DIY Bass Trap....Will it Work ?

[Marks57]

Hi, I have an 11' x 13' room that I have converted to just a 2 channel listening room with some pretty nice equipment, i.e. Marantz, Musical Fidelity, Tannoy Saturn S10 towers. I have treated the side walls with 2' x 4' 1" thick 703 Owens in wood frames covered with burlap. The wall/ceiling are treated all the way around with 2" thick 703 Owens with 14" wide panels and are angled between the wall/ceiling area. The front wall has a 2' x 4', 2" thick panel on each side.

Now I am ready to start treating the corners. I read on a DIY site to use Sonno Tube (concrete forms) and fill them with sand for bass tubes. Then, I read a reply from Ethan Winer that this would have no positive effect at all.

I bought 2 of the Sonno Tubes anyway....12" in diameter. I heavily duct taped each end and inside of them I put a 2" thickness of 703 Owens in a + (plus sign) configuration and capped each end with a round cut of 2" 703 Owens, then duct taped it air tight.

I have only made one of these so far and don't really know how to tell if it is effective or not. I do not have an SPL meter, nor the software to measure the room. Furthermore, when I look at the examples of the EQ readouts on some sites, it's like a monkey doing a math problem. I don't understand it, therefore have not downloaded the software and bought a meter.

Has anyone tried this method with the Sonno Tubes and have you found them worthy? In theory, they are similar to the bass trap drawings Ethan Winer shows on his website, but may not be doing a thing for me. If not, I haven't wasted much $$.

Thanks in advance for any input.

Mark

[bpape]

Don't bother with the Sonotubes. The sand filled thing doesn't work at all - not sure where they ever got that idea but whoever did it, I'd never hire them - they obviously don't understand how things like that are supposed to work. The bass absorbers on Ethan's site operate as a membrane absorber - a completely different principle and very effective - though not broadband.

If you want tube shaped absorbers, get some pipe insulation and fill it with fluffy fiberglass and cap the top and bottom. Just understand that with a tube design, you'll need to be looking at 16" diameter minimum to get into the subwoofer range.

One other suggestion... For the panels on the upper horizontal corners, you'd get a lot of good broadband bass control if you doubled the thickness to 4". In a small room like that, you'll need a proportionately higher amount of bass control.

Good luck,

Bryan

[scott]

i originally posted about seeing the sand-in-a sono diy. it was shot down quickly.since then i have seen several other sites and people filling their stage with sand, their risers and more sono tubes. john mellencamp's personal recoring studio has tons of tubes, risers and a knee wall filled with sand. something is being dampened, their not to keep the floor from jumping up.

there is a reason for this i think some of us would like an answer to, not just "sorry, no, won't work"

not being rude...just why not?

[Marks57]

Bryan, since I am not using sand and am using 703 Owens would that not give it some type of a membrane type of absorber? Mark

[bpape]

The tubes with 703 might do something though without testing them, I have no idea how much or in what range.

Sand in stages, walls, risers, etc. is to damp them and deep them from resonating, not provide absorbtion. At most, they'd act as diffusers down to a few hundred hz


Bryan

[drf]

They probably got the idea for filling sonotubes with sand from an old speaker design style, which has the bottom filled with sand to stop them from resonating and to give them a heavy physical grounding.
however as stated once sound is airbourne (so to speak) sand will do very little.

[Anthony]

I think the sand/Sonotube idea came (or at least was reawakened) through the DIY Network mini-series on Home Theater. I remember watching the episode on room acoustics -- it had a lot of good tips like wall isolation, hat channel, floating floor, panel absorbers at the reflection points, etc. But I remember scratching my head when I saw the sand/tube arrangement. I'm pretty sure it was on that show, but alas, most of my audio/HT knowledge gets jumbled together now

I believe you can make an absorber by bending the rigid fiberglass over a hollow inside form (chicken wire comes to mind) and then covering it, but unless you just want diffusion, the sound wave has to be able to travel through the absorber, otherwise it can't effectively slow down the air being moved by the waves.

This is why the sonotube won't work -- the wave will travel through the outside layer, but then reflect off the hard surface of the sonotube and come back out. When waves reflect off a hard surface, they are usually at minimum air movement (but highest pressure). The fiberglass works best resisting the air movement. Since the air isn't moving much at all at the sonotube bass trap, it can't trap much bass.

