[smccull]

I've been reading about open baffle speakers for some time now and am very intrigued. I listened to a couple designs at the last RMAF, Nola speakers and a model by GR Research, and was very impressed with the openness and soundstage. However, I have a rather unfortunate room delimna and want to get your impressions on whether OBs would work in my room.

I have a den that doubles as HT and two channel audio. I have a rather large entertainment center that hold my LCD and associated gear and it sits right between the speakers. My current speakers sit with their front planes about a foot in front of the cabinet and that's about as far out into the room as anything will go.

I have a rather poor soundstage with almost no depth. One of the things I like most about OBs is their ability to throw a stage. I am wondering if OBs will work in my room, or will the entertainment center reflect too much from the back and side wave, making the imaging even poorer than I have now?

Does anyone have any experience with this? HT is a secondary concern for me, so I'm not too worried if it isn't the perfect solution for HT. 2 channel is always my highest priority.

Many thanks!

[Paul Hynes]

Hi Smccull,

Check out the “open baffle line array – need advice” thread. Line arrays have very low room interaction by virtue of their wavefront propagation pattern. The ones I am using are around 2 feet drive unit distance from the rear wall, at present, and the rear wall reflections are not upsetting the imaging depth. By the time these reflections reach the listening position they sound like part of the hall acoustic. My system setup is two channel for music with the AV kit grafted in (still in stereo) all racked up between the speakers. Good program sounds very live with a natural, three-dimensional, soundstage perspective. Dynamic range is awesome and subtle at the same time. All types of music are very well presented and blockbuster movies are spectacular with these speakers. The whole family are in love with the sound of these speakers because they sound so musical. My lady has asked me not to remove the speakers from the system under any circumstances if I want a happy life. I concur with her enthusiasm.

Regards
Paul

[JLM]

I'd get rid of the "entertainment center".  (Never did understand how furniture entertains or why you'd want to spend money to limit yourself into whatever sized cabinet you bought.)   No speaker is going to image through a large box sitting between speakers.  And the little "caves" that the speakers sit in will just make the bass excessively boomy.

By definition OB speakers are open.  They radiate both in front and behind.  They need room to "breath".  Most speakers are designed to be located at least 3 feet from any walls or large obstructions.  It should be obvious that anything called "open" works best with even more clear space.  As it stands, your situation is almost the worse possible scenario for OB.

There is another version of OB that this circle hasn't covered much, the IB (Infinite Baffle).  These are used primarily for bass reinforcement and typically wired like a subwoofer with their own amp).  The speakers are mounted on the wall (or in a small recess) and the back wave goes into a large space (attic, garage, basement, spare room, even outdoors).  Using IB speakers allows smaller OB (or any other kind of speaker) to be used.  Goggle the cult of the infinitely baffled.

[smccull]

I'd love to get rid of the entertainment center, or move the 2 channel to another room. However, I also want to stay married. 

[Paul Hynes]

Hi JLM,

I agree it would be nice to get rid of the “entertainment centre” but unfortunately many have limited space in their homes, particularly over here in the UK. At present, I am limited to one reception room, where all entertainment functions have to be integrated. This will change shortly as we are moving house soon and I will have a specific room for the sound system. I am quite sure that I will then be able to benefit from the ability to optimise the listening room.

Whilst compromise may be necessary for many people, with care and attention regarding choice of equipment and positioning, you can reduce room/equipment interaction effects to levels where they are not particularly problematical. A lot of equipment in the marketplace is just incapable of good, three dimentional imaging, or accurate tempo for that matter, no matter what you do, so be careful what you buy. Avoiding loudspeakers that excite room resonances and resonant equipment cabinets is a good idea. I am fortunate that I have solid concrete block walls to mount equipment shelves on. This is a relatively low resonance arrangement compared to equipment cabinets. The floors are also concrete and we can dance as energetically as we want without bouncing the cartridge across the record.

