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Thread: Room geometry question (bass "trapping")

  1. #11
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    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.

    Quote Originally Posted by sasquatch View Post
    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
    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.

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    Quote Originally Posted by spitzer View Post
    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.

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    Quote Originally Posted by miroslav View Post
    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.

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    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.

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    Quote Originally Posted by spitzer View Post
    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.

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    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!)

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    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.

  8. #18
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    Quote Originally Posted by sasquatch View Post
    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
    Attachment 105825
    This drawing shows a very poor way to build a trap. Yes, it works a little bit. But it is very poor.

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