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#268623 - 08/08/09 11:18 AM Re: Simple sound treatment [Re: mikeak]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7031
Loc: Canada
 Quote:
After that I am looking for material readily available to build sound panels and besides the acoustic fabric in-front of the speakers that is going to be "all" that I do as start-up for the HT.

I assumed from the above that you would be covering the false wall in fabric, though re-reading it I don't know why I reached that conclusion. Thats why I suggested putting the fibre board behind the false wall.

Putting fiber board behind drywall would still give you absorbtion, but I don't know what the effect would be. That would be a question to post on one of the two forums I linked to.
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#268625 - 08/08/09 12:16 PM Re: Simple sound treatment [Re: mikeak]
alan Offline
connoisseur

Registered: 01/29/02
Posts: 3186
Loc: Toronto/New York/Dwight
Hi Mikeak,

With all due deference to SirQuack, the advice on the first reflection zones is wrong, based on bogus information often intended for studio control rooms.

"Secondly, you have FRZ's (first reflection zones) which are placed on the side walls and ceilings to tame the first reflection to the listener. Otherwise, the sound that arrives, direct and indirect, is skewed at your ears."

When you place absorbers to kill the first and secondary lateral reflections from the main left and right front speakers, you greatly lessen the spacious character of the stereo soundstage. MOre than 20 years of research at Canada's National Research Council led by Dr. Floyd Toole established this beyond question. A normal mix of reflective and absorptive surfaces is ideal. Axiom goes to great lengths to design its speakers to have excellent on- and off-axis frequency responses, and when you damp the lateral reflections, you significantly alter the mix of on and off-axis delayed sounds that normally reach your ears and give a speaker a wide and spacious soundstage.

Concert and recital halls never install absorption panels on the side walls because the lateral reflections are key to giving the hall a spacious pleasant sound quality.

You don't want everything reflective, of course, but it's essential to maintain the lateral reflections if you wish to preserve the speaker's essential balance and spatial character.

Regards,
Alan
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#268628 - 08/08/09 12:27 PM Re: Simple sound treatment [Re: alan]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7031
Loc: Canada
 Quote:
With all due deference to SirQuack, the advice on the first reflection zones is wrong, based on bogus information often intended for studio control rooms.

I have a question for you on that Alan. It is my understanding that reflected sound that arrives at less than 10ms. after the direct sound actually negatively affects the soundstage, collapsing it. This is supposed to be an issue in very small rooms. Do you disagree with this as well?

It seems to me that there is no 'one rule' that applies in all situation and that you need to take a look at the specifics of size construction materials and furniture in each room to decide how to tackle room response issues.
_________________________
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#268631 - 08/08/09 12:51 PM Re: Simple sound treatment [Re: fredk]
alan Offline
connoisseur

Registered: 01/29/02
Posts: 3186
Loc: Toronto/New York/Dwight
Hi FredK,

I can't comment on the 10-ms statement other than to say that it doesn't make sense, because our ears and brain combine the on-axis sounds arriving directly from the speakers at our ears with the lateral first and secondary reflections, which contribute a great deal to the perceived sound quality of the speakers. I don't see how the 10-ms sounds could "collapse" the soundstage; they'd have the opposite effect, of widening the soundstage, because they're slightly delayed, but our brain integrates them with the direct sounds so the lateral image is widened (the 10-ms reflections are from points beyond the physical boundaries of the speakers, hence we seem to perceive a wider, more expansive soundstage).

The tests at the NRC were all double-blind and the speakers that had smoother and more linear frequency responses off-axis (which were congruent with the on-axis responses) were all judged in the double-blind tests to be more "spacious-sounding".

Regards,
Alan
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Axiom Resident Expert

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#268651 - 08/08/09 05:20 PM Re: Simple sound treatment [Re: alan]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13318
Loc: Iowa
I spent a lot of time researching this topic, and I highly respect Toole's work, however, he is one human being. There are many other scientists and audio engineering experts that have been around just as long, and provide factual proof that proper acoustics in a home theater environment are every bit as important than in a recording studio.

I can assure you I have lost no lateral reflection issues by placing ONE 2x4 panel at each first reflection location. There is truth about over deadening a room, that is not what I have done.

My sound stage is still VERY wide, and the vocals are dead center and very tight and clear. What your doing is flattening the frequency response in the lower regions, say 60hz to 300hz, high frequencies are not affected.

Since this topic comes up all the time, I ran a little test not long ago. I had 3 friends sitting in the front row. I blind folded them. Over the next hour I played a variety of classical, rock, blues, soft pop, etc. music. I would play the same track twice, randomly removing my side panels which are hung by wire and light weight. The users would raise their hands and either hold up 1 or 2 fingers, telling me which time the song sounded the best.