Single driver OB speakers benefit from lack of cabinet resonaces but can still be prone to room/equipment interaction problems via floor, ceiling and wall reflection, which can interfere with imaging. A single driver open baffle loudspeaker propogates a spherical wavefront which expands into the room encouraging reflections off floor, ceiling and walls. These reflections have a short time delay due to increased path length from source to destination. The ear/brain mechanism uses the initial wavefront to localise the source of the sound, and the short time delays of the reflections can confuse the perceived location of sound sources, consequently muddling the imaging.

The open baffle line source configuration changes everything whilst retaining the advantage of the lack of cabinet resonances. The line propogates a cylindrical wavefront over it’s full length. This wavefront is much more directional than the spherical wavefront of the single driver. The wavefront doesn’t bounce off the floor and ceiling and has a much reduced energy level by the time it hits the wall. Because of this the imaging is much better than any single driver speaker in the average room. Also, any energy that makes it to the edge of the baffle, benefits from phase cancellation, reducing sound pressure level to the sides of the speaker considerably. This leaves the rear reflections from the back wall. Fortunately the time delay for this wavefront is long enough not to interfere with the initial wavefront that we use for sound localisation, and it appears to us as part of the room reflections of the recording acoustic. This is a generally benign addition to the sound field. Because of the low interaction with it’s surroundings, the open baffle line source is a very good option if you have to site your equipment between the speakers. Also the bass is very natural and open and it is certainly not boomy even though I have had to site mine near the corners of the room.

Placing objects between the speakers will only affect the image if they resonate due to energy from sound waves, or if they reflect energy from sound waves, so it makes sense to minimise these effects as much as possible. A sound source in the image may appear to emanate from the same position as the object between the speakers, but it is not generated at this position. The sound source is generated by the speakers to the left and right of the object and placed in the sound field by our brain’s analysis of the phase and amplitude information the ears receive. Keep that information as clean as possible and you will have a good image.

In practice, my line source speakers are behaving very well, even in a smallish room. The image is very solid and three-dimensional. I would certainly recommend this type of speaker for it’s very tangable benefits.

Regards
Paul

[JLM]

Paul,


I have two issues with line arrays:

1. Blending of the sound waves from each driver for a given driver size and frequency ends up requiring literally dozens of drivers and a great deal of cabling, all of which adds complexity and cost (unless quality of driver/cable is sacrificed).

2. With the vertical line the speakers cannot differentiate sound vertically, so I don't know how a such a speaker could image vertically.


I too like the open baffle sound, but I like deep/clean/musical transmission line bass/midrange even more.


What might work best in this case is a rather forward sounding speaker along the lines of a Klipsch Heresy (high efficiency with a horn tweeter) to get the sound out front of the TV and furniture.

[smccull]

Paul,

Thank you for the well written and detailed reply. I've been intrigued by single driver OBs but you make some very valid points. Ones I've been concerned about.

Are there any OB line arrays you'd recommend that I seek out to listen too?

Thanks!

[Paul Hynes]

Hi JLM,

I understand your concerns with line arrays. Before I began designing my array I spent a lot of time looking for information and was almost discouraged by some of the issues raised by my search results. Fortunately I tend to consider things carefully and try to look at all the angles before making any decisions. One such issue was “comb” effects from using multiple drive units. Loudspeaker measurements are often taken at 1 mtr distance from the front of the drive units and everybody happily considers this to be normal, but it doesn’t give a true picture at the listening position. If you run the measuring microphone (or your ears) up the line at a distance of 1 mtr the amplitude response is very bumpy, hence the term comb effect. At 2 mtrs the response is much smoother. In fact the futher away you measure the smoother it gets. If I am in a serious listening mood, I usually sit at around 3 mtrs where the comb effect has become negligable, especially as I don’t keep moving my head up and down. Any frequency dependant lobing effects are also smoothed out at this distance and I have tried many other types of speaker, particularly those that use separate bass, mid and treble units, that are audibly much worse in this respect than the line array.

