AudioCircle
Industry Circles => GR Research => Topic started by: harley52 on 25 Mar 2014, 09:42 pm
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Danny,
Hey young man :icon_lol:, Mcintosh has a stand mount speaker with 5 tweeters running horizontal. What does that do? Does it give a larger sweetspot? Please explain this.
I could ask Mcintosh :duh: but I'd rather have it come from you.
Thanks you
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Does this Mcintosh speaker have a flat, convex or concave front baffle?
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Something like this?
(http://i.imgur.com/1VdEIe1.jpg?1)
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Must be an older model? Their current lineup only shows just one bookshelf speaker (XR50) with one tweeter and two tiny midranges in a vertical array (TMT).
Their larger home theater speakers have multiple tweeters.
The XRT2K 110 driver floor standing speakers has 40 tweeters flanked by 64 midranges (32 on each side) in a vertical line array with 6 - 12"woofers directly behind the midrange/tweeter array and looks like it has a flat baffle. (7 ft. tall, 450 lb. monster in sealed aluminum cabinet)
The XCS2K 55 driver center channel speaker has 20 tweeters flanked by 32 midranges (16 top, 16 bottom) in a horizontal array with 3 - 12" woofers directly behind the midrange/tweeter array and this one has a curved convex baffle (McIntosh's "exclusive" Arc Array).
Steve
(http://www.audiocircle.com/image.php?id=96818)
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5 horizontal tweeters is the LS360 model:
(http://www.hifido.co.jp/photo/08/164/16499/a.jpg)
http://www.hifido.co.jp/?code=607&back_uri=%2Fbuying_list%2FMcIntosh.html
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Destroy your hearing?
I think a great question is, what does the crossover look like? Perhaps they do a lot of fill in a more narrow band?
Danny talked about tweeters on opposite sides of a speaker, and the problems with that. But what happens when there's no gap?
Well, I'm curious now as well. Is it a compromise?
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From the AES library:
http://www.aes.org/e-lib/browse.cfm?elib=6012
The Bessel array is a configuration of five, seven, or nine identical loudspeakers in an equal-spaced line array that provides the same overall polar pattern as a single loudspeaker of the array. The results of a computer simulation are described, which uses point sources to determine the effective operating frequency range, working distance, efficiency, power handling, maximum acoustic output, efficiency-bandwidth product, and power-bandwidth product of the array. The various Bessel configurations are compared to one-, two-, and five-source equal-spaced equal-level equal-polarity line arrays. As compared to a single source, a five source Bessel array is 14% (0.6dB) more efficient, can handle 3.5 (+5.4dB) more power, and has 4 times (+6dB) the maximum midband acoustic output power, and is usable for omnidirectional radiation up to the frequency where the overall length is 11 wavelengths long. As compared to a two-source equal-level in-phase array, a five-source Bessel array is 43% (2.4dB) less efficient, can handle 1.75 (+2.4dB) more power, has the same maximum midband acoustic output power, and is usable for omnidirectional radiation 10 times higher in frequency. A working distance of 20 times the length of the Bessel array was assumed, with the length of the Bessel array (center-to-center distance of outside sources) being four times that of the two-source array. Analysis reveals that the three Bessel arrays have equal maximum acoustic output, but that the five-element Bessel array has the highest efficiency and power-bandwidth product. The seven- and nine-source Bessel arrays are found to be effectively unusable, as compared to the five-source array, due to much lower efficiency, requirement for more sources, and poor high-frequency performance. Judging polar peak-to-peak ripple and high-frequency response, the performance of the Bessel array is found to improve in direct proportion to the working distance away from the array. Unfortunately the phase versus direction and phase versus frequency characteristics of the Bessel array are very nonlinear and make it difficult to use with other sources.
Author: Keele, Jr., D. B. (Don)
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On the cover of Stereophle....
8+ years ago was a well reviewed Speaker
((Weeg?)) which had 5 tweeters in a semi-circular arc with Midranges contained
within this arc of tweeters.
If I recall the reviewer & JA both found them to sound good & measure well.
Of Course M&K have had two or Three vertical tweeters for years.
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(http://www.audiocircle.com/image.php?id=96818)
Hmmmm. Were those things designed by Daleks? :scratch:
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Hmmmm. Were those things designed by Dalek? :scratch:
"Exterminated!"
(Your bank account, that is: $100K for the mains, $35K for the center)
Steve
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"Exterminated!"
(Your bank account, that is: $100K for the mains, $35K for the center)
Steve
The Doctor would be proud. Made me laugh :lol:
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For decades McIntosh speakers have had multiple tweeters/midranges/woofers, why? Can't they get loud enough with one of each (like most manufacturers)? I know distortion goes down and power output goes up with more drivers, and I'm not smart enough to quite understand how a Bessel array works, but as Carl quoted the phasing issues must be an absolute mess. Frankly I've never been able to hear coherent imaging from an array (except a curved array, but then only from far field).
