Room geometry question (bass "trapping")

spitzer

New member
This is something I was researching yesterday and couldn't really find an answer.

It's said that in any regular (rectangular/cuboid shaped) room, the most "problematic areas" are the corners.

Basically my question is: isn't the simplest way to correct the problem then simply to do anything to get rid of the 90 degree angles? What if you just placed small panels at 45 degree angles, covering each corner (with just air behind them, sorry would attach a diagram if I could)?

How much of the problem is only the shape of the room?
 
I think the best way to handle bass build-up in the corners is to absorb the energy rather than reflect it back into the room. Putting 45 degree panels would only bounce the sound waves back into the room. For a smallish room, that could possibly make it worse.

And the problem with testing different methods is you really can't hear the difference in the room. It's not until you try playing your mixes back elsewhere that you can hear a difference. With bass trapping, without... with 45 panels, without... you're going to make subtle changes to your mixes so it sounds good to you, in your room.

If you're really concerned about your room's response, buy a measuring microphone and use RTA software to measure the room. Behringer has one for not a bad price.
Behringer ECM8000 Measurement Condenser Microphone | Sweetwater
 
I think the best way to handle bass build-up in the corners is to absorb the energy rather than reflect it back into the room. Putting 45 degree panels would only bounce the sound waves back into the room. For a smallish room, that could possibly make it worse.

Bingo! :)

It's the same thing as in the other discussion about using only hard surfaces to "block" the sound. The sound has no place to go, and is not being absorbed by anything, which for any smaller room is a nightmare....which is why absorption for small spaces is generally the best solution.

If you deflect a LF wave to another surface, it just bounces back...and since LF waves carry substantial energy, the LF buildup in the room is increased as more LF signal is generated by the sources.
The LF needs to either pass through or be absorbed for proper control.
 
In the other thread, he was asking about sound isolation. This question is about acoustic treatment. At least that's how I see it. ;)
 
Another quiz,I didn't study...

Pressure(zero particle velocity) is at a maximum at a tri-corner boundary therefore the most efficient place to damp(absorb) it mechanically.
Or not.

g
Screenshot_2020-03-10 0071603336 pdf - HandbookAcoustics pdf.png
 
In the other thread, he was asking about sound isolation. This question is about acoustic treatment. At least that's how I see it. ;)


May be you're right...kinda hard to tell where it's all going.
I'm still puzzled by the avatar change to that of a bullet...kinda unusual, especially for an audio forum, but maybe he's building an indoor shooting range, and that's what the soundproofing and 10 layers are for...? ;)
Around here...we just go out into the woods for some target practice...though you guys in Texas probably are less concerned about where you shoot! :p


Another quiz,I didn't study...

Pressure(zero particle velocity) is at a maximum at a tri-corner boundary therefore the most efficient place to damp(absorb) it mechanically.
Or not.

g
View attachment 105825

I have pondered that design approach...the use of a hard/plywood layer to create a resonant absorber. I know back in the day Ethan Winer, designer of the "Real Traps" products, use to have plans on his website for making large resonant absorbers out of plywood sheets of different thicknesses...with each thickness and overall size targeting a specific LF to treat....then he came up with the Real Traps, and kinda moved away from them.
The resonant absorbers were/are a very legit way to control LF...but you needed a lot of space, and you needed several of them at different dimensions in order to properly cover the whole LF range...or you could use just one LF target panel if you had a specific LF issue.

They make smaller traps these days that incorporate some sort of limp mass like with MLV, or a tuned resonant surface, both of which work well...but they are harder to build, since the layers have to be properly sealed to work right, and you have to get the absorption stuff right, since it's all one system.

Acoustic Geometry makes some cylindrical traps of that nature...that also provide diffusion due to their cylindrical surface. I've been considering a few of them.
I have a bunch of deep LF bass traps I made a couple of years ago...but I didn't include any hard/resonant layer, other than have one side of the trap with the foil-faced fiberglass board, and the other side with just the soft fiberglass...with a total of 6" fiberglass panels. I plan to stick two of them in each back corner, angled across the corner...and I was considering about adding some additional limp mass or resonant LF trap behind them...like a double trap approach...which I think should significantly absorb the LF buildup in the corners...but I have to do some more research...it might be a waste setting them up like that, though of course, I can try it a couple of ways if I get the cylindrical traps...and see what sounds best.
 
How much of the problem is only the shape of the room?
The overall size of the room, materials and method of construction all play a factor.
Putting a 4" thick rockwool 'trap' across a corner will absorb soundwaves, reducing the reflections; a hard surface will reflect them, but not the multiple reflections you get out of a corner with no trapping.
 
