• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Acoustic treatment with slats - before-and-after measurements

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
Recently, I installed some acoustic panels in my listening room of the "slat wall" type, and I took the opportunity to make some before-and-after measurements. I'm posting it here as a service to the community, in case it is of interest.

For some background, I live in an apartment with an L-shaped living room as my listening room. The front wall is plaster/drywall, the back wall is concrete. Open on the left side, windows with curtains on the right side. I have a NAD M33 running Dirac Live. Two subs. The sound was quite good, but I had some issues with reverberation. Also, the speakers and my head are a bit too close to the walls, so there are - I assume - boundary effects in the 100-300 Hz region. This is what I wanted to fix.

Why slats? I first considered conventional acoustic absorbers from RPG, GIK, etc. Maybe mounted behind the speakers and behind the sofa where my listening position is. However, I was troubled by uncertainty about how effective they would be - at least in my use case. Besides, I find this kind of panels extremely ugly... Then somehow I came across slats. You can find a number of these slat panels on the internet, marketed as acoustic panels. Mine are from Fibrotech. The panels are 9 mm thick felt mats with slats in MDF glued on. A test sample I ordered looks like this:
IMG_0286.JPG


Panels like this don't seem to be much discussed for audiophile purposes compared to conventional absorbers. The few discussions I have seen have been mixed. Anyway, even if they would not be as effective, they cover more wall - and look a lot better. So I figured that even if they would end up doing nothing for the acoustics they would look good enough to be worth it. Here is how my living room looks now:
IMG_0282.JPG
IMG_0283.JPG


OK, enough talk, lets see some measurements. Here is a graph of the RT60 before and after (Topt is shown):
RT60.jpg


The only things that changed from before to after are the wall panels. The position of furniture, mic, etc. are essentially the same. Dirac Live was used with the exact same filters for comparison. As you can see, the region from about 300 Hz and upwards has significantly reduced decay time. Now it doesn't exceed much above 500 ms.

Here is the frequency response (both measurements are volume adjusted to roughly 75 dB on the REW SPL meter):
FR.jpg


Unfortunately, the troublesome region from 100-300 Hz is still troublesome, or maybe slightly less so. I'll know more when I get around to re-running Dirac and do the sub integration again from scratch. (The response looks somewhat bass heavy, but actually it doesn't sound as bad as it looks.)

And here are left and right speaker ETC curves:
L-ETC.jpg
R-ETC.jpg


So how does it sound subjectively? First of all the level of sound is lower. I need to turn up the volume a bit to play at the same perceived level. This makes sense to me, because some sound energy is removed by the absorption. Second, reverberation is perceivably lower. I would subjectively describe it as being "closer to the music" - especially for vocals. This also makes sense, I guess, since reverberation may be associated with large rooms, thereby distance. Finally, I think I can hear more details now, like in drumming and other "rapid impulse bursts". The first two of these effects, I feel certain to pick out in a blind test - the third, I *think* I would, but I don't know.

To conclude, I'm very happy with my new slat wall panels. They look good, and I think they solved at least some of my acoustic problems. They may be slightly less effective than conventional absorbers, but they work. My impression is that they are not highly regarded by audiophiles, but I really don't understand why. I think at least they should be in the toolbox.

OK, that's it. I hope this was useful.
 

ozzy9832001

Senior Member
Joined
Feb 19, 2023
Messages
409
Likes
261
My speakers are close to the wall as well and absorption behind them made it worse. Mine are rear ported so I'm sure that didn't help, but it seemed there was all sort of cancellations going on when the gap was too small.
 

DavidMcRoy

Addicted to Fun and Learning
Joined
Jul 10, 2018
Messages
584
Likes
1,015
I've seen ads for those, too and I think they look great. I'd buy them just for visual aesthetics. I was a little skeptical that they'd affect acoustics much, so your results are encouraging.
 
Last edited:

Trdat

Addicted to Fun and Learning
Forum Donor
Joined
Sep 6, 2019
Messages
973
Likes
400
Location
Yerevan "Sydney Born"
To be honest, there is a lot of heated, scientific and general discussion in gearspace on slats configurations. Regarding how much is taught in university from an acoustician point of view I would personally love to know.

Generally speaking standard slat configuration will only reflect some of the highs depending thickness and width.

1D random binary slat configurations could add some basic, weak diffusion which is better nothing or a bare wall and is often used though not necessarely preffered over the 2D random binary panels such as the bad RPG.

There are other slat configurations such as Newell seuquence incuding many others from people in the trade who tweak and adapt the sequence according to their needs.

