Placement options – Impacts of location, orientation and treatments

Jon,

I would also like to add my sincere thanks for your thread. It will directly affect my panel choices for when I split off my 2-ch, which I hope will be sometime next year. While there is probably no substitute for serious experimentation, as done by Rich for example, your recommendations will be my command!

benleeys said:

I thought you would say that. Unfortunately, my experience with heavy curtains covering the wall behind my Summits was a sonic disaster. Vocals sounded very much like the singer had a bad cold. Push the curtains aside and the cold disappeared. I wish I have the facility to take measurements like you do to find out the reason why. Obviously heavy curtains was the wrong idea for an absorbent.

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Since I am one of the people who use absorption on their front wall, I can concur with your findings. Too much absorption can really kill the sound to the point of sounding muffled - or the singer having a bad cold as in your analogy.

What I had to do with my space is try different amounts of mid/high absorption along with the corner-ceiling bass trapping (I do not have a very wide front wall). After much trial and error, I found a very happy medium with some absorption, some open bare wall spaces, and the bass traps. But again, in my room, for my setup, and my tastes, this absorption pattern worked the best.

benleeys said:

Unfortunately, my experience with heavy curtains covering the wall behind my Summits was a sonic disaster. Vocals sounded very much like the singer had a bad cold. Push the curtains aside and the cold disappeared. I wish I have the facility to take measurements like you do to find out the reason why. Obviously heavy curtains was the wrong idea for an absorbent.

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My guess is the problem with using heavy curtains was an uneven absorption across the frequency range. In other words, they probably completely absorbed some of the higher frequencies and didn't absorb any of the mid to lower frequencies. Reflection in the midbass can really muddy the soundstage. This is why you want a product that will absorb at an even rate throughout the frequency range (which is what the Real Traps High Frequency Mini Traps do) or you might want a prudent combination of diffusion and absorption behind the panels.

As Dan says, this is all room, system, and individual taste dependant, so the more experimentation you can do the better. If you can spring for a couple of panels from Real Traps or GIK or something similar, I highly recommend it. Even if you don't like them behind the speakers, I am certain there will be somewhere in the room you can place them where they will improve your sound.

DTB300 said:

...
While I would agree that both products are the usual way to go, but don't you think that each room is different hence there is no real "best way"? Going through some trial and error with both products in ones room, and then listening and/or testing will show the best results. Yes?? No???

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Hi Dan, absolutely agree, there is no one formula that can applied to any room. There are guidelines that are pretty widely applicable, but ultimately, initial calculations, backed up by post-installation measurements and listening are the way to go.
What I’m hoping to get form my measurements is some of the generalized guidelines for our type of speakers in the types of rooms we typically put them in.

Now, some of us are lucky and have dedicated spaces, so we can go crazy with the treatments and what not, but even then, there is no real clear guideline for what helps and where should it go.

DTB300 said:

...
Agree. When talking with people in the know and you spurt out the word Electrostatics, they usually come back and state their experience is very limited with them and their products. Have you considered sharing your charts and graphs with people like Ethan to help him sell his products to other ML people - then sign the contract for your percentage of the profits!!! Seriously...I do think they would be very happy for the information on planar speakers and the results of acoustical treatments with them.

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What? Actually make money on my hobby? the horror

But good idea to engage them in positioning their products for the dipole market place (there are maggies as well).

Rich said:

Jonathan, please do a test for me when you get your products in and start placing them. Please do a comparison between placing just the two HF mini traps behind your monoliths and then place the real traps diffusers in front of the HF mini traps (still behind the monoliths). I am have a theory that this would provide some ambiance by diffusing some of the higher frequencies of the rear wave, while providing even greater absorption of the mid and lower bass frequencies. Or just a comparison between the HF mini trap vs. the diffuser alone behind the monoliths would be great. For these tests, I am primarily interested in two-channel sound and imaging. Depending on your results, I may decide to purchase a couple of those diffusers as well. Thanks so much.

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Hi Rich, sure thing, that's a good series of tests to try.

The doubling up of the traps and diffusers should increase bass and mid-bass absorption, as the diffuser also includes absorption elements as well.