May be you're right...kinda hard to tell where it's all going.
I'm still puzzled by the avatar change to that of a bullet...kinda unusual, especially for an audio forum, but maybe he's building an indoor shooting range, and that's what the soundproofing and 10 layers are for...? ;)
Around here...we just go out into the woods for some target practice...though you guys in Texas probably are less concerned about where you shoot! :p




I have pondered that design approach...the use of a hard/plywood layer to create a resonant absorber. I know back in the day Ethan Winer, designer of the "Real Traps" products, use to have plans on his website for making large resonant absorbers out of plywood sheets of different thicknesses...with each thickness and overall size targeting a specific LF to treat....then he came up with the Real Traps, and kinda moved away from them.
The resonant absorbers were/are a very legit way to control LF...but you needed a lot of space, and you needed several of them at different dimensions in order to properly cover the whole LF range...or you could use just one LF target panel if you had a specific LF issue.

They make smaller traps these days that incorporate some sort of limp mass like with MLV, or a tuned resonant surface, both of which work well...but they are harder to build, since the layers have to be properly sealed to work right, and you have to get the absorption stuff right, since it's all one system.

Acoustic Geometry makes some cylindrical traps of that nature...that also provide diffusion due to their cylindrical surface. I've been considering a few of them.
I have a bunch of deep LF bass traps I made a couple of years ago...but I didn't include any hard/resonant layer, other than have one side of the trap with the foil-faced fiberglass board, and the other side with just the soft fiberglass...with a total of 6" fiberglass panels. I plan to stick two of them in each back corner, angled across the corner...and I was considering about adding some additional limp mass or resonant LF trap behind them...like a double trap approach...which I think should significantly absorb the LF buildup in the corners...but I have to do some more research...it might be a waste setting them up like that, though of course, I can try it a couple of ways if I get the cylindrical traps...and see what sounds best.

Chapter 14 will be of interest to you...
Might be able to glean some ideas and some of the math has been done.

How To Build A Small Budget Recording Studio From Scratch By F. Alton Everest : Free Download, Borrow, and Streaming : Internet Archive

g
 
Chapter 14 will be of interest to you...
Might be able to glean some ideas and some of the math has been done.

How To Build A Small Budget Recording Studio From Scratch By F. Alton Everest : Free Download, Borrow, and Streaming : Internet Archive

g


Which part in chapter 14 are you referring to?
I have the Ron Gervais book...which pretty much covers the same topics...so I've already gone through that.

It was the idea of using a "dual" set of corner traps...one basic absorbing trap, like the 6" deep ones I have, and then behind it a limp mass or resonant type of additional trap...I've never seen any of that mentioned, but I'm curious if it would make a differences, and I will try when I have the traps in the new studio.
It might be of no additional value...but I was thinking the big absorbent trap out front will also work as broadband, plus suck up anything that pass back from the second one behind it.
It's just an idea I will try out.
 
You can look up "spitzer" on wikipedia. In addition to a name, it refers to a particular type of bullet design (pointed, high efficiency). There's a connection there, but the avatar has no particular meaning beyong that. It's been my profile picture for ages, I just never found where the "set avatar" option was before a couple of days ago.

Another quiz,I didn't study...

Pressure(zero particle velocity) is at a maximum at a tri-corner boundary therefore the most efficient place to damp(absorb) it mechanically.
Or not.

g
View attachment 105825

In a nutshell, I was wondering what would a super simplified version of this type of thing do. The principle of these things is that sound waves/particles hit the front, some sound goes through the barrier, some of it goes through the wall behind it, the rest of it bounces around in the corner, and eventually some of it bounces back in the room through the same barrier. That would happen whether or not there was anything behind that plywood (and let's make that 1" instead of 1/4"). Anything like this should disturb the sound waves there and figuring out how exactly is probably quite complicated.

I'm well aware there are commercially available ready made bass traps and excellent DIY articles available on the internet. I'm just interested in something completely different. I'm sure someone understands.

Appreciate all the good info here. Thanks.

If I had to choose between being a carpenter, audio engineer, etc. right now, I'd pick none of them. And unfortunately I'll have to come back later to read/peruse ALL of this stuff.

I'm off for a while because I absolutely need to work on an ongoing music project, in many capacities... none of which involve soundproofing or room acoustics/physics. Thanks again and see you later.
 
I'm just interested in something completely different. I'm sure someone understands.

We are trying to.
If you can be more detailed about what that something different is, and why you need to go "different" instead of known...it might help. :)
 
We are trying to.
If you can be more detailed about what that something different is, and why you need to go "different" instead of known...it might help. :)

Well THAT I can explain very easily. There's a LOT of information on the internet, for example, on how to make "bass traps" etc. And the articles themselves are well presented. But... SO often, it turns out that when people talk about "bass", they actually mean something down to 150 Hz, let's say. You can simply stack triangles cut out of rockwool to make corner traps, that do exactly nothing to frequencies lower than that.