Also most line source arrays are wired in a series/parallel configuration to keep the overall impedance at a managable value to remain compatible with normal amplifiers. Unfortunately the reactive impedance of a drive unit in series with another drive unit causes interaction between the drive units and loss of electrical damping from the amplifier. I have wired my speakers in such a way that I can program the impedance with banana plugs. I can wire in series parallel for either 3 ohms or 12 ohms, or I can wire all drive units in parallel. I much prefer the parallel arrangement, even though the impedance is 0.75 ohms (I had to re-design my amplifier to drive this load). If I wire in the series/parallel configuration the imaging and musical tempo looses cohesion and becomes poorly defined.

Although the ears can resolve height information in real life due to the ability to differentiate small time delays from reflections around the ear lobes, a point source single drive unit can’t resolve a vertical image. You would need additional microphones to record vertical information, additional vertical channels in the signal processing and additional speakers above the normal stereo speakers to do this reasonably well. That said, some systems can give the illusion of physical height and it would be interesting to understand this mechanism more fully. I suspect that amplitude and frequency lobing effects may contribute to the illusion, but I have not done any tests in this area. It is possible that the brain is helping a little here as well.

The line source presents a solid body of sound, which I think helps with the illusion of physical height. It certainly gives a good illusion of a live music performance. I’m sure that the high efficiency (105 dB for 1 watt at 1 metre) and effortless dynamic reserve helps with this also.

I’m not keen on forward sounding speakers. I prefer my speakers to disappear leaving the original recording perspective and acoustic for me to enjoy. This line source achieves this and the equipment between the speakers is not getting in the way.

I know that the cost of this line array is somewhat above the normal DIY budget for a single project, but it sounds so good that I consider it to be an excellent investment.

It’s getting very late over here and I have to be up and about early tomorrow, so I am off to sleep. Goodnight all.

Regards
Paul

[Paul Hynes]

Hi smccull,

Thank you for your comments. I try to make things as clear as I can, within the boundaries of my experiences, but sometimes the posts can get a bit long.

I don’t think that there are many OB line arrays in production. I haven’t seen any in the UK. And unfortunately I can’t advise you here because I haven’t tried any comercial offerings, as I don’t normally use other manufacturers products as a reference. Only live music. One thing I am certain of is that cheap £5 drive units will likely give rather indifferent results. It’s definitely worth spending on good drive units. The baffles, stands and wire don’t cost much.

Goodnight.

Regards
Paul

[stereogeek]

I have been a lurker here for a long time,but had to register to put in my 2 cents worth on this subject.

I have a very large entertainment center myself.The wife would rather shoot me than get rid of the entertainment center! It is about 7 foot tall and wide enough to hold a 35 inch glass tube TV.

I also have Hawthorne Audio Silver Iris OB's on either side of the entertainment center.The back wall is only 12 foot wide.I have the OB's centered between the entertainment center and the side wall and 2 feet out from the back wall(about the depth of the entertainment center).

Some of my reasoning behind choosing the OB's,was the figure 8 radiation pattern and the nulls to the sides.The reflections off the entertainment center was a major concern.

When listen to the system,I can not tell a difference between the OB's normal position and when I pull them out in the room(to reduce the reflections off the entertainment center).I guess I've accomplished my goals of reducing room interaction with the OB's!

Steve

[JLM]

Paul,

In my experience OB provides more of a "wall of sound" and less pin-point imaging that audiophile main stream goes for.  This more detailed imaging is more accurate and allows for greater levels of detail as I've found switching amps which has resulted in smaller, better defined, and more detailed sound from a given instrument (like taking glasses on and off a nearsighted person).  OTOH the recording industry has gone "over the top" with hyper detail, IME.  I may not care to know what the singer had for breakfast or to sit on their lap during the performance.  OB helps the brain "relax" from trying to analyze precise imaging and detail so that it can concentrate on the emotive aspects of the music.

