to bug you Danny. you are just providing some very useful information, which is not easy to find.
Not to jump in here but earlier in this same thread Danny said that "21 Neo 3 tweeters and each one with a sensitivity of 96db. Note the total sensitivity of the whole speaker is only 96db" Sounds like multiples do not increase sensitivity. Probably just lower distortion and are easier to drive,,, but that is me guessing.
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So, how do I know what frequencies will couple and what frequencies will cancel each other out?
It is all about wavelength and distance.
Take two drivers and a distance to ear (or mic), then vary the distance of one driver in relation to the other from the distance to ear (or mic). Whatever the distance is the wavelength out of phase.
so, do those stacked planars actually increase high frequency sensitivity?
In the top octave or in about half of the top octave, no they do not couple (no increase). However, as frequency decreases the output spreads out more in all directions (off axis response increases) and they begin to couple and output levels increase.
Instead of various ribbons tweeters I would prefer the Carver Amazing 60 inches ribbons and a half dozen of subs like the Gilmore Audio Model1, now with a SPL of 91,5dB. Anyone know if this Carver 60'' is sell as raw driver??
I can get the big BG planars all day long. But honestly, the long line of the smaller Neo's sound better and have much higher sensitivity.
HT oOz, I think you are starting to get this all figured out.
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Dear Mr. Danny,
Just see this BG RD75 at Partsexpress, nice to know Bohlender is making a 75 inches driver. They are magneplanar system with poliester membrane, this is not a problem.
But Iam afraid all this BG RD line is monopole, firing sound front only and need a box as used in VMPS.
The beauty of the Carver Amazing is in the (Dipole) Soundstage, it is really adictive (you do not listen the music, you feel the music etc).
If this BG is a Dipole driver it is a alternative to the widows of the Carver Ribbon like me.
Regards.
P.S.: If this BG are monopole only I have to reject it, it have no effect in my brain or heart, Iam a Dipole junkie.
Impressive statement below from a BG RD75 user at PartsExpress:
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Difficult to use.
Friday, June 12, 2009
Paul from Madison,WI
I have long been a fan of electrostatic loudspeakers and when I heard that the RD 75 B&Gs are even better than electrostatics I was eager to give them a try. I have found it very difficult to get these to perform at the level I have come to expect. First, there is the 5K anomaly that requires a notch filter to tame. Instead I cross over to a RAAL 70-10B at 4K via a Pass Labs XVR1 electronic crossover to avoid this and to get extension up past 20K. Next, there is the dipole issue. I like the dipole nature of electrostatics, but on the Bohlender...mmm not so much. Soon I will try them in an enclosure to see if this helps. Finally, there is the usable range. As others have noted, you really should cross these over at a much higher frequency that the 150Hz stated. I have tried many and settled with 220HZ with a 4th order 24/db octave slope mated to an array of 6 Usher 8955A in sealed enclosures with 1cuft of space per driver. All in all many dollars spent for sound that doesn't necessarily sound better than my electrostatics. Don't get me wrong, these are phenomenal drivers; however, they are just plain difficult to implement sucessfully.
-----------------
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So, how do I know what frequencies will couple and what frequencies will cancel each other out?
Have a go at using this simulator -
http://www.pvconsultants.com/audio/radiation/vpr.htm
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FULLRANGEMAN:
The RD75 can be used as an OB. The rear of the driver is internally damped with acoustic foam, so less high frequency sound is emitted from the rear than from the front. The RD50 can be used as a direct replacement for the Carver driver. I have built both a RD75 OB and an OB line array using multiple 4" full range drivers. The 4" plays louder, needs far less watts to boogie and can be crossed over at 100Hz. The RD75 is more coherent, focused, transparent, faster, less coloration.... You can hear what Danny is describing above 2K. The RD75 allows you to hear (and see in your mind's eye) the individual strings resonating on an acoutic guitar or closely miked violin----with the 4"ers, it is not so clear. Cymbals are cleaner, better defined in size/shape with clearer, longer sustain. On good recordings (like the Blue Coast) the RD75 captures the space between performers far better---you can hear a performer, then a defined dead space, then another performer. With the 4"ers, the individual players spaces are not as defined. With the RD75 depth and layering is better as well. On the down side, the RD75 is expensive, requires a notch filter, dramatically rolls off above 10KHz. and can only play at very high levels when crossed over around 300Hz. or higher. You can get around some of these problems using DSP, but that introduces more cost and other problems (phase). No free lunch, here.
