Diffusers vs. Absorbers: When and where to use these?

[hydra]

As much as I've been reading up on the subject of diffusion vs. absorption, I really don't quite get when we should use diffusion, and when we should use absorption.

What I could gather (I could be wrong, and I'd love comments on this) is that:

1) Smaller listening spaces benefit better from absorbers.

2) Diffusers should generally be used only on the middle of the wall behind the speakers, or on the wall behind the listeners.

3) Diffusers are best avoided in smaller listening spaces. If the gap between the listener's head and the front/rear wall is less than 3.5 meters (or 11 ft.), diffusers are best avoided.

4) Diffusers are best avoided on the side walls. For the side walls, absorbers are best, and these should be used to tame the first and secondary reflection points.

5) Too much absorption tends to deaden the room. Diffusion when used properly, can keep the room "live" enough.

Are these conclusions of mine correct? I'm most confused about the use of diffusers.

The reason I got to thinking about all this, is that my 40" TV is right between my speakers, just about a 16" behind the front baffles of the speakers. The speakers are 6ft apart. I've always suspected that the TV was messing with the staging & imaging quite bit, and that I could get a sharper and wider soundstage behind the speakers if I could remove the TV, or fix the reflections from the TV. Somebody who had a listen at my place last week commented on this right away. We covered the TV with a large thick towel and we both felt that it improved things.

1. Removing the TV is unfortunately not an option. So, I have to fix the reflections. To do this, I was planning to paste some eggshell foam, or foam with a vertical slat design on some light panel (foamboard maybe), and then lean the contraption against the TV. The TV is about 8 ft. from my head when I'm in the listening position.

Now the question is, do I use foam (absorbers), or something designed as a diffuser for this? I'm tending towards going with absorption here, but would diffusion be better?

2. A second doubt I have is this: The baffles of the speakers are about 3 ft away from the front wall (the wall I face when I'm listening) and they are about 7 ft away from my head. If I were to use something on the front walls behind the speakers, when should I be using?: absorbers or diffusers?

Do let me know what you folks think!

 

[Pitchucold]

Hi Hydra,

I guess we share the same problem. I am trying to get my bed room sound better. Based on the discussion in the thread i created on bass traps and The following are the recommendations provided by FM like Sanjay, Magma

1. Do Broadband absorpers behind the speakers. I am planning to go for a sliding door like system with rockwool absorpers on top for 10 CM to cover the TV. I plan to use it to cover the TV while listening to music and move it aside while watching TV.

I Plan to get qoute from my carpenter this weekend, shall share it with you if interested.

2. PLace absorption panels on the first relection point. Sanjay has explained in that thread on how it can be done. It sounds simple.

3. One of the other FM West01010 has mentioned during a offlnie discussion, carpeting the floor between the speaker and sweet spot helped in better sound stage.

4. Try speaker stands for better positioning in case ur using bookshelves.

Regards,
Prasanna KV

 

[arj]

hydra,
my suggestion is not to use absorbers without professional help. absorbers work at a moderate broad range and not easy to predict as they also absorb harmonics falling in their range which Can cause problems. typically used in corners. since the material and thickness affect the freq absorbed this needs to be planned well.

Diffusers are more predictable and are easier to use. you use them on all 1st reflection points ie on the wall behind speakers (between them) , wall behind the head And on the first reflection points for both speakers on each sidewall (using the Mirror trick). but too much of anything can make the sound a bit dead...so better to err on the less side

 

[hydra]

Thank you for your comments, folks!

@pitchucold, I (think I) already have my room dialed in pretty well, including speaker placement (on stands). I've placed DIY eggshell acoustic foam panels on the first reflection points on both sides, and I have a rug between the speakers and my listening chair. Pic below for reference:

I'm a little leery about using rockwool (for now), and frankly, my room doesn't really have the space for thick-ish panels and bass traps

@arj, as mentioned above, I already have eggshell foam on the first reflection points (absorption) and I find them quite effective in improving the staging and image. But then the foam is only 2" thick (pasted on 12mm ply and leaned against the walls), so it may not be doing a lot in terms of absorption.

My room is quite narrow, but I think I'm blessed with a reasonably good room, in the shape of a long trapeziod, with the side walls of slightly different lengths.

I've found many discussions that lean towards absorbers and many that lean towards diffusers, which is what are confusing me.

I agree with you completely that a live-ish room is better than a dead room. Better leave well-enough alone huh? I'm mostly happy with the way the room is. Perhaps I'll just stop with some kind of mild absorption in front of the TV

 

[arj]

A thick blanket over the tv works just well

 

[hydra]

^^ It did work for sure! I think I'll just stick to that.

 

[Thad E Ginathom]

How far is the TV from the wall? It looks to me that any sound bouncing off the tv would bounce off the wall if the tv wasn't there, and thus, must be bouncing off the rest of the wall?

A second thought is that the tv might resonate more than walls do --- but I'm clutching at mental straws here

 

[hydra]

The panel of the TV is about 8 inches from the wall. You're right, if the TV didn't catch and reflect the sound, the wall would! Only, I think the TV is far more reflective, and the 8 inches would make things a bit worse.

If it were the wall, I could have easily hung some foam there. With the TV, I'll need something removable. And when I use the TV as the display for the Music PC, that would make things a bit cumbersome.

A thick blanket, or a custom TV cover of fabric, with a 1" or 2" foam sheet inside, is what I'm thinking of now. But a cover would make my OCD self want a nice graphic print on the front, and then that print would have to be non-reflective...

Just joking (a bit) on the last part I'll go with the blanket for now. Easier to remove and put back.

 

[Thad E Ginathom]

Are you sure that you are not equating more-reflective-to-light with more-reflective-to-sound? I haven't a clue, to be honest.

And when I use the TV as the display

Really, this deserves a cartoon if I could draw. The family is sitting, watching a film, except that there is something mattress-shaped in front of the screen. You say, "Ahh, the sound is so much better since we got rid of the reflections from that tv!" :lol:

 

[captrajesh]

Really, this deserves a cartoon if I could draw. The family is sitting, watching a film, except that there is something mattress-shaped in front of the screen. You say, "Ahh, the sound is so much better since we got rid of the reflections from that tv!" :lol:

ROFTL. Now that Suri is banned and Gobble is not frequenting the forum as often as before, we are missing their wily wit. Your post would sure make the two of them proud.hyeah:

 

[Thad E Ginathom]

Hey, don't make me nervous! :lol:

Seriously, though, and no, I haven't tried this except for noticing the difference in sound with/without a sofa behind me... I think it takes more than a layer or two of even quite thick cloth/blanket. Well, perhaps that scatters the sound a little.

I remember a thing from the net: a demo of how to make a quick&dirty&DIY isolation area for home recording. What the guy used was the heavy-but-soft stuff that packers use for wrapping valuable furniture. multi layer, I think heavy-weight paper and fibre. I don't know if it used here, or available. coir might serve for the fibre? It would be good to have some to experiment with.

 

[vijwilso]

Are you sure that you are not equating more-reflective-to-light with more-reflective-to-sound? I haven't a clue, to be honest.

Really, this deserves a cartoon if I could draw. The family is sitting, watching a film, except that there is something mattress-shaped in front of the screen. You say, "Ahh, the sound is so much better since we got rid of the reflections from that tv!" :lol:

Please draw one ... LoL imagining what you described

 

[hydra]

I gave it a try yesterday. I'm quite happy with the results.

I pasted the foam onto 5mm foamboard. The removable panel is a bit rough around the edges, but that's easy enough to fix