[Ethan Winer]

Scott,

> john mellencamp's personal recoring studio has tons of tubes, risers and a knee wall filled with sand. something is being dampened, their not to keep the floor from jumping up. <

Yeah, this is a huge problem - just because someone is famous does not mean they know anything about acoustics or any other aspect of audio science. Month after month the home recording type magazines interview one clueless musician after another, and each thinks he's an expert and is qualified to explain sample rates, bit depth, phase shift etc ad nauseum. It's pathetic. Really. It's gotten so bad over the past 20 years that most of the technical stuff I read in these magazines is just wrong. And Yes, I am serious!

> there is a reason for this i think some of us would like an answer to, not just "sorry, no, won't work" <

Not rude at all.

As Bryan explained, these are totally different issues. Sand can minimize vibrations in things like a floor that flexes and resonates. Or it can at least lower the resonant frequency to be below the important parts of the bass range. But it's not the same as absorption which is needed to reduce peaks and nulls and ringing in a room. Further, sand seems to me a poor choice for reducing resonance too. If I were building a riser for a home theater I'd make it from wood, with a rigid wood top, and then fill the cavity with fiberglass. That would damp the resonance and also add a small amount of bass trapping into the room.

--Ethan

[scott]

i appreciate the explanation of both ethan and bryon. i personally don't agree with the whole sand thing either, just looking for an explanation.

ethan.....just FYI, i didn't read read about john's studio. his second wife was my cousin. we are still fairly close friends, and get together every now and whip stitch for dinner at his place. but between you, me and the rest of the forum, i think he's a......never mind.

[bpape]

On a riser, I'd agree with the insulation. On a stage with a sub sitting on it trying to bounce the top plate all over, I'll take the sand. In that case, I want to stop the vibration before it starts as opposed to trying to absorb it after it's already vibrating.

Again, there is no single answer. Depends on the room and the application.

Bryan

[Anthony]

Yeah, my riser had terrible effects on the acoustics when I first built it. Nasty "suckout" of a wide region of bass with a pronounced "ring" at certain frequencies.

I added a layer of 1/2" ply over the existing 3/4" and stuffed it with insulation (batting with paper back). Immense change. Much tighter bass, no more boom at some notes, nonexistant at others. I didn't know it at the time, but I was basically "tuning" a big panel absorber.

[scott]

hey bryan, not to get off track of the original question, but is it possible to place the subs in the riser, sectioning off portions, and insulating? or would that be too much BOOM?

i think i should ask this in the DIY section.

[wlmirage]

There is a DIY Tube Trap posted by Jon Gale. I am not sure how effective it is but I am planning to do two or four to try out. Here is the link. http://www.teresaudio.com/haven/traps/traps.html

[bpape]

Good luck with the tubes. They'll do something. Problem is to get them to work down in real bass frequencies, think 18-24" diameters and then fill them with regular fiberglass at a minimum.

Scott - sorry I missed your question.

Yeah - you can do that - but it presents issues since you can't have it where you have walkway but only under the seats. Then, that can weaken the support requiring additional supports. Don't get me wrong - it can be done - it just needs to be planned correctly from the start.

Bryan

[Hitmaker]

Hi Scott ,

I'm hoping this explanation helps ...
Membrane bass traps , as per Ethan , rely on the front membrane vibrating , and that vibration being damped in the sealed airgap behind it ....
In the case of a concrete tube , this vibration will be minimal ... for two reasons .
Firstly , be as dense as it is , concrete will vibrate very little ( compared to say plywood ) ...
And , secondly , being of circular shape , it is far less able to flex ...
In a way , the face of a membrane trap behaves as a piston ... Curved concrete couldn't do that .....

My thoughts on Mellencamp's use was that is was an attempt at sound isolation , not absorption ... and the interest in such devices probably a confusion between the principles of a porous absorber ( which a 'tube trap' is .... ) and a membrane trap .... based on shape ...

However , they would make great speaker stands ....

Cheers ,

Evan .

[bpape]

I think the tube he's considering is just a cardboard form used to pour concrete into - it wouldn't be concrete per se. That said, I still stand by my previous statements and recommend other types of treatment as more effective and taking less space.

