# My crazy bass trap design, with waterfalls!



## Jakay

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).









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.









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. 









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:








The room with the traps in the corners as seen above:








An overlay of the two (which I found more useful for deciphering, myself):








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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## Talley

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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## Jakay

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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## Talley

Jakay said:


> 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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## Blacklightning

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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## Lumen

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


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## Jakay

Blacklightning said:


> 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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## Lumen

Jakay said:


> 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

Sent from my iPad using HTShack


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## Blacklightning

Jakay said:


> 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.



Jakay said:


> 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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## Jakay

Blacklightning said:


> 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. 



BlueRockinLou said:


> 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...







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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## Blacklightning

After looking at your full spectrum response I think the last thing you should be doing is a Bass Trap.

Can you do me a favour and run REW in your LP with just the left speaker and then just the right speaker. You can do this with or without the Trap. Then Post the REW file so we can look at your Data. I have found that the Impluse response to be the best tool.


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## Jakay

I'm sure that you mean my studio space, but I have no idea what "LP" stands for. Can't even fathom a guess in fact. Long Play, all I can think of. 

Anyhow, I'll go do that, no doubt you can give me a piece of advice or two, plus I don't really know what the impulse response is actually measuring, so I should probably go learn that anyhow.


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## Blacklightning

LP = listening position


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## Jakay

Ah, good to know. Luckily I just did that anyways, measuring L speaker with basically my left ear and right with right ear position.

So, as requested:








My traps are big (~10 ft^3) and heavy, and my ceiling isn't high enough, so I put the left trap mid room on the right hand side and measured the left speaker only here. I suppose I should measure the right speaker with it there just because why not.








Left speaker impulse with traps where they were in the picture








Same with the right

I'll be honest I have no idea what I'm looking at here. Just reading up on IR now.

Also the impulse response for L speaker with the trap moved looks pretty much exactly the same maybe minus 2 db at most across the board.

Oh, heh, you said the full file... 
View attachment June 11.mdat

I have four measurements saved there. It's pretty clearly labelled though.

Thanks for the help btw


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## Blacklightning

Okay, with my limited experience, your Impulse looks good to me.
I don’t think I can offer you any help maybe someone with more REW knowledge could help out. 
Just looking at your data the high end seems to be dropping, I’m guessing it’s the close seat position to the speakers with the speaker pointed to the back wall. I would say toe them in more but do what is best for imaging.

Have you done any close mic test of your speakers?


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## Jakay

No I haven't... does close testing do a better job of revealing the native frequency response (I would guess)?

And I did notice the high end dip too, but with the way the no trap version looked, I'd say I had a build of harmonics going on there too. I do worry I created a bit of a null mode there, but I'll wait until I've done a bit more high end conditioning in the future before I worry too much about that.

I'm moving in a month anyhow, so it's not worth dwelling too much on this particular set-up, this is mostly educational for me right now, and thanks for your input, I'll definitely turn my speakers slightly towards me to break up the parallel surfaces going on there, which is a good suggestion.


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## robbo266317

Close testing will show the speakers response better, I believe you can also gate the response to remove room effects.


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## Jakay

I think the room effects would be obvious enough to be able to see past them with close miking like that. I'd rather not mess with any of my transients by mistake in such an endeavour, which I'd be prone to do, not being really all that great with noise gates.


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