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Discussion Starter #1
I'm at the stage where I need to really think about accoustical treatments, as I was going to "see what it's like" and deal with it then, BUT I will not have to sweat the fine details of spackling if I'm covering up the walls with treatments.

So the question is, now that the rock is up, WOOOOW what a difference when you clap in there, or talk....the echoes are bouncing all over the walls. (15x15 room)

Of course no carpet or couches yet, but how critical is it to do the front wall ?

Logic tells me the speakers are facing forward, in a 6" bump out on each side, and my subs are in the floor in the middle of the room.

I do plan on some decorative curtains around the screen, do I need to treat the front wall ?
 

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I could be way off here, but...

I thought the main point of treating the front wall was so that you only get sound from the front speakers, you don't want the sound from your rear/surround/popcorn crunching bouncing off the front wall and coming back mixed with your L/C/R audio.
 

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mbennum is exactly correct. Curtains will help some with that but only at high frequencies. Depending on what you can do with the rest of the room, you may need something thicker. Also, you'll want some sort of bass control up front in the corners.


With a square room (and presumably an 8' ceiling that's almost exactly 1/2 of the L and W dimensions, you're going to have a lot of really serious peaks and dips in reponse so bass control will be more needed proportionately than in larger, non-square rooms.


Bryan
 

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Discussion Starter #4
I have a 6.1 setup, but may goto 7.1 now that I fried my 6.1 Onkyo502, but my current rears are on the side walls facing in, so no bouncing there.

I have one rear on the back wall set to face forward, but that's really an "effects only" type speaker, that doesn't get a huge % of play time.

An occasional plane overhead, or train wizzing by, but for the most part, that speaker is mute.


Bpape...we know your the resident here....I guess we both need a small lesson on what treating the front wall is for ?

and if it applies to my specific situation, or is worth the time/money.

8' ceiling above the 10' deck, 9' ceiling on the 5' deep floor at the front wall.

TIA
 

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Hopefully Brian will give you a lesson beyond what he has already said here. but the plain answer is YES you do need it, and don't think that because those sides are facing in and not front that you are not getting reflections off that front wall from them at all.
 

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Discussion Starter #6

I'm not disagreeing with you at all, but I guess I would love a more detailed explanantion than, you have to....I'm a former eingineering student, and love the detail lingo of the Physics of High Fidelity (got a B)

Considering the simple direction of 90% of the audio (while watching TV or Movies) is coming OUT of the front speakers directly perpindicular to the back wall, L/C/R, wouldn't it be more important to deaden the rear wall, and treat the side walls ?
 

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Quote:
Originally Posted by Plasma George /forum/post/0

I'm not disagreeing with you at all, but I guess I would love a more detailed explanantion than, you have to....I'm a former eingineering student, and love the detail lingo of the Physics of High Fidelity (got a B)

Considering the simple direction of 90% of the audio (while watching TV or Movies) is coming OUT of the front speakers directly perpindicular to the back wall, L/C/R, wouldn't it be more important to deaden the rear wall, and treat the side walls ?

George- My smaller room is quite similar to yours; it is 16x15x8 and, believe me, every bit of acoustic treatment I can manage makes a difference. The beginning was a slew of RealTraps that I borrowed from Ethan Winer which convinced me and my wife of the necessity of treatment. She nixed those for appearance reasons but approved treatments in principle.


Since then, I have added an 8' long bass trap (2' x 1') along the front wall at its junction with the floor, two diffusors on the front wall flanking the PDP, two 2'x4'x2" panels spaced off the rear wall and just behind the listening couch (I'll bet your rear wall is pretty close to your ears, too) and, recently, a pair of RealTraps TriCorners in the rear lower corners. The floor has a large rug with undercushion.


This is not a dedicated room, so I am limited in what I can do but the dimensions demand as much, and more, than I have already done. Now, while you are still building, do not skimp.
 

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Quote:
WOOOOW what a difference when you clap in there, or talk....the echoes are bouncing all over the walls.

I think you answered your own question in your original post.



I associate sound waves in a 15x15 drywall room to a bullet fired from a gun in a 15x15 concrete room.. Sound waves (the bullet) are just going to keep bouncing around in the room until they a.) loose energy naturally over time, or b.) are absorbed by a material they come in contact with.


Just because your fronts are radiating the sound toward the listening position, don't think for a minute that the waves aren't hitting the rear wall, reflecting back toward the front wall, then back off the front wall AGAIN toward the listening position.


The "echo" you heard when you clapped your hands,,,, is the sound waves passing your ears multiple times as they bounced from wall to wall to wall.


