Axiom Home Page Forums General Discussion Technical Questions Room treatments - what and where?

Hello Axiomites.

I've got a 5.1 setup, with M60v2s, VP150v2, and a pair of QS8v2. Sub is an AV123 MFW-15.

I'm probably going to add another pair of QS8v2, and may eventually upgrade the fronts to M80s (I wish I had known my Denon could handle them when I ordered as I would've gone straight for them at the beginning).

What I'm concerned with here is room treatment.

I'm working on finishing up the room - a riser for my rear seats, crown molding to cover surround wires, and acoustic treatments.

I don't have much of a clue what I'm supposed to do for treatments though. I would LIKE to hang movie posters around the room, but I don't want to hang anything until I know where I need treatments, or if I even need treatments at all. It sounds really good to my semi-trained ear, although I know I'm hearing a lot of reflections.

I found a room mode / standing wave calculator online (excel file from Harmon Kardon) and it says my standing waves are as follows. I'm listing by height, then width, then height.
1st axial mode: 71 hz, 52 hz, 23hz
2nd: 141hz, 104hz, 45hz
3rd: 212hz, 155hz, 68hz
4th: 283hz, 207hz, 90hz

I have very little idea what I need to do with this data now that I know the modes though. :p

I've seen people on AVSforums hang the generic "acoustic panels," but from what I've been reading at other sites, they don't help much. Apparently the main range to quiet reflections is 500hz-100hz, and unless you have a 4-6" thick piece of foam, you aren't going to stop stuff in the lower frequencies. Does this mean that hanging GOM stretched over a frame with foam in it is pointless, even though half of AVS seems to do it?

I haven't had any major bass problems. The sub was a bit hot when I had it back in the corner, but I didn't mind the bass. Only problem was that it made the plastic front of my LED DLP rattle, so I've moved it up the wall a bit and out of the corner.

I know that people will want pictures and measurements, so here are some links.

Floor layout with measurments. Sub is on the "left" (top in the picture) long wall between the TV and the seats. L/R M60s are almost right next to the TV, VP150 is below the TV.

This is before I had the sub in, M60s are now closer to the TV.


Apparently my lens is dirty. You can see a QS8 poking out in the top right.


My wife next to the TV. She's 5'2". You can see the QS8s now. Not exactly sure where I should put the second set for 7.1 - hang them behind the 2nd row of chairs from the ceiling, maybe?


View from the sweet spot. L/R are much closer (maybe 2-4" away) to the TV now. Sub is sitting roughly where the plastic guitar is, speakers had to come closer to the TV so the sub wouldn't block them.


Standing in front of one of the M60s, shooting to the back. Pardon the dusty lens again. Looking for pointers on where to put a second pair of QS8s, on the side walls behind the 2nd row, or should I pick up FMBs and hang them from the ceiling? The back wall wouldn't work due to the door...


You can see I have a lot of bare wall, and I'd like to hang framed posters there, but not if acoustic treatment belongs there instead.

Your thoughts?

Braden, those modes are of course created by a room about 8X11X25(1130 ft./sec speed of sound divided by twice the dimensions since the sound makes a back and forth circuit), as yours is. That isn't bad, and it can't be said that your room "sucks" as does that of certain of our members who shall remain nameless.

In addition to the room modes, there's the matter of reflections, which all listening rooms other than an anechoic chamber have and which contribute to the sense of spaciousness in the sound from the speakers. Too "live" a room isn't good either, but Dr. Toole in his new book cautions against overdoing room treatments beyond typical room furnishings such as carpeting which help to keep things under control. In particular, he emphasizes the beneficial first reflections and cautions against trying to muffle them. It's possible that the answers to your question may be none and nowhere if your room isn't excessively live at this time.

As to the back surround speakers, they should be on the back wall just high enough to clear the door to the garage and spread as widely as possible, say about 6" from the side walls. If that leaves them too close to the ceiling(say less than 4")then a few inches lower on the side walls about 6" from the back wall.

{{Welling Up}}}



{{Heavy Sniffling}}



{{Seriously Bawling}}



That's IT! ::Runs Away Crying::

>>In particular, he emphasizes the beneficial first reflections and cautions against trying to muffle them.

It's funny, I was midway through typing "yeah, like JohnK says, you gotta do something about those first reflection points (where the sound bounces off the side wall to the listener's ear) when it finally sunk in that you were saying maybe *not* to treat those points.

