Debating options for Bass Traps

[pratul]

So, I am planning on adding base traps to the front of my theater and am debating between the two designs shown in the picture below. The triangular one on the right is what everyone uses and aesthetically, that looks good. However, I feel that it will be less effective towards the corners where the insulation isn't thick enough to trap to lower frequencies. Plus, it doesn't take advantage of having an air gap behind the insulation panels.

So, I started thinking of an alternate design shown on the left below. This way, it will have the same amount of insulation from all sides and should perform better but will not look as good in a typical room. Fortunately, my theater design is such that these will just blend in.

Each of the insulation boards is 2" thick so, the entire thing will be 16" x 16".

The other thing I am evaluating is the thickness of the insulation vs the air gap using the calculator at http://www.acousticmodelling.com/porous.php.

Since I am mainly interested in frequencies below 200Hz where I am having issues, it looks like I can reduce the amount of insulation and increase the air gap and get better results. If I maintain the 16" x16" cross section the best results are from 3" of insulation and 13" of air gap behind it.

What do you guys think? Will this work better?

Thanks!

 

[Sonnie Parker]

As I've always understood it, the more space you have to trap, the better, so it makes sense. However, there is also the placement factor as to how effective it will be on the lower frequencies. I spoke with a fellow one time who builds Helmoltz resonators and it was quite the task to determine what was needed, and very expensive. Hence I turned to multiple subs and EQ... problem solved mostly with multiple subs and a few bands of PEQ on the subs themselves.

 

[pratul]

Thanks @Sonnie
I have some left over isul-SHIELD from when I built the theater so this will be a cheap experiment I just wasn't sure if having the bass-trap at an angle makes a different hence the question. Logically and based on what I have read so far, having a square profile should cause a problem and option 1 should work better. Will let you know what I find. If this doesn't work, I have my eye on two SVSs'

Isn't this a fun hobby ?

 

[Sonnie Parker]

Isn't this a fun hobby ?

And can be expense.

 

[SRW1000]

Please post your results when completed. From what I've read, at those thicknesses you're just as well off with the fluffy stuff. But since you've got left overs, you might as well try using them. I'd pick the square one, since it's got more space and insulation.

I've been planning on making my own for a few years now, but just couldn't devote the time. i started with two designs close to what you're showing in your first post, but then decided to go with a different style. I bought some rolls of insulation at Menards years ago, when it was on sale and had a super rebate attached. I stacked them, still wrapped, in the corners. It did affect the sound, but not to the point where I could heartily recommend it, and it looks extremely ugly. That was only supposed to be a temporary situation.

Here's what I'm going to turn some of them into:

I built one prototype using 1 x 2 furring strips, but it wasn't quite as strong as I had hoped, so went back to the store to buy some 2 x 2 furring strips, and picking out the ones that looked the best. They will be covered with either speaker cloth or velvet, maybe with a sheet of 6mil plastic underneath (I've seen positive reports of this in some of the threads). Depending on how the first two work, I may build two smaller ones to stack on top of them so it comes close to the ceiling, and/or also build some for the back of the theater.

 

[Mike-48]

I am hardly an expert; rather, a user who has a lot of acoustic treatment in a couple of rooms. I would do what you propose (the square traps) -- similar to commercial items like the GIK Soffit Trap. I believe triangular traps are used mainly for aesthetic reasons and to save space. Perhaps it's also to interfere less with speakers that would be mounted on or close to the front wall (as sometimes done in commercial installations to reduce SBIR). Anyway, if increased bass trapping is your goal, I think you're on the right track.

 

[ddude003]

@pratul, Since the rectangular one is most like the GIK Soffit Traps I suggested to you in another thread, go with those... Or make something like what SRW1000 suggests... I am not sure that the triangular traps are so much for looks as they are easier to build... And yes, both kinds of traps could be made much larger... Adding a "strike plate" to the front and some mass loaded vinyl towards the back will help "tune" the trap to lower frequencies and allow the mids and highs to reflect/scatter/diffuse... And there are lots of materials you can use besides commercial insulation products... I always wonder how well Cheetos would work...

Wondering which is more expensive base traps or moar subwoofers... Hey @Sonnie, I'm looking at you and your 4 SVS SB16-Ultras...