I found when I treated the front wall,,, the rear channel became more distinctive. I'm pretty sure that's because I was no longer getting the reflections from the rear channels off of the front wall.
 

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Quote:
Originally Posted by Plasma George /forum/post/0

I'm not disagreeing with you at all, but I guess I would love a more detailed explanantion than, you have to....I'm a former eingineering student, and love the detail lingo of the Physics of High Fidelity (got a B)

Considering the simple direction of 90% of the audio (while watching TV or Movies) is coming OUT of the front speakers directly perpindicular to the back wall, L/C/R, wouldn't it be more important to deaden the rear wall, and treat the side walls ?

Well, yes and no.


The classic design is a dead-end live-end design, deader towards the front of the room, and more diffuse towards the back. This is kind of a simplistic summary, since you want some absorption in the back too, especially if you're going for a deader HT space, and diffusion in the front can also work quite well. But the reverberation to the rear is more delayed, and adds to spaciousness, while the early reflections from the front will not add spaciousness too much, but will destroy imaging accuracy. Obviously you don't just want a big flat surface in the back for a giant slap echo, so diffusion or absorption is important there.
 

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George,

Quote:
Considering the simple direction of 90% of the audio (while watching TV or Movies) is coming OUT of the front speakers

You nailed it, and this article shows polar plots and comes to the same conclusion - at least for conventional cone driver loudspeakers:

http://www.realtraps.com/art_front-wall.htm


However - and this is a big one - the front wall is just as good as any other for generally reducing the overall level of room ambience. Often, people who have no treatment at all will put absorption on their front wall (because everyone says to) and they notice an improvement. Well, duh!



But the front wall is not a major source of early reflections. Indeed, the rear wall often is, at least if it's less than ten feet behind you. So it's much more important to treat the rear wall, even if farther back than ten feet. And of course all first reflection points on the side walls, floor, and ceiling need treatment too.


--Ethan
 

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Discussion Starter #12

Quote:
Originally Posted by Ethan Winer /forum/post/0


George,

However - and this is a big one - the front wall is just as good as any other for generally reducing the overall level of room ambience. Often, people who have no treatment at all will put absorption on their front wall (because everyone says to) and they notice an improvement. Well, duh!



But the front wall is not a major source of early reflections. Indeed, the rear wall often is, at least if it's less than ten feet behind you. So it's much more important to treat the rear wall, even if farther back than ten feet. And of course all first reflection points on the side walls, floor, and ceiling need treatment too.


--Ethan

Now I don't know what to do.

If you check out my Thunder Deck thread, you'll see the screen wall is set back 6" from where the L/R's are, so it would be easy to treat the screen wall, also because it will be black.

The wife wants the Maroon/Burgandy that's in our Dining Room for the sides and rear wall, so treating that might not look right, or harder to keep that look.

UNLESS I make the back wall flat black as well....you're not seeing it when you're sitting in there, only when looking at it from the door.
 

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Thinks fo the speakers light spot lights and the walls, ceilings, and floors are light mirrors. You will get lots of unwanted reflections unless you put materials on the walls ceilings and floors to scatter or absorb sound.


While speakers radiate most of their energy forward a small amount is radiated in other directions. Low frequencies tend to spread out more than high firequency. If you have front speakers that are bipolar or dipolar (where there is a rear firing speaker), that helps make the sounds seem "fuller" but less precisely located. Speakers like Definitive Technology BP10 have rear firing speakers.


However the main reason for treating the front wall is to deaden unwanted sound that comes from surround speakers or the audience, so that the main sound you hear comes from the front and center speakers.


There are threads on how to treat rooms to cut down on unwanted sound reflections. I think the Dennis Erskine method is to fully treat the front wall with Insulshield or other insulation designed to cut down on reflected sounds across wide ranges of frequencies. On the side wall use that material up slightly above seated ear height. In the back, also go up to slightly above ear height. Then on the side and back walls, use cotton batting of similar thickness to the Insulshield and cover all the insulation and batting with fire retardant cloth. There are lots of threads that explain this better than I did.


In a square room, certain frequencies will echo very loudly because they are multiples of the room dimensions. To avoid this either make the room rectangular, or use acoustic treatments to cut down on unwanted sound reflections.


Some people go overboard and put acoustic treatments everywhere. That leaves a room sounding "dead" because the echos are weak or nonexistent. That sounds unnatural so people usually don't want to do to that extreme.
 

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I don't see any color problems since GOM comes in most colors. you just cover your treatments with it. why is that an issue?
 

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Black front/rear walls,,, burgandy side wall decor would be UUUUGLYYY!!



See!