Not surprisingly even as a former McIntosh owner I've never been impressed with the sound of their speakers (or the sound of their big blue meters).
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The stand mounts, XLS 320, was first made in 2005. It has a 6.5 bass/mid driver and the 5 tweets are directly above the 6.5" driver in an arrangement going left to right. Horizontal may be the better word. The baffle is standard flat piece.
I understand a line array going from top to bottom, but these are side ways. Wouldn't that arrangement be different from the line arrays we're all familiar with that go top to bottom.
I was thinking there must be a good reason that Mcintosh went with that configuration. There's a pr. of them for sale at A-gon. One of the Italian speaker manufactures has like 2 or 3 tweets on the front and the back on one of their speakers in a horizontal arrangement. I think S-file did a review of it in the last year or so.
Thanks for all your input ladies and gentlemen.
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The only time I've heard Mcintosh speakers sounding good is in very large rooms (25' x 40' +) where I'm well back from them. If I'm at a show with my wife and their speakers are in a small room, she won't even go in the room. :dunno: All I can get from her is that she doesn't like them and they sound "wrong".
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The theory I hold to is that arrays cannot image in the direction they're oriented in. So vertical arrays cannot image vertically (and unless they extend very nearly floor to ceiling will not load the room in a cylindrical versus spherical pattern for improved efficiency).
Waiting now for the flames...
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Danny,
Hey young man :icon_lol:, Mcintosh has a stand mount speaker with 5 tweeters running horizontal. What does that do? Does it give a larger sweetspot? Please explain this.
I could ask Mcintosh :duh: but I'd rather have it come from you.
Thanks you
Let me explain how this whole multiple tweeter deal works. And this isn't just what Danny thinks, or the opinion of one guy. This IS what happens.
Anytime you have multiple drivers or output from multiple sources you will get some coupling and cancellation effects. In low ranges the wavelengths are long and couple easily. In the upper frequency range where wavelengths are short then they cancel each other out easily.
Anytime one driver is delayed in time by half of a wavelength then it is out of phase from the other. The effect is cancellation. Check this wavelength chart to get an idea on the distances: http://www.soundoctor.com/freq.htm
With planar magnetic drivers the whole driver is the voice coil. So it is a little different animal, but with standard drivers we can take the center of the driver as the acoustic center. Center to center spacing on standard tweeters need to be within a wavelength of the upper range they cover to avoid driver to driver cancellation patterns. So a dome tweeter needs to be within an inch or so of one another center to center to avoid cancellation up to 20kHz.
And anytime ANY driver plays a frequency range where the wavelength is shorter than the diameter of the diaphragm then it is in what we call its beaming range. In other words its off axis response falls off dramatically. The same holes true for multiple drivers. If you create a line of small woofers 4 feet long then what you really have is a driver that is as wide as the width of one woofer by as long as the length of the line. So it's off axis response will be very limited vertically if it is a vertical line. The same is true for a tweeter line. In a line source like the LS-6 or LS-9 the high frequency output changes before you even reach the end of the line. And outside the length of the line the highs fall off so fast they are practically gone. You have to stay within the length of the line.
So if you make a small line of tweeters the off axis effect is the same as a single tweeter that is the length and height of the group, and that is if there are no driver to driver cancellation patterns from over spacing. So a 6" ribbon or a 6" line of 1/2" dome tweeters will have the same off axis response as a 6" woofer. The highs will fall off quickly outside the width of the driver.
So speaker like this will have a very limited horizontal coverage in the upper ranges.
(http://www.hifido.co.jp/photo/08/164/16499/a.jpg)
Just move off axis and the highs will be gone.
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For decades McIntosh speakers have had multiple tweeters/midranges/woofers, why? Can't they get loud enough with one of each (like most manufacturers)? I know distortion goes down and power output goes up with more drivers,
Actually as frequency increases coupling decreases. So in the end it doesn't matter how may tweeters you line up, the total output level at 20kHz is about the same as a single tweeter because they are in a beaming range at 20kHz.
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The theory I hold to is that arrays cannot image in the direction they're oriented in. So vertical arrays cannot image vertically (and unless they extend very nearly floor to ceiling will not load the room in a cylindrical versus spherical pattern for improved efficiency).
Waiting now for the flames...
You are close. Just replace the word image with off axis response.
Imaging refers more to layering and separating the sound stage. Line sources can do that quite well.
But the have no real off axis response in the direction they are oriented. That is why line sources need to be near ceiling to floor to cover the whole room well.
