Greetings folks, today I want to bring up for discussion a topic that I think is relevant for most of us.

Here we got a video by a well-known Jesco from the "Acoustic Insider" channel, where he and his subscriber discuss a process of trapping a small room and compare measurements. It must be noted that subscriber used some recommendations given in Jesco's paid course "Build A Better Bass Trap", but long before that he also created a free guide about bass traps, which I found simply more than sufficient. I will add the file of free course at the bottom of this post.

The part that interest me is where they share the measurement graphs:



As you see, the large mode at 42 herz is gone, and overall Freq. res. became more "appropriate". What worries me is the reverberation time for bass, which is shown in the graph as depth (third dimension). As you can see, decay time for bass is HUGE. I wounder - how does that affect the sound? Because, theoretically, if decay is still in the air while next note already begins to play, it simply CANNOT be unaffected...

I came with this to the sound-engi. thread on imageboard, and one user gave me some insights, which I want to share with you as well. Citation (AI translated):

"Bass Traps are basically illiterate bullshit, unless you're ready to put a couple meters of thick absorbent cotton on the wall, not in homeopathic quantities to hang... It is written in books, for example Acoustic Absorbers and Diffusers: Theory, Design and Application, have a look. You can look at anechoic chambers and their measurement limits and think. Or just check in practice and make sure that these "traps" are absolutely unable to cope with bass."

Here I stopped him and said that he's BSing, because as we can see on this image from Jesco's guide, 16cm basstrap (with some kind of air gap between it and the wall) has 0.4 coefficient absorbtion at 50hz. Which is already something:


My correspondent from imageboard said that "standing wave disappeared because he was measuring at one point and he had the geometry of the room changed". At this point, I didn't really believed to get any other useful information from that thread, so I came here.

How important do you think bass decay time is? How to dry a reverb in a room? I want to hear some thoughts, then I will share my own.

 

I recommend getting opinions from Ethan Winer & Rod Gervais…. Aiming around 200ms -30db (400ms for RT60) in the bass is considered good for residential studio spaces.


are you truly making bass traps or broadband traps? Pink fluffy R-30 corner-floor-ceiling super chunks made a world of a difference in my small room. I originally used rigid Owens Corning super chunks, but learned that the pink fluffy actually performs better than compressed fiberglass for lowend & it was both a measurable and audible improvement once installed.

 

Last edited: Oct 6, 2023

We don't have OC in Europe, but "new generation fiberglass" looks really promising

AFAIK, material plays less role than things such as thickness, air gap and placement.

I've red Ethan's website; he's a real wondermaker.

I plan to make something like this, with traps thickness from 30 to 50 cm (image below). Hence all these green panels are bass traps. Covering all corners (except floor for walking) and I also wanna have em in the center of parallel surfaces to deal with targential modes.

 

Or simply measured a different spot in the room. Hard to say without knowing how and when the measurements were taken.

Very, but it becomes noticeably annoying when the decay of the low end is way longer than the mids and highs, some people can live with that but i personally just find it unconfortable to work with. And of course the importance also depends a little on what type of music you make/work with.

There's actually a few recomendations for what the difference should be depending on type of room and literature, but the short version is: LF decay (below 200Hz) should be 25% longer than that of the longest decay above that. Slapping regular porous absorbers everywhere usually causes that difference to be a lot higher (you decrease decay above 200Hz, but not below that). So, you know, if can't "attack" the low end decay, don't overdo it in the mids and highs. Diffsorbers are a popular option to avoid that from happening while still getting decent overall absorption.

THICC. I love it. I installed some 30cm ("roll" type lightweight fiberglass) ones on the sidewalls of a firend's studio and they work pretty damn well. He didn't want anything thick in the ceiling because apparently the ceiling is just about to fall off as it is, but personally i think the danger adds spice, idk.

Room modes can be a little tricky to deal with using porous absorption only, specially if they are tangential since you have to deal with more than just one pair of parallel surfaces. You absolutely can, but hanging a pannel specifically for that might not work as well as expected. Pressure absorbers are the way to go for that. Other hings you can do is find a good listening possition (super important) or just fluffing the hell out of your room entirely (not optimal, but possible)

I tested this gap thing a while back, just putting a wood mount thing behind the pannels to make a 10cm gap and using that online calculator to see how much absorption i should "gain", and found this gap idea pretty useless in practical terms (will post measurements if i find them). BUT, turns out there's a reason for that. Here's a little video about it:

 

Last edited: Oct 6, 2023

Oh so that's why there are common opinions that treating your room can potentially make harm! I see now...

 

Unless you are doing crucial mixing or mastering, for a regular musician I say take care of the worst offenders like dips and peaks over 6 db, specially in the lows, those are lethal and will make music work impossible, but you don’t have to have a perfect room to simply compose whatever genre. Do what is within reach but don’t torture yourself over it

 

that's a really good advice! however, I just scrolled through Ethan Winer's "Audio Expert" book where he mentions that "reverberation time is as crucial as frequency response" in terms of reproduction problems.

So honestly, I see now why people in commercial or just simply well-made studios are so obsessed with combining all kinds of methods to get good sound. By putting simply lots of fiberglass, you can get only so far... Especially with my amateurish approach.