Kruppy said:

Jonathan,
Can you please post the manufacturer and name of the diffusers you used for your measurements in the first couple of posts. The white one looks like an Auralex MetroFusor. The darker/black one I can seem to place, looks like an Auralex product.

Right now I'm looking for a combo diffuser/absorber but I don't see anything that is more my (insert deep voice) "budgetary style".....specially if this is something that is experimental/trial and error and may not be permanent.

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Kruppy, that product is RPG ProFoam http://www.rpginc.com/products/profoam/index.htm
In this application, it’s primarily a mid to high-frequency absorber , with an NRC of 1.0 from 500 hz on up.

The 2D difusors are indeed Auralex MetroFusor’s http://www.auralex.com/sound_diffusor_metrofusor/sound_diffusor_metrofusor.asp

The Auralex stuff is fine for HF absorption and diffusion, where I think they miss the mark is on low frequency management. At least as compared to realTraps and GIK.

JonFo said:

Hi Dan, absolutely agree, there is no one formula that can applied to any room. There are guidelines that are pretty widely applicable, but ultimately, initial calculations, backed up by post-installation measurements and listening are the way to go. What I’m hoping to get form my measurements is some of the generalized guidelines for our type of speakers in the types of rooms we typically put them in.

Now, some of us are lucky and have dedicated spaces, so we can go crazy with the treatments and what not, but even then, there is no real clear guideline for what helps and where should it go.

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Like I stated before, there is really no information out there on room acoustics for people with Planar speakers. Your information should prove very valuable for not only us "ML groupies", but hopefully others too.

What? Actually make money on my hobby? the horror

But good idea to engage them in positioning their products for the dipole market place (there are maggies as well).

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GIK and Real Traps have been very informative not only online for information, but also in private emails with myself. Maybe I can get them to stop by and comment on this thread??

Kudos to Jonathon for this thread! I've long wanted to conduct my own speaker/room acoustic response measurements, only lacking both equipment and time!

Anybody know if the Denon 3808CI (or 4308CI) with the built-in Audyssey MultiEQ XT can interface with a PC to display and/or print the frequency responses they measure? I know both receivers are "Audyssey Pro Installer Ready", but I'd prefer the DIY approach.

An interesting opinion...

Serendipitously, I stumbled upon an audioasylum thread from Charles Hansen of Ayre (who makes some of the best SS equipment of the planet at most affordable prices) regarding room treatments.

By the way, I tried the chair method he talks about, and it works a bit. I wonder how this would measure.

.... FWIW, here are my opinions on these topics:

1) When TubeTraps came out 20+ years ago, I bought as many as I could afford. The theory made perfect sense, and they seemed to provide significant gains in the overall sonics. But over the years I have become less and less enchanted with room treatments.

The first truly negative experience was at the January 1994 CES (the debut of Ayre). We had a CAT preamp, an Ayre V-3 power amp, and a pair of Avalon Eclipse loudspeakers. There was a nasty bass bump around 80 or 100 Hz. We tried all kinds of TubeTraps in all locations and combinations, but could not get rid of the bass bump in the room. About midnight before the show opened, a very nice gentleman (I think his name was John Gallas) stopped by with his version of bass traps. He was a math teacher from LA and just made the traps on the side. I'm here to tell you that two of his traps outperformed a dozen or more TubeTraps. The problem with the TubeTraps were two fold:

a) They didn't really absorb much energy below 100 Hz (even the big 16 inchers). So they sucked all of the impact out of the mid-bass (100 - 200 Hz) without solving the hugely audible problem below that.

b) They have an absorptive side and a reflective side for frequencies about 500 Hz or so. But no matter how you rotate them, the will create uneven absorption versus frequency, skewing the tonal balance.

The trap by Gallas were much better. We ended up using these for a few years. But by then we were on a "less is more" approach. Our German distributor showed us that putting a small armless chair (with a lightly padded seat) in the corner worked even better. The seat breaks up the vertical standing waves in the corner, but sound even more natural (every room has chairs in it, so everyone is used to how chairs sound.

We tried all kinds of things on the wall, but kept going less and less absorptive until we ended up with woven grass mats (from Pier One). These provide just enough absorption to kill the worst of the slap echoes, but don't color the sound too badly.

