My crazy bass trap design, with waterfalls! - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 18 Old 06-08-15, 05:39 PM Thread Starter
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My crazy bass trap design, with waterfalls!

Hi everyone, first real post. I used REW to measure my bass traps, and picked up a few good construction tips from this site, so I figured I should make at least one post about how they went.

So it's a variation on a limp mass absorbers, or membrane absorbers, whatever. The real difference in design is having a series of internal resonator panels to capture different angles, and a front loaded suspended mass with a striking plate mounted to an airtight membrane. It's basically a reverse speaker cabinet with reverse spring reverb.

I have a few more pictures on my own website linked here:
SHAMELESS SELF PROMOTION

But I'll cover the pertinent info here, and maybe someone can even give me a bit of feedback on overall impact, since I have no experience with traps before this, and therefor no real idea of how well they work (other than they seem to a bit).

My crazy bass trap design, with waterfalls!-basstraps10.jpg

So that's the core of the inside. Three large absorbing panels, with vertically stacked one for good measure. I tried to keep in mind room for air, but the idea was that as the bass frequencies move through the enclosure, they hit multiple dampeners, and any reflections still have to pass through multiple dead zones. This isn't really any different from a basic sealed cabinet design from what I can tell, except for the use of the other walls. Also maybe having suspending striking plates was kind of a brainwave.

My crazy bass trap design, with waterfalls!-basstraps13.jpg

So here's one with the front membrane off alongside a finished one. This was he real experimental bit. That center box is suspended from those chains (it's not touching the bottom resonator panel, about an inch gap) and then is firmly attached to the membrane, which is acoustic foam cork for flooring, via the striking plate mounted to the outside. So basically it's a big speaker cone, in a way. Much like the front face of a membrane absorber, this should move with low frequencies, but given that it has no set position, I was hoping it would be a bit more sympathetic than a rigid face. The inside of the box is airtight, and it really does spring back nicely to the touch.

My crazy bass trap design, with waterfalls!-basstraps15.jpg

Looking sweet in the corners of my studio! Total show-off pic.

So, onto what I'm actually interested in hearing back about. The physical dimension are 4'x2' on the front face, 16" deep.

The room with empty corners:
My crazy bass trap design, with waterfalls!-no-traps-log.png

The room with the traps in the corners as seen above:
My crazy bass trap design, with waterfalls!-traps-log.png

An overlay of the two (which I found more useful for deciphering, myself):
My crazy bass trap design, with waterfalls!-overlay-log.png

So you can see they do work to some degree on the low end, and they seem to blanket the low end nicely down to 30hz. The overall curve seems to fit the frequency response of my NS10s, and using REW's room simulator, they did attack a couple room modes well, although I'd have to input it all again to remember which ones it predicted exactly.

It definitely nipped a few reverb tails well, especially that offender right around 32Hz, and took a solid swath out of the 60-70hz region and 200hz region, but did introduce a bit more... oomph... to the 80-90hz region. Seemed to address the reverb tails to some degree fairly uniformly though, and had a couple interesting effects on the full spectrum.

But I have no basis for comparison. I couldn't really find many waterfalls of "successful" traps, so other than they work a bit, I don't know to what degree these help, nor how much my design influenced the outcome over a regular membrane absorber (aka big cabinet with a bit of foam on the back, and maybe a hanging sheet inside).

So any insight into that is most welcome, and if nothing else, thanks for having a quality forum to run ideas against, and especially to that John fellow for making REW available!

Anyhow, it was a lot of work for a shot in the dark design, that I'll say.
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post #2 of 18 Old 06-08-15, 09:52 PM
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Re: My crazy bass trap design, with waterfalls!

made problem worse. it looks like your only running the monitors and if so your not hearing much below 80hz over the higher levels of the 80+.

and if I"m not mistaken you need at least 1/4 wavelength in trap size to capture low frequencies and the key element is thickness and/or spring type membranes.