It does seem that the room is relatively narrow and so the negative impact of the first reflection points would be greater than in a wider room, which might argue for treating them.

There is a side window on the left but not the right; I *think* the drapes on the side window are sufficiently high that they wouldn't affect the sound much, but I would be tempted to keep the corresponding area on the right free in case you decided to hang "dummy" drapes there for symmetry. Then again, I might be more sensitive than most people to uneven reflections from left and right.

Overall the room does seem to have a reasonable amount of absorbent "stuff" already, so adding more is probably not needed with the possible exception of the first reflection points. What it does seem a bit light on is diffusion, ie randomly shaped hard stuff like bookcases or big junky things on the upper walls to "spread the reflections around".

I'm not really sure how much diffusive effect the chairs and occupants will have -- my guess is that you have more than enough in the lower part of the room but something to help diffuse reflections between the upper side walls or back wall might help. This is getting way past my knowledge level though, so take this with a grain of salt.

Nice room, by the way !!

Here are a few useful sites: Room Treat DIY ; Hodas . On the second one,check out he index at the bottom for other articles of interest.

I did a foam core wall panel last weekend. Not much noticable but I'm forging ahead with more of them.

I wouldn't go worrying about treatments unless you hear something you don't like. In my concrete box (room that sux) I can hear boomyness in the bass at certain frequencies and on some music like pipe organ I can feel the energy buildup at high frequencies.

Take your time and get used to the sound of your speakers and room. If you hear things you don't like look to treatments as a possible solution.

On reflection point treatments, I believe the current thinking is to treat with caution. In pro recording rooms it is often a combination of absorbtion and difraction so as not to deaden the room too much. Diffraction is hard in a small room, but I have seen pannels made of wooden slats in front of 1-2" of rigid fiberboard so that you only get partial absorbtion.

Wow, awesome advice and no stupidity like I expect from AVS. Thanks guys.

Re: construction...

The left wall with long window is an exterior wall (obviously) and has insulation in it. The right wall with the large opening is interior and hollow. The lower 4 ft of the walls (painted darker brown) I believe has framing in front of cinder block, but I'm not 100% sure on this. There are outlets on that wall and I highly doubt they flushed the boxes into cinder block or concrete, nor do I think they ran romex through it, so I'm guessing it's 2x4's in front of cinder block.

As you all can see, yes there is a lot of soft with the chairs. The rear row is eventually going to be up on a 20" riser as well, which should help break up the "air" a bit more. The carpet is also a fairly deep / long pile, almost like shag but not that furry.

When I first listened to the M60s in there, with chairs in place but without the sub or surround turned on, I thought I was hearing sounds behind me even though the QS8s weren't hooked up yet. I'm guessing this is due to either "good" reflections or just the fantastic sound stage of the M60s. Source was HD-DVD of Planet Earth, the first episode.

I think that some of the reason I'm not having too much of a problem from the sides is that the right side of the room has the big opening to the laundry, stairs, and bathroom. I will probably hang a thick curtain there eventually for light purposes, but it will probably cut down reflections a bit as well.

I do have a few pieces of movie-theater art that I'm going to hang that should help with diffraction, they're 3d and metal, but they don't have that much mass.

JohnK: re: the rears for 7.1, you really feel they should be on the back wall instead of hanging from the ceiling? I've seen the dolby positioning diagrams, and to have them at ~150-135 degrees for the sweet spot, they end up nearly in the back corners of the room. I was thinking they may work better if I hang them behind the 2nd row of seating instead of on the back wall, simply because the back wall is going to be too high if I want them to clear the door. (That door is open most of the time as you see in the picture.) There's quite a bit of space from the back row to the rear wall, and there's even more space from the front row to the rear wall. I Could cut it down by hanging them behind the back row... although then I'm cutting into the ceiling for wiring (ick).

Since I'm posting... Does Axiom offer a credit if I want to trade-up to the M80s? I'm actually still within my 30-day eval window I believe...

If you're still within your 30 day window, you get the full $ amount back. If not, well, you'd have to talk to Axiom.

I thought reflections in small rooms were more trouble than in large rooms. In small rooms doesn't the tight timing of the reflection to the direct sound cause muddiness b/c your brain can't separate out the reflected sound from the original sound? I ask b/c my room is small, about 1,900 cubic feet, and I have been planning to tackle the first order reflections but have not gotten too far.

