complete beginner starting treatment behind AT projector screen.

Dirt9

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I have two options for sound panels,24x48x4" roxul-60 and 30x48x6" fire/sound rock wool batts and am looking for advice on what graphs looks best.
I have LCR behind the screen with four panels on the wall.there are no other treatments in the room....yet
disregard the spf levels,
 

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Negatron

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On my last setup...we used Roxul r69 on the complete wall behind the AT screen, and it improved our soundstage depth. A friend of mine came over and listened, and he liked the results so much he did it in his HT. He told me it was def a positive experience, and he recommends it too.
 

ddude003

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Throw rug, saddle blankets and base traps...
Why not use both? The 6 inch thick stuff in the corners... All the corners... Use the 4 inch think stuff everywhere else...
 

Dirt9

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I'm planning a full treatment but for some reason I'm getting a suck out when there's absorption behind the front speakers.
 

ddude003

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Location
Somewhere Northeast of Kansas City Missouri
My AV System  
Preamp, Processor or Receiver
PrimaLuna Dialogue Premium TubePre (2 channel+sub)
Main Amp
McIntosh MC152 SS Amp (2 channel)
Additional Amp
Yamaha RX-A850 Pro (the other 5 channels lol)
Other Amp
LuminU1 Mini Streamer/Transport & ChordQutest DAC
Universal / Blu-ray / CD Player
LG Blue-Ray
Front Speakers
Martin Logan ElectroMotion ESL
Center Channel Speaker
Martin Logan Motion C2
Surround Speakers
Martin Logan Motion 4
Surround Back Speakers
Martin Logan Motion 4 (yes, another set of these)
Subwoofers
Martin Logan Dynamo 700
Other Speakers or Equipment
Cifte 12AU7 NOS & Genalex Gold Lion Tubes in Pre
Video Display Device
Sony TV KDL50W700B
Remote Control
AudirvanaPlus, QoBuzStudioPremier & Lumin iApp...
Other Equipment
Throw rug, saddle blankets and base traps...
Dr. it hurts when I do this... Dr. said "son don't do that!"... Try nothing... Or try a little diffusion...
 
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Dirt9

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Haha Im leaveing the screen wall until last.
Everyone's treating the front wall so I thought I should.
 

ddude003

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Location
Somewhere Northeast of Kansas City Missouri
My AV System  
Preamp, Processor or Receiver
PrimaLuna Dialogue Premium TubePre (2 channel+sub)
Main Amp
McIntosh MC152 SS Amp (2 channel)
Additional Amp
Yamaha RX-A850 Pro (the other 5 channels lol)
Other Amp
LuminU1 Mini Streamer/Transport & ChordQutest DAC
Universal / Blu-ray / CD Player
LG Blue-Ray
Front Speakers
Martin Logan ElectroMotion ESL
Center Channel Speaker
Martin Logan Motion C2
Surround Speakers
Martin Logan Motion 4
Surround Back Speakers
Martin Logan Motion 4 (yes, another set of these)
Subwoofers
Martin Logan Dynamo 700
Other Speakers or Equipment
Cifte 12AU7 NOS & Genalex Gold Lion Tubes in Pre
Video Display Device
Sony TV KDL50W700B
Remote Control
AudirvanaPlus, QoBuzStudioPremier & Lumin iApp...
Other Equipment
Throw rug, saddle blankets and base traps...
I would suggest you treat the issues you have in your room and not worry what everyone else is doing in their rooms... Every room and system and ears/brain are different...
 

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Couldn't agree more. Just understand 3 things to address:

Frequency response
Decay time
Early reflections

.... And reflections don't always have to be absorbed pending the frequency range in question
 

DanDan

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"I'm planning a full treatment but for some reason I'm getting a suck out when there's absorption behind the front speakers."
Many Recording Studios and other critical listening spaces do not treat behind the speakers.
 

Bpape

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Agreed but in a multi-channel setup, you want to block reflections from the surround channels coming off the front wall. Doesn't need to be really thick. You can make it thin enough to avoid the suckout in most cases.
 

DanDan

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Good point. I would favour full range speakers for surround, in which case it would seem desirable to treat the FW same as the others.
We are obviously talking about different frequencies of suck out. I wonder what Dirt9 was referring to?
 

