Acoustic treatment with slats - before-and-after measurements

[janbth]

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.

View attachment 268990


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

View attachment 268994

Thanks! Good suggestion about level matching the graphs for low frequencies. I will look into that as soon I am able to sit down at my computer.

And thanks for the tip about the ceiling treatment!

 

[ozzy9832001]

What do you mean? Thicker absorbers absorb less??? Anyway, there is still life in the music.

Thicker absorbers work in the low end where most people actually need treatment. If you have thin panels it may absorb the highs, but it will leave the lows completely unchecked. After enough of them, it will sound muddy and boomy.

 

[Absolute]

Thanks! Good suggestion about level matching the graphs for low frequencies. I will look into that as soon I am able to sit down at my computer.

And thanks for the tip about the ceiling treatment!

I forgot to applaud the looks of your project, it looks brilliant. So nice to get some kind of visual life back in fashion.

 

[janbth]

I forgot to applaud the looks of your project, it looks brilliant. So nice to get some kind of visual life back in fashion.

Thanks!

 

[bloodshoteyed]

i've got a coouple of basically the same panels waiting that i find some time and finally mount them, glad to see someone post a bit more info on them tho

btw, a quick question, did you mount them on a brick wall or drywall? in case of brick, was contruction glue enough or did you put in some screws also? mine are primarily going onto a hollow drywall but i might go for another segment of brick/mortar behind my working area and was wondering if construction glue would be enough

 

[janbth]

i've got a coouple of basically the same panels waiting that i find some time and finally mount them, glad to see someone post a bit more info on them tho

btw, a quick question, did you mount them on a brick wall or drywall? in case of brick, was contruction glue enough or did you put in some screws also? mine are primarily going onto a hollow drywall but i might go for another segment of brick/mortar behind my working area and was wondering if construction glue would be enough

The front wall is drywall and the back wall is concrete, and I used construction glue on both. The glue was No More Nails from Pattex, and I used half a 300 ml cartridge of glue per panel (60 x 244 cm). I think it holds well to the wall, but I'm not planning on attaching anything heavy.

 

[Bjorn]

I hate to be a party pooper, but slats aren't really a serious acoustic treatment for music. In regards to minimize flutter-echo for speech it's fine. But for music we want either absorption or diffusion or normally a combination. Slats don't function well at neither.

That being said, if that's only treatment one can do because of WAF, it's certainly much better then a flat reflective surface. A RT60 measurement is invalid in a small room like this BTW.

 

[juliangst]

These slat panels look really nice but with only 1-2cm of thickness they'll do hardly anything.
What I plan to do for my next setup is builing a 'fake wall' out of 60cm insulation and covering it up with those kind of slat absorbers.
That should absorb a good amount of bass energy while the wood slats reflect mids and highs for not making the room too dead.

 

[Absolute]

These slat panels look really nice but with only 1-2cm of thickness they'll do hardly anything.
What I plan to do for my next setup is builing a 'fake wall' out of 60cm insulation and covering it up with those kind of slat absorbers.
That should absorb a good amount of bass energy while the wood slats reflect mids and highs for not making the room too dead.

If you want to go all-out like that, would you consider replacing slats with something dedicated for the purpose? I think I would place dedicated diffusors in front of an absorptive wall - but would carefully consider aesthetics before deciding how.

I'm not well-informed on the different existing diffusors, but the new Arithmetic looks like good stuff that I would like to try;

DIFFUSE | Arithmetic Design

arithmetic-design.com

 

[juliangst]

If you want to go all-out like that, would you consider replacing slats with something dedicated for the purpose? I think I would place dedicated diffusors in front of an absorptive wall - but would carefully consider aesthetics before deciding how.

I'm not well-informed on the different existing diffusors, but the new RPG Arithmetic looks like good stuff that I would like to try;
View attachment 269322

I didn't decide yet if such a project is even worth it or if I should stick to normal corner traps with a few absorbers along the back wall.

I'm sure that calculated diffusers are more effective but building them or getting finished products is way more labor intensive/ expensive than placing a few wood slats in front of stacks of glass wool.
I want to maximize treatment per euro so most of the stuff has to be DIY.

For first reflection absorption I'll most likely get a few more 10cm basotect absorbers; for the front corners I'll stack glass wool triangles to the ceiling and hide it with a wood frame covered with fabric.

It'll certainly be an interesting project

 

[janbth]

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.

Thicker panels may be more effective at low frequencies, but note that this was not a problem in my case. I did not seek to fix any problems in the bass region. Dirac Live and two subs take perfect care of any problems I have with bass.

What are «consistent decay times»?

 

[tifune]

. A RT60 measurement is invalid in a small room like this BTW.

Can you elaborate on this, or point me towards some reading that explains the small room aspect?

 

[janbth]

I hate to be a party pooper, but slats aren't really a serious acoustic treatment for music. In regards to minimize flutter-echo for speech it's fine. But for music we want either absorption or diffusion or normally a combination. Slats don't function well at neither.

That being said, if that's only treatment one can do because of WAF, it's certainly much better then a flat reflective surface. A RT60 measurement is invalid in a small room like this BTW.

I disagree with this. In my case, working within contraints (aestethics and space), and trying to fix an explicit problem (flutter echo), I think slats should be considered a «serious acoustic treatment». The measurements I showed in the first post are exactly the kind of information I would have wanted to see, if I had started again from the beginning.

Out of curiosity, what would it take for you to consider an acoustical treatment effective? Could you please quantify this? What kind of measurements, and what *numbers* would you require to declare a successful reduction of flutter echo?

Regarding RT60, that terminology comes from REW. In my graphs, the plotted quantity is Topt (which is REW specific and defined here). I could have used others, like T20 or T30, but does it really matter? They are all quantifying decay times.

 

[janbth]

These slat panels look really nice but with only 1-2cm of thickness they'll do hardly anything.

What do you mean by «hardly anything»? I have shown the graph of what they do. What would it take in terms of numbers - what changes in decay times - to move from the «hardly anything» category to the «something» category?

 

[alex-z]

Thicker panels may be more effective at low frequencies, but note that this was not a problem in my case. I did not seek to fix any problems in the bass region. Dirac Live and two subs take perfect care of any problems I have with bass.

What are «consistent decay times»?

Your own RT60 and SPL graphs show the bass region problems.

1. At 100Hz your RT60 is 300ms, 750ms at 160, 550ms at 250Hz. RT60 is not actually accurate in small rooms, but for the purposes of acoustic treatment can still provide some insight. Effectively, depending on the tone being played, it will dissipate at different rates.

2. Even with Var smoothing, you have peaks and dips in the response from 100-400Hz.

Multiple subwoofers + Dirac has done an excellent job at making the response from 20-80Hz look good.

 

[juliangst]

What do you mean by «hardly anything»? I have shown the graph of what they do. What would it take in terms of numbers - what changes in decay times - to move from the «hardly anything» category to the «something» category?

Acoustic foam with 1cm thickness will only absorb the upper treble.
That doesn't mean that it's completly useless but in general you want absorption across the whole frequency range to get uniform decay times.
Thicker absorption is the only way to achieve this.

Don't get me wrong; your treatment seems to be effective in the treble and is better than just bare walls, but thicker absorption would obivously be more effective.

This is 10cm of foam compared to 1cm:

what changes in decay times

I guess the RT60 would be more linear, but it's honestly hard to tell from those measurements

 

[DVDdoug]

They do look really nice but generally you want more randomness so they work across a wide range of frequencies, and they need to be wider and/or thicker for lower frequencies.

Unfortunately, the troublesome region from 100-300 Hz is still troublesome,

300Hz has a wavelength of about 4 feet and lower frequencies have longer wavelengths.

For lower frequencies you need really thick absorbers/reflectors which aren't practical in most home situations, but there are thinner tuned/resonant bass traps. Note that bass traps kill the reflected bass so they smooth the dips and the bumps.

