Question: Sound Treatment behind the Listener?

It depends how far behind you the wall is; in my space, it is far enough back that reflections have a minimal effect. That is partly because there is a hallway and an open doorway.

I am sitting about 1/3 from the rear wall, or about 8 feet.

ozzy

Diffusors high up help also, so if your rack comes to waist-high it's worth putting diffusor panels above.

ozzy OP

6,511 posts

04-10-2023 at 08:34am 

I am sitting about 1/3 from the rear wall, or about 8 feet.

ozzy

I would recommend diffusers on the back wall, given your room's layout. I use the following in 6" thickness: https://www.gikacoustics.com/product/6a-alpha-panel-diffusor-absorber/

There in fact a combination diffuser / absorber / bass traps

You don't wall sound directly behind you bouncing back at your head. Directly behind I use absorption and then to the L and R I use 3D diffusors, maybe try either of these:

https://auralex.com/tfusor-3d-sound-diffusor/

or

https://auralex.com/geofusor22/

Thanks for the help.

The DIY cd rack at the back wall (behind me) starts at about 4 foot high and does go to about a foot from the top of the ceiling. It covers the width of the room. The rack does have many open spaces between the cd's. Again, I thought it would help with "scatter affect." But I’m not sure where I got that idea, and I did need a place for the CD’s.

These days I don’t play CD’s and I thought about taking down the racks. The Gika Acoustics or the T’fusor, looks to be an interesting option. Should they be placed in the center of the rear wall?

BTW, the rear wall is about 17 wide and 8 feet high.

ozzy

when i designed and built my listening room, i purposefully put a room length storage closet behind the listening position, then mounted heavy duty curtain rods above that area, hanging heavy velvet curtains to help absorb the sound from behind

i think this contributes quite a bit to the room being well damped... as i can open the curtains and hear a difference

this may be worth your giving a try ozzy

So, you think absorbing material should be used?

ozzy

For my room, I treated all walls plus ceiling.

Room sound went from bright and edgy to calm and peaceful.

Bigger improvement in SQ than any gear swap.

See my pics in virtual systems.

So you also went with sound absorbing material?

ozzy

For some reason I thought one end of the room (behind the speakers) should be the "dead zone" and the other end (behind the listener) should be the "live zone".

No credence to that notion?

ozzy

Mostly absorption, a little diffusion

Ozzy, I followed the Anthony Grimani acoustic recipe, here is a diagram. Notice absorbers behind the MLP and 3D diffusors to each side:

Wow! Some very good information.

ozzy

He breaks it down from the :59 minute mark in this video and reviews the "recipe" at the 1:04 mark:

https://www.youtube.com/live/Eo5fDGGmAyw?feature=share

Ozzy, Live end/dead end is a credible notion for set up. Speakers on dead end. listeners chair on live end. This has been around for years. Obviously how well it works depends on your room and how its executed.

For OP, if you feel you must, I'd recommend diffusors on the wall behind you, but personally I think your CD storage if they are spaced irregularly would be better than a flat surface and all you need unless you are pretty anal.  Spend some time with experiments  and see what you can actually hear as opposed to 'theories'. For example take down your CD's, what to your hear? Place a heavy wool blanket on the wall, what do you hear? As Ozzy suggested, think live end/dead end and experiment with deadening some, or a lot, of the rear and side walls relative to speaker placement. FWIW I use room furnishings to solve reflection problems not only because they look better (to me of course) but they make reflections less uniform, which I think is good, but I realize others may disagree and want to have identical reflections thinking that they will increase depth of image, etc.  That said, speaker and chair set up can go a long way in solving a lot of 'room' issues. For example, bass issues, I see folks trying to kill excess bass with corner traps when the problem is that the listener chair is in a bass node and all they have to do is move the chair a tad (out of the node) or that they measure bass in the corners where it always dwells and conclude that by killing this bass (which they can't do by using domestic bass traps). I guess the message is to solve actual, extant, problems, not theoretical ones. Have fun but take your time. :-)

kota1.

I will check out that video soon. Thanks for sharing it.

ozzy

@ozzy 

When you stand in the back of your room do you  hear any echo? Clap your hands, can you hear a reflection? If you hear anything then yes, some absorption and maybe something in the top corners as well. 
 

I found In my rectangular room 12" of the wall and 12" of the ceiling full length of the rear wall and corners with absorption panels sounds the best. Like yours, my rear wall also has household objects that act as diffusion. +1 curiousjim... the clap method was how I arrived at my room correction. My system is very lively and this final treatment went a long way in taming Klipsch Heritage speakers at the higher volumes I prefer. Good luck.

How you treat your room is somewhat based on what type of speakers you have, monopole, dipole, omni. For example, a “dead” front wall is not ideal for dipoles. 
To your OP, we typically suggest wide-band absorption at the middle of the back wall about 4’ wide (maybe wider) with diffusers flanking left and right. 