Chris H.
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FULLRANGEMAN:
Chris is correct on all accounts. I completely agree.
Personally though, I prefer a line of the smaller Neo's. The top end is more extended, but they don't play as low. But I have found that running the big ribbons down low is not an advantage. 300Hz is the heart of the mid-range and crossing in that range with good integration is not easy. With like drivers, it can be done, but with dissimilar drivers with different off sets it is pretty tough. I prefer crossing them in the 850 to 1kHz range and letting a row of small woofer handle up to that point.
The smaller Neo's have much higher sensitivity to. And to me sound cleaner and more dynamic.
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I'm thinking, high frequency cancellation may be an advantage for a short array of full range drivers.
most of paper full range drivers have rising frequency response.
say we build sealed or ported enclosure and add just enought drivers to balance low frequency gain and high frequencies cancellation.
of course top end response will be rough, but I bet it will sound better that single full range used without any sort of filter.
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I'm thinking, high frequency cancellation may be an advantage for a short array of full range drivers.
most of paper full range drivers have rising frequency response.
say we build sealed or ported enclosure and add just enought drivers to balance low frequency gain and high frequencies cancellation.
of course top end response will be rough, but I bet it will sound better that single full range used without any sort of filter.
Nope, it will have a worse response than a single driver and the dips and peaks will vary with distance and height.
Just let the single full range driver cover the full range and bring the other drivers in to cover lower frequency ranges only.
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Thankyou Danny/BPT for sharing your impressions about the BG RD75, if it have a nice Dipole Soundstage it have some sex appeal to me,
cause it is bigger than the 60'' Carver Ribbon, bigger is always better, as all women knows (sorry).
Iam illeterate in xovers, what is this notch filter after all??
Kinds, Gustavo
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Thankyou Danny/BPT for sharing your impressions about the BG RD75, if it have a nice Dipole Soundstage it have some sex appeal to me,
cause it is bigger than the 60'' Carver Ribbon, bigger is always better, as all women knows (sorry).
Iam illeterate in xovers, what is this notch filter after all??
Kinds, Gustavo
Gustavo,
How can you have an icon saying Use a crossover? AARGh and also If tweeters look like targets then shoot them and then ask a question like what is notch filter?
It just doesn't add up!!!
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Excuse-me if you like xovers. I do not know xovers why I do not like then, and mainly tweeters.
I have a friend repair man that like shape the sound modifying the xover, and do not have interest in fullranges...
What I can do for him? He likes two way pocket monitors!! Patience!
Regards,
(sorry for my explicit banners)
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Fullrangeman:
A notch filter is usually a combination of a capacitor, inductor and resistor designed/tuned to reduce/dampen a resonance in a speaker driver.
I was mistaken before. The RD48 is designed for use with the Carver and Genesis speakers.
Chris H.
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I don't see how anyone could like a crossover except when comparing one to another. Surely if we can do without then all the better? I don't see why all discussions need to conclude with the same similar consensus.
I have learnt that you can have the most faithfully reproduced sound that lacks all emotional involvement (most hifi to be honest) but you can allow your mind to wonder and let the emotion of music take the concentrations of your consciousness away and leave you with unperfect sound and perfect involvment.
If we can see past measured responses I think a better understanding of why we listen will arise. The best performances I have experienced have not been so because I was sat in the correct seat of the hall but the ones where I have formed an emotional response to the music and performer.
How do we put emotion into the music we make?
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Well said.
Back on topic (this is the open baffle circle...) - Gustavo, one way you go about it might be with nine drivers wired series/parallel for an 8 ohm load (assuming 8 ohm drivers). And if it doesn't work out, then rewire to run the top driver full range (I am assuming we are talking about smallish drivers here), and rewire the bottom 8 drivers to 4 ohms and drive them with a separate filter and amp. Since this last part is just augmenting the bottom and compensating for dipole rolloff, it doesn't really count as an AAARGH! crossover ;)
Just a thought :)
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Thankyou for the info BPT!! >> Who knows do it live! (Brazilian saying).