Bpape

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Well, that's personal preference. For pure HT, one would cut off LCR and all surrounds at 70-80 Hz then fill in with a sub. I suspect he is getting SBIR from the front wall and the mains. You wouldn't get that from surrounds that far away. Or if he wants to go thicker, just move the mains forward or back to mitigate the suckout.
 

DanDan

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Hmmm, all preferences are personal I guess. But a significant body of Mixers did quite a bit of work on this. They recommend, to the point of 'must' identical 40Hz -18K speakers plus a Sub for the LFE. http://www2.grammy.com/pdfs/recording_academy/producers_and_engineers/5_1_rec.pdf
I am becoming more and more convinced that treatment between speakers and FW won't help unless it has a big area and depth. The typically recommended 100mm panel trap is about 1/3 of the distance from woof to wall.
and the 0.6 x1.2 M size seems small compared to the wavelengths involved.
 
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Matthew J Poes

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"I'm planning a full treatment but for some reason I'm getting a suck out when there's absorption behind the front speakers."
Many Recording Studios and other critical listening spaces do not treat behind the speakers.
I don't know that we need to treat what studios do as a gold standard for appropriate treatment. The research into preferences for rooms doesn't match common studio treatment techniques and the arguments in favor of things like zero reflection zones are more about creating a kind of acoustic scalpel rather than what sounds best. The same is true of the ITU listening rooms. They were designed specifically to allow a listener to discern small differences in equipment or encoding systems. Not what sounds best overall.

In a 2-channel room, the room itself contributes the 3rd dimension of sound, the room reflections, necessarily to create a sense of apparent source width and envelopment. The music is encoded only with the reverb, it is impossible for a reflection free listening space and 2 speakers to recreate these effects and so good room designs for 2 channel would need to be optimized to contribute this effect. Since real music in real spaces are acoustically larger than our listening space, the treatment of the room needs to focus on making the room sound bigger than it really is. Hence the use of diffusion, reduction of very early reflections, and that initial gap.

In multichannel things change. There actually becomes two arguments here. The room should not contribute anything, so theoretically, an anechoic room is desirable. However, when our brain is faced with acoustical cues of a large and small acoustic space at the same time, it tends to filter out the small cues in favor of the big cues. That means we hear the larger room through the smaller room. For multichannel, no treatment at all doesn't have the same detriment as it might in a 2-channel room. On the other hand, that doesn't mean our perception of reality would not be improved if we did treat, and so, even in an multichannel setup, it still makes sense to treat.

So then what to treat? Well, the live end dead end thing no longer makes any sense here. We don't want the room to contribute. That means we need to treat all walls in much the same way and for similar reasons. But in practice, most people wall mount their surround speakers but space their main speakers out into the room 2-3 feet if not more. This causes severe SBIR effects off the side and front wall. That is why I always treat the front wall, but I treat it using thick bass absorbing panels.

I've thought about the benefit of diffusion in a multichannel system and I've wondered if it helps or not. I recently had the chance to measure such a room and what I found was that the room was pleasant to be in. Sounded good just carrying on a conversation. With music and 2 channels it sounded good too. With movies, everything seemed to lack clarity. Measurements of the room highlighted why this might be. The diffussion was too much for such a small space and the RT60 was now very uneven. There was now more absorption above 3khz and below 500hz and the RT60 curve was very non-flat. Sound didn't decay evenly in the room. We pulled out the diffusion as a test and the room instantly improved in measurements. When listening to 2-channel none of us thought it sounded any worse, and with movies, everyone thought it now sounded better. Proof of anything, I don't know.

I've been really moving more and more towards a view that when it comes to multichannel, the room needs are very specific and not what is best for 2-channel, but ultimately superior. That a room should absorb quite a bit, especially in the bass, and the use of a good upmixer is best when listening to 2-channel sources. That overall, we want the industry to move toward multi-channel music and for mixing engineers to learn how and why this is true. @DanDan, I trust you more on how likely this is. This is actually going to be the focus of my talk at AXPONA this year.
 

Dirt9

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this is the treatment approach I think I'm going with,except with all 6" panels and 34"wide super chunks in the corners floor to ceiling.The suck out I got was with 6" panels across the front wall,im open to suggestions.speakers consist of two JTR cap 1400's 18" ported subs and seven psa mt-110 sealed with a 10 driver an a compression driver in each.Disregard the spl level in the graph.
 

