How to get started with room treatments for the home

[radix]

I have a room 3.4m wide, 5.4m long, and 2.5m tall with a 7.2 home theater setup. Is there a good post or link about how to get started with room treatments. I'm especially interested in if there's a process to determine what's the biggest ROI for treatments. For example, should I start out with corner bass traps or do wall reflections or rear speaker treatments or something else first?

I've seen a reference to, Speaker Boundary Interference Response (SBIR), but what is the best way to use that information? My speaker positions are pretty fixed based on where they can be mounted and where the TV is and such.

I'm also interested in what would be good brands of room treatments for the home that work well, look ok for a living space, but don't break the bank.

I do have a UMIK and can use REW. The AVR is a Denon 6700, and I can use the Audyssey app for PEQ.

Thanks,
Marc

 

[Adam Bernau]

I have a room 3.4m wide, 5.4m long, and 2.5m tall with a 7.2 home theater setup. Is there a good post or link about how to get started with room treatments. I'm especially interested in if there's a process to determine what's the biggest ROI for treatments. For example, should I start out with corner bass traps or do wall reflections or rear speaker treatments or something else first?

I've seen a reference to, Speaker Boundary Interference Response (SBIR), but what is the best way to use that information? My speaker positions are pretty fixed based on where they can be mounted and where the TV is and such.

I'm also interested in what would be good brands of room treatments for the home that work well, look ok for a living space, but don't break the bank.

I do have a UMIK and can use REW. The AVR is a Denon 6700, and I can use the Audyssey app for PEQ.

Thanks,
Marc

Hi Marc, the best would be if you could share simple sketch of the room floorplan, seating size and position and speakers placements.
Also ceiling height info could be helpful.
Cheers
AB

 

[Sancus]

Unfortunately this is one of the more complicated topics out there, because it's so dependent on your situation and preferences. There are also a lot of contradictions in the professional advice you'll see.

If you genuinely want to learn the details, Dr. Toole's book covers this from section 6-10, and 15 or so. I can summarize basic points, this is my understanding of some complex material and not direct quotes so any errors are likely my fault:

• Use fibreglass/rockwool absorbers. Diffusers are situational and have to be very deep(8-12").
  • Toole does suggest diffuser use for the sidewalls in a home theatre to improve envelopment from the surround speakers, but otherwise mostly not.
• 0-100hz: Don't bother trying to treat this, it requires an insane amount of bass traps and/or frequency targeted membrane traps and such. Use a multi-sub, bass managed system instead.
• 100-300hz: You need pretty thick absorbers(4"-6") to affect this region. It can be worthwhile but you have to measure your space, figure out your SBIR situation, etc. Having speakers with controlled directivity down to 100hz also helps with this.
  • There is a lot of advice on how to avoid boundary interactions in section 9 but most of it is impractical except for trying to make sure your sidewall/floor/ceiling distances to speakers are all different to avoid reinforcing modes and to use EQ and absorbers where possible.
• Sidewall Reflections: Toole recommends 2-3" thick as a minimum and states that using absorbers thinner than this can actually make things worse because they will distort the frequency of reflections instead of absorbing them.
  • Toole suggests not absorbing sidewall reflections for stereo use, only for multi-channel, and optional in a mixed-use space.
• Ceiling/Floor: Ceiling absorption should be considered if the speakers have poor vertical off-axis response, floor generally nothing more than a thick carpet. Both of these seem to be a lower priority and not discussed as much. There is a study that showed heavily absorbing the floor reflection makes the sound unnatural.
• Front/Back wall: Absorbers are suggested here and my personal impression is they should probably be at least 4" thick.

Toole cautions against overdoing absorption repeatedly in the book, and that it is very possible to make a space sound "dead". There is a happy medium of reflections that you want and it varies significantly based on the space. You must do listening tests in your own space.

There is an example layout from the book, which is the only thing I'm going to directly quote, in respect of copyright:

 

[sigbergaudio]

Since you have REW, a good starting point would be to measure your room to inspect the frequency response (preferrably from several positions, for instance three seats of your sofa (assuming you have one and not just a single listening position), and also varying height (head, stomach, knees).