Psychoacoustics (the study of how we hear, not of audio nuts  ) might help explain how much the brain augments what a given speaker produces to provide a more complete picture.  For instance, from an old LP (using small two-way stand mounted speakers) I’ve heard a coin roll off the bar, hit the floor, and roll around with sufficient detail to be able to point exactly where the coin was and how far it dropped.  Such point source speakers have always provided a more coherent sound.  Which design provides a more natural sort of sound is certainly open to many viewpoints.

I’m of the KISS (keep it simple stupid) camp and your description of various wiring patterns, lots of wiring, multiple banana plugs/drivers, and having to re-engineer the amp all goes against my grain.  A line array OB takes the “wall of sound” to a new level.
 It’s hard to imagine all that sounding better than my $375 USD full range drivers wired directly to monoblocks.  With my nearfield setup we’re at different ends of the audio universe, but to each their own.  I’m very glad we’re not all alike and eager to celebrate the differences.

OB is my second favorite form of speakers.  If I could have two main systems, these are speakers I’d start the system out with:  DIY Loudspeaker Project: Feasting on the Feastrex full range driver and Augie woofer. Review By Dick Olsher


BTW I don’t care for speakers with a “forward” presentation either, but in the case at hand it might offset some of effects from the speakers being located in the recessed corners of the room.

[Paul Hynes]

Stereogeek

Hi Steve,

It’s great that you have your wife on your side with the entertainment centre. Many I know just get grief about their systems. My family love listening to music of all types but also enjoy a good blockbuster movie. They are not interested in the technicalities but they give me unbiased opinions about any subliminal problems with the sound, which is beneficial to my system development. Whilst the present frequency balance is something we can live with, the consensus of opinion at the moment is that we could do with a little more treble extention. Not surprising if you look at the B200 response curves. I suppose I will have to put this on the list of jobs to do. I will try passive EQ in the line preamp first and if that is not satifactory I will have to pester circle members for information on suitable super tweeters.

It looks like you face similar space restrictions to me and have found a suitable solution. How is the imaging from your Hawthorne drive units? I haven’t found imaging to be a problem with the B200 OB line source. They are just very good at disappearing sonically.

There is a lot of work going on with OB speakers all around the world and drive unit availability and quality is improving. This can only be a good thing for our quest for good sound.

Regards
Paul

[Daygloworange]

2. With the vertical line the speakers cannot differentiate sound vertically, so I don't know how a such a speaker could image vertically.

If what you are referring to is the vertical height of the soundstage, I would think that a line array by virtue of low distortion due to the multiple drivers sharing the work, should perform better in all areas of soundstage. Anything you do to lower distortion is going to improve the spatial cues recorded in the music.The early and late reflections that propagate after a sonic event are paramount to localizing sounds.Hearing them reproduced clearer will add to realism. In an ambient miking recording, you are (for the sake of illustration) using 2 mics to pick up a stereo signal. They cannot in and of themselves separate sounds vertically and horizontally. Neither can a speaker. The early and late reflections, and amplitude differences between right/left are what give us cues to spatial positioning. The better the resolution, dynamics, frequency response, and the lower the distortion, the better the imaging.

In my experience OB provides more of a "wall of sound" and less pin-point imaging that audiophile main stream goes for.  This more detailed imaging is more accurate and allows for greater levels of detail as I've found switching amps which has resulted in smaller, better defined, and more detailed sound from a given instrument (like taking glasses on and off a nearsighted person).  OTOH the recording industry has gone "over the top" with hyper detail, IME.  I may not care to know what the singer had for breakfast or to sit on their lap during the performance.  OB helps the brain "relax" from trying to analyze precise imaging and detail so that it can concentrate on the emotive aspects of the music.

