does anyone know?

[nineballg]

i've got all the first reflections covered with panels but i'm running 7.1 system and i was wondering about the reflections for the surround speakers. dont they need panels for their reflections?

[eugovector]

nineballg wrote:

i've got all the first reflections covered with panels but i'm running 7.1 system and i was wondering about the reflections for the surround speakers. dont they need panels for their reflections?

It doesn't hurt, all though, the goal is diffused, non-directional sound from those speakers, so you want a little reflection, especially with di-poles. There's probably a much more scientific way to do it, but I use the 7.1 clicks on AVIA at a good level to see how much reflection you're getting. With my absorption for my fronts on the front, back, and side walls, I didn't address the surrounds directly, just let the existing panels do it.

Since only about 10% (fake number pulled out of my end) of the movie sound comes out of the surround channels, I wouldn't lose any sleep over it.

One caveat, it probably would be good, if your surrounds are within 2-3 feet of a side wall, to treat that wall next to them with a small panel. It should help with speaker boundary interference response (SBIR).

[Ethan Winer]

nineballg wrote:

i was wondering about the reflections for the surround speakers.

My philosophy is to absorb first reflections for all speakers in a system. The problem with early reflections is they create a skewed frequency response known as comb filtering - a series of many peaks and deep nulls. If you don't want a badly skewed response for your mains, I can't see why you'd want that for the surrounds either.

--Ethan

[nineballg]

thanks guys

[avaserfi]

Ethan Winer wrote:

My philosophy is to absorb first reflections for all speakers in a system. The problem with early reflections is they create a skewed frequency response known as comb filtering - a series of many peaks and deep nulls. If you don't want a badly skewed response for your mains, I can't see why you'd want that for the surrounds either.

--Ethan

Is this your methodology for all forms of treatment? What about a two channel system in which the off axis response of the speaker is near identical to that of the axial response?

It has been shown through perceptual research that these first reflections actually increase enjoyment. Would you recommend treating anyways, if so why?

[Ethan Winer]

avaserfi wrote:

Is this your methodology for all forms of treatment?

Yes.

What about a two channel system in which the off axis response of the speaker is near identical to that of the axial response?

Same advice. If you think about it, when the off-axis response is the same as on-axis, that makes the resultant comb filtering even more damaging because all frequencies are reinforced and canceled maximally. Assuming perfect reflectivity of course.

It has been shown through perceptual research that these first reflections actually increase enjoyment.

My research shows exactly the opposite.

It might be that in a very large room - and I'm talking 20 feet wide or wider - that side-wall reflections are less damaging than in a more typical size room. But generally speaking, small-room reflections are always best avoided IMO. Especially if the reflecting surfaces are closer than ten feet to your ears. BTW, this includes the rear wall behind you too.

--Ethan

[nineballg]

i'm not sure. too technical for me, i'll let the pro ethan explain it

[Kal Rubinson]

avaserfi wrote:

It has been shown through perceptual research that these first reflections actually increase enjoyment.

Enjoyment is highly subjective and multivariate. Can you offer a link to such research?

[avaserfi]

Ethan Winer wrote:

Same advice. If you think about it, when the off-axis response is the same as on-axis, that makes the resultant comb filtering even more damaging because all frequencies are reinforced and canceled maximally. Assuming perfect reflectivity of course.

You are right there would be comb filtering created as a side effect of this methodology, but in Floyd Toole's research it was shown that despite this comb filtering the slightly delayed reflections were still found to be more enjoyable than use of an unreflective surface. All relevant articles are cited below.

Ethan Winer wrote:

My research shows exactly the opposite.

What kind of research is this? How was it done? Do you by any chance have the publication listing so I can read it?

Ethan Winer wrote:

It might be that in a very large room - and I'm talking 20 feet wide or wider - that side-wall reflections are less damaging than in a more typical size room. But generally speaking, small-room reflections are always best avoided IMO. Especially if the reflecting surfaces are closer than ten feet to your ears. BTW, this includes the rear wall behind you too.

While a large room would be beneficial in reduction of comb filtering as previously mentioned the preference still lay with a reverberant surface in place.