Out of about 10 songs, there was only 3 occasions where one of the guests picked the wrong song.

In follow up, I've posted my graphs many times and not going to do it again, but it was pretty obvious how the frequency response improved by adding the bass traps in the corners.
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#268652 - 08/08/09 05:22 PM Re: Simple sound treatment [Re: SirQuack]
MarkSJohnson Offline
shareholder in the making

Registered: 09/27/04
Posts: 10832
Loc: Central NH
Yeah, but your room is haunted. So there's a variable that needs to be factored in.
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::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::

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#268654 - 08/08/09 05:24 PM Re: Simple sound treatment [Re: MarkSJohnson]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13318
Loc: Iowa
\:\)
_________________________
M80s-VP180-QS8s-EP600-2xEP350 Denon3808 Outlaw7700
M22-OWM22-VP100-Denon2805
Audio Nirvana

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#268657 - 08/08/09 06:12 PM Re: Simple sound treatment [Re: SirQuack]
EFalardeau Offline
connoisseur

Registered: 08/27/07
Posts: 3270
Loc: Laval, Quebec, Canada
Since vampires don't have reflections, how big/small is their soundstage?
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Audiobytes! 2M22! 2VP150!

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#268675 - 08/08/09 09:50 PM Re: Simple sound treatment [Re: alan]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10363
Just to perhaps clarify or at least expand upon Alan's comments about early side wall reflections and the work of Dr. Toole and his colleagues, some references to his book "Sound Reproduction" might be helpful. There are numerous discussions, including graphs, which cite his research and other scientific investigations in this area over many years. Just a few relevant summaries will be quoted.

At p.161: "In the audio community,it is popular to claim that reflected sounds within small listening rooms contribute to degrade dialog intelligibility. The concept has an instinctive "rightness", and has probably been good for the acoustical materials industry. However, as with several perceptual phenomena, when they are rigorously examined, the results are not quite as expected. This is another such case".

After pointing out that the architectural acoustics field has long recognized that early reflections improve speech intelligibility, there follows at p.162: "For speech, reflections at the same level as the direct sound contribute usefully to the effective sound level, and thereby the intelligibility, up to about a 30 ms delay".

Suggestions about acoustical treatment which is actually beneficial for home listening are given at several points, but as to attempting to eliminate early side wall reflections, this was due to "...alarmist cautions about comb filtering(see Chapter 9)or degraded speech intelligibility(see Chapter 10)or masking of other reflections within recordings(Olive and Toole, 1989). When examined, none of these turned out to be problems"(p.503). Specifically, p.504: "If the loudspeakers have good off-axis performance, and especially if the customer likes to listen to stereo music, my recommendation is to leave some blank wall at the location of the first lateral reflections from the front loudspeakers. An area with a small dimension of at least 4 feet(1.2 m) centered on the reflection path is sufficient".
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#268677 - 08/08/09 10:40 PM Re: Simple sound treatment [Re: JohnK]
grunt Offline
connoisseur

Registered: 12/04/06
Posts: 3569
Loc: Nirvana
I guess my experience more or less fits with what you posted John. I haven’t noticed speaker placement near the wall degrading speech intelligibility, I have however, noticed that it effects the discrete placement of sounds tending to smear or spread them out, but keeping the driver portion of the speakers about 3 1/2 or more feet out from the front and side walls eliminates this.

Adding temporary acoustic treatments (pillows/cushions) at the first reflection points narrows the width of the front soundstage and reduces how enveloping it sounds. The only place where I’ve had wall treatments at the first reflection point help was in the apartment where there was a wall 3’ from the right main and out to 8’ from the left main. Here absorbing the first reflection from the right main balanced out the front soundstage, however, adding a reflecting surface 3’ feet from the left main not only balanced the soundstage but widened and made it more enveloping.

Before I ramble on to much Mike, my point is to listen to your system in your room for a while. Move your speakers around play with the toe-in, height use temporary treatments and see what various thing do before starting down a treatment path based on theory. I guaranty your room is too complex for anything but your ears to tell you what does and does not work for you.

I have proven to myself time and again that theory and conventional wisdom seldom stand up to the complexities of real world situations. I wouldn’t buy a speaker based on other peoples opinions or how it should theoretically sound based on it’s design neither would I (this time around) treat my room based solely on theory or other people’s opinions. IMO the best way to tweak your system is to learn what various tweaking sounds like to you in your room and then start adjusting things from there.
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