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...