The above standard slat configuration at least from my understanding doesn't do much other than aesthetics and keep a little of the upper frequencies. Plus, on a back wall, sitting so close to it demands absorbtion.

You have made the move I don't think it will be detrimental to the sound though there always is a better way.

I don't really see a more diffused field from the ETC graph the better decay could be from absorbtion.

Anyway, I will let the expert chime in.
 

Puddingbuks

Addicted to Fun and Learning
Forum Donor
Joined
May 31, 2020
Messages
593
Likes
1,003

ZolaIII

Major Contributor
Joined
Jul 28, 2019
Messages
4,238
Likes
2,502
Results of your acoustic treatment are somehow mixed bag. Somehow refractions in treble range got worse and it vent from very bright to head chopping.
I advise that you lower a bit sub's SPL, then PEQ the peak in 20 - 100 Hz region and address the brightness with high self filter @ 1 KHz low Q value and only then engage Dirac. You should also try adjusting speakers to off tweater horizontal angles and properly position them (60 cm from back wall and 50 cm from side wall) before all. There is no substitute for positioning!
 

abdo123

Master Contributor
Forum Donor
Joined
Nov 15, 2020
Messages
7,449
Likes
7,976
Location
Brussels, Belgium
I would not bother with anything thinner than 5 cm. You’re basically absorbing all the life out of the music.
 
OP
J

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
...

The above standard slat configuration at least from my understanding doesn't do much other than aesthetics and keep a little of the upper frequencies. Plus, on a back wall, sitting so close to it demands absorbtion.

You have made the move I don't think it will be detrimental to the sound though there always is a better way.

I don't really see a more diffused field from the ETC graph the better decay could be from absorbtion.

...
I agree about the ETC graph, but I think the shorter decay is noticeable - but not revolutionary.
 
OP
J

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
OP
J

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
Results of your acoustic treatment are somehow mixed bag. Somehow refractions in treble range got worse and it vent from very bright to head chopping.
I advise that you lower a bit sub's SPL, then PEQ the peak in 20 - 100 Hz region and address the brightness with high self filter @ 1 KHz low Q value and only then engage Dirac. You should also try adjusting speakers to off tweater horizontal angles and properly position them (60 cm from back wall and 50 cm from side wall) before all. There is no substitute for positioning!
Thanks for the suggestions. I don't perceive the sound as very bright, so I suspect the FR graph is not completely to be trusted. I will re-run Dirac again when I have time and do the whole subwoofer integration again then. Unfortunately, there's not much room to pull out the speakers from the wall.
 
OP
J

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
I would not bother with anything thinner than 5 cm. You’re basically absorbing all the life out of the music.
What do you mean? Thicker absorbers absorb less??? Anyway, there is still life in the music.
 

Koeitje

Major Contributor
Joined
Oct 10, 2019
Messages
2,314
Likes
3,985
Thanks for the suggestions. I don't perceive the sound as very bright, so I suspect the FR graph is not completely to be trusted. I will re-run Dirac again when I have time and do the whole subwoofer integration again then. Unfortunately, there's not much room to pull out the speakers from the wall.
Its a 100% bright you are just used to your PMC loudspeakers. PMC is not known for their wel balanced sound. I had Twenty.22s: bright and boomy with some weird issues in the low-end. Never got them so sound right.
 
Last edited:

alex-z

Addicted to Fun and Learning
Joined
Feb 19, 2021
Messages
918
Likes
1,701
Location
Canada
Those results are to be expected with such thin absorption. Thicker panels are better because you get more effectiveness at lower frequencies, which is where the majority of problems in residential spaces exist. The goal is not chasing low decay times, you want consistent decay times.
 
Last edited:
OP
J

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
Its a 100% bright you are just used to your PMC loudspeakers. PMC is not known for their wel balanced sound. I had Twenty.22s: bright and boomy with some weird issues in the low-end.
OK, maybe. To comment on the speakers: I bought these *before* I discovered ASR, Floyd Toole, spinoramas, etc.! I don't know of spinorama measurements for my exact speakers. (The only other PMC measurements I am only aware of is the Twenty.21 here on ASR.) If I would buy speakers today, I would get something with known spins, probably KEF R3. Anyway, I don't perceive the speakers as the biggest problem in my setup, so will keep them for now.
 