Someone know what is the Brand or maker of the woofers of the GilmoreAudio (Carver Amazing clones) ?
I ask in amail to Mr. Mark Gilmore, but after 6 months seems he will not reveal...
Thanks,
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Browntrout,
Once again I have to agree with you. This is why I am not particularly keen to mess around with anything that could take away the emotional hit that I get with the B200 line array in my system. I am not concerned how it measures as the presentation has that magic that eludes much audio equipment.
By the way, I like your avatar. It triggers an emotional response to the area that I live in, as the scenery has similarities. There are also several thousand fresh water lochs along the island chain and many of them have a good stock of wild brown trout.
General discussion,
I still think the series/parallel verses parallel wiring issue should be considered further. As I am not commercially active in line array loudspeaker production I have no vested interest either way. I do not have a PHD in Mathematics so do not expect to see any rocket science equations in this post. It is purely an exercise in logical thinking and if I miss any points you think are relevant please feel free to add to the discussion. There will not be any measurements either as I do not have the specialised test equipment required for this.
The reactive impedance of a moving coil drive unit is more complex than just inductance. It consists of resistance together with capacitive and inductive reactance. These parameters are not fixed values, as they are modified by mechanical motion, drive unit loading, driver resonances and temperature. The resulting load impedance and phase angle varies considerably with frequency. The output impedance of the amplifier is in parallel with this varying load impedance and would tend to act as a damping mechanism reducing the effect of the back EMF caused by the reactive loudspeaker load. There is also some self-damping caused by the resistive element of the drive unit impedance.
If two drive units are placed in series the amplifier damping is reduced considerably as each drive unit sees the reactive impedance of the other drive unit between itself and the amplifier. The resistive impedance of the drive units will double, the inductance will double and the capacitance will halve. This will allow the drive unit back EMF to reach a higher amplitude, and exhibit more influence on the resultant acoustic waveform generated by the drive units, compared to the single drive case. As the increased back EMF voltage is time delayed, when it mixes with the following program signal, it is going to smear the waveform more. I would suggest that this should have profound effects and could easily cause increased confusion in time and space in the presented music.
If two drive units are wired in parallel they both see the amplifier damping and the resistive value of the composite drive unit load impedance is halved, the inductive value is also halved and the capacitive value is increased although the reduced parallel resistance would tend to reduce the effect of the capacitance increase a little. The back EMF voltage shows a small reduction in level caused by the reduced inductance and the lower parallel resistance compared to that of a single driver. This is going to have much less effect on the music signal than the series/parallel case.
In line arrays it is logical to conclude that increasing the number of drive units wired in series will exasperate the problems caused by series wiring. Conversely when drive units are wired in parallel the back EMF damping is more optimally maintained, by the amplifier output impedance and the reduced inductance and impedance of the parallel drive units. This should allow better signal integrity.
The difference series/parallel and parallel wiring is easy enough to hear as opnlybafld found out with his basic experiments with his B200 drive units. There seems to be a reluctance to accept this concept and I can understand the hassle factor of re-wiring a line array and building new/more amplifiers, but on a DIY level it is relatively inexpensive to implement. You will never know until you try it.
Incidentally comb filter effects are not confined to line arrays. They are also produced by two or more sources of the same frequency and even one drive unit and the reflections from room boundaries can generate them. Because of this we are all used to comb filter effects in our sound systems, and, as I do not see everyone rushing to dump their loudspeakers in the bin, I would suggest that comb filtering is relatively benign on the grand scale of annoying distortions or perhaps the majority of us have learned to filter the effect out of our minds.
Regards
Paul
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Excelent balanced (pardon the pun) panoramic vison about the issue Mr.Paul. Maybe a big parallel output Bryston amp have some utility, after all.
Cheers.
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...dramatically rolls off above 10KHz.
Dear BPT,
...dramatically rolls off above 10KHz. >> I think the human hearing love attenuated treble, at least this ears around me. I work some time with pro-sound and my ears has been fried manys nights by the horns of the stage/PA system, strong treble is awful.
Cheers.
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Incidentally comb filter effects are not confined to line arrays. They are also produced by two or more sources of the same frequency and even one drive unit and the reflections from room boundaries can generate them. Because of this we are all used to comb filter effects in our sound systems, and, as I do not see everyone rushing to dump their loudspeakers in the bin, I would suggest that comb filtering is relatively benign on the grand scale of annoying distortions or perhaps the majority of us have learned to filter the effect out of our minds.