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Matthew J Poes

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View attachment 29147 View attachment 29148this is the treatment approach I think I'm going with,except with all 6" panels and 34"wide super chunks in the corners floor to ceiling.The suck out I got was with 6" panels across the front wall,im open to suggestions.speakers consist of two JTR cap 1400's 18" ported subs and seven psa mt-110 sealed with a 10 driver an a compression driver in each.
A 250hz suckout is often caused by ceiling/floor reflections. Are you treating the ceiling?
 

Dirt9

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yeah I have a 8'x4'x6" cloud going up,i'm making panels today,making 20 6" and 8 34" wide corner traps,then I plan on bringing life back into the room with wood slats over the panels as needed.im open to suggestions.
 

Matthew J Poes

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There are lots of ways to do this. There are ways to calculate the precise source of a reflection, but it can be time intensive. In the absence of a 3D impulse response, you have to do all the math manually. Looking at the ETC, you can look at peaks and the timing of those peaks, measure out the various reflection points around the room, and match them up. Often many reflections have the same timing or very close and its hard to tell them apart. What I do in that scenario is categorize all the likely reflections that could be falling into each of those timing windows.

Then what you can do is apply treatments to specific reflection locations and see the impact on the amplitude of the spikes in the ETC.

However, I've been moving more and more away from ETC for this and using wavelets instead. I find them easier and more effective. Listen inc. wrote a whole article on their use in acoustics and I translated that to REW and have been doing it ever since. It's got far higher frequency and timing resolution than you would otherwise get. I do also look at filtered impulse response in 1/3 octave intervals centered around the problem area. That helps. I'm working on a room right now that has problems where the reflections are stronger than the direct sound and highly problematic. There is next to nothing separating them in time. they are basically combining with the direct sound to cause the sound to smear over time for twice the normal period of the cycle.

One more thing to keep in mind, we often treat reflections as if sound waves are laser beams. It's more like a spot light where by the spot changes in size as you get lower in frequency. Below about 500hz the spot is quite large and in most rooms it will be most or all of the wall, not a specific spot. The notion of a "first reflection point" becomes nonsense at such low frequencies. That is why treatment for low frequency problems need to be spread out.

Edited to fix brain fart. EDT=ETC. Sorry.
 
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Adhoc

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What Matt wrote about sound not being a lazer beam is true. Especially for lower midrange and bass where the wavelength are meters / 10ths of feet long. The typical dips in the frequency curve you get from the wall behind front speakers, the ceiling, the floor and possibly side wall are typically fairly broad in frequency because of the long wave lengths reflecting from them. Often there are 3 of them found between about 80 to 350 Hz, it depends on room size and position speakers <=> reflecting surface.

For me that means the treatrment should be comparable in width and length to the wavelength and be "sufficiently deep" also. For this reason I would enlarge the cloud and increase its thickness if possible. If ceiling height is very low, one way to improve low bass absorbtion is to angle it down with ceiling hooks + chains towards the front speakers and have hinges towards you. -You keep a a decent height were you sit and walk around but get some better low frequency absorbtion closest to the front wall were free height is of less importance. Another gain with the down angled cloud would be that possible reflection from it would pass over your head towards the back wall, instead of being directed down at listering position (if flat against the ceiling).
 

Dirt9

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What Matt wrote about sound not being a lazer beam is true. Especially for lower midrange and bass where the wavelength are meters / 10ths of feet long. The typical dips in the frequency curve you get from the wall behind front speakers, the ceiling, the floor and possibly side wall are typically fairly broad in frequency because of the long wave lengths reflecting from them. Often there are 3 of them found between about 80 to 350 Hz, it depends on room size and position speakers <=> reflecting surface.

For me that means the treatrment should be comparable in width and length to the wavelength and be "sufficiently deep" also. For this reason I would enlarge the cloud and increase its thickness if possible. If ceiling height is very low, one way to improve low bass absorbtion is to angle it down with ceiling hooks + chains towards the front speakers and have hinges towards you. -You keep a a decent height were you sit and walk around but get some better low frequency absorbtion closest to the front wall were free height is of less importance. Another gain with the down angled cloud would be that possible reflection from it would pass over your head towards the back wall, instead of being directed down at listering position (if flat against the ceiling).
 