REW will also tell you your current decay time by looking at the waterfall plot or the RT60 graph.

Sancus post above sums it up pretty well. SBIR is difficult to address with absorbtion too. Alternative ways to fight it is controlled directivity speakers and/or multiple subwoofers that are crossed over pretty high.

 

[abdo123]

The best way to deal with SBIR is to cross your speaker with a subwoofer above the SBIR frequency and placing absorption behind the speaker for the second and third harmonics.

 

[radix]

Thank you @Sancus and @sigbergaudio. I've watched Bobby Owsinsky's video (referenced in this post) and he suggests that 2" rockwool or similar can make a decent absorption panel. I will read through some of those sections of Toole.

I am hoping to also find a method to first evaluate where I have problems, or at least treatable problems. I think I need most help cleaning up lower register speech, at least to my ear without doing measurements on it.

I am also hoping that there's some method to using REW, for example, and moving an absorber around a wall to find the key places to block primary reflections for the main listening positions. I'd also like to be able to see how effective different absorbers are for my specific situation (e.g. thin panels vs 2" frames vs 3" frames).

It looks like the RT60 measurements are what I want to start making. I just found another thread that talks about about the RT60 measurement.

Marc

 

[Sancus]

Alternative ways to fight it is controlled directivity speakers and/or multiple subwoofers that are crossed over pretty high.

Curious, have you attempted this high sub crossover thing? I feel like it'd have to be at least 200hz for most rooms, and then I figure it'd be too much localization. But maybe it'd be OK if you have at least 4? I dunno... (Yes, I know the answer is save my pennies until I can afford W371As )

REW will also tell you your current decay time by looking at the waterfall plot or the RT60 graph.

I also find the spectrogram good for pinpointing specific problem areas. Here's mine. Even with only 2 subs, my 20-100hz range is pretty decent. But I obviously have some significant SBIR issues from 100-300hz. And overall probably a little too much reverb, RT60 mostly shows the same issues.

This room is completely untreated of course. I'm also thinking about the best way to add some myself.

 

[sigbergaudio]

Here a similar wiew of my main setup for music, this is a treated room (not in the sub 100hz area though), dual mono subs, both on the front wall. Cardioid speakers. Decay around 0,2s. Pretty quiet in wavelet/waterfall after 120-150ms. Reasonably free of SBIR issues as well (will never be perfect), the dip around 300-400hz can be EQed up. If you are to use subs to tackle SBIR you are right that you need to have some of them in the front to ensure the bass is focused there.

 

[abdo123]

Here a similar wiew of my main setup for music, this is a treated room, dual mono subs, both on the front wall. Cardioid speakers. Decay around 0,2s. Pretty quiet in wavelet/waterfall after 120-150ms. Reasonably free of SBIR issues as well (will never be perfect), the dip around 300-400hz can be EQed up. If you are to use subs to tackle SBIR you are right that you need to have some of them in the front to ensure the bass is focused there.

View attachment 173353


View attachment 173351

Are you using any smoothing for the frequency response? looks amazingly good!

 

[sigbergaudio]

Are you using any smoothing for the frequency response? looks amazingly good!

Edited now, realized the wavelet/spectrogram only went down to 100hz, replaced with one that goes down to 20hz.

The frequency response graph is 1/12th smoothing if I'm not mistaken.

 

[abdo123]

Edited now, realized the wavelet/spectrogram only went down to 100hz, replaced with one that goes down to 20hz.

The frequency response graph is 1/12th smoothing if I'm not mistaken.

the response almost has 10 dB error rate, which is outstanding for a small room (axial room modes in the audible band).

 

[sigbergaudio]

Curious, have you attempted this high sub crossover thing? I feel like it'd have to be at least 200hz for most rooms, and then I figure it'd be too much localization. But maybe it'd be OK if you have at least 4? I dunno... (Yes, I know the answer is save my pennies until I can afford W371As )


I also find the spectrogram good for pinpointing specific problem areas. Here's mine. Even with only 2 subs, my 20-100hz range is pretty decent. But I obviously have some significant SBIR issues from 100-300hz. And overall probably a little too much reverb, RT60 mostly shows the same issues.