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post #3 of 18 Old 06-08-15, 11:49 PM Thread Starter
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Re: My crazy bass trap design, with waterfalls!

That's something to go by, for sure. I know there's not much bass to begin with, but I don't have a sub yet; that's in the longer range plans when I can find one/afford one. I know NS10s are notoriously skimpy on the low end, monitors alone withstanding.

That said, bass traps don't actually trap bass, they just tame it by absorbing some of the energy out of the wave. If I wanted something to capture 30hz, I'd need an enclosure at least 9 ft deep. Seems... impractical.
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post #4 of 18 Old 06-09-15, 07:39 AM
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Re: My crazy bass trap design, with waterfalls!

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That's something to go by, for sure. I know there's not much bass to begin with, but I don't have a sub yet; that's in the longer range plans when I can find one/afford one. I know NS10s are notoriously skimpy on the low end, monitors alone withstanding.

That said, bass traps don't actually trap bass, they just tame it by absorbing some of the energy out of the wave. If I wanted something to capture 30hz, I'd need an enclosure at least 9 ft deep. Seems... impractical.
True but your speakers do not produce audible 30hz so bass traps right now are doing nothing.

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post #5 of 18 Old 06-09-15, 10:53 AM
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Re: My crazy bass trap design, with waterfalls!

The only problem I see with your comparison is that the bass trap itself is a fake wall so placing it directly behind the speakers might be affecting your frequency response in a negative way.
I would place the traps in another corner and re test or you could stack the traps in one corner and only test the opposite speaker. That way you can really see what the traps are doing.
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post #6 of 18 Old 06-09-15, 12:09 PM
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Re: My crazy bass trap design, with waterfalls!

Just having traps in the room affects acoustic response. Better to remove them entirely for a base (bass? haha) measurement.

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post #7 of 18 Old 06-09-15, 02:28 PM Thread Starter
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Re: My crazy bass trap design, with waterfalls!

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The only problem I see with your comparison is that the bass trap itself is a fake wall so placing it directly behind the speakers might be affecting your frequency response in a negative way.
I would place the traps in another corner and re test or you could stack the traps in one corner and only test the opposite speaker. That way you can really see what the traps are doing.
But isn't the point to absorb it from where that bass collects in those corners? I'm measuring from where I sit only. Legit question; I'm just catching up to speed on how to properly measure room analytics. Wouldn't measuring the opposite speaker of the traps still fall prey to the natural build up in a square corner like that right behind it?


BlueRockinLou - That's "bass"ically exactly what I did. Actually exactly what I did.
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post #8 of 18 Old 06-09-15, 09:11 PM
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Quote:
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But isn't the point to absorb it from where that bass collects in those corners? I'm measuring from where I sit only. Legit question; I'm just catching up to speed on how to properly measure room analytics. Wouldn't measuring the opposite speaker of the traps still fall prey to the natural build up in a square corner like that right behind it? BlueRockinLou - That's "bass"ically exactly what I did. Actually exactly what I did.
Yes and no. Sound pressure will be highest in the corners, so that's a good place to start. You'll also find resonances at other areas in the room which depend on where you sit, and where your speakers are positioned. The speakers will stimulate fundamental modes, as well as harmonics. Understanding what modes are, how they're stimulated, and their relationship with speaker/listener location are all needed to effectively use broadband traps. If you know at which frequencies a given trap is effective, you can position it where it will provide the most benefit: along the sidewalls, behind the LP, or across the front wall.

Now here's the kicker... To absorb mode buildup in room corners, you need pressure traps (air has little or no movement). To absorb it along wall boundaries, you need velocity traps (air has low pressure). Some interesting reading on the subject can be found here http://www.tubetrap.com/tubetrap-art-noxon.htm

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post #9 of 18 Old 06-10-15, 09:57 AM
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Re: My crazy bass trap design, with waterfalls!