Dirt9

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I'm working with a 8" ceiling.i would be ok with bringing the cloud down 12".honestly I thought about making all the side wall panels 12" but $ said no way plus they would encroach into the room.am I wasting my time with the 6".I'm feeling the hint that I should go thicker. There's two windows 35"x45" that are getting plugged with 12" absorbers. One's dead center on the the screen wall and the other is 7' into the room from the screen wall on the left.
this is the treatment approach I think I'm going with,except with all 6" panels and 34"wide super chunks in the corners floor to ceiling.The suck out I got was with 6" panels across the front wall,im open to suggestions.speakers consist of two JTR cap 1400's 18" ported subs and seven psa mt-110 sealed with a 10 driver an a compression driver in each.Disregard the spl level in the graph.
yeah I have a 8'x4'x6" cloud going up,i'm making panels today,making 20 6" and 8 34" wide corner traps,then I plan on bringing life back into the room with wood slats over the panels as needed.im open to suggestions.
 
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DanDan

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Hi Matt, good to see you again, although I am about to savage your rhetoric!

"I don't know that we need to treat what studios do as a gold standard for appropriate treatment. The research into preferences for rooms doesn't match common studio treatment techniques and the arguments in favor of things like zero reflection zones are more about creating a kind of acoustic scalpel rather than what sounds best. The same is true of the ITU listening rooms. They were designed specifically to allow a listener to discern small differences in equipment or encoding systems. Not what sounds best overall."

Well that old Big Wheel (of Confusion) Keeps on Turning.
I can assure you that the best of Studio Control rooms/Speaker systems, are extremely high resolution, and sound way better than anything one hears really anywhere else in the world.
Obviously such spaces have the size and funds to go all the way. But it is the responses which matter and many/most/all of the same 'wishes' apply to any listening environment.
BUT, from memory, Toole concluded in one text that the lack of any clearly defined Mixing environment is an utter shambles. A scenario of full of contradictory facts and theories also described by Olive.
My reading of the ITU specs is that the rooms were designed to work in and to deliver a reliable result EVERYWHERE. A high resolution space with enough creature comfort room feedback to enable long periods of work .
Unbiased enough that any engineer is likely to deliver a similar tonal product. But actually IN the listeners' myriad environments, Buds to Car to Cinema.
i.e. Sorry Matt but that translates to What sounds best OVERALL.

The Scalpel. You have touched on an elephant of CR acoustic practice. Many were and are designed to be Anechoic. Non Environment.
Lack of reflections definitely makes it easier to hear details, chose reverbs etc. However such a response is devoid of normal room gain, and is thus HF boosted from norm by at least 6dB.
Oddly some 'top' designers deny this is a problem. While others advocate simulating the average listeners experience. e.g. The curves researched by B&K, Harman, Sonarworks, Dirac Live.
Any experience of Mixing will readily show that one delivers the opposite to any room or speaker bias. Bright room, dull mix.
One notes that nobody listens on Audiometric Headphones, i.e. Lab perfectly flat, highest resolution.
Boggy, RIP, designed rooms, which complied with ITU desires, had the highest resolution, lack of colouration, but included both creature comfort reflections and a perfectly balanced albeit short ambience.
Massenburg and D'Antonio, fulfilled the same set of wishes. Here is Blackbird Studio C with a 'proper' surround setup.

"In a 2-channel room, the room itself contributes the 3rd dimension of sound, the room reflections, necessarily to create a sense of apparent source width and envelopment. The music is encoded only with the reverb, it is impossible for a reflection free listening space and 2 speakers to recreate these effects and so good room designs for 2 channel would need to be optimized to contribute this effect. Since real music in real spaces are acoustically larger than our listening space, the treatment of the room needs to focus on making the room sound bigger than it really is. Hence the use of diffusion, reduction of very early reflections, and that initial gap."

Sorry Matt, but no. Recording played without local ambience deliver the recorded space much better than a small room with it's contradictory early clutter and a spectrum of short decay utterly different from a Concert Hall or Reverb Chamber or Plate. Such a lack of 'noise' reveals the ambience and envelopment of the recording in a spectacular fashion.
This is just a clarification of the old adage that one hears the ambience of a larger recording space better in a low ambience CR. Lowest ambience delivers the maximum recorded ambience.
Anyone can test this readily. Headphone listening is highly immersive. The Boggy and Massenburg/D'Antonio rooms similarly deliver a virtually anechoic response, hi res, followed later enough not to interfere by a local bloom.
Such spaces see no difference between Stereo and Multichannel playback
 
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Matthew J Poes

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"I don't know that we need to treat what studios do as a gold standard for appropriate treatment. The research into preferences for rooms doesn't match common studio treatment techniques and the arguments in favor of things like zero reflection zones are more about creating a kind of acoustic scalpel rather than what sounds best. The same is true of the ITU listening rooms. They were designed specifically to allow a listener to discern small differences in equipment or encoding systems. Not what sounds best overall."