So it IS KNOWN to me those things do THAT, but that doesn't interest me much. In the context of "studio building", the problem areas are bass drums, low toms and bass guitars that go down to below 50 Hz.

I need to "go different" because I know higher frequencies are easy to deal with and in general don't present any problems anyway.
 
Also one thing that makes an important difference here I think is the difference between what do you mean by "studio" or what do you actually do in the "studio".

If you're in some sort of "control room" listening to something through speakers, you can EQ the signal and adjust the volume to your liking.

However, an acoustic bass drum naturally produces enormous SPL at low frequencies. There simply are no knobs that you can turn left or right to "correct" that.
 
Well THAT I can explain very easily. There's a LOT of information on the internet, for example, on how to make "bass traps" etc. And the articles themselves are well presented. But... SO often, it turns out that when people talk about "bass", they actually mean something down to 150 Hz, let's say. You can simply stack triangles cut out of rockwool to make corner traps, that do exactly nothing to frequencies lower than that.

So it IS KNOWN to me those things do THAT, but that doesn't interest me much. In the context of "studio building", the problem areas are bass drums, low toms and bass guitars that go down to below 50 Hz.

I need to "go different" because I know higher frequencies are easy to deal with and in general don't present any problems anyway.

Well, there are KNOWN solutions to LF below 150Hz.
You can go with bigger/deeper traps...or there are tuned membrane traps...and then there are the limp mass vinyl traps...etc.
They can handle stuff down to 35Hz...and all include some form of fibrous absorption material along with additional design elements.
Tuned traps are not simple to build...and LMV traps also need to be constructed properly to work right...but the easiest way to build, is to just go bigger with fiber material traps....or of course, buy some of the others, ready-made.
The point is...the solutions already exist...so you don't need to invent something different. :)
 
You are correct in that I don't "need" to invent anything. No one particularly needs to invent anything, we already have everything we need, right? :)

The point is in trying to understand HOW those things work. That's why I asked in my previous post up there, why wouldn't a variant of what sasquatch posted work with a thicker front? Thicker front would just mean HF would NOT pass through, and if it's plywood or something, it ITSELF absorbs sound. I can do this more quickly actually by quoting myself: "...sound waves/particles hit the front, some sound goes through the barrier, some of it goes through the wall behind it, the rest of it bounces around in the corner, and eventually some of it bounces back in the room through the same barrier..." and asking directly whether this is correct or not.

edit: add to that... of course, the assumption is that because the sound has to go through a barrier, not once but twice, sound is absorbed, to whatever extent the build-up/echoes are reduced. Actually, the first reason being just simply no 90 degree angle, the second reason being whatever is absorbed, scattered (or whatever would happen there? I don't know!)
 
By the way, I was... or still am, considering writing a computer program that would calculate what happens when sound waves strike for example an angled corner trap, the kind with the panel at at 45 degrees, like in the diagram and discussed above (whichever variant). This is the kind of thing where the easy part is to make a neat animated thing that shows the waves going here, then there, and then back here again. And the difficult part is figuring out what actually happens to a sound wave when it strikes a concrete wall, or a piece of plywood etc. How much energy is absorbed, how much is reflected, scattered etc. Does the wave change direction when going through a different medium? If so, is the change random? Lots of actual data would be needed for this program to produce correct results. But in principle it's doable. If I had even a rough simulation of something indicating it would be effective, I would he more inclined to actully build something and test it in real life. Less trial and error involved. (In general, I usually don't plan anything or make very vague sketches and make up most of it on the fly. But THIS would be something that I would like to see existing and usable, because these things are simply so complex and often "common sense" does NOT apply.)

I did find and test a couple free/tryout versions of some sort of "room simulators" but the problem there (like with so many specialty apps) is that they have WAY too many "advanced features", unintuitive user interfaces... and no help, no tutorials, nothing. Sometimes these things REALLY are such that writing a similar program from scratch yourself (even if it's simplified) takes LESS time than trying to figure out how some other program works. Oh well. Mad world.
 
Another quiz,I didn't study...

Pressure(zero particle velocity) is at a maximum at a tri-corner boundary therefore the most efficient place to damp(absorb) it mechanically.
Or not.

g
View attachment 105825

This drawing shows a very poor way to build a trap. Yes, it works a little bit. But it is very poor.

---------- Update ----------

You guys are trying to DIY design again, aren't you?
 
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