Kal Rubinson wrote:

Enjoyment is highly subjective and multivariate. Can you offer a link to such research?

You would actually be surprised how many facets of speaker design have been solidified as ideal and non-ideal. While certain tendencies lay with preference credible research has shown that most do not. Some of these are obvious such a smooth on axis frequency response and the ability to dynamically produce lower frequencies. Some others include a lack of all audible resonance, off-axis response similar, if not matching, the axial response, a gradual roll off of the treble to match how the human ear works (this one in part lies with preference as some people prefer a larger roll off than others).

There are various papers on these subjects. Floyd Toole has many regarding relating measurements to listener preference as well as room interaction.

Some notable articles of his include (I will not be able to link these as they aren't posted online your local library would be your best bet):

Listening Tests-Turning Opinion into Fact JAES Volume 30 Issue 6 pp. 431-445; June 1982

Subjective Measurements of Loudspeaker Sound Quality and Listener Performance JAES Volume 33 Issue 1/2 pp. 2-32; February 1985

Loudspeaker Measurements and Their Relationship to Listener Preferences: Part 1 JAES Volume 34 Issue 4 pp. 227-235; April 1986

Loudspeaker Measurements and Their Relationship to Listener Preferences: Part 2 JAES Volume 34 Issue 5 pp. 323-348; May 1986

The Modification of Timbre by Resonances: Perception and Measurement JAES Volume 36 Issue 3 pp. 122-142; March 1988

The Detection of Reflections in Typical Rooms JAES Volume 37 Issue 7/8 pp. 539-553; July 1989

Loudspeakers and Rooms for Sound Reproduction—A Scientific Review JAES Volume 54 Issue 6 pp. 451-476; June 2006

Well it looks like I have listed all of his articles. I guess this is because simply put he is the leading researcher involved with perception in relation to loud speakers. Also, if you look up Ian Paisley's research you will see that through thousands of blinded trials with thousands participants, that wider and smoother frequency responses were highly preferred in a controlled environment.

[Ethan Winer]

avaserfi wrote:

You are right there would be comb filtering created as a side effect of this methodology

Exactly, and I can't imagine how anyone could consider such a terribly skewed response to be a desirable artifact. Worse, the comb filtering response changes dramatically over tiny distances, like an inch or less. This is why untreated early reflections are so damaging to imaging. You move your head just a little and everything changes. Versus how imaging should be where everything is locked into place, and comes from the same location no matter where you are in the room.

in Floyd Toole's research it was shown that despite this comb filtering the slightly delayed reflections were still found to be more enjoyable than use of an unreflective surface. All relevant articles are cited below.

I've read Floyd's position and I respectfully disagree. I don't know of one other expert who agrees that early reflections in a typical domestic size room are desirable. And by expert I include every professional designer of recording studios I know of.

Do you by any chance have the publication listing so I can read it?

Here ya go:

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

Figures 1 and 2 tell all. This is in addition to many listening tests.

Do me a favor? Please describe your own listening room and its acoustic treatment. If you can post a photo of the front of the room too all the better. Thanks.

--Ethan

[avaserfi]

Ethan Winer wrote:

Exactly, and I can't imagine how anyone could consider such a terribly skewed response to be a desirable artifact. Worse, the comb filtering response changes dramatically over tiny distances, like an inch or less. This is why untreated early reflections are so damaging to imaging. You move your head just a little and everything changes. Versus how imaging should be where everything is locked into place, and comes from the same location no matter where you are in the room.

Perhaps I have not made myself completely clear. It is well known that proper distances between each loudspeaker as well as the listener is needed for proper speaker placement in any room. Although, it doesn't seem that a room the size you have previously mentioned would be required. I am speaking of a system with proper placement and full treatments under the methodology that first reflections should be encouraged with proper off-axis response.

I fully understand the idea of comb filtering and the artifacts that occur from doing so, but the relevant credible research shows that in spite of this artifacts the slightly delayed reflections are desirable for stereophonic listening.

Also, I am very well aware of the factors effecting imaging: Loudspeaker room interaction, symmetry of response with respect phase with response to listener position and lastly treble response. All these variables can be controlled with proper treatment and equalization even with first reflections left "live."