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Hi Danny,
Very interesting information you have provided. I was not really aware of what was happening when designers used multiple tweeters but your comments helped me understand. What about designs like the one on the link below. It uses two tweeters placed side by side. Is this done to limit dispersion?
http://www.daedalusaudio.com/Argos.html
Thanks again. You are a real asset to AC and I hope you continue in some form if your company is purchased. This is not as good a place without you.
Jack
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Hi Danny,
Very interesting information you have provided. I was not really aware of what was happening when designers used multiple tweeters but your comments helped me understand. What about designs like the one on the link below. It uses two tweeters placed side by side. Is this done to limit dispersion?
http://www.daedalusaudio.com/Argos.html
Thanks again. You are a real asset to AC and I hope you continue in some form if your company is purchased. This is not as good a place without you.
Jack
Those will have considerable cancellation in the vertical off axis and leave holes in the response down to about 2kHz. This will also show up in the room response with a very uneven reflection pattern in the room.
If you want to see a little meat on the whole coupling and cancellation effects that is easy to understand then here it is.
I took these measurements several years ago when some guys were asking about stacking speakers on top of each other.
So I took a pair of A/V-1's and stacked them on top of one other tweeter to tweeter. The acoustic centers of the tweeters were 6.5" away from each other.
A/V-1: (http://gr-research.com/images/av1m1.gif)
I then put the microphone 1 meter away and just off of dead center between the two boxes. So almost inline with the top of the box. I'd say it was about 1" off dead center.
I then measured one speaker only and saved it in red. Then I measured both speakers playing together and saved it in purple.
Next I moved the mic up 2". Yes just 2" up vertically at 1 meter.
I played the single speaker only and saved it in orange. I then measured them both playing together and saved it in blue.
Then I moved the mic up two more inches and measured again. With the single speaker playing I saved it in yellow and with both speakers playing I saved it in green.
One last time up another 2". I measured the single speaker and saved it in grey and the two playing together and saved it in light blue.
Here are the measurements of the signal speaker moving up 2" per measurement:
(http://gr-research.com/images/av1test5.jpg)
Here are the measurements of them both playing together with the mic in the same places moving up 2" per measurement.
(http://gr-research.com/images/av1test6.jpg)
As you can see it doesn't take much vertical movement to put the tweeters out of phase. And the further off axis you go the longer the time delay gets and the effect reaches lower as the wavelengths get longer.
Here is an overlay of all of the curves so you can see where they couple (more output) and where they cancel (less output than a single driver).
(http://gr-research.com/images/av1test4.jpg)
Pretty clear huh.
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It's clear when even someone like me can understand it! Okay, last question, why would anyone use multiple tweeters in this configuration? Power handling? It's an added expense and more complexity but I don't understand the payoff. In line arrays I can understan the benefit but in designs with just a few tweeters (or two) stacked vertically or horizontally, I don't see the benefit. :scratch:
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It's clear when even someone like me can understand it! Okay, last question, why would anyone use multiple tweeters in this configuration? Power handling? It's an added expense and more complexity but I don't understand the payoff. In line arrays I can understan the benefit but in designs with just a few tweeters (or two) stacked vertically or horizontally, I don't see the benefit. :scratch:
If there is more of something it has to be better right? More is better than less...
https://www.youtube.com/watch?v=XLHglL7FCNY
Just marketing...
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I guess the question is: What do they believe that does better? What is their goal when placing 5 tweeters like that?
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I guess the question is: What do they believe that does better? What is their goal when placing 5 tweeters like that?
That's what I should have said! I heard the Mac speakers at Axpona and they sounded pretty good. Didn't check the dispersion or how they sounded outside the sweet spot. Looking forward to doing this at this year's Axpo with speakers that have lots of tweeters. Danny's explanation was perfect and I have a much better understanding.
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Danny, you are such a nice guy and so free sharing your knowledge. THANKS!
Your experiments with the stacked A/V-1s certainly illuminate how Dynaudio's "Dynaudio Directivity Control " works.
http://www.dynaudio.com/int/home_loudspeaker_systems/evidence/ddc.php (http://www.dynaudio.com/int/home_loudspeaker_systems/evidence/ddc.php)
(http://www.dynaudio.com/images/systems/lines/evidence/opener/ddc_evid_int.jpg)
I will point out multiple tweeters as in the McIntosh and Dynaudio Evidence and Confidence really help with the power handling of these big statement series models. At a CEDIA demo I was shocked to see those big blue meters nearly pegged while the very loud sound from the McIntosh many-many-many tweeter speakers remained effortless. On the way out of the demo I asked the McIntosh rep "how many watts does that demo peak at?" He replied "about a kilo-watt". And that demo was running all day long at a trade show. I doubt a single pair of 1" done tweeters would have been up for that abuse!