Yes indeed. Yet one might have hoped that in the open baffle circle, where interference between wavefronts is a given, some consideration might have been given to the room and other effects.
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I think we have been talking about open baffle speakers. Even my non technical post was intended to be on topic.
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JohnR,
Considering room interaction was part of the design exercise when assessing which design to use for my system loudspeakers. Reducing cabinet interaction was also given consideration as I have a fair amount of experience with loudspeaker cabinet construction. I assumed, rightly or wrongly, that open baffle enthusiasts would be aware of the benefits of removing cabinet interaction from the equation. There is plenty of discussion about this topic in this forum circle. Combining these OB benefits with those of a line array is less well documented in DIY circles as few enthusiasts consider building a line source and fewer still make it open baffle.
I chose to use a full range driver open baffle line source array for a number of reasons. Firstly I do not like using crossovers to split the frequency range into sections and I prefer the musical presentation from full range drivers. This is purely my preference. Feel free to differ. Aside from the sonic benefits I perceive with the full range drivers there are financial benefits, when constructing a line array with full ranger drivers, as you do not need a crossover or more amplifiers. This helps compensate for the cost of the drivers, baffle etc.
Another reason is the theoretical advantage of the way the waveform is propagated into the listening room in the near-field area, which in my room includes the listening area. The OB line exhibits a dipole response, which reduces output to the sides of the array. You can easily hear this by walking over to the array and into the null area. The cylindrical wave front that the array propagates into the room reduces floor and ceiling bounce allowing noticeably less colouration from room interaction. There may be some reflection from the side walls where the cylindrical wave front hits the wall, but I suspect these are delayed enough to not interfere with the initial direct wave front that we use to mentally construct the image of the recorded musical events. The reflections sound similar to acoustic reverberation and add air to the performance, as does the reflection from the wave front propagated from the rear of the array that bounces of the rear wall.
The reason that I chose to use eight inch drivers in the line is that I wanted to be able to move enough air to reproduce big drums without resorting to a sub woofer and the attendant interface issues. I have used eight inch full range drive units in the past, and achieved a satisfactory musical performance with them on open baffles, so I was not too concerned about the frequency extremes of the B200.
I have already gone through my reasons for parallel wiring the drive units. On a DIY basis it is easy enough to build a purpose built amplifier to deal with the low impedance load of parallel drivers, certainly 8 B200s in parallel. All you are really doing is re-scaling the voltage and current relationships in the output stage and ensuring the output stage can handle the required current. There is also a benefit I did not highlight. My line array is quite efficient and requires little power to generate high sound pressure levels. I am currently using a stereo amplifier that is configured for 2.5 watts into 0.75 ohms. The voltage swing required for 2.5 watts into 0.75 ohms is around 2 volts peak. This is the sort of voltage swing you would easily expect from a line preamp. In practice this allows me to use a Lightspeed LDR volume control followed by a high power mosfet source follower. Absolutely no voltage gain is required in these two stages, as all my music source equipment can easily provide enough output to go well beyond this voltage swing requirement. This allows very simple low distortion circuitry and the system is particularly transparent to the musical performance because of it.
If anyone wants to discuss the above further or has anything to add that might be of benefit please feel free to join in.
Regards
Paul
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Hi Paul, got any pics? :D
I think your project is interesting and enlightening, I was trying to suggest that the concern about theory and measurements expressed earlier in the thread might have more validity and interest if the actual combination of factors under consideration were taken into account.
One doesn't necessarily amps capable of driving 0.75 ohms, though - multiple amps would do the trick as well.
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Dear Mr. Paul,
I also like FR, LA and OBs. When I see the B200 at the Visaton Site I was very excited, but when I found its Freq. x dB chart I was sad why the Bass is very attenuated.
But as you said the Bass performance of your B200 LA OB are good, Iam curious as you managed to get a hi dB Bass response of the B200?
Do you use a active SubWoofer? Tone Controls at Preamp? A filter to boost the low freq.?
Please inform us, as Iam in search for a FR + LA + OB loudspeaker afew years...