You will get some reflection from the back wall but it will be low intensity as those waves will have travelled some 20 feet before they reach you.

Being of a practical disposition, I suggest you hang some heavy blankets on the wall behind you and listen to see how the presentation has changed and whether you like it.  If that may be too much damping try it with thin cotton sheets.  You will be able to gauge what is required and what suits your tastes.

Hi ozzy: Absorbtion panels for me work best at that position.

@ozzy why not reach out to GIK Acoustics

I’m working with Mike Major to finalize everything I need for my room and I find Mike to be very knowledgeable. Provide your room dimensions and photos and see what they say. 

I did reach out to Mike at GIK. Sent him pics of my listening room. 

He suggested, and I bought, 3 acoustic panels to go on the wall up and behind my listening position. Which was on a couch with a wall right behind it. 

Timely thread as I'm looking into this as well - absorbsion and/or deflection on the rear wall. @vinylshadow  , which GIK panels did you put up? Thanks.

Also, the ceiling in the room has acoustic tiling glued and stapled over the drywall and there is 6" insulation in the jousts. There is no slap echo at the back of the room.

I was ok with the sound with the Cd’s/rack combo, just thinking of removing it now that I don’t play the CD’s.

I have already in the room Stillpoint Aperture 2’s at the 1st and 2nd and center points, perhaps adding a couple more of these in the back? I also will check out the GIK and see what suggestions that adds.

ozzy

@laynes

I put up 3 square 242 Acoustic Panels With Scatter Plate (+$30)
Pure White Fabric (standard) to better blend into the white wall.

https://www.gikacoustics.com/product/gik-acoustics-242-acoustic-panel/

They are about 18" above and behind my head evenly spread out with about 2" in between them.

Perfect, thanks. I'm thinking about moving my 242s to the rear wall but they don't have scatter plates - maybe I can buy those sep and then pull the staples out of the fabric and put those in and restaple. I'd probably make a big mess of things though.

That youtube vid posted earlier is excellent. I'm thinking about ordering  2D / GIK polys to put next to (new and larger) GIK 242 panels on my side walls. 

I just need to take a smidge of treble energy out of the room - not much but some - well quite a bit for some recordings but none to very little on others. Resisting buying an EQ.

Well, I submitted the form to GIK. Before being able to submit the form, I must say the constant need for showing that I am not a robot is annoying. Especially so for the GIK website. Why is that necessary?

ozzy

I ended up going with GIK 6A Alpha diffusor/absorbers to go behind my listening position. Granted, my room constraints necessitated something that would work relatively nearfield which these do. Highly recommend these.

There is a rule-of-thumb (a formula in acoustical engineering terms) for how far one must be from the wall behind the listening position when using diffusion rather than absorption. I didn’t bother to memorize it, as it told me I couldn’t use diffusion on that wall, my currently situation requiring me to sit too close to be able to do so. I'll bet a Google search will lead one to the answer.

With approximately 8' behind you to the wall, the sound level is only attenuating 3.52dB, plus whatever the absorption coefficient of the building materials (ie CD cases are which is probably very low), and another 3.52dB attenuation on the reflection. I do not believe that is near enough. I would be shooting for no less than 10dB if not 15dB. The only options are increasing the distance (which is probably not an option), or adding sound absorption material0, which can achieve that.

@ozzy I'd be curious to hear what GIK says. That's a great service they provide - it was somewhat of an education to me in terms of the information they provided (and why). 

The best situation is to have no wall behind the listener. An open concept situation open to the rest of the house. The rear is then open between various rooms. This keeps reflections as late as possible and fractured as much as possible. 

Greetings 

I have open book shelves on my back wall. They hold my technical books and years worth of audio magazines. Also a few diffuser/absorption panels and record cabinets.This has worked very well for me. I will add 2 bass tube traps soon. At the moment I prefer diffusion on my back wall. I’m 99% done with my room, not sure when I’ll get to the last 1%.

My head is 6 feet from back wall.

Maybe repositioning your CD’s in a random pattern might help? 6000 CD’s my goodness. Good for you.

Joe Nies

Christian5s4,

How many of the GIK 6A Alpha diffusor/absorbers did you use?

I haven’t heard back from GIK yet, but Stillpoint’s says behind the listener treatment is not really necessary.

joenies,

BTW, the cd rack has many spots where there are few/none cd’s which creates alot of voids etc., in a random manner.

ozzy

@ozzy Give GIK a few days. Their recommendation for my room was pretty accurate. 

People often seek to apply a solution when they don't know what the problem is. Diffusion and absorption each help resolve different issues applying the wrong one makes them worse. 

@bdp24 

Careful.

Google will lead one to AN answer.

Probably a lot more than one.

