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-   -   Help addressing slap echo (https://www.hometheatershack.com/forums/home-audio-acoustics/164298-help-addressing-slap-echo.html)

nickwin 01-28-17 02:43 PM

Help addressing slap echo

6 Attachment(s)
I've been slowly working on my combined music/theater room for a while but I've really struggled with a slap echo problem and I'm not sure how to address it in this particular case. Its a pretty crazy/complex room to deal with (and I am by no means an expert). Its a small rectangular room about 14'x10' but its open with a large hallway in the from left corner. My fronts are 7' apart and 7' from the listening position. Its in a basement, concrete bricks with drywall over it. Most of the front wall is exposed concrete brick, there is a glass sliding door on the back wall with a light curtain over it. The floor is carpet over concrete and the ceiling is about 1/3 "acoustic tile" around the edge and 2/3 drywall.

In this little room I have 2 Magnepan 1.6's, a CC3 center and 2 MC1 on wall dipoles. Bass response in this room is pretty bad even with two subs in opposite corners, so I'm using 2 GIK corner traps, one in each back corner. I also have a GIK standard bass trap on each side wall at the first reflection points of my fronts in an effort to tame the high end reverb and tighten up the image. Im using Dirac for EQ.

Its been a long process of trial and error taming the bass resonances, maintaining a solid image for my fronts, eliminating slap echo while not making the room completely dead. Iv learned that in this small of a room a few panels go a long way.

With the two corner traps and 2 bass panels I think Im already on the verge of over treatment but I am pretty happy with how it sounds, EXCEPT I still have a nasty slap echo from from an untreated section of the side walls directly to the right and left of the listening position. This spot is right in front of my on wall surrounds and I get some nasty sibilant echo from the surrounds because of it.

I tried using one 2x4' 2" absorption panel in this spot on the right wall only and found that while it did get rid of the echo, just adding that one panel really killed the sound in the room. I kept having to crank the volume up to get it to sound full and even cranked up it still sounded spot of dead. Removing this panel brought some much needed life back to the room and seemed to improve the image of the fronts, maybe because there was more absorption on one side wall then the other?

So to the real question: What's the easiest way to address this slap echo without over dampening the room or hurting the imaging by having non symeyrical absorption, AND not getting in the way of my on wall surrounds? My understanding is I only need to treat one side wall to fix the slap echo, but should I treat both walls the same to preserve the stereo image? Im thinking this is probably situation where diffusion would be ideal, will all commercial diffusion products work for slap echo? Or do I need something specific to address this?

To complicate things further this needs to work with my on wall surrounds, I worry that a thick panel to close to the speaker will block the rear firing sound from them and might be problematic. So, the solution either needs to be thin or recessed into the wall which is something I would like to avoid if possible for obvious reasons.

I've never really shared pics of this room so go easy on me! If you see any red flags please let me know because Im still learning. I do have some REW graphs I can post if that would help. The FR graph attached is my front left and right (Red is right), with EQ and 1/12 smoothing.


bpape 01-28-17 02:57 PM

Re: Help addressing slap echo

Which color plot is which channel?

You can help with flutter with diffusion certainly and not take any life out of the room.

nickwin 01-28-17 03:11 PM

Re: Help addressing slap echo

2 Attachment(s)
Sorry, red is the right speaker. The rear of the left speaker is firing down the hallway, while the back of the right speaker is firing into a cubby that houses my electronics. Its about 4.5' from the back of the right speaker to the back of the cubby. I have the back of the cubby mostly covered in 2" absorption material. Considering how different the placement is between the two speakers imaging is surprisingly good, but as you can see the midrange is less linear in the right speaker because of the close proximity to the rear wall and interaction with the reflections.

If I where to address the slap echo, or flutter as you call it, with diffusion, would I want it the same on both sides or is that not a concern? Is there a low profile diffusion option that could sit up close to the on-wall surrounds without getting in the way of the sound coming from the back of the panel? The tricky part here is getting the diffusion close enough the surrounds to fix the slap echo without obstructing the sound path of the speakers. Im hesitant to put a 4-6" panel right up to the back of the surround, as you can see it would really box them in.

The 2" absorption panel you see in this picture DID seem to stop the echo, and didn't seem to interfere with the response of the speaker next to it, but it just killed the room. Diffusion products by nature are going to be a lot more than 2" thick though right?

Recessing a diffusion panel into the side walls seems like the ideal solution, but the cost involved with that is pretty prohibitive. I wonder if a very minimal absorption, some kind of fabric on the wall, could fix the echo without dampening the room noticeably?

EDIT: sorry about the picture being side ways, not sure why it did that.

nickwin 01-28-17 03:52 PM

Re: Help addressing slap echo

3 Attachment(s)
A couple additional measurements: Subwoofer waterfall and RT60 of left and then right front. I honestly don't know how to analyze the RT60 graph, but something seems weird here even to me. Can anyone help me make sense of these? These are with no filtering selected.

These measurements where done with the 2x4' 2" absorption panel in question in place (I thought it sounded very dead and removed it).

EDIT: Ignore this, I realized these measurements where to low level to be relevant.

nickwin 01-28-17 07:08 PM

Re: Help addressing slap echo

I wonder if something like a GIK "Evolution PolyFusor" on either side would work here? With the round shape I could put it closer to the surrounds without blocking the rear of the speaker. I also wonder if my room is overly damp as it is, could two GIK corner traps and two 244 bass traps be to much in this small of room?

bpape 01-28-17 11:27 PM

Re: Help addressing slap echo

Seriously doubt it's too much. That said you have to also consider carpet, furniture, people, curtains, etc. The polys are an excellent choice and the widest range of diffusion we offer at a very reasonable price.

nickwin 01-29-17 10:13 AM

Re: Help addressing slap echo


bpape wrote: (Post 1546386)
Seriously doubt it's too much. That said you have to also consider carpet, furniture, people, curtains, etc. The polys are an excellent choice and the widest range of diffusion we offer at a very reasonable price.

I really didn't think so either, but the one piece of advice I see more than any other is "don't go overboard with absorption" so I did wonder. Maybe the reason why I didn't like the sound with that one additional panel had more to do with absorption in that particular spot, or the fact that it was asymmetrical than what it did do the overall reverberation times of the room?

bpape 01-29-17 12:42 PM

Re: Help addressing slap echo

It could well be asymmetry. That can do funny things sometimes. Your waterfalls show the room is already plenty damped. As I said, diffusion is likely your answer and won't create the asymmetric absorption issues.

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