We started off with a nice wool Berber wall-to-wall carpet and a jute (natural fiber) underpad. But that tended to suck the "life" out of the music. After suffering with an expensive mistake for over 10 years, we finally ripped out the expensive carpet and replaced it with very short loop-pile nylon carpet (like found in the cheapest office buildings and *no* underpad. There is also a beautiful Persian rug between the listening position and the speakers, but it is fairly small (5' x 7').

So I have come full circle. I'm really not a fan of room treatments. Here's another example. A few years ago RH of TAS wrote a review of a room treatment system that cost around $50,000. I have never heard his room, but another manufacturer that heard it before and after said that is sounded *much* better before. Shane Buettner bought the same system for his new house a couple of years ago. I heard it with the room treatment and was completely underwhelmed. I suggested that he try removing some of it. He did and liked the results so much that he ended up removing it *all*.

One problem with room treatments is that they can be very expensive if they are custom designed for your room. And their resale value is essentially zero. I would be very cautious before spending more than $1000 on room treatments....


.... I promise you that I've tried every permutation under the sun. This was not a case of play around for a day or two. This was a case of trying dozens of different arrangements in dozens of different rooms. We even used the TEF 12 analyzer to look at the spectral decay vs. frequency (waterfall plot) of the room to target things. We also used several different kinds of RPG diffusors and "abfusors".

I'm not just some guy sitting on the bar stool next to you. I've been doing this full-time for over 20 years....

Hi Folks,

DTB300 invited me to chime in with my comments, so here I am. I usually work best with specific questions but I see a few things to discuss.

There seem to be two philosophies about the back radiation of dipole speakers. Some argue it's an important design feature, and others (like me) see it more as a by-product of the design. As JonFo clearly showed, leaving the front wall untreated (the wall you face when listening, behind the speakers) creates severe comb filtering. I can't imagine how a response so severely skewed would ever be considered desirable. So the next step is how best to treat those reflections to achieve a truer response.

The diffusor Jon shows in Post #11 is very thin and looks to be made of styrofoam. This sort of diffusor is not very useful because it's not deep enough to work to a usably low frequency. The material is also too "squishy" (technical acoustics term) to reflect very well. Most "real" diffusors are at least 3 inches thick, and RPG's 9-inch wood model is a staple in professional recording studios. The deeper the wells, the lower in frequency it will work to. Most diffusors either pass or reflect frequencies below their working range. Stryofoam passes, but then the waves are reflected by the wall behind. Wood reflects. As Jon mentioned, the RealTraps diffusor absorbs bass, which is more useful because it reduces comb filtering to a much lower frequency. I'm not here to tout my company's products! I'm just explaining the science.

My personal preference is to absorb front wall reflections rather than try to diffuse them. Diffusion can be great in a room! But in this case the reflections are very strong in most rooms because the wall is not far behind the speakers. Maybe in a very large room, where the speakers are 5 to 10 feet away (or more) diffusion might be useful. But good absorption costs a lot less than good diffusion. So I usually recommend absorption on the front wall when using dipole speakers.

I also saw comments about how significant small changes in placement can be. And this is true in all untreated rooms. But once a room is well treated to reduce or avoid the reflections, placement is then much less critical. This is true with all speakers, not just dipoles.

As for the Golden Acoustic diffusors, I have never seen or heard one in person. But I agree with DTB's points. These have been on the market for a long time, so there's no excuse for not offering performance data. More to the point, they are indeed too thin to do what is claimed. And even more to the point, in a domestic size room bass frequencies are best absorbed, not diffused. Reverb and ambience can sound great at mid and high frequencies, but not so great at bass frequencies where the result is a lack of clarity. If you play a triad chord on a piano at different octaves, chords played up high sound great while chords a few octaves below middle C sound awful. When bass notes sustain due to room reflections, the same sort of thing happens. A walking bass line becomes like a chord with multiple nearby notes all sounding at once. This is a Bad Thing.

I hope this helps, and I'll be glad to chime in further if the group would like to hear more.