Got a reply from GIK. I need more info.

"OK, yeah that's a fair amount of space to work with. It will really come down to tolerance of thick panels and of course budget. If you can fill the entire wall with sound blocks that will work very well but that's a bit of a space commitment. 

If not getting Alpha 6As for that wall will help quite a bit still, and take up less space. 

We can also mix things up a bit, using Range Limited bass traps low near the floor and high near the ceiling, with the Diffusors (Alphas or others) in the middle at ear level."

ozzy

@ozzy  makes sense I think. You have a decent size room so they’re recommending abfusors.
FWIW, for my room, which is smaller, Mike recommended absorbers on the sides for early reflections and tri traps with range limiter in corners behind speakers. 

Thanks,

I'm not sure how many of the Alpha 6a's would need to be acquired. 3 of them with shipping is $763.

ozzy

I use Rockwool @ 35Kg per M3 floor to ceiling in height as a Absorption Room Corner conditioners. Directly behind and spanning between the Speakers I use a Diffusion Panel.

Each Side Wall has a diffusion pane.

The Rear Wall has a Aborption and Diffusion Panel set at a height of the listeners ears.

The sound is managed in a manner that has improved attraction with these measures in place.

Would it be identified as a accurate treatment using tools the can measure room modes is an unknown for me. 

Thanks Vinyl Shadow for the info.

I'm getting some advice from GIK but also just started a dialogue with Jeff at HD Acoustics who I found when searching here. It won't be free but it will (should?) be unbiased and sounds like he knows what he is talking about....because I don't w/ acoustic treatment on the rear wall.

I have found the Acoustic Insider channel on YouTube to be a good source of information around treating your room.  He mostly discusses treatment for small home studios, but the theory still applies to a listening room.  

As far as I can tell, he's not selling anything.  He does reference a document you can download, and I have no idea if he charges for it or if that is a gateway to purchase other stuff, but I've never looked into that.

Thank you, I will check out those sites.

It sounds like GIK wants me to get 6 of the Alpha 6's. I'm not sure if $1500 would better the sound that I have now with the cd rack.

I may try some convoluted foam I have behind me first just to see if absorption is where I wanna go.

ozzy

One of the things that I consistently hear in my research on acoustic treatments is that you can never have too much bass absorption. The problem is that you need really thick panels to get into the lower frequencies. If you use thinner panels, they will just absorb the higher frequencies (which has its place in making a room less reverberant or maybe comb filtering) but won’t help you with bass nodes or standing waves.

Even if you get thick absorption panels. they still absorb the top end so the theory is that you should just have the thickest absorption panels you can so that you get as much bass absorption as possible.

So if you decide not to get the Alpha 6s, try to make sure you make your panels as thick as you can. The Alpha 6s are six inches in depth with a scatter plate so the theory is that they would absorb the lower frequencies while providing diffusion for the upper frequencies.

And, in my experience, it’s so hard to tell. I mean, while I get controlling excessive reverb and reflections makes total sense on paper, there are so many options and so many people (including me!) who just repeat what they’ve heard without direct scientific experience it’s frustrating. But you have time. And it never hurts to try the free or cheap route and work your way up to more expensive things.

Good luck on this journey!

@charliech , do you think having Townshend Podiums would reduce the need for so much bass absorbsion? I still need to measure my room but when walk around the room I don't sense that much bass pretty much anywhere. That said, I still feel it in my listening chair when rocking out.....which is a good thing for ....for me anyway.

I honestly have no idea.  The Podiums maybe help with vibrations, but I don't think it would help with bass?  But I am not an expert.

If you think the bass sounds good from where you sit, I would just not worry about it.  In the end, do you enjoy listening to your system?  That's all that matters.  

You may not need any (or you may need a lot?) of extra bass absorption.  It really has to do with your room geometry, where the speakers are placed, and where you sit.  The guy from Acoustic Insider always suggested figuring out where the best place to put your speakers and the best place to sit is the first step in "treating" your room and that is free.  

If you are sitting in a null, you won't hear much bass and if you are sitting in a node, the bass may sound too loud or weird, so you'd move your seat up or back to see if that helps.

Your original questions was about if you need to do anything behind your listening position.  The challenge with your CD wall is that it could be very reflective and late reflections from that back wall could cause some issues.  If it sounds good to you right now, again I wouldn't worry.  If you want to experiment, try something behind your listening area that is not super expensive (couch cushions?  Thick blankets?  I don't know....) and, if you feel it helps, then consider purchasing or making something more permanent.   

I have a window behind my seat (about 5 feet behind me) and I have two 4" panels on stands that I just put in front of the windows.  To me, it helped a LOT.  It was probably one of two room treatment things that made me go "yeah, I can tell a difference".  But that was when I had no other treatments up at all.  You already have a room that is treated so your experience may be different.