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Danny, you are such a nice guy and so free sharing your knowledge. THANKS!
Your experiments with the stacked A/V-1s certainly illuminate how Dynaudio's "Dynaudio Directivity Control " works.
http://www.dynaudio.com/int/home_loudspeaker_systems/evidence/ddc.php (http://www.dynaudio.com/int/home_loudspeaker_systems/evidence/ddc.php)
(http://www.dynaudio.com/images/systems/lines/evidence/opener/ddc_evid_int.jpg)
I will point out multiple tweeters as in the McIntosh and Dynaudio Evidence and Confidence really help with the power handling of these big statement series models. At a CEDIA demo I was shocked to see those big blue meters nearly pegged while the very loud sound from the McIntosh many-many-many tweeter speakers remained effortless. On the way out of the demo I asked the McIntosh rep "how many watts does that demo peak at?" He replied "about a kilo-watt". And that demo was running all day long at a trade show. I doubt a single pair of 1" done tweeters would have been up for that abuse!
I don't know that I'd call comb filtering cancellation patters "controlled directivity".
And I have seen the McIntosh display at CES where the guy running the control room quickly cranked the level up to a point that had everyone in the room covering their ears. He then claimed the speakers just handled a thousand watts from each amp. And I think they had four of those amps on them.
Then Gary Dodd reminded me as we walked out of the room that the system was on a 20 amp circuit. Total max output from the 20 amp circuit was 2400 watts. If the amps were 60% efficient (being generous) then 1440 was the total max output of all four amps. Divide that by 4 and each amp could only draw enough current to max 360 watts. And it would be likely that a circuit breaker would trip before then.
So it wasn't near as much power hitting those speakers that they claim. However, using that many drivers power handling will be high.
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I did measure a pair of these things. They also used two tweeters.
(http://www.axiomaudio.com/global/images/products/main/M80CherryGrilleOff2.jpg)
Here is the on axis response of the tweeters and mids individually (green line), then the lower woofers (blue line), and then the red line shows them all playing together. There was actually comb filtering effects going on between the woofers and the mids from 600Hz to 2.5kHz as the combined output was less than the individual output of the mids alone.
(http://gr-research.com/pics/Ax2.jpg)
Okay here is the on axis at 1 meter and then each additional measurement is made by going up 4" at a time.
(http://gr-research.com/pics/Ax1.jpg)
There were a lot of cancellation effects going on over the whole range, but the tweeter peaks and cancellation effects spanned more than a 25db range.
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Then Gary Dodd reminded me as we walked out of the room that the system was on a 20 amp circuit. Total max output from the 20 amp circuit was 2400 watts. If the amps were 60% efficient (being generous) then 1440 was the total max output of all four amps. Divide that by 4 and each amp could only draw enough current to max 360 watts. And it would be likely that a circuit breaker would trip before then.
That would be true for a continuous sine wave load which music is not. However amplifiers with very large power supplies and storage capacitance can supply instantaneous and peak current and power on demand that can surpass what is available from the external AC supply circuit.
Steve
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That would be true for a continuous sine wave load which music is not. However amplifiers with very large power supplies and storage capacitance can supply instantaneous and peak current and power on demand that can surpass what is available from the external AC supply circuit.
Steve
That is true. It is hard to say just how hard the speakers were hit for that brief second where the dial was whipped to ten and back, but for sure it was not appreciated by the small crowd of people and it certainly didn't help sell the speakers. Everyone looked at the guy with the look on their faces that clearly said, why did you do that?
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Danny, thanks for the measurements. I would never consider those speakers because I would hate to listen withy head in a vice. Why would anyone buy them? Also, it's interesting the manufacturer ident seem to have measurements on the website. I wonder why?
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Danny thanks a bunch for the clear explanation.
Jackman upper tweeter has a waveguide on the Argos making the sweetspot larger. And that's always a good thing imho.
I did find a review of that Mac speaker and moving from left to right the #2 and #4 tweeters are wired out of phase which as you guys know cancels the output of tweeters #1 and #5. Leaving the output of #3 tweeter being the one we hear. I don't get that as being a logical and efficient way of producing a speaker. Btw I ran across a Mac dealer who is selling those speakers for $499 each. That's for a $2000 retail of each speaker. That speaks loudly of a speaker that isn't selling. And for the dealer to sell them at a discount would require the ok from Mac themselves. In other words the speakers just, suck.
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Danny thanks a bunch for the clear explanation.
Jackman upper tweeter has a waveguide on the Argos making the sweetspot larger. And that's always a good thing imho.