Well that old Big Wheel (of Confusion) Keeps on Turning.
I can assure you that the best of Studio Control rooms/Speaker systems, are extremely high resolution, and sound way better than anything one hears really anywhere else in the world.
BUT, from memory, Toole concluded in one text that the lack of any clearly defined Mixing environment, is an utter shambles, full of contradictory facts and theories.
My reading of the ITU specs is that the rooms were designed to work in and to deliver a reliable result EVERYWHERE. A high resolution space with enough creature comfort room feedback to enable long periods of work .
Unbiased enough that any engineer is likely to deliver a similar tonal product. But actually IN the listeners' myriad environments, Buds to Car to Cinema.
i.e. Sorry Matt but that translates to What sounds best OVERALL.

The Scalpel. You have touched on an elephant of CR acoustic practice. Many were and are designed to be Anechoic. Non Environment.
Lack of reflections definitely makes it easier to hear details, chose reverbs etc. However such a response is devoid of normal room gain, and is thus HF boosted from norm by at least 6dB.
Oddly some 'top' designers deny this is a problem. While others advocate simulating the average listeners experience. e.g. The curves researched by B&K, Harman, Sonarworks, Dirac Live.
Any experience of Mixing will readily show that one delivers the opposite to any room or speaker bias. Bright room, dull mix.
One notes that nobody listens on Audiometric Headphones, i.e. Lab perfectly flat, highest resolution.
Boggy, RIP, designed rooms, which complied with ITU desires, had the highest resolution, lack of colouration, but included both creature comfort reflections and a perfectly balanced albeit short ambience.
Massenburg and D'Antonio, fulfilled the same set of wishes. Here is Blackbird Studio C with a 'proper' surround setup.



"In a 2-channel room, the room itself contributes the 3rd dimension of sound, the room reflections, necessarily to create a sense of apparent source width and envelopment. The music is encoded only with the reverb, it is impossible for a reflection free listening space and 2 speakers to recreate these effects and so good room designs for 2 channel would need to be optimized to contribute this effect. Since real music in real spaces are acoustically larger than our listening space, the treatment of the room needs to focus on making the room sound bigger than it really is. Hence the use of diffusion, reduction of very early reflections, and that initial gap."

Sorry Matt, but no. Recording played without local ambiance deliver the recorded space much better than a small room with contradictory early reflections and a spectrum of short decay utterly removed from a Concert Hall or Reverb Chamber or Plate. Such a lack of 'noise' reveals the ambiance and envelopment of the recording in a spectacular fashion.
Anyone can test this readily. Headphones are highly immersive.

DD
It can't, what you say is impossible. A room with no reflections cannot provide any spatial cues for envelopment or apparent source width. It's impossible. The only way that can be true is multichannel. On top of that, the research has never shown that removing reflections from the sidewalls improves the sense of ambiance or is even preferable or desirable. The opposite is true. And it's not one research study or one group. What you say is an opinion not supported by acoustic theory, explicit research, or our understanding of psychoacoustics.

As for headphones, come on? Immersive? First, headphones and speakers feed sound to the ears quite differently. There is little need to have surround speakers to create immersiveness because the recordings can be encoded using binaural encoding. This requires modeling of the HRTF which is rarely done and not a part of recordings. Your example is not a good example of immersiveness.

Envelopment or spaciousness are defined acoustic terms and rely on reflections coming from all around us. Reveberb is presented by temporally and spatially. 2-channel can only reproduce the temporal aspects of reverb, it cannot immerse us because it cannot surround us without the room. Apparent source width, what provides space between the instruments is a function of sidewall reflections. So much so that is precisely how its measured. Two speakers in a dead room simply have no spatial cues for envelopment or ASW.

Also note I didn't suggest adding early reflections, but sidewall reflections are not necessarily early or perceived as such. That would depend on their distance from the wall. Which, I must add, is just a theory. The research about leaving in or removing sidewall first reflections explicitly found time and time again that it was prefered to leave them in and MUSHRA studies then showed that the preference was because it added spaciousness (which is totally consistent with acoustic theory and psychoacoustic concepts of spaciousness. The obsessions with removing first reflections is nothing more than a theory with contradictory evidence to support its use.
 
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