Gustavo
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If drivers with 16ohm impedence were used would I be right in assuming the amplifier could be a SET 300B type and not need to be purpose built for very low values?
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Hi JohnR,
If you copy the following link to your web browser it should take you to an old photo of the line array taken at our old house in Cumbria, England.
http://s700.photobucket.com/albums/ww7/paulhynes/th_Picture036.jpg
It is certainly more sensible to consider all the factors of a design when making an assessment. Comb filtering effects are only one factor, and in my system they are not giving me any real concern. It could be that the cumulative benefits of all the design parameters are far outweighing the effects of comb filtering.
You can easily use multiple amplifiers to drive the parallel-wired line array, if you happen to have them. However if you are building from scratch it is easier to build a stereo amp, or two mono power amps with the design adjusted for low impedance loads. I am happy to help DIY enthusiasts to do this and I have freely published the two depletion mosfet designs in the lab circle. This will be followed with the lateral enhancement mosfet version, shortly, when I can find a little time to prepare the drawing.
Hi Gustavo,
I am not using and electrical compensation or subwoofers on the line array. Mutual coupling between the drive units increases the efficiency at low frequencies and this reinforces the low frequencies. Danny kindly explained the reasons for this in his earlier posts. The bass sounds very natural and has very good extension. You can feel the deep bass as well as hear it. Distortion is low as the drive units are barely idling under normal listening conditions and there is certainly no confusion with regard to the type of instrument being played. If you like your bass larger than life then you may prefer to implement some bass boost by whatever means you like. There is plenty of scope for this as the power handling of each array is 320 watts continuous and 560 watts for transient peaks. I am very happy with the bass as it is well balanced with the rest of the frequency spectrum. Whilst I have stated that I only use live acoustic music as a reference, I do listen to all types of music and the line is equally at home with rock, jazz, and classical.
Hi Browntrout,
It would depend on the taps available on your output transformer. Incidentally I have driven the SE current amplifier output stage from a current source loaded 300B valve with no output transformer (capacitor coupled) and really liked the resulting sound quality.
Regards
Paul
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Many thanks Paul.
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I have seen more than one set of Lowthers in a baffle (one the Web). The design that I saw had one set of drivers mounted facing forward, and the other set facing backward (one forwarrd, one backward on each side). I e-mailed the guy about his design but I never heard back.
But I don't think that it would be desirable to have more than one Lowther per side. Although there may be benefits, the downsides would likely dominate. Lowthers are pretty good drivers so a single set of drivers can handle the job, providing that a couple of adjustments or accomodations are made to the drivers.
First, I would use a Lowther line with a stronger set of magnets. This provides more detail in the music. For example, the DX4 line is excellent, although a guy named Chopper has compared different Lowther drivers and swears that the PM2AMKII drivers are the best in open baffle. I cannot confirm his claim. However, I did try DX4 drivers with and without an enABLE treatment and the effects of the enABLE treatment are worth the time and effort. The sound is more dynamic and more focused and the tone of the drivers is improved as well (they sound less like paper drivers). I would opt for the 15 ohm drivers because of the greater x-max.
I would roll the drivers off at 150 hz, and rely on a good woofer to handle the low frequencies. This reduces the doppler distortion of the midrange amps and drivers (the Lowthers), and allows for the use of a sand amp where it is best. The complexity with this approach is that getting a good blend between the two drivers is very challenging.
I hope that this helps. EnABLEd Lowther drivers are probably some of the best sound that I have heard in audio.
Retsel
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Interesting discussion.......... One thing that is sometimes overlooked is that what we hear can be very different. Some find the B200 to hot, I dont, well my ears dont. But they must be put into a baffle that does them justice, thats IMHO anyway. Other dont like them, still other say they are no good without even hearing them. Thats OK, but none of us has the last word on what is right or wrong. Its is just personal preference. I would like to comment about the Lowthers drivers, but because I have never heard them, there is not much I can say, other than I would like to listen to them.
I agree, that if you have a great point source driver, I dont see much point in a line array of them, but I would still like to try a line array.......well a true floor to ceiling array anyway. But there are as many minuses as the are pluses for any alignment of driver/drivers, nothing will be perfect.
I think that for a line array to work properly, you may have to consider power tapering, or building a top to bottom curved baffle. :thumb:
Mr C :D