This brings up another question with an omnipolar speaker would you treat the first rear to the speaker reflection? This is another situation that would cause even more comb filtering and has been proven through credible research to increase stereophonic listening pleasure.

Ethan Winer wrote:

I've read Floyd's position and I respectfully disagree. I don't know of one other expert who agrees that early reflections in a typical domestic size room are desirable. And by expert I include every professional designer of recording studios I know of.

I have talked to multiple professionals [same meaning as yours] who have differing opinions on the subject. For strictly two channel listening in a completely dedicated room with proper treatments I have gathered that many of them follow Toole's research. In fact, one specifically told me the gut reaction to treat first reflections is an outdated practice from treating recording studios.

It seems logical that application would change treatment needs after all.

Ethan Winer wrote:

Here ya go:

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

Figures 1 and 2 tell all. This is in addition to many listening tests.

Do me a favor? Please describe your own listening room and its acoustic treatment. If you can post a photo of the front of the room too all the better. Thanks.

--Ethan

I am aware of your website, but there is a difference between that and Toole's work. No offense is intended by this statement, but Toole's research methodology was peer reviewed before being published in the JAES while your studies were not. Furthermore, there is no discussion of the listening tests and the methodology of your research on the site you supplied as far as I am aware.

My current room is not dedicated and laid out in an asymmetric way in which treatment of the first reflections is necessary. I am referring to an ideal circumstance far from my own. I do however have a friend with an extremely high quality omnipolar 2-channel system with axial and off-axis response near identical to each other. He personally conducted blinded studies with both musicians as well as other individuals with his results mimicking Toole's. Personally, I have gone into a Hi-Fi shop and played with such treatments in a subjective manner to the same effect as well.

[Ethan Winer]

avaserfi wrote:

I fully understand the idea of comb filtering and the artifacts that occur from doing so, but the relevant credible research shows

Look guy, if you like the comb filtered sound of untreated early reflections, and the resultant affect on imaging, more power to you. But tossing out the names and credentials of other people means nothing to me. For every pro you cite who says untreated reflections are good I can point to ten others who say that's wrong. So what? It seems to me the best approach is for people to hear for themselves and draw their own conclusions. I've done this enough times to know how damaging those reflections are, and I intend to continue advising people to use absorption there.

--Ethan

[avaserfi]

Ethan Winer wrote:

Look guy, if you like the comb filtered sound of untreated early reflections, and the resultant affect on imaging, more power to you. But tossing out the names and credentials of other people means nothing to me. For every pro you cite who says untreated reflections are good I can point to ten others who say that's wrong. So what? It seems to me the best approach is for people to hear for themselves and draw their own conclusions. I've done this enough times to know how damaging those reflections are, and I intend to continue advising people to use absorption there.

--Ethan

I simply was trying to have an open discussion about a specific methodology within the world of acoustics. I have now realized this is not possible at least in terms of this thread.

On another note I am not sure I understand how citing relevant research is inappropriate. In fact it is my understanding properly conducted peer reviewed research should be used and applied otherwise what is the point?

Have a good day.

-Andrew

[bpape]

Early reflections from the main 3 speakers are definitely undesirable. In the rear, it's not AS critical since you want a non-localizable 'soundstage'. In multi-channel, we always treat the front and rear differently. We always kill the front wall completely but never kill the rear wall completely.

This is not to say that there is not comb-filtering, there is. It's not to say that it doesn't have an impact on frequency response, it does. What it is, is a tradeoff. One can have no comb filtering for the rear by creating an RFZ for all of those too - but at the expense of the diffuse soundstage that is desirable.

It's a lesser of 2 evils and most won't lose the soundfield envelopment and be able to pinpoint their surrounds to save a bit of frequency response abberations. If you stop and think about it, diffusion can cause some of the same issues due to out of time arrivals and some cancellations in the wells but the effect it gives is still more desirable than the flat wall. Same kind of trade off.

And no, before someone jumps on me about diffusion and specular reflections being the same thing, they're not. They can just yield some of the same kinds of effects. It's all in what you're trying to accomplish. If I can let part of the room work for me instead of deadening even more of the mid and high frequencies, I'll do that. If we were to plot every reflection point for all 7 speakers for all seats in a room, almost every single surface in the room would be 90+ % covered with absorbtion. Then you've shot your balanced target decay time curve all to hell.