--Ethan

Ethan, thanks for joining in on the conversation. I am a satisfied Real Traps customer. Currently I have HF mini traps behind my Martin Logan Summits, to great effect. I am wondering if you could comment on my idea of placing your diffusers in front of the mini traps, for some high frequency diffusion to add back some ambiance, in addition to providing extra mid and low frequency absorption. Might this help or would it tend to be detrimental to the sound, in your opinion? Just curious. Have you experimented with placing your diffusers behind dipole speakers? If so, how did you find it to sound?

My room is about 14' wide by 19' long. The speaker panels sit about 3 feet out from the mini traps and my listening position is about 9-10 feet from the speakers. All corners are treated with Corner mondo traps and tri-corner traps, first reflections treated with RFZ panels, and a couple of micro traps are placed about as well. The sound and imaging is excellent, but it does seem just a tad too absorptive overall. I think I am missing some of the ambiance you get with dipole speakers.

A few specific questions for Ethan:

Ethan Winer said:

Hi Folks,

As Jon mentioned, the RealTraps diffusor absorbs bass, which is more useful because it reduces comb filtering to a much lower frequency. --Ethan

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Ethan,

Thank you very much for joining the conversation. Can you please explain this statement? What exactly is comb filtering? Why would absorbing a long bass wave reduct it? What happens to the shorter waves and would why would they not contribute to comb filtering?

Also, my general understanding of applying room treatments is to treat all corners with your mini or mondo trap products. Then to listen the room with less muddied bass and place additional products based on experience. Is this correct?

Martin Logan speakers have a very small sweet spot. It is very difficult to dance and to enjoy the music at the same time. How realistically can this sweet spot be increased with effective room treatments or should this limitation be accepted?

What is your take on Charlie Hansen's comment that most products do not absorb below 100 Hz, which seems to be the reason he lost faith in them.

What is your take on Cardas ratio of speaker placement, taking room treatments into account?
The distance from the center of the woofer face to the side walls is:

Room Width times .276 (RW x .276)
The distance from the center of the woofer face to the wall behind the speaker is:

Room Width times .447 (RW x .447)



Thanks much!!!

Hi Rich,

Rich said:

I am wondering if you could comment on my idea of placing your diffusers in front of the mini traps, for some high frequency diffusion to add back some ambiance, in addition to providing extra mid and low frequency absorption.

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I've never experimented with diffusion in the front of the room, and I don't have dipoles. I've heard them of course! And I've experimented with absorption behind dipoles, but I never tried diffusion there. My gut feel remains that the absorption you already have is most likely better, because the main issue is avoiding the skewed response caused by reflections. Diffusion will scatter those reflections, which helps, but they'll still be "early" due to the close proximity of the speakers.

My room is about 14' wide by 19' long. The speaker panels sit about 3 feet out from the mini traps and my listening position is about 9-10 feet from the speakers. All corners are treated with Corner mondo traps and tri-corner traps, first reflections treated with RFZ panels, and a couple of micro traps are placed about as well. The sound and imaging is excellent, but it does seem just a tad too absorptive overall. I think I am missing some of the ambiance you get with dipole speakers.

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I tend to prefer a room that's more on the dead side. Not totally dead, of course. But maybe more dead than many people (think they) prefer. In my experience, when a room has no early reflections at all, the perception is of more ambience and spaciousness because then you can more clearly hear the ambience that was embedded in the music by the recording engineers. Here's another way to look at this:

In my opinion, small room ambience is always bad ambience. The vast majority of rooms have no acoustic treatment at all, so the inherent small room ambience dominates, and overshadows the deeper, richer reverb that's already in the music. I see people try in vain to get a "big" sound in a small room, trying hard not to kill the very reflections that damage the sound the most!

In your case you have bass traps and first reflection treatment. So you're already 99 percent of the way there if not 100 percent. For how long have you had the treatment you described? I ask because sometimes a well-treated room can take getting used to, almost like an acquired taste.

--Ethan

David,

David Matz said:

What exactly is comb filtering?