I looked again, whether they go by ship, purchase, or date of delivery, I'm still a few days past 30. Hopefully if I am considering stepping UP to M80s they can overlook this though?

I'm fairly happy with the M60s, but I'm curious about how the extra mid and tweeter fill out the M80s. I've read that they do OK on a Denon receiver even if it isn't "rated" for 4 ohm operation, how much wattage do they need to sound good? My Denon AVR-789 is only good for ~90w/ch...

You are correct Zimm, reflections will be more of an issue in a small room. It probably still partly depends on how much reflection there is as well.

You are in a small room so 90w will be enough. I am running a Sherwood receiver rated the same and in my 11x20x8 room I can play music at 95db (too loud) without any noticable clipping.

John, my reference to Dr. Toole's expertise is based on his book "Sound Reproduction-Loudspeakers and Rooms". Modes and reflections are discussed in detail at several points, but the specific question of side-wall reflections was discussed in summary at pp. 503-504 "...because of the widespread belief that these reflections should be eliminated as a matter of ritual"(p.503). He explains how these reflections in fact are somewhat beneficial in aiding spaciousness for home listening in relatively small rooms and states that "...my recommendation is to leave some blank wall at the location of the first lateral reflections from the front loudspeakers"(p.504), and that "There appears to be no evidence in the now substantial literature that these first-order lateral reflections are problems in normally furnished or the equivalent moderately treated rooms"(p.504).

Various absorption and diffusion possibilities are suggested for other areas of the room, but it's emphasized that the absorption should be down to about 200Hz, which requires treatment at least 3-4" thick . "If only part is absorbed, then the performance of the loudspeakers is compromised, and some of the reflection remains; there is just no point"(p.504). Coverage in the middle portion of both the front and back walls is specifically suggested.

Braden, yes, as was said, the back corners are the suggested mounting area for the back surrounds. If the door is about 78" high and the ceiling 96", the QS8s could be mounted with the bottoms at about 79", allowing room for the top mid-woofer. The height would be good and not significantly different from the side surrounds, and the 9' separation is suitable for the distance behind the seating area.

John, that's very interesting. But I have to admit, it makes me feel a bit helpless. I can't figure out if change is worthwhile or not.

Interesting comments John. I really need to pick up that book. I debated between it and Everest's Master Handbook of Acoustics and ended up going with the Everest book.

I find all of this very interesting, but I don't know that I can jump in 500+ pages of it - I read enough at work. Anyone see the Cliff Notes?

You've been reading them in each one of John's posts.

Stick around here awhile. There's plenty of stupidity!

Reading this thread makes me want to cancel my order. I know there's this whole science thing to room treatments but I don't intend or hope to do anything. Does that mean my room will suck too?

Bob, rooms of typical dimensions(e.g., not square)and typically furnished don't "suck". Some modest room treatments may be helpful, because all rooms affect the sound from the speakers, but it isn't as big a deal as some indicate.

I thought the 30 day policy was for a full refund and I thought I read here on the forum that the trade up policy was much longer.

In any case I would call Axiom. It don't hurt to ask.

Nope. Only two members at a time are allowed to have rooms that sucketh. Right now its me and Mark. You'll have to wait your turn.

Even in a room that sucks, the M80s sound great. Way better than that Mini stereo I had.

My room sucks because of two flaws: concrete walls (very reflective to both high and low frequencies, its basically square. Because of that, I will get a lot of milage out of some some basic treatments.

Actually, I am picking up a used parametric equalizer this weekend to tame a major peak in the bass region. If it works, I should get rid of some major boom that hopefully also tanslates to more LFE impact and more bass detail in music.

Bob, the trade up policy does go longer, however, the longer you wait the value of what your trading goes down. This does not make sense to you? If you sell a car to someone that is 1 year old, compared to the same car that is 5 yrs old, the new one will be worth more on a trade.

Also, why would you cancel your order because your room MIGHT suck? The problem with room acoustics as nothing to do with Axiom speakers, all speakers are affected by your room, this has been the case since God created the Earth.

My advice is don't sweat the room treatments so much at this time. 99% of people never modify their room and live a very happy normal life. If you seek advice on audio forums, you are hearing from the 1% or whatever that truly enjoy tweaking their systems and rooms to push the top levels of performance.

Yes, a room can make a big difference in sound properties but I'm betting that your enjoyment levels from the new speakers will surpass your expectations even without delving into finessing the room. There is tons of time to play around with that later.