This room is completely untreated of course. I'm also thinking about the best way to add some myself.

This is already somewhat off-topic but perhaps relevant for OT as well
Do you have a frequency response graph as well? Based on the wavelet your response / level looks very even all the way, while you'd likely be looking for a gradual decline in the response.

 

[Sancus]

Here a similar wiew of my main setup for music, this is a treated room (not in the sub 100hz area though), dual mono subs, both on the front wall. Cardioid speakers. Decay around 0,2s. Pretty quiet in wavelet/waterfall after 120-150ms. Reasonably free of SBIR issues as well (will never be perfect), the dip around 300-400hz can be EQed up. If you are to use subs to tackle SBIR you are right that you need to have some of them in the front to ensure the bass is focused there.

Thanks. Pretty cool to see what a well treated room looks like to use as a goal. I doubt I'll be able to get that much in here(it is still a living room...) but I'm sure I can make some big improvements.

 

[sigbergaudio]

the response almost has 10 dB error rate, which is outstanding for a small room (axial room modes in the audible band).

It could be EQed to track even better, but that doesn't necessarily sound better. I mostly apply broadband ajdustments except in the sub 100hz area.

 

[sigbergaudio]

Thanks. Pretty cool to see what a well treated room looks like to use as a goal. I doubt I'll be able to get that much in here(it is still a living room...) but I'm sure I can make some big improvements.

This is a dedicated room. I have a setup in my living room as well, that looks more like yours Decay time of around 0.5s.

 

[abdo123]

It could be EQed to track even better, but that doesn't necessarily sound better. I mostly apply broadband ajdustments except in the sub 100hz area.

What percentage of the wall is covered with treatment? or is the wall built from the ground up with absorption in the walls?

 

[sigbergaudio]

the response almost has 10 dB error rate, which is outstanding for a small room (axial room modes in the audible band).

But yes, I'm pretty happy with how it tracks. I'm going to lift the area around 3-400hz too, which is the main thing that stands out now. I'm prototyping speakers at the moment so perfect in-room response hasn't been the main focus.

 

[sigbergaudio]

What percentage of the wall is covered with treatment? or is the wall built from the ground up with absorption in the walls?

Actually not that much on the wall. There's thick wall to wall carpet on the entire floor, and treated ceiling above the main listening area (around 6^m2 covered), and in additon to that there's 8 120x60cm absorbers placed around the room, mostly on one sidewall (where one speaker stands pretty close to it), as well as behind the listening position. And a large couch. Oh, and also some absorbers in two of the corners.

 

[Sancus]

Do you have a frequency response graph as well? Based on the wavelet your response / level looks very even all the way, while you'd likely be looking for a gradual decline in the response.

Sure. The actual FR is sloping down somewhat. Also my listening position is only about 2.5m from the speakers, so it's more direct sound dominant than typical, I'd guess.

P.S. Don't ask why I only measured up to 10khz for this one... lol.

there's 8 120x60cm absorbers placed around the room, mostly on one sidewall (where one speaker stands pretty close to it), as well as behind the listening position.

One wall of my room is open and the other has a silly electric fireplace covering most of it, with the right speaker quite close to it. I bet 4" absorbers in front of that fireplace would help a lot and since I live alone there is no one to complain about the dumb fireplace that I don't use

 

[sigbergaudio]

Sure. The actual FR is sloping down somewhat. Also my listening position is only about 2.5m from the speakers, so it's more direct sound dominant than typical, I'd guess.

View attachment 173357
P.S. Don't ask why I only measured up to 10khz for this one... lol.



One wall of my room is open and the other has a silly electric fireplace covering most of it, with the right speaker quite close to it. I bet 4" absorbers in front of that fireplace would help a lot and since I live alone there is no one to complain about the dumb fireplace that I don't use

Yes, that could be worth a try. But your response is very good even in the SBIR-area, so doesn't look very problematic to begin with So it's more of a general reduction in decay time you're looking for probably.