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Comb filtering is a specific type of frequency response error that's characterized by a series of many peaks and deep nulls. It's almost always caused by acoustic reflections, but it can also be created electronically using a delay. This graph shows comb filtering:



The graph above is from this article on our web site:

http://www.realtraps.com/art_spaces.htm

There's also a video on our site that let's you hear what it sounds like here:

http://www.realtraps.com/videos.htm

Why would absorbing a long bass wave reduct it? What happens to the shorter waves and would why would they not contribute to comb filtering?

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All waves can create comb filtering. Comb filtering occurs whenever you combine a source signal with a delayed version of the same signal. Depending on the delay time, some frequencies are combined in phase (peaks) and some are out of phase (nulls).

Also, my general understanding of applying room treatments is to treat all corners with your mini or mondo trap products. Then to listen the room with less muddied bass and place additional products based on experience. Is this correct?

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It's even simpler than that. My approach is as much bass trapping as possible, plus absorption at the first reflection points. If the wall behind you is very close by, additional absorption on that wall is needed to avoid comb filtering. If the wall is 3 to 5 feet or more behind you, then diffusion is a good alternative to absorption. But what you choose behind you is about the only "season to taste" aspect as I see it.

Martin Logan speakers have a very small sweet spot ... How realistically can this sweet spot be increased with effective room treatments or should this limitation be accepted?

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Adding first reflection absorption will absolutely increase the physical size of the area where the response is more or less flat. Which is how I'd define a sweet spot.

What is your take on Charlie Hansen's comment that most products do not absorb below 100 Hz, which seems to be the reason he lost faith in them.

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As I read his post his experiments were a long time ago. Our bass traps are effective to much lower frequencies than 100 Hz, and with enough of them (8 or more) I've measured an improvement to as low as 30 Hz. Yes, I've seen plenty of really expensive "acoustically treated" rooms that sounded terrible. The problem is not the presence of acoustic treatment, but rather an improper use of it. For example, a lot of people use too-thin foam or fiberglass panels all over their room. So the room is too dead, yet boomy at the same time. Sadly, and maybe not surprisingly, how much something costs seems to have little relation to how good it is.

What is your take on Cardas ratio of speaker placement, taking room treatments into account?

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There are a lot of opinions on this stuff, and I admit I have not tried them all. But I think it's too simplistic to expect any "one size fits all" philosophy to work in all rooms. My approach is described in this Room Setup article on our site:

http://www.realtraps.com/art_room-setup.htm

This method identifies the ideal listener placement first, then uses actual measurement (when possible) to find the best places for the speakers. Understand that measuring the low frequency response at high resolution is the only way to know which placements are best. There are too many variables to be able to predict what happens in a small room. For example, if the walls are thick sheet rock, or thin sheet rock, or the space inside the wall is insulated or not insulated, and the proximity of furniture, and what the furniture is made from - all of these have a direct impact on the bass response you'll actually get.

--Ethan

David Matz said:

What is your take on Cardas ratio of speaker placement, taking room treatments into account?
The distance from the center of the woofer face to the side walls is:

Room Width times .276 (RW x .276)
The distance from the center of the woofer face to the wall behind the speaker is:

Room Width times .447 (RW x .447)

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I'll take a stab at this one for you, David. I think Cardas' "formula" is probably a good starting point in speaker placement, and nothing more. It takes nothing into account except the width of the room. All dimensions in a room affect the sound -- the height, length, and width all play a role in the reflecting sound waves and exciting room modes. Accurate placement of speakers will depend on many variables (as Ethan pointed out) and be different for every room. This formula takes none of that into account. Whenever someone gives you a one-size-fits-all rule for acoustics, you should be very skeptical. Every room is different and every speaker is different and each will require individualized placement based on the particular needs of the situation.

I do believe that with proper acoustic treatment, exact speaker placement becomes less critical. Many times I have read people on this forum stating that they hear a huge difference just moving their speakers 1/2 inch or so. That is certainly not the case in my room.

Rich said:

...............
I do believe that with proper acoustic treatment, exact speaker placement becomes less critical. Many times I have read people on this forum stating that they hear a huge difference just moving their speakers 1/2 inch or so. That is certainly not the case in my room.

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Whew ! Glad I'm not the only one who does not hear huge differences.