 

[pratul]

Adding a "strike plate" to the front and some mass loaded vinyl towards the back will help "tune" the trap to lower frequencies and allow the mids and highs to reflect/scatter/diffuse...

I thought about the strike plates but couldn't find details on how to best construct them.

And there are lots of materials you can use besides commercial insulation products... I always wonder how well Cheetos would work...
LOL.. I hear activated carbon works really well. Very expensive though but still cheaper than 4 subs
BTW: I did try using a foam mattress just to see if it did anything.. it didn't.. at least I couldn't measure any difference.

I am also looking into the semi cylindrical diffusers. Easy to build and seems to do a decent job. I will make one and give it a try.

 

[what bass]

LOL.. I hear activated carbon works really well. Very expensive though but still cheaper than 4 subs

I've looked into activated carbon, Dennis Foley of Acoustic Fields videos, https://www.acousticfields.com/ got me interested in the technology. I can definitely see where it would make a terrific absorber. Best price I have found online without calling a manufacturer with my ridiculous notion is $89 for .5 cu/ft. of 4mm pellets. A 2'x8' absorber 12" deep would be 16 cu/ft. Lets suppose you want to make 4 absorbers. 64 cu/ft. equates to 3/4t of pellets. 128x$89, $11,392 not including shipping. I have no idea what that would run.

At $2500 a pop for SVS' flagship model x4 price is about even, if we forgo shipping costs. I suppose you could buy it a few bags at a time from a local farm fleet store.
Lest we forget, you still need to buy the subs.

 

[ddude003]

Dennis says that each of the ACDA-10 Activated Carbon Diaphragmatic Absorber units contains 65 pounds of carbon as well as the other techniques and materials with a cost to the end user of about $1,150.00... I am pretty sure you could DIY for less than half that cost...

By the way... Using Activated Carbon is not a ridiculous notion... Kef uses the stuff in their speakers and I use it in two of my DYI absorbers...

 

[what bass]

Thanks for clarifying that ddude,
Where the hell did I come up with those numbers? I think in my mind the absorber was filled, that's the only way I could have come up with such a high number.

So the ACDA-10 has roughly 4 cu/ft. of carbon in each absorber, much less than I imagined. That seems more affordable. Still $700 per absorber in carbon. I wonder what his price is on carbon if you buy through him?

I didn't mean to say that carbon was a ridiculous notion but in the quantities I was thinking would be needed was ridiculous.

 

[ddude003]

@pratul might also be interested in GIK US Patent 9,091,060 in regards to that FlexRange tech... Something I think of as simple "floppy" strike plate...

@what bass, I still think you are very high on the cost of carbon... I think I have about $125.00 worth of carbon into my traps... 1 ft x 2 ft x 4 in of carbon... The bottom foot of two traps...

I think the ACDA-10s have about 4 1/2 inches, total thickness, of carbon as well as the other trix in them...

I remember seeing a U-Tube video, some years ago, of some DIYer making a box, maybe 4ft x2 ft x 6 inches with 1/2 in ply, and filled it with carbon... He was pretty amazed with the results...

And then I have my own experiences with carbon filled, bit-banging acoustic couplers (think telco hand set modems) in the early eighties...

 

[SRW1000]

Wondering which is more expensive base traps or moar subwoofers... Hey @Sonnie, I'm looking at you and your 4 SVS SB16-Ultras...

I have four JTR Captivator 1400 subs in my theater room, but still want/need to add bass traps. Having four solid concrete walls may be a contributing factor.

 

[Sonnie Parker]

I don't know... just never heard of anyone taming bass below about 120Hz or so, and even that low is not easy. I think if you get too heavy with acoustical insulation type traps, you end up taming a lot more in the mid/high frequencies and your room gets dead. The Helmoltz resonators actually have traps/slots in huge panels/covey holes, etc... that are extremely heavy and take up a lot of room, and have to be strategically placed. My cure has always been more subs, tame the peaks with filters... no need for the huge concoctions.

 

[Mike-48]

just never heard of anyone taming bass below about 120Hz or so, and even that low is not easy.

Me either. I think your solution (more subs and EQ) is just more practical in home listening areas. It doesn't hurt, if you're going to build an absorber, to absorb as low as possible, though -- that will reduce the reverb time, don't you think? which will be a benefit to the sound.