 

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George:

I'd encourage you to do some research on SBIR ... Speaker Boundary Interference Response. Speakers will 'couple' to a nearby boundary such as the front wall. Take a friend out to a big empty field. Have the friend turn his back on you (sounds like a Soprano's episode) and start talking. Can you hear him? Enough said.


As the sounds reflected from the front wall reflect back and pass the speaker, those sounds have a path difference (ie, a phase difference) and will create notches and peaks. The primary notch frequency will be that frequency with a 1/4 wave length equal to the distance between the front of the speaker and the front wall. While several adverse impacts occur, the larger impact is with dialog intelligibility. If you cross over your mains at 80Hz and place your LCR's at a distance greater than 3.5' you can eliminate the notch but not all of the other issues without front wall (and immediate side wall) treatments.


Another solution is to baffle mount your LCR's. [Ethan could likely do well building and selling curved speaker baffles.]


The back wall is more typically treated with diffusion to enhance the surround effects; however, in many rooms, absorption is required on at least a portion of the back wall to decrease decay time over all.


If you are building a rear seating platform, there's a perfect opportunity to use that as a broadband bass trap.
 

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Quote:
While speakers radiate most of their energy forward a small amount is radiated in other directions. Low frequencies tend to spread out more than high firequency.

If you want a simple method to determine the point at which a larger share of the energy 'wraps around the speaker', measure the width of the face of the speaker. Determine the frequency with a wave length equal to the width of your speaker. Frequencies below that will easily radiate behind the speaker itself.
 

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Dennis hit on the other reason to do the front wall - the SBIR. Also a good reason to do a lot on the side walls for the first few feet depending on how close your speakers are to those boundaries.


The idea in general in killing the front wall other than the above is to not have sound from the surrounds coming off the front wall and 'contaminating' the front soundstage. If we minimize this, then the front soundstage locks to the screen much better and presents a better aural imagerelating to the action on the screen.


Bryan
 

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Quote:
Originally Posted by bpape /forum/post/0


Dennis hit on the other reason to do the front wall - the SBIR.

I agree completely, and I made that point in my article linked above. But then this is a bass issue, not one of traditional early reflections that mainly affect mid and high frequencies. Of course, Dennis is correct too, that some amount of sound is audible behind a speaker. That's why I showed those polar plots in my article. So I think we can all agree that most of what comes out the back of a loudspeaker is below the midrange - let's say from about 300 Hz and lower. And for that you need more than the typical 1 to 2 inch thick absorbers.


--Ethan
 

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Ethan


You don't seem to agree with your linked article - which concludes that a better treatment would be first reflections for treble and corners for modal - and if broadband that takes care of reverb.


If someone has an HT without an acoustically transparent screen and no room for a proper soundstage - then it is very likely that LCRs are too close to the wall.


front wall treatment is a good solution for that SBIR problem - needs to be effective at woofer frequencies.


If someone has an HT with typical sidewall bipoles/dipoles that are wall firing rather than monopoles that fire across seating - then you have a situation of surround sound interfering with LCR soundstaging - a problem that does not exist in a commercial theater.


front wall treatment is a good solution for that surround reflection, needs to be effective at tweeter frequencies.


And your length modes are usually worse than any other (it is usually the longest dimension in an HT) - so front wall treatment dampens those more than the others.


And front wall treatment is as good a place as any to get some reverb control, and in a media room that has multiple uses - it may be the best place so that you get local reverb control. Who cares what the reverb is by the pool table and fireplace?


And consider visual WAF of it being the one place that you can get away with black traps covering the wall, and it enhances the visual contrast of the movie screen. Making for his-n'-her happiness. And not to be cynical or anything - increases the trap sellers happiness when buyers cover their front walls.



So there are many reasons to do front wall treatment - yet your article says do corners and side reflections first. It would seem the better recommendation would forgo the rear corners and put them on the front wall first if you have the above problems.


Or you could say use monopole sides and move your LCRs off the walls and use a sound screen and avoid the problems in the first place. But space limits on seating arrays and soundstage - means most HT's cannot afford to do that. Exception being high priced designers with customers that have big rooms - such that modal treatment is done in other locations, and SBIR is not an issue by design - leaving front wall left behind the soundscreen as a great place for invisible treble reverb treatment effectively treated with ductliner.


One general placement recommendation does not work when seating and speaker locations cannot be generalized.


All of my HT's have front wall treatment - it was needed to solve one or more of the above problems. I would say the case is rare that it is not needed in an HT. Maybe studios have different seating/speaker patterns and it is the opposite case that it is rare that front wall treatment is needed. But it does not make either treatment pattern wrong - the only wrong treatment pattern is one that does not solve the rooms problems.
 
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