If you are talking single driver open baffle, perhaps that is the case. I suspect that might be due more to the limitations of the driver than the open baffle concept it resides in. In my GR Research OB 5's the imaging is really a step above what I had previous. Partly due to the sheer performance of the Neo3 planar magnetic tweeter, and the uncolored sound of the mid drivers in the open baffle section.

I don't think that it's the case at all that the industry has gone towards "hyper detail" in a negative way. Hyper detail is just the result of audio equipment performing closer to the theoretical optimum.

I'm not sure what you mean by OB helping the brain relax from trying to analyze hyper detail. One would only conclude from that statement, that a live performance, would be un-enjoyable, due to too much realism.    If anything, the much improved resolution of my system over time has allowed me to fall even deeper into an almost trance like enthrallment of the music I happen to be listening to.

Cheers

[Paul Hynes]

Hi JLM,

A “wall of sound” implies a flat, two-dimentional image. I don’t have that with my system. The image is three-dimentional with good depth and width, and it’s stable and solid in that it doesn’t get muddled or shift around under any dynamic condition at realistic listening levels. There is no hint of the actual physical position of the line arrays as the sound field is completely divorced from them. Also there is a wealth of detail in the musical events they portray that allows the music to sound like a live performance with real people playing and singing. I’ve been to many live unamplified classical, jazz and folk music concerts and instruments and singers sound much larger than a pinpoint. I have also played a vintage Fender Stratocaster through a marshall stack (two cabs) when I played in bands as a teenager. The line source can reproduce this without wilting.

When I trialed the B200 as single driver OBs they just didn’t have the weight and scale of the line and they sounded more coloured as I had to drive them a lot harder the get the required listening levels. I have to admit that, at first, they sounded diffuse and didn’t image well, but they had to burn-in for a while to achieve their best imaging performance. They were on song after about a month of usage with approximately 6 hours per day playing time.

I like to keep things simple. The banana plug impedance programing is a compromise I had to make to enable me to demonstate the speakers with normal amplifiers. I would prefer to have just hard wired all units in parallel so they behave as one drive unit. This will happen in time.The power amplifier is a single mosfet with the source is DC coupled to the load. With an efficiency of 105 dB for 1 watt at 1 Metre I don’t need any voltage gain as the line preamp has enough gain for all my music sources. The re-design was simple. It was originally designed to give 10 watts into 6 ohms for the single B200. I just had to drop the supply rail voltage and increase the standing current to drive the low impedance line. The line preamp is a single FET voltage gain stage (very neutral and transparent) for every day use. You can’t really get much simpler than this. I sometimes use my 300B line preamp, when I want a warmer glow to the music.

The path to audio nirvana is littered with moments of “it’s hard to imagine a better sound” until the next upgrade comes along.

Regards
Paul

[Paul Hynes]

Hi Daygloworange,

You are right about the low distortion of the line array. The cones are hardly moving most of the time. This is bound to reduce cone breakup and resonance nodes considerably for a given SPL and you can hear the improvement over the single drive unit version instantly. Really there is just no comparison.

If cheers means you are going for a drink, I’ll join you.

Regards
Paul

[Daygloworange]

Hi Daygloworange,

You are right about the low distortion of the line array. The cones are hardly moving most of the time. This is bound to reduce cone breakup and resonance nodes considerably for a given SPL and you can hear the improvement over the single drive unit version instantly. Really there is just no comparison.

I spent some time listening to a pair of McIntosh line arrays in a dealers room. It was a complete McIntosh setup. It was a unique experience. Some point source speakers are better than other's at disappearing in a room, but the line array is the best I've ever heard at that. Placement of sounds is really accurate, as is the delineation around them. The space between instruments is more clearly defined as well. The outer edges of the envelope in which the sounds are residing in, within the soundstage are crisp, well defined, and clear.



It's kinda like HDTV, compared to DVD. DVD being really good, HD being better.

If cheers means you are going for a drink, I’ll join you.