 

[pratul]

Adding a "strike plate" to the front and some mass loaded vinyl towards the back will help "tune" the trap to lower frequencies and allow the mids and highs to reflect/scatter/diffuse...

I looked at the GIK Patent you mentioned in a later post (Thanks!) It adds the mass loaded vinyl on the front. I modeled that at (http://www.acousticmodelling.com/multi.php) and it does limit the frequencies to the lower end. I guess I will try adding that. Stay tuned!

 

[ddude003]

Choices are good... And we are lucky there are many choices and methods to tune a room... Vast assortments of DIY Traps, Absorbers and Diffuser designs... Vast assortments of off the shelf Traps, Absorbers and Diffuser designs... Vast assortments of Subwoofers and so many ways to EQ it all... Life is good here in AV NIRVANA!!!

 

[hreindl]

I don't know... just never heard of anyone taming bass below about 120Hz or so

looked in the mirror

 

[DanDan]

Forget that Calculator. It does not include corner boost. BBC modular traps were done within 12" afaik. Calculating based on algorithms which do not apply and misunderstandings will divert you from the simple and most effective choices. . Big corner traps like GIK Soffits will work very well. Light cheap fibre will work better than denser varieties. Air is not better than fibre. A trap with an air gap is not as good as 100% fibre. 24" would be much better. Bogic Petrovic sadly RIP shows fully professional studio builds on his Instagram and FaceCloth pages. The LF treatments are almost always cheap light 2x4 foot batts or rolls in simple framing. He publishes the results, which are up to and exceeding EBU standards.

 

[dengland]

I am another person that is NOT an expert.....In my reading, area covered rather than volume consumed is the more important factor. I have about 1/2 the area covered that the calculator said I needed for my room volume/dimensions. It made a positive audible difference, by my graphs don't look good yet.

I say that because you MAY not be able to tell how effective your Left 16"x16" is if you build just one to evaluate.

 

[hreindl]

I am another person that is NOT an expert.....In my reading, area covered rather than volume consumed is the more important factor. I have about 1/2 the area covered that the calculator said I needed for my room volume/dimensions. It made a positive audible difference, by my graphs don't look good yet.

I say that because you MAY not be able to tell how effective your Left 16"x16" is if you build just one to evaluate.

if you have room-eq in the mix you may not see most of the difference in measurements BUT after changing room and new measurement on the AVR/Antimode in reality supressed stuff because it got doubled from the room will no longer or less supressed which means it not only works where the microphone was placed on the sweet-spot

a hard mode as result of the room-size won't go down that much but look at the timing of the max energy level which is now half then before "perfect-acoustic" "giga bass panel with membrane"

 

[BenToronto]

Best move is to use Tectum (looks like Shredded Wheat panels) instead of drywall over big pieces of walls, esp with double-depth studs. One of the few materials with some low freq benefits and you can install a lot without much ugliness.

B.

 

[pratul]

So, I built and installed the bass traps with the square cross section (16" x 16") with 8" of Rockboard 60 on each side. Happy with what it did. It removed a lot of the peaks and valleys and smoothened the response overall. This is without any EQ. More importantly, the system sounds a lot better than it did before.

I think I will build similar bass traps for the rear as well. However, this time I will use the fluffier fiber glass wool instead of the denser roackboard. Understand that the lighter stuff is better for bass traps.

 

[BenToronto]

Thanks much. Great to see data.

But what would be of truly great value is to see the eigentone pattern for your room. You could simply enter it into one of the several website that instantly do the calculation (or leave it one of us to do it from your measurements). That way we could see the relationship of first order, second, etc reflections to the results you got.

If you go with the lighter fluff, you should stuff the whole box. My guess is the effect is proportional to the total weight of stuffing, using almost any kind of fluff (OK, maybe long hair English sheep wool has mystic properties).

B.

 

[pratul]

Thanks much. Great to see data.

But what would be of truly great value is to see the eigentone pattern for your room. You could simply enter it into one of the several website that instantly do the calculation (or leave it one of us to do it from your measurements). That way we could see the relationship of first order, second, etc reflections to the results you got.

If you go with the lighter fluff, you should stuff the whole box. My guess is the effect is proportional to the total weight of stuffing, using almost any kind of fluff (OK, maybe long hair English