Quote:
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But isn't the point to absorb it from where that bass collects in those corners?
Yes this is true. but for right now you are just checking to see how your bass traps are working.

Quote:
Jakay wrote: View Post
Legit question; I'm just catching up to speed on how to properly measure room analytics. Wouldn't measuring the opposite speaker of the traps still fall prey to the natural build up in a square corner like that right behind it?
Yes, but your bass trap has a rigid face so it's acting like a false wall. So with the bass trap your speakers are now closer to a wall so it will affect the frequecy response more then the bass trap.
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post #10 of 18 Old 06-11-15, 07:26 AM Thread Starter
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Re: My crazy bass trap design, with waterfalls!

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Yes this is true. but for right now you are just checking to see how your bass traps are working.


Yes, but your bass trap has a rigid face so it's acting like a false wall. So with the bass trap your speakers are now closer to a wall so it will affect the frequecy response more then the bass trap.
Well that makes sense as far as measuring their effectiveness goes. Insofar as acting like a wall, I hear what you're saying, but that photo belies the space I've given the speakers. They do sit slightly more than 15" away from the traps, so I feel like they're getting the room they need to properly operate, but perhaps I'm missing the point there. I do see what you mean in the higher end of the spectrum, where my SPLs are variously frequency shifted (albeit to a slightly more uniform curve) so I do get that they're affecting the overall response on some level, but overall the two curves do follow a very similar path.

I'll get around to measuring them as you've suggested, although they'll need to be away from the corner to stack them, the ceiling isn't quite 8' in the corner.

Quote:
BlueRockinLou wrote: View Post
Yes and no. Sound pressure will be highest in the corners, so that's a good place to start. You'll also find resonances at other areas in the room which depend on where you sit, and where your speakers are positioned. The speakers will stimulate fundamental modes, as well as harmonics. Understanding what modes are, how they're stimulated, and their relationship with speaker/listener location are all needed to effectively use broadband traps. If you know at which frequencies a given trap is effective, you can position it where it will provide the most benefit: along the sidewalls, behind the LP, or across the front wall.

Now here's the kicker... To absorb mode buildup in room corners, you need pressure traps (air has little or no movement). To absorb it along wall boundaries, you need velocity traps (air has low pressure). Some interesting reading on the subject can be found here http://www.tubetrap.com/tubetrap-art-noxon.htm

Sent from my iPad using HTShack

Okay, so the differentiation between pressure and velocity traps is a bit lost on me, as to what sort of system they represent. I would guess that the bass traps are a pressure trap, certainly from how I made them it would make sense, though they are a bit of a hybrid if I'm not mistaken, whereas that cubicle wall behind my desk and the two blackout curtains which are actually lined up with my sitting position (another thing that's hard to tell from that pic) would be velocity types? Btw, that cubicle wall is amazing; if you talk into it it just takes everything away. Anyhow I assume velocity types are more akin to mounting foam panels with no air pocket, and are more of use in the midrange if I'm not mistaken.

Just for good measure, those bamboo curtains are my cheap cheap version of a diffuser, and the couch is there to break up any standing waves and absorb whatever frequencies it can. Just going by bits I've picked up along the way there.

Ultimately I do care to find out more about the traps, but I'm really mostly interested in making sure I maximise my listening position for mixing, which I suppose you all are too, in a way. I've followed a live-end dead-end approach here, which I realize that window in the back isn't helping, but I have plans for a diffuser/velocity (?) type sine wavish type curve face for that... at some point.

And why not, let's just post the full spectrum response...
My crazy bass trap design, with waterfalls!-spl-full.jpg
Now I would assume that 1-2k region would be due to exactly what Blacklightning was referring to, specifically. Incidentally, that 200hz dip is specifically an NS10 thing, going by the frequency response chart I have for them in the Yamaha literature.
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My crazy bass trap design, with waterfalls!-no-traps-full.png  

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Last edited by Jakay; 06-11-15 at 07:55 AM.
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