Ethan Winer said:

There's also a video on our site that let's you hear what it sounds like here:

http://www.realtraps.com/videos.htm

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Everyone...

There are many great videos to view on Ethan's site to give you an idea about room treatments, the sound improvements you get, and how to go about doing it. There are also many great articles and information on the site to get you started on the right path.

In the video, when they are adding Bass Traps to the room, Ethan and Doug mention the change in the sound of the room and you can actually hear the difference in the video as they add the traps compared to the start of the video.

Make sure to stop by Ethan's site and start to learn how to improve your room. As you see from JonFo, Rich, myself, and others, this is a great way to get the most out of your ML's and your setup.

Dan

Ethan Winer said:

Hi Rich,


I've never experimented with diffusion in the front of the room, and I don't have dipoles. I've heard them of course! And I've experimented with absorption behind dipoles, but I never tried diffusion there. My gut feel remains that the absorption you already have is most likely better, because the main issue is avoiding the skewed response caused by reflections. Diffusion will scatter those reflections, which helps, but they'll still be "early" due to the close proximity of the speakers.

...

--Ethan

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Hi Ethan, thanks for joining our discussion on this topic. It's great to have a truly knowledgeable person chime in.

I agree that diffusion is tricky behind diploes, as the ‘early reflections’ are generally in the sub-10ms range. So while it helps preserve energy, it still imparts a time smear (impulse is spread out across a few ms) and comb filtering results.

The questions might be: Can the dipole rear-wave be angled and delayed enough that it adds the ‘ambiance’ people seek from this class of speaker?
That is, if the travel time of the rear wave is long enough (Speaker -> wall -> side wall -> Listener) and attenuated to the right level, would that impart any benefit to the sound?
And by long enough, I mean >15ms, and by attenuated I mean >12db down.

I hear what you say about not trying to let the room impart a signature on the sound, and depend on the recordings capture of it. I find that quite logical and attractive, but I still wonder if a correctly managed rear wave has positive attributes that can be leveraged. That’s one of the things I’m exploring in my metrics.

I might wind up at the ‘dampen the rear wave as much as possible’ point, but wanted to travel the road of exploring how the rear wave might be correctly managed and get some benefit.

I also acknowledge this is akin to engaging a full-time DSP soundfield mode on a processor to add ‘ambiance’, but then again, I run all my 2ch music in ‘TriField’ mode on my Meridian (a 7.1 mode)

For rear channels, I’ve found that there is definite (at least in my setup) benefit to diffusion. And I’m really looking forward to my RealTraps difusors to improve on what I currently have.

One reason the diffusion helps in the rear channels is that it really does cause more perceived sound to come from the side wall reflections of the rear wave. This broadens the soundstage (in the rear) substantially. Which for both movies and DVD-A sourced music is quite pleasant. Better than without it at least.

Rich said:

I think Cardas' "formula" is probably a good starting point in speaker placement, and nothing more. Every room is different

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I agree Rich, and while we try to achive as flat a freq response as possible I also believe our brain has some built EQ capabilities as well.
What I mean is, that ones auditory senses, while varying in sensitivity are all adaptive (to a point) to what they take in. It is one reason why we have a 'comfort level' with our own systems, after we have gotten are rooms as good as we think we can.

Jonathan, thank you very much for starting this informative thread; along with Rich and Dan (bringing in Ethan), this is what good constructive dialogue is all about !!

Jon,

diffusion ... helps preserve energy, it still imparts a time smear (impulse is spread out across a few ms) and comb filtering results.

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Exactly.

Can the dipole rear-wave be angled and delayed enough that it adds the ‘ambiance’ people seek from this class of speaker? ... I hear what you say about not trying to let the room impart a signature on the sound, and depend on the recordings capture of it.

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This is why I'd rather see the rear waves absorbed and removed from the equation completely. But that's me, and others may prefer to keep some of the room tone. One thing that makes it so difficult to speak in absolutes is that all rooms are different. My advice for someone with a 10x12 room is very different than with an open room that's 35x40 or similar.

The good news is you don't need to nail it on the first try. I've added to the treatment in my living room at least three times in three years, and during that time I also moved things and upgraded speakers twice. I think I finally have it now though!

--Ethan