I built a few DIY tweaks I'm trying out now. I found some pink dense foam insulation that is folded accordion style. The nice thing is you can make it as thick as you want, and the folding actually leaves air space in between the layers. My first version is 2 inches deep in a corner, with about 6 layers of this insulation board. Not sure the reflective attributes but I was very surprised that sound moves through them very well - perhaps too well.

Putting a think layer in front of a speaker barely decreased the spl level just behind it. Yet, while hanging on the wall, you can fell them move like a slow moving bass driver. That leads me to believe they are absorbing the sound (thus transforming the sound back into mechanical motion). So in theory I think they "work" but I can't tell you that I notice much difference in sound. I need to build a few more and see how it goes once I have the back wall of small room treated.

Going to cover one with wine corks to give it a more artistic flair. (Can never have enough flair, right!) Anybody know the reflective attributes of cork? I'm hoping the round surface and soft skin will result in good diffusion and absorbsion, but I might be preventing the pink stuff from doing anything with cork on the surfact??? (Some studying would probably be helpful, but winging it is so much more time consuming!) If anybody has a surplus of wine corks send them down! On second thought, just send the wine and i'll send the corks back to you so you can build your own. Yeah, that's a better approach.

Ha ha! make sure no-one sends you screw-on caps instead of corks, Charles!
So what constitutes the 'proper' or 'perfect' room for HT. Unless someone is building a dedicated home theatre from scratch, we've got to work with what we've got. My room (actually a family room) is abooot (couldn't resist) 20 ft x 14 ft with 8ft ceiling. The floors are 3/4 hardwood covered with an 11x9 thick wool rug, side wall on the 20 ft has two glass doors, oposite wall is clear (drywall), the 14 ft wall at one end is mostly fireplace and at the oposite end the room opens diagonally on both sides to hallway/breakfast area. Does this sound like a nightmare for HT? I think I need to empty a few bottles myself before I tackle this one.

Better than a shoe. Those things have horrible accoustics! ...Unless your room is das Boot, in which case your sunk.

Fred, you need to audition for Yuk-Yuk's!!!
BTW, re Das Boot....that's one sub that can really go deep!

Adrian. The 'perfect room' would be [bilatterally] symetrical with a mix of absorbtive and diffusive characteristics.

Drywall over studs will act as a resonant absorber at certain frequencies, depending on the density of the drywall and debth of the cavity, and reflective at higher frequencies (say above 500Hz to 1KHz).

Glass would be transparent at low frequencies (resonates and allows low frequencies to be pased through because it is not covering an enclosed space [resonant absorber]) and reflective at high frequencies.

Having differences from one side to the other may have a noticable affect in imaging. As and example, the couch I have along the left wall blocking part of my left speaker shifted the whole soundstage noticably right. I had to boost my left speaker by about 2db to center the image, and I suspect it still affects the 'placement' of instruments on the soundstage.

Probably the main reason I am aware of some of the defficiencies of my room is that I had the chance to audition the system I bought in a symmetrical and acoustically good room at Axiom.

I was wowed by the difference between two channel and 5.1 music on one of the live discs I took with me to demo. I do not get that same wow difference in my room. Had I never listened in such a good room, I would probably be ignorant of the shortcomings of my room. [As a side note, I wonder how many people are underwhelmed by 5.1 music because of less than good/perfect acoustics in their room.]

Being a perfectionist/pedant, I now feel bound to chase acousic perection. Being free of WAF, that could be dangerous.

Having babbled all that, if you don't notice anything wrong with your room, don't worry about it too much.

I have to agree. My room is okay now, but my last room was very unsymmetrical and the image showed it. Soundstage was weak and mobile. So a certain range was centered, but as the range moved (like a guitar chord change) the image moved. That was real noticeable to me on music, but not for movies. In my new, smaller room, I don't have that as much, but I have a 7 db spike in low bass (I'm guessing about 50hz) right behind my listening position. I also have some harshness in the highs at loud volumes that I think are reflective issues as the highs get bouncing around my small room. So I'm trying to tame with basic treatment before I go full bore or give up. I’m preparing to run REW, but don’t have all my ducks in a row yet. Not sure that will tell me much, but can’t hurt.

It generally sounds great, so i'm not going to over do it. ("Not going to over do it, not going to over do it." I have to keep saying that to myself!)