Bryan

[Hitmaker]

Hi Bryan ,

Cheers for explaining a Sonotube .. and I heartily agree with you ...
Would such device act as a ( fairly compliant ) membrane .... like a poly that's a full circle , as opposed to a segment of one ?????
Or a diffusor , with inefficient central absorption ????
In that regard , I'd suggest placing the fibreglass around the inner circumference ... to give it most apparent depth .... But then you might as well use fibreglass tubing , with the foil facing , as per the link a few posts ago ...
However , I'd echo Ethan's , and Bryan's view that a sealed membrane trap would be more effective than a porous device for trapping bass frequencies ... at least you would have the area within abutting the boundary ( the zone of maximum pressure ) , as large as the face , unlike a circular device ....

Cheers ,

Evan .

[bpape]

Let's put it this way - people make DIY Subwoofers out of Sonotube. If it's stiff enough for that, I really don't think it will make a very good absorber. If it does, it would be VERY VERY narrow in the nature of its absorbtion.

Now, if you want to fill it with absorbtion and stick them around the room for some diffusion, that's a more likely use for them - though againm, there are better things to use that would take up less floorspace.

Bryan

[Bluum]

bpape wrote:

there are better things to use that would take up less floorspace.

Like what?

I have a room that I am intending to acoustically damp, but for now I only have gotten as far as installing six 5cm thick Rockwool acoustic plates. Now I need something that could help removing cancelation in the 50 to 80Hz area, and something that evens out the mid-bass. My REW graph looks like a very fun rollercoaster from about 90Hz and upwards. And there is one large peak around 46Hz that I would like to reduce a little bit, but that is not the most important issue, because mye SVS SB12+ has this PEQ that allows me to reduce it to about normal level.

I have been thinking of Helmholtz, sandfilled Sonotubes and corner bass traps, but I don't know what will work. Besides, I only have two corners to "use". The room is kind of "L"-shaped, so there is just three corners, and the subwoofer occupies one of them.

I hope someone can answer me politely even though I bring back this old thread

[bpape]

Skip the sand filled Sonotubes - seriously.

Do you know what is causing the response abberations? That'll dictate the best way to deal with it and where. What does the decay time look like? That's as or more important than purely frequency response. Potential materials are thick fiberglass with an FSK face or a sealed membrane absorber if it's narrower in nature and the rest of the decay time is in range.

Getting the sub out of the corner will likely help things a lot. While giving the most sheer output, it also unfortunately usually gives the worst frequency response since you're maximally exciting all the room modes by sitting at the end of all 3 room dimensions.

Bryan

[Bluum]

Wel, since part of my room is pretty much square; I have a very strong peak in that part of the room, in addition to the same nulls. This results in a very uneven response.
Now, I have a pretty flat response from about 22Hz up to about 47Hz, but from there and up to about 83Hz, it is poor.

If you want; I can post a couple of graps and waterfalls

You see, I don't have that much money at the time, so I prefer cheap sollutions. And sollutions that's not to dominant in the room.

Thanks for answering

[Hitmaker]

Hi ,

I'd begin by feeding your room dimensions through a program like ModeCalc , to see if you can figure what boundary dimension is causing your spectral 'hump' ... Even better , go here http://www.hunecke.de/en/calculators...igenmodes.html... which will show you the planes/positions where that stationary wave will be sitting .... An effective pressure-quelling device anywhere in that node will reduce the whole thing ( a little ) ... it need not be in a corner ( though corners are eloquent .. in that they do two surfaces at once ... )
Regards trapping devices to use ... only a Helmholtz , polycylindrical , or panel trap will be rationally effective ... as long as it's placed on the node .... Conversely .. putting your sub on a node will be a very bad place for even reproduction from it .... Panel traps are easier to design ... the critical variables being density ( surface mass ) of the front panel ... and depth of box ... Adding some internal damping ( not touching the front panel ) will lessen the 'Q' of the trap's resonance ... making it's effect less narrow in frequency ...

Try here http://www.mhsoft.nl/Helmholtzabsorber.asp for the formulae ....

My suggestions for 'cheap' .. use an actual pressure-active device ... and put it where it will be most effective ....

[Bluum]

Hi, thanks for those great links

But I don't know if I can trust what the model in the first link shows me, because my room isn't square, it is like this: