Need some tips on cheap acoustic treatment

[Tupisac]

First part: https://www.audiosciencereview.com/...-measurement-is-my-lsr310s-sub-toasted.39892/

Hello,

this took a while but I've moved some furniture around, bought new desk, played a bit with various knobs, EQed back and forth and it looks like I've finally tamed my subwoofer. Now it all sounds all-right in sub-bass department, but the rest appears 'slightly' combed:

Psycho-acoustic looks kinda nice tho:

But spectrogram shows the truth:

Now it's time for some treatment. I've found some cheap foam panels claiming to be meant for audio. Only 4 cm thick tho. Planning to put them as drawn below. Is it all right?

Also, I don't think those can help with 100-1k range much. Any tips on that? And not only that, actually ANY tips will be greatly appreciated.

BTW, I've attached the measurement file if anyone wants to play with it.

 

[fpitas]

Only 4cm thick? Uhm...

 

[fpitas]

I use 4" thick panels from ATS, sprinkled liberally around the room.

4 Inch Acoustic Sound Panels | BASS TRAPS | Acoustic Ceiling Panels

4" fabric wrapped acoustic sound panels! Absorbs sound & unwanted noise. Ships Fast, Low Price & Guaranteed For Life. Out performs panels for sale at Home Depot

acousticsoundpanels.com

Pulling the panels a few inches away from the ceiling and wall helps, too. You could build your own panels easily enough.

 

[kemmler3D]

Absorptive materials will help with the combing, but you're going to want more than 4cm thick. The good news is many materials are good for absorbing HF, almost too good in many cases. The bad news is there is no free lunch... you need them thicker to go to lower frequencies, and you need more coverage to absorb more energy in the room.

The good news is there are pretty cheap and reasonably effective options out there. I wouldn't recommend foam (I used to sell it for a living, it's not the best you can get) but e.g. PET felt is only $20 per square meter, and looks pretty nice to boot. Foam is OK if it's all you can afford but don't expect good performance below 400hz or so, and it really only gets going above 1khz.

25mm 100% Polyester Fiber Recycled Acoustic Wall Panel Pet Felt Panel For Office And Home - Buy Acoustic Panels wall Panels acoustic Wall Panels Product on Alibaba.com

25mm 100% Polyester Fiber Recycled Acoustic Wall Panel Pet Felt Panel For Office And Home - Buy Acoustic Panels wall Panels acoustic Wall Panels Product on Alibaba.com

www.alibaba.com

An old rule of thumb is that to fully control high frequencies you need about 25% coverage of walls and ceilings.

However, I think that will often tend to over-deaden the room, but since it looks like you're listening nearfield that might be OK. Diffusion is what you need to break up the reflections and smooth out the combing without reducing HF energy too much, but it tends to be more expensive. A good overall treatment regime tends to use both.

 

[Tupisac]

I was talking about those: https://allegro.pl/oferta/wygluszenie-wytlumienie-panele-akustyczne-basotect-9725688266

DIY option is also tempting.

What do you think about wooden diffusers like these: https://allegro.pl/oferta/panel-akustyczny-drewniany-30x30cm-buk-dyfuzor-3d-11873381659
I'm considering them for aesthetics reasons on the front wall between the monitors.

But it's all shooting in the dark. Is my placement plan even valid? Are those triangular foam bass traps worth considering?

 

[dshreter]

Room treatment that is too thin or ineffective at lower frequencies can be counterproductive. Knocking down the treble but not absorbing midrange can lead to an unbalanced dead sound.

Your measurements also don’t look bad. Some smoothing is necessary to translate to how we actually hear. What measurement has you concerned about comb filtering specifically?

 

[kemmler3D]

I was talking about those: https://allegro.pl/oferta/wygluszenie-wytlumienie-panele-akustyczne-basotect-9725688266

DIY option is also tempting.

What do you think about wooden diffusers like these: https://allegro.pl/oferta/panel-akustyczny-drewniany-30x30cm-buk-dyfuzor-3d-11873381659
I'm considering them for aesthetics reasons on the front wall between the monitors.

But it's all shooting in the dark. Is my placement plan even valid? Are those triangular foam bass traps worth considering?

Those will work, but basically limited to very high frequencies, and even then just OK. If you cover less area with thicker panels, or you cover more area with thinner panels, at some point it balances out. "no free lunch" after all. I would advise fewer, thicker panels - you get more broadband absorption, less over-absorption in the high frequencies.

DIY is a good route but you still need fiberglass / rockwool or something in there. But if you get creative (say you find a whole lot of scrap cloth and stuff it into a wooden frame) you can save money.

Those wooden diffusers aren't "real diffusers", it turns out. Diffusers must be built according to a specific mathematical formula so that they actually diffuse rather than just cause weird unwanted reflections in your room. @sarumbear can also explain this stuff pretty well.

This site explains it all if you are interested: https://www.subwoofer-builder.com/qrd.htm

Wooden diffusers are really big / heavy / expensive, but if you get creative you could in theory build them some other way. They do not need to be solid, if you have access to a 3D printer, building one that way is possible. So you can achieve with $100 worth of plastic what would otherwise cost $1200 in wood...

Is my placement plan even valid?

Depends on what the exact problems are, a rule of thumb is to place the panels at the first reflection points, between your speakers and your listening position. You can find those using the 'mirror method'. From the picture your placement points might be good, hard to know if they are exactly right.

Are those triangular foam bass traps worth considering?

No, not really. They're basically snake oil. They do absorb lower frequencies (into the 100s) but not below 100 really. To absorb a frequency you need (IIRC) 1/4 wavelength of thickness - at 20hz this measured in meters.

 

[Tupisac]

Thanks for the tips. I'll look into felt panels.

I'm mostly concerned about 100Hz - 1kHz range (100-300 Hz looks most offensive). The speech and voices are somehow wonky. Can't really describe, kind of hollow, nasal, a bit dry? Not right, that's for sure.

Also, imaging is slightly smeared, especially the right half (the one next to a corner). I've put some fluffy pillows on the wall to test and it helped a bit, but it's a very temporary solution:

Here are graphs with 1/24 and var smoothing applied:

 

[Sokel]

This graph looks like it's been taken 5cm from the subs driver,it's impressive,never seen one like this in a room.
Where have you crossed it to the mains?

 

[Tupisac]

This graph looks like it's been taken 5cm from the subs driver,it's impressive,never seen one like this in a room.
Where have you crossed it to the mains?

80 Hz, sub's default crossover.

Very simple trick - I've pumped the sub volume up (3 'clicks' on the knob above volume set on monitors) and squashed the massive bump with simple EQ.
Also, there was a huge dip around the crossover frequency, but setting +2 LF trim on monitors helped a bit with that.

This is how it looks without EQ and pillows:

 

[Tupisac]

I've done some reading and the 100-300 Hz range seems a bit beyond the scope of reasonable solutions. Like >20cm thick panels and huge columns in corners... Bummer.

 

[kemmler3D]

Indeed, the lower you go, the harder it is to treat. Look into DIY limp mass / membrane style bass traps if you want to get into that range or lower.

The fundamental problem is that sound waves in that range are big. They are simply too long to interact with small / thin absorbers properly.

There are also metamaterials that can "cheat" and go lower with smaller structures, but I have not found any instructions on how to design those for a given frequency range or absorption level... they're mostly in scientific papers for now, but from what I've seen could be built using a normal 3D printer. I just don't know enough math to translate their results into a general DIY project...

 

[Peterinvan]

I used Roxul mineral fibre panels covered in hemp cloth for my DIY panels.

 

[Tupisac]

I've googled "diy limp mass" and quickly noped out of there

So far this QRD build seems like a nice DIY project for a lazy summer weekend. Looks like it could touch up some problems under 1k and has a decorative potential.
Question is how effective it could be as a one wide piece between monitors, 120 cm wide and 30-60 cm high.

I guess I could also go with Space Odyssey cosplay and maybe stick one diy monolith filled with dense rockwool onto the slanted ceiling part.

 

[kemmler3D]

how effective it could be as a one wide piece between monitors, 120 cm wide and 30-60 cm high.

You need to sit far enough away from the diffusers, I think one wavelength at the design frequency, so it may not work right if you place it that close to the listening position. On the back or side walls, diffusion would probably be good, but for the slanted ceiling above your desk I would go with absorption, so the Space Odyssey idea is probably better.

DIY rockwool projects are common, but just remember to be careful as the fibers are pretty nasty especially for your lungs. So make sure to wear proper PPE while making them. Otherwise it's pretty straightforward.

 

[Tupisac]

You need to sit far enough away from the diffusers

Thank you, you've just saved me at least one summer weekend.

I definitely need to fix the slanted ceiling - it's just gypsum board on a frame and it's pretty loud. I feel like it's responsible for most of the mess.

I've recorded some finger snaps and knocking:

I've used my TSB2555B based diy mic close to listening position. It is technically a cardioid and it was pointed at whatever, but it's quite sensitive in picking up the details of the room. Here is the recording:

https://drive.google.com/file/d/14endZKjtmzvV6ygo_A8g3fymGVm46mHi/view?usp=sharing

I think I'll go and buy 20 of those cheapo foams just for testing. I can stack them for proper thickness and test various positions before commiting to some more complicated diy projects.

 

[abdo123]

Your measurements are perfect, just add some corner bass traps (DEEP) to reduce the ringing between 100Hz and 200Hz a bit.

 

[Flaesh]

(100-300 Hz looks most offensive)

 

[bpb]

Lots of good science based advice here:

https://www.youtube.com/@AcousticsInsider/videos

Focused on professionals / home studios.

I've had really good results from following his guidance.

 

[Tupisac]

Your measurements are perfect

I don't know, those just seem like random lines beaten into submission by a monkey that has no clue.

(100-300 Hz looks most offensive)

This looks scary AF. Can you tell me more about it? Is this caused by +2 Lf trim? What am I looking at and where to begin on correcting it?


Also, I've made new recording, previous one was fudged (lousy plug). This one is slightly hotter (preamp at max). Shows all the echoes and noises (like car passing by at the beginning or a clock hanging from a back wall):

https://drive.google.com/file/d/1XUddsWm7pcmKZXEEpZ-G10J58zIExmOF/view?usp=sharing

I do occasional webinars and speech recording quality matters for me too, so no REW equalization can help me here much.

I don't know what to think anymore... Is it as bad as I feel or am I just imagining things and need a break?