Absorb or Diffuse Behind Listening Position?

A few more numbers, size of the room.

Why so close to the back wall?

Regards

I would diffuse behind your speakers/system and absorb behind your listening position. I also prefer diffusing on the ceiling.

The ASC Matrix panel is designed for when you are close up against the rear wall. It was tested by ear and has a combination of absorption and diffusion. https://www.acousticsciences.com/products/matrix-panel

I've used the 'Live End/Dead End' concept in all my listening spaces. Nothing behind speakers and absorption panels on wall behind listening position. First reflections are the strongest and the ones that need to be addressed. Avoid overdamping!

Here is a room calculator to find where your first reflection points are and the size of absorption panels you’ll need. Just punch in your measurements in inches, feet or meters.

https://www.acoustic.ua/forms/calculator4.en.html

The treatment of a sound room is not generic. Bass issues are largely determined by the room dimensions and size. Using bass traps (real bass traps) is almost always beneficial. Moving into the mid and high frequencies, the treatment often depends on the speaker placement, type of speakers, wall covering, floor covering and furniture. Real diffusors should not be placed directly behind the listening position. The listening position should not be close to any real diffusors. How close depends on the type of diffusion and possibly room size. Minimum 5 to 6 feet. Place absorbers behind you and avoid over-damping as stated previously.

summadoggie, that is one of the worst listening positions you could have for a number of reasons. You can use absorbers behind you but that will do nothing for the bass which will be exaggerated by up to 6 dB.  You need to pull yourself at least three feet away from the wall. The best listening position is always somewhere towards the middle of the room. 

What mijostyn said +1, but for the middle of the room position.    My present seat is right at 35% of room length, from the back wall, with Auralex absorption and LENRDs behind me.    Diffusion behind the speakers.    Some tips: (http://arqen.com/acoustics-101/room-setup-speaker-placement/)     and: (https://www.gikacoustics.com/basics-room-setup-acoustic-panels-bass-traps/)

I think a combination of absorption and fine-grained scattering would probably give best results. One option is the ASC Matrix Panel (as mentioned ty @asctim above). Based on the quality of their other products (I have plenty), I’m sure it’s a great product.

Another option is some 4" thick BAD panels from RPG. I used those in a similar situation and was quite satisfied. There undoubtedly are other similar products on the market.

The objective is that the wall behind you disappears acoustically, neither giving a strong echo (reflection) nor a dead zone, as a pure absorber would create.

Having the listening position against the back wall is not ideal. I assume the OP has no other possible listening position available or perhaps it's a multi-purpose room and there must be a compromise. With that listening position you definitely don't want any reflective surfaces behind you. Diffusers do reflect sound but in a scattered pattern. It's easy to understand why sitting close to a real diffuser isn't ideal. Speak into one that is about 12 inches away and you will know.

What we have recommended before is to use broadband absorbers about 4 to 5 feet wide behind the listening position. Flanking the absorbers can be left reflective but diffusion is better.

Hey folks. Of course I’m working with compromises here. To start with, the compromise is the room: only a "semi-dedicated" listening room; lots of glass; a good bit longer than it is wide; a pair of glass french doors flanking the wall behind my listening position. The system is on the long wall. I’ve talked this through with the speaker designer and we decided that long-wall placement is best, but didn’t completely suss out the rest of the room treatment. Next, the speaker manufacturer’s geometry of 1 (speaker center to center) x 1.18 (perpendicular speaker plane to listening position). If I set up the system on the short wall, paying attention to how near the speakers are to the corners, I might only be 6’ deep in an 18’ long room with a sofa, rather than a listening chair as the center of attention. These speakers are supposed to placed as near to the wall as possible to take advantage of bass boundary-loading, and I’ve put a 2’x4’x2" mineral rock filled panel behind each speaker-pair (I have two pair of monitors spaced and inverted on each other, as recommended by the designer). So the wall behind me - in this semi-dedicated listening room - is the main issue. I’m not far enough for diffusion and more absorption panels might be too dead. I’m setting up some adjustable curtains to take some of the heat off the back wall. Surprisingly, bass problems aren’t that awful. Not sure why. It’s the high-mid and over-bright high frequencies which I’m working to damp at this point. One side wall is good, another is a bit reflective and will probably need something. Ceiling will come last if still needed. Thanks for all the input!

What is your RT-60 ?

6.5 seconds.  But I was faster in college.

To answer the question you actually asked -- I repeat -- try something like the ASC Matrix Panel or RPG BAD panel. They are made for the application. The GIK Alpha line might work, too, but I’ve not tried it in that application (very close to the listener).

Unlike "real" diffusers, you can speak right into these products and not get phasey or unpleasant sound. And unlike broadband absorbers, they don’t create acoustic dead spots. If you are going to sit near the back wall, I don’t think you will do better.

Check on the Matrix and BAD panels.  Visited their websites.  Look great.  Thanks.

Hello,

i'm seating near the rear wall. i don't have other option really. My ears are about 30cm from the back wall. So i read here some comment's about using an absorver panel (fiberglass) so i went for that but...after i put the panel in the back wall the voices turn out flat instantly, so that is no solution.
Any ideas please?
Thank You

In fact it could be either one dependent upon the rest of the room.
From the description absorption is needed on the side walls when it is possible to fit a panel in.
Start at the front end of the room then experiment at the back wall for the type that works. Do keep the listening position away from the wall.
Again it depends on how the room sounds at this position.
Definitely use the French Doors to adjust the balance as well.

I would absorb the back wall behind the listening position, you're sitting too close for diffusion to work properly. Bass trap corners if you're in a dedicated room and diffuse everywhere else especially first reflection. It's trial and error and no two rooms are exactly the same so you just got to experiment. Listening preference differs also. Good luck on your journey!

As others have said, binary amplitude diffusion on the back wall would be a good solution for you. From reading about them, it's less important how far away from them you are, as compared with say quadratic diffusion. And you do get a nice balance of both absorption and diffusion with than technology.

I have a little more space, and I'm personally looking at building some folded well (FWD) diffusers, they fold the wells that are longer at 90deg behind shorter wells. In conjunction with this I want to try the fractal diffuser well plates.
It uses a scaled down diffuser as the face of the bottom or back of the wells, simply put, if you DIY your quadratic diffusers, cut scaled down diffusers as the end of the well.
At less than 4" they won't protrude much into the room, and will cover a broad range of higher frequency diffusion as well.

Please keep us posted, it's good to share these experiences, as room treatment isn't highly prolific as far as threads go on the Gon.

Please keep us posted, it's good to share these experiences, as room treatment isn't highly prolific as far as threads go on the Gon.

I concur....

As others have said, binary amplitude diffusion on the back wall would be a good solution for you. From reading about them, it's less important how far away from them you are, as compared with say quadratic diffusion. And you do get a nice balance of both absorption and diffusion with than technology.

+1 to that, based not only on ideas, but also my experience using BAD on the back wall when sitting close. Neither absorption nor many kinds of diffusion will sound right, but BAD will generally do a fine job, even when the listener is close.