Regards
Paul

Ok, but you're buying. 

Cheers

[stereogeek]

Paul-

You're right about my wife being a good sport.Originally,the entertainment center had side cabinets(glass front nic-nac cabinets).They were moved to the bedroom to make room for the new speakers.She did say I went too far when I got Alpha 15's to go under the SI's for additional bass for LFE duty.

Right now,the SI's are on temporary MDF baffles and are hooked to the old Sony HT in a box receiver.I'm building a Charlize to replace the Sony.My wife is unknowingly is breaking in the SI's for me.She runs them 12-15 hrs a day for me.

I am a former live sound engineer.Being that the SI's are based on Eminence pro drivers,I was worried that they would have the "baseball stadium sound".This sound has disappeared after a couple of weeks and are really turning out to be great sounding drivers.Last night while watching regular TV,I noticed how accurate these things are! I watched a live concert of Elton John on VH1.The stage was very wide with very distinct space between the instruments.While watching an adventure show on Discovery,I noticed that the male voices had quite a bit of depth to them.If 2 people were standing in front of each other,you could tell who was in front and how far the person in back was behind the other person.The SI's very accurately presented what i was seeing on the TV,whether it was a "wall of sound" or one person standing in a certain spot.

I have just started this project.I have a long list of things to do.With what I have heard so far,I am expecting great results from these drivers.

Steve

[Paul Hynes]

Hi Daygloworange,

Your appraisal of line source performance is spot on. Even line source speakers I’ve built using some low cost drive units display much of the line advantages, although, as ever, the better the quality of the drive units the better the performance. A good line, like the McIntosh, will take you to the performance, which is all I care about.

Other loudspeaker designs may have their merits, and I have tried most of them (I’ve been an audio fanatic for 39 years), but none of those designs can do it like a good line array. That said I have had some fun moments with some horns that I designed using Jack Dinsdale’s Wireless World horn theory articles (UK magazine) from the seventies. They were around 2 metres high as well. I think one key issue was that, like the line, they could move a lot of air easily and efficiently, which gives tangable body to the performance. I still prefer the line array that I have at the moment, probably because they have less audible colourations than the horns, and my perception of the timbre of the instruments is closer to reality.

If I ever get over to your part of Canada, I will buy you a drink.

Cheers

Paul

[Daygloworange]

Paul,

Can you give some more details about your arrays? Do you have some pics?

I have also played a vintage Fender Stratocaster through a marshall stack (two cabs) when I played in bands as a teenager. The line source can reproduce this without wilting.

If you come over to Canada, you'll have to bring a Strat along with you. Don't worry about an amp, you can plug into one of mine.



All I play are Strats as well. 5 Fenders, and 2 Schecters. Amps are '72 Mrk II 50 watt, '69 Super lead 100 watt, '78 JCM Lead Series 100 watt. Can you spell "TONE" ???? 

Cheers 

 

[Paul Hynes]

Stereogeek

Hi Steve,

Looks like you have a good assistant there to help with the tedious stuff like breaking drive units in.

I think that a lot of knowledge from the pro audio sector is applicable to music reproduction in the home. You guys have to get things right first time and each venue can be so different from the last, indoors, outdoors, big, small and awkward shaped spaces to fill. You get a feel for things with that accumulated expereince that the average DIY enthusiast may not have.

I’ve had a similar experience with UK based Precision Devices drive units. TurboSound used them in their concert riggs. They make good hifi units once they have run in and they are very efficient. I used them to design a PA for local folk musicians. I had some in my home system at the time and some friends who were part of the local folk club circuit were impressed enough to ask me to set up a PA for them. They wanted an invisible PA so that you couldn’t tell they were using it (they liked playing unamplified). I also designed a tube mixer and tube instrumental preamps for them as well as a heavy-duty mosfet current feedback power amplifier. The whole thing was very transparent and dynamic. They were happy.

Good luck with your project.

Regards
Paul