Last edited:

Koeitje

Major Contributor
Joined
Oct 10, 2019
Messages
2,314
Likes
3,985
OK, maybe. To comment on the speakers: I bought these *before* I discovered ASR, Floyd Toole, spinoramas, etc.! I don't know of spinorama measurements for my exact speakers. (The only other PMC measurements I am only aware of is the Twenty.21 here on ASR.) If I would buy speakers today, I would get something with known spins, probably KEF K3. Anyway, I don't perceive the speakers as the biggest problem in my setup, so will keep them for now.
I also bought mine based on hype reviews back in the day. When I got them I used them for like two months and just couldn't get used to it. They sounded so different than my old DIY speakers (a well known DIY model at the time with high quality Scanspeak Revelator drivers). Best I could describe the PMCs is unbalanced with some weird port noise at very low frequencies. Luckily I kept those DIY speakers and sold off the PMC. When I finally replaced my old DIY speakers with Revel I didn't have that whiplash of a completely different sound. The Revel speakers sounded different of course, but more as an evolution of my old DIY speakers than something completely different.

But if you are having issues right now then your speakers are for sure part of the problem. How a speaker sounds in your room is for 99% the loudspeaker and the room. The brightness, which you seem to like or are used to, is primarily the loudspeaker. The 200-300hz issue is largely the room I'm guessing, but if your speaker isn't nicely flat in the 100-500hz region then it might be adding to the problem. I wouldn't count on these being well behaved in that region.
 
  • Like
Reactions: TSB

ZolaIII

Major Contributor
Joined
Jul 28, 2019
Messages
4,238
Likes
2,502
It's all relative regarding "bright" sounding. Firstly to what you personally might like and secondly towards your hearing state and hearing deficits (from aging, helt...).
It's a good thing when member's fill in profile data like location and age because it helps pore bloke's trying to recommend them what to do to determine what's probable or available and better determine how so.
It's really easy to regulate from horizontal axe placement (depending on speakers) to high self filter or tone controls.
 

Koeitje

Major Contributor
Joined
Oct 10, 2019
Messages
2,314
Likes
3,985
It's all relative regarding "bright" sounding. Firstly to what you personally might like and secondly towards your hearing state and hearing deficits (from aging, helt...).
It's a good thing when member's fill in profile data like location and age because it helps pore bloke's trying to recommend them what to do to determine what's probable or available and better determine how so.
It's really easy to regulate from horizontal axe placement (depending on speakers) to high self filter or tone controls.
There is no downward slope in his measurements, it is for sure bright. If you look at this "after" measurements you can even see a boost above 5kHz. You will hear that regardless of age. The Adam T5Vs I have on my desk need a 3dB shelf filter at that frequency upwards to stop them sounding bright, the bump I'm seeing in his measurements is higher than those 3dB. But I can understand that one might not consider it bright, because you can get used to it. I just have other neutral speakers as a reference to which I'm used (Revel and JBL 305).
 

ZolaIII

Major Contributor
Joined
Jul 28, 2019
Messages
4,238
Likes
2,502
@Koeitje I whose talking more generally I hope you understand that.
I even used head chopping bright in description to describe response he is currently getting regarding shown measurement plots.
Best regards and have a nice time.
 

Absolute

Major Contributor
Forum Donor
Joined
Feb 5, 2017
Messages
1,085
Likes
2,134
Very nice @janbth ! Thank you for sharing. First thought is that you should level match graphs in the range below 100 hz since that's the area where you'll see least differences.
Then the RT60 and ETC will be more relevant for comparisons.

I've been thinking of doing the same with my concrete wall in a similar apartment, but I'm so lazy it hurts my head thinking about it. I have RPG 4 inch Absorbors behind the head that are effective, but likely a bit too much so. As for ceiling treatment, I went with 10 cm isolation and Ecophon Focus panels to make it look like a normal living room.

20220824_210023 (1).jpg



The ceiling treatment made significant differences to ETC and perceived sound, take a look before vs after;

giphy1.gif
 
OP
J

janbth

Member
Joined
Aug 29, 2021
Messages
63
Likes
82
Location
Norway
It's all relative regarding "bright" sounding. Firstly to what you personally might like and secondly towards your hearing state and hearing deficits (from aging, helt...).
It's a good thing when member's fill in profile data like location and age because it helps pore bloke's trying to recommend them what to do to determine what's probable or available and better determine how so.
It's really easy to regulate from horizontal axe placement (depending on speakers) to high self filter or tone controls.
I'm 50+, so it's probably true that my hearing isn't great for high frequencies...

Like I mentioned, I will re-run Dirac again at some point, and I will then play around with the new Auto Target Curve interface and pull down the highs to hear what happens.
 
Last edited:
Top Bottom