I did find a review of that Mac speaker and moving from left to right the #2 and #4 tweeters are wired out of phase which as you guys know cancels the output of tweeters #1 and #5. Leaving the output of #3 tweeter being the one we hear. I don't get that as being a logical and efficient way of producing a speaker. Btw I ran across a Mac dealer who is selling those speakers for $499 each. That's for a $2000 retail of each speaker. That speaks loudly of a speaker that isn't selling. And for the dealer to sell them at a discount would require the ok from Mac themselves. In other words the speakers just, suck.
Hi Harley,
Thanks for the info but I'm now confused. How can a waveguide make the sweet spot bigger? I thought waveguides controlled directivity and that waveguide looks too small to do that. Also, in my understanding, two tweeters used in this manner results in comb filtering which reduces the sweet spot, right? I was under the impression this cannot be corrected with a crossover or other means. Hopefully the experts will chime in. Also, I'd love to see some off axis plots. Cool looking speakers by the way, I'm just trying to learn.
Thanks
Jack
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The McIntosh are the only speakers I've seen with horizontal tweeter arrays except for some center speakers where they are placed between woofers.
Although somewhat of a rarity, here are some other speakers with multiple vertical tweeters (that aren't line arrays) that also seem to buck the acoustic theory:
Two vertical tweeters:
Axiom M80 v3, M100
Bryston A1, A2, A3, T
Two vertical tweeters separated by 5" midrange (TMT):
Opera Grand Callas (also has 3 vertical tweeters in rear)
Three vertical tweeters:
RBH (multiple tower models)
Steve
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If you had an active crossover network you could possibly do something... "special" with that many tweeters. Would it be worth your time? Hm...
The one huge line array I distinctly remember wasn't too cheap at $25k a pair or so, but it wasn't that impressive either. Did it sound low effort? Yes. But that doesn't explain why it was so boring. The imaging was good in the spot, very good. But I don't prescribe to being overly interested in an overly prescribed sweet spot. Frank Sinatra also sounded like he was shrunk. Are giant line arrays meant to make you and the people in the music feel small? :lol:
It seems to me on the electronics side you can tame (or let free rather) a lot of the "constricted" feel a stereo can give.
The speakers with only a couple tweeters beg the question, what's the crossover like? They may not be playing all of the same frequencies.
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Although somewhat of a rarity, here are some other speakers with multiple vertical tweeters (that aren't line arrays) that also seem to buck the acoustic theory:
Two vertical tweeters:
Axiom M80 v3, M100
Bryston A1, A2, A3, T
Two vertical tweeters separated by 5" midrange (TMT):
Opera Grand Callas (also has 3 vertical tweeters in rear)
Three vertical tweeters:
RBH (multiple tower models)
Steve
They don't really buck the acoustic theory or the laws of physics. They confirm what is known and are actually examples of why such designs are avoided by most companies.
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A follow up question. What happens when a planar or ribbon type tweeter is used in multiples?
Steve
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Just what I was going to ask, Steve. Amongst Eminent Technology LFT-8 owners, there is a set-up called "stacking" two pair of the speakers. It's not literal stacking, it's placing two of the speakers (which are mirror-imaged, tweeters on opposite sides of the left and right speakers) side-by-side, with the edges that the quasi-ribbon tweeters are mounted right up against placed together. This creates a sort of large co-ax driver, with the two quasi-ribbons surrounded by magnetic planar mid/woofers. The problem I saw with the arrangement is that, though the ribbons are next to each other, there is still a couple of inches separating them. Comb-filtering?
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The basic purpose of a waveguide is to control dispersion (popularly now also termed constant directivity), so that in the crossover frequency range, the dispersion of next lower frequency driver (woofer or midrange) matches that of the tweeter. By limiting dispersion the waveguide also helps concentrate the sound into a smaller space thereby increasing ultimate output and efficiency. Amphion is just one company that successfully relies on waveguide design (they also use it to lower the crossover frequency). Although looking similar waveguides are not considered horns which pressurize the sound wave.
By the way this whole effect we're discussing can happen with every speaker designed with a crossover if the size of the sound wave at the involved frequency is high enough compared to the distance between drivers being crossed over (which is one reason why midrange drivers are placed close to the tweeter in most designs).
So, as Tannoy knew decades ago and a few other vendors also apply nowadays, the best application of midrange/tweeter (or woofer/tweeter) is a coaxial driver design which takes care of the comb effect and provides the advantages of a waveguide.