 

[ernestcarl]

@janbth

Some people here at ASR are quite particular with how data is presented. To make your original post more "complete", I suggest attaching a zipped (or compressed) before and after mdat file to let others do their own "in-depth" analysis and breakdown of the provided information however they will.

What are «consistent decay times»?

Maybe something like this:

Arguably maybe too "dry" but at least it's flattish for the most part


Not so "consistent" decay across the FR:

Other graphical views of the second measurement:

 

[Inner Space]

What I plan to do for my next setup is builing a 'fake wall' out of 60cm insulation and covering it up with those kind of slat absorbers.
That should absorb a good amount of bass energy while the wood slats reflect mids and highs for not making the room too dead.

This is a great idea, and I once saw it done - with an extra enhancement. The slats were suspended vertically from a top rail, with door hinges. The principle was that bass waveforms can be bled of energy by making them move objects hanging in space. Like a membrane mechanism, but divided into strips. Then your 60cm of absorption becomes more effective because it's dealing with less energy at the input.

A personal preference of mine is to use sheep's wool wall, loft or attic insulation, instead of fiberglass. Not only way more healthy, but also better at the job. It's becoming easier to get now, because there's excess capacity in wool, plus a burgeoning movement toward natural and organic products for household use. What would you rather stuff in the walls of your baby's bedroom? Win-win.

 

[tmtomh]

These look great, and thanks so much for sharing your before and after measurements and listening impressions!

Sorry if I'm being daft, but don't the MDF slats primarily serve as diffusers rather than absorbers? And if so, doesn't their standardized/non-random orientation and depth make them rather poor diffusers? Not trying to criticize the OP, just asking.

As for the rest of the absorption discussion, I'd say that like any room treatment discussion, it's really multiple discussions.

First, flutter echo, or the perception of excess reverb/liveness in the midrange and lower treble frequencies we humans are most sensitive to, is probably the most extreme and worst acoustic problem. But it's also the easiest to treat. Pretty much any kind of room treatment - thick absorber, thin absorber, homemade diffuser, bookshelf with books, carpet/rug, curtains, furniture, wall hangings - is going to instantly reduce or eliminate the extreme reflections and resonances at those higher frequencies.

Second, as @Puddingbuks notes - and as many of @amirm 's speaker review measurements show - ceiling and floor absorption is arguably more important than anything else, and again it's pretty easy. Any old floor covering is going to make a major difference compared to a wood floor. (I see the OP already has a rug; again, this is not directed at the OP, just a general statement.) And while those $20 homemade ceiling panels are great, you don't need to cover all or most of the ceiling with panels to make a big difference. I have only two ceiling panels, albeit rather thick ones, mounted more or less halfway between my speakers and my listening position, and no measurements are necessary to tell if they have an effect. The entire room is nicely controlled (well, above about 200Hz anyway) and not "live" overall, but when you are sitting in the couch at the listening position and go to say something to the person sitting next to you, it's almost like you're listening to the inside of your own head - there's just no echo, and the effect on the perception of soundstage precision is obvious to everyone who's ever sat there and listened to the system.

Finally, as many have noted, dealing with reflections and resonances below about 300-350Hz - the range where it becomes more about the room than the speaker - is a whole other enterprise and it requires care in speaker placement and, if you are going to use room treatments, some pretty darned thick treatments covering a pretty darned decent percentage of the room's surfaces, especially corners. In my case my room has significant space constraints when it comes to placing corner absorbers on the rear wall. So I make do with thick absorbers at the front-wall corners, and homemade 6-inch thick absorbers with another 4” of airspace behind them at the middle of the rear wall (rock wool insulation wrapped in black fabric and inserted into Ikea Billy bookcases). If I go to either rear corner of the room, there's instantly more bass. But no one would ever stand in those corners to listen to music, and from the listening position it's fine so overall I can live with it; most of us have to make do with what we have, and if we have a pleasant listening space and a nice system we are already so fortunate.