Just my 2 cents.

Bryan

[WmAx]

Ethan Winer wrote:

But tossing out the names and credentials of other people means nothing to me. For every pro you cite who says untreated reflections are good I can point to ten others who say that's wrong.

In regards to your general statement regarding universal absorption of the 1st horizontal reflection points......

The difference between avaserfi's citations and your claims, though, is that it appears that yours are not from sources that have performed careful, scientifically valid experiments to come to their conclusions.

You have every right to believe what you want. But the credible evidence available does not appear to support you.

-Chris

[Ethan Winer]

WmAx wrote:

The difference between avaserfi's citations and your claims, though, is that it appears that yours are not from sources that have performed careful, scientifically valid experiments to come to their conclusions.

Most of the research I'm aware of that concludes early reflections are desirable focused on speech intelligibility, not music. So right off the bat the research is invalid in the context of this thread.

I repeat this again - every professional designer of recording studios I know of agrees that first reflections are damaging and should be absorbed.

--Ethan

[Ethan Winer]

More thoughts on this:

There are educated listeners and uneducated listeners. Often I hear from what I consider uneducated listeners that they prefer the sound of their room rather than a treated room. To me this is related to the conventional wisdom that a 2-channel room should be more live sounding than a home theater. I happen to disagree with that - most movies have music, and that music should sound as the mix engineers intended. If absorption in a home theater improves imaging, then it does the same for a 2-channel setup. So I guess you could say a well-treated room can be an acquired taste. In my experience small room ambience is always bad ambience. Versus a room large enough to have true reverb. But then we're outside the realm of home listening environments.

I work with many professional recording and mastering engineers, and I consider them to be educated listeners. These people listen to music for a living, and if they can't hear clearly how the music really sounds, without being influenced by the sound of their own room, they can't do their job. From my perspective, the listener at home should aim to hear the same quality as the engineer heard when mixing. And that means not leaving early reflections untreated.

Of course, there's no accounting for taste, and it's not my job to tell someone what they should or should not prefer and enjoy. All I can do is address the science of audio, and from that perspective it's clear (to me, anyway) that comb filtering due to early refections is best avoided.

--Ethan

[bpape]

Ethan.

Not to get into a tiff, but some real questions.

- How many of those guys mix multi-channel?

- How many of the mixing rooms have 90% of their wall surface covered in broadband absorbtion (which is what it would take to catch all the reflections from all of the speakers to all of the seats in a home theater)?

And sorry, but I'll disagree that a 2 channel room and a multi-channel room should be treated the same. In multi-channel, I have independent speakers to reproduce the diffuerent aural cues of the space. In a 2 channel system, you don't and you HAVE to count on the room to help you a little bit.

Have you ever listened to a good 2 channel recording outside? If it's anything that has 'space' to it like an orchestral piece or a choral piece recorded in a hall or church, it'll sound awful. It sounds thin and uninvolving. Now, if you listen to the 'in the box' over produced, electronic stuff that HAS no 'space' to it, then it'll sound about the same.

Guess that's up to 4 cents now

Bryan

[WmAx]

Ethan Winer wrote:

Most of the research I'm aware of that concludes early reflections are desirable focused on speech intelligibility, not music. So right off the bat the research is invalid in the context of this thread.

I repeat this again - every professional designer of recording studios I know of agrees that first reflections are damaging and should be absorbed.

--Ethan

The work by Ando, and analysis by Toole, all contained in Loudspeakers and Rooms for Sound Reproduction -- A Scientific Review, goes as far as examining both speech and classical music, and 1st horizontal reflections with the appropriate time delay and amplitude enhanced perceived sound quality to subjects. In Toole's summary, it is determined that reflections need augmentation by additional channels in order to be at a high enough level to be fully satisfactory to subjects. It should also be noted, that in the paper titled Modification of Timbre by Resonances, it is found that an increased reflective fields reveals more timbre information within a recording. This is also one suspected factor.

-Chris