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It's clear when even someone like me can understand it! Okay, last question, why would anyone use multiple tweeters in this configuration? Power handling? It's an added expense and more complexity but I don't understand the payoff. In line arrays I can understan the benefit but in designs with just a few tweeters (or two) stacked vertically or horizontally, I don't see the benefit. :scratch:
The same thing happen in the tubes amps of this expensive brand, its circuits are know to use alot of parts, much more than the average joe amp.
They are not minimalist amps.
Why use huge blue VUs and output transformers in solidstate amps?=Marketing.
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Deadalus also uses two tweeters. I still am not sure what they (think/believe) they gain if what Danny says is 100% accurate.
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A follow up question. What happens when a planar or ribbon type tweeter is used in multiples?
Steve
If you run them in a line with the playing surfaces within or less than an inch apart then you get about the same response as a single continuous driver of the same length.
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Just what I was going to ask, Steve. Amongst Eminent Technology LFT-8 owners, there is a set-up called "stacking" two pair of the speakers. It's not literal stacking, it's placing two of the speakers (which are mirror-imaged, tweeters on opposite sides of the left and right speakers) side-by-side, with the edges that the quasi-ribbon tweeters are mounted right up against placed together. This creates a sort of large co-ax driver, with the two quasi-ribbons surrounded by magnetic planar mid/woofers. The problem I saw with the arrangement is that, though the ribbons are next to each other, there is still a couple of inches separating them. Comb-filtering?
You will not only get comb filtering between the two lines of tweeters but within the planar magnetic sets of drivers as well. And the planar magnetic drivers already play up high enough that they cause cancellation effects with the tweeter in the off axis. Even on their website it clams an accurate phase relationship only to 20 degrees off axis. Beyond that there are some out of phase holes in the response caused by comb filtering. Stacking two side by side like that would greatly compound the problem and limit the sweet spot to about a foot wide spot in front of each speaker.
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The basic purpose of a waveguide is to control dispersion (popularly now also termed constant directivity), so that in the crossover frequency range, the dispersion of next lower frequency driver (woofer or midrange) matches that of the tweeter. By limiting dispersion the waveguide also helps concentrate the sound into a smaller space thereby increasing ultimate output and efficiency. Amphion is just one company that successfully relies on waveguide design (they also use it to lower the crossover frequency). Although looking similar waveguides are not considered horns which pressurize the sound wave.
By the way this whole effect we're discussing can happen with every speaker designed with a crossover if the size of the sound wave at the involved frequency is high enough compared to the distance between drivers being crossed over (which is one reason why midrange drivers are placed close to the tweeter in most designs).
So, as Tannoy knew decades ago and a few other vendors also apply nowadays, the best application of midrange/tweeter (or woofer/tweeter) is a coaxial driver design which takes care of the comb effect and provides the advantages of a waveguide.
Yep, that's all right on the money.
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Hey Jackman,
Here's what I was told about my speakers and from reading article's. To get a look at my speakers go to Vapor Sound to the Aurora. The White pr. are mine. The waveguide of the tweet is rather large and the mid/bass has a much smaller wg. The wg on the tweeter makes it possible to lower the xover to 1000hz. How steep the xover is I don't know as I never asked, as I was very surprised with the xover point and had to know how that was possible!! Apparently, the wg increases the output of the sound from the tweeter so the xover can be lowered and another benefit is lowering of distortion as the tweeter isn't working as hard. Currently I have a sweetspot about 4' wide. Imaging suffers somewhat at the outer edges of the sweetspot but, there is still a credible soundstage. I look at imaging as an audiophile thing that has no place in music. It just isn't how we ear at a live event so it doesn't bother me. That's the info as I understand it. I hope I haven't made it more complicated than it has to be in my explanation.
Danny, do I have it right or I'm I just in the ballpark. I do look forward to the facts from Danny.
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You will not only get comb filtering between the two lines of tweeters but within the planar magnetic sets of drivers as well. And the planar magnetic drivers already play up high enough that they cause cancellation effects with the tweeter in the off axis. Even on their website it clams an accurate phase relationship only to 20 degrees off axis. Beyond that there are some out of phase holes in the response caused by comb filtering. Stacking two side by side like that would greatly compound the problem and limit the sweet spot to about a foot wide spot in front of each speaker.
Do Magneplanars also, then, suffer from comb filtering, as they have narrow quasi-ribbon or true-ribbon tweeters running vertically, side-by-side with wider quasi-ribbon or magnetic-planar midrange and bass drivers? Then there is Peter Gunn, who removes the Magnepan cross-over and replaces it with symmetrical first-order filters as part of his Maggie mod. Do the 6dB/octave slopes engender more comb-filtering than do higher-order slopes? Bruce Thigpen, the designer of the Eminent Technology speakers, credits the first-order cross-over in his LFT-8 for the excellent blend between the push-pull magnetic planar mid-range driver and 8" cone-woofer in that speaker that reviewers have noted.
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Hey Jackman,
Here's what I was told about my speakers and from reading article's. To get a look at my speakers go to Vapor Sound to the Aurora. The White pr. are mine. The waveguide of the tweet is rather large and the mid/bass has a much smaller wg. The wg on the tweeter makes it possible to lower the xover to 1000hz. How steep the xover is I don't know as I never asked, as I was very surprised with the xover point and had to know how that was possible!! Apparently, the wg increases the output of the sound from the tweeter so the xover can be lowered and another benefit is lowering of distortion as the tweeter isn't working as hard. Currently I have a sweetspot about 4' wide. Imaging suffers somewhat at the outer edges of the sweetspot but, there is still a credible soundstage. I look at imaging as an audiophile thing that has no place in music. It just isn't how we ear at a live event so it doesn't bother me. That's the info as I understand it. I hope I haven't made it more complicated than it has to be in my explanation.
Danny, do I have it right or I'm I just in the ballpark. I do look forward to the facts from Danny.
Yep, the wave guide will increase the tweeters output in the lower ranges and allow a much lower crossover point.
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Do Magneplanars also, then, suffer from comb filtering, as they have narrow quasi-ribbon or true-ribbon tweeters running vertically, side-by-side with wider quasi-ribbon or magnetic-planar midrange and bass drivers? Then there is Peter Gunn, who removes the Magnepan cross-over and replaces it with symmetrical first-order filters as part of his Maggie mod. Do the 6dB/octave slopes engender more comb-filtering than do higher-order slopes? Bruce Thigpen, the designer of the Eminent Technology speakers, credits the first-order cross-over in his LFT-8 for the excellent blend between the push-pull magnetic planar mid-range driver and 8" cone-woofer in that speaker that reviewers have noted.
The side by side placement of the drivers in the Maggie does open the door for out of phase cancellation in the horizontal off axis. How much or how bad depends on the slope and crossover point.
Shallow slopes do often allow smooth driver transitions. But because each driver plays further over into the range of the next it does open things up for more cancellation patterns in the off axis when one driver is delayed in time verses the other. And while at the crossover point a given off axis may not have enough time delay for complete cancellation, but one octave above that there is still plenty of output left to cause cancellation and a big dip in the response. So with first order crossovers dips in ranges above the crossover point are common.
Crossover point is critical in these alignments. Let's say the crossover point is 4kHz. At that frequency range the wavelengths are less then 3.5" long. So 15 to 20 degrees off axis is enough to create 180 degrees or more of phase rotation. But if the crossover is low like our LS-9 for instance, then everything changes. The LS-9 crosses over at 850Hz. In that range the wavelengths are over 15.5" long. So 15 to 20 degrees off axis might only cause 10 to 15 degrees of phase rotation. Even 90 degrees off axis is only about 80 degrees of phase rotation.
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About how much phase rotation need be present for it to cause an audible problem, with cancellation?
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About how much phase rotation need be present for it to cause an audible problem, with cancellation?
If phase rotation at a given frequency is out by 90 degrees between two drivers then they neither couple or cancel each out out. The output is the same summed as they are individually.
If you start reducing that phase rotation back to less than 90 degrees then they start to couple and you get gain with a maximum amount of gain at 0 degrees of rotation.
If you start increasing the phase rotation past 90 degrees then you get less output than from either single driver. And at 180 degrees out they are completely out of phase and cause maximum cancellation.
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Here is a good illustration.
These are the measurements of two 3" full range TB drivers. They are in separate boxes but the drivers are near the ends of the box. They are on top of each other keeping the acoustic centers to within 5" pf each other.
They are measured at 1 meter and with one watt. The mic is dead center between them.
Red and green lines are each driver playing individually, and the blue line is the two drivers playing together. Note too that it was not easy to get the mic dead center. Just a fraction of an inch up or down and cancellation would occur in the top end.
(http://gr-research.com/pics/dead%20on%20in%20the%20middle.jpg)
Now this is what happens when the mic is moved up 4". Note how the shorter wavelengths in the upper range are now out of phase.
(http://gr-research.com/pics/up%204%20inches.jpg)
Here is what happens moving the mic up another 4". It is now 8" above center. Note now that cancellation points are in two places.
(http://gr-research.com/pics/up%208%20inches.jpg)
Okay, up 4 more inches making the pic 12" above center. Now there are three cancellation points.
(http://gr-research.com/pics/up%2012%20inches.jpg)
The change in vertical off axis hardly effects each individual driver, but you can see the curves change some from the mic being off axis to them. But the cancellation effects are tremendous. Dual tweeters stacked one over the other has the same effect.
This causes an irregular floor and ceiling reflection that takes away some of the airy spacial cues that help create a layered sound stage.
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Thanks for the Acoustical Engineering 101 class Danny. :green: It should be required for subjective reviewers!
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"Thanks for the Acoustical Engineering 101 class Danny."
+1
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The ET LFT-8 has a 10K Hz x/o from the midrange panels to the Quasi-Ribbon tweeter strip (not a typo.....10,000 Hz!), with 1st order slopes in both directions. Will stacking the tweeters next to each other (with, say, three inches separating them) result in comb-filtering, at that high a frequency? The lower x/o, from the panel to the woofer, is also 1st order, at 180 Hz. The Magnetic Planar driver has a 180 to 10,000 Hz bandwidth in the speaker! The cone woofer is 8", and it's in a 0.75 cu.ft. sealed cabinet. Anybody thinkin' what I'm thinkin'?
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The ET LFT-8 has a 10K Hz x/o from the midrange panels to the Quasi-Ribbon tweeter strip (not a typo.....10,000 Hz!), with 1st order slopes in both directions.
That will cause cancellation in the left and right off axis response as just a little movement in either direction will make them out of phase.
Will stacking the tweeters next to each other (with, say, three inches separating them) result in comb-filtering, at that high a frequency?
Sure. They would easily cancel each other out. The further you separate them the worse it gets.
The lower x/o, from the panel to the woofer, is also 1st order, at 180 Hz. The Magnetic Planar driver has a 180 to 10,000 Hz bandwidth in the speaker! The cone woofer is 8", and it's in a 0.75 cu.ft. sealed cabinet. Anybody thinkin' what I'm thinkin'?
Servo woofers baby! All open baffle!
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Danny, here is one other configuration that I've not seen anywhere else. Although XTZ uses a single tweeter for all of their stereo speakers, their "Cinema Series" M6 (LCR) speaker has a "Quad-Tweeter array".
The explanations given are:
"M6 is separate Left and Right speakers to avoid mid mounted tweeter problem"
"The four 1" soft dome tweeters are arranged in a special way to ensure not only a perfect balanced dispersion between to cover the listening room whith same timbre and on the other side not to wide spreading to get negative influenced sound from the room .The controlled dispersion is possible because of the usage of four tweeter and this is also the reason for the clean sound even the level is very high ."
"3 of the tweeter works from 1.2kHz to 3kHz and they control the dispersion in this very sensitive frequency range. This means no phase problem in the very, for the ear, sensitive range 2-6kHz there is no crossover point as in most speaker."
"The quattro tweeter also helps to control the spreading perfectly both in tweeter range and in the midrange. It gives a optimized vertical directivity to reduce floor and sealing reflections and a controlled dispersion in horizontal direction."
"Controlled directivity but still no “beaming” effect . Quatrro array give also advantage like avoid early reflections from sidewalls.The placement of the four tweeter improve the diffraction effect and the extra baffle improve it further.But by use take advantage of placement and using the baffelstep effect the energy is pointed into the listening room and less on the outside and this reduce the early reflections from sidewalls."
What is your take on this very unusual tweeter grouping?
Steve
(http://www.audiocircle.com/image.php?id=97080)
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Steve,
If three of the tweeters are only playing up to 3kHz then there will likely be little cancellation between them even in the off axis. The 3kHz wavelength is about 4.5" long.
If they all played to the top then there would be a comb filtering effect that will limit the off axis to about the same as the small woofers used with them.
2kHz to 6kHz is not a critical range for the ear though. You are already getting out of fundamentals and into harmonics in those ranges.
And despite what they may think, it will NOT "help to control the spreading perfectly both in tweeter range and in the midrange". Most people don't realize that the mid-range is in the 300Hz to 500Hz range.
And I am not really sure what they are thinking on this one:
"Controlled directivity but still no “beaming” effect . Quatrro array give also advantage like avoid early reflections from sidewalls.The placement of the four tweeter improve the diffraction effect and the extra baffle improve it further.But by use take advantage of placement and using the baffelstep effect the energy is pointed into the listening room and less on the outside and this reduce the early reflections from sidewalls."
None of that is really true. And did they really use grammar errors in their ad? It reads like it was written by a Chinese fellow that really is not fluent in English.
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That will cause cancellation in the left and right off axis response as just a little movement in either direction will make them out of phase.
Sure. They would easily cancel each other out. The further you separate them the worse it gets.
Servo woofers baby! All open baffle!
Exactly! I'm using 12's, but three 8's would make for a narrower cabinet. And for he who, for whatever reason, doesn't want to go OB, one of the Servo 8's could be put in the sealed 0.75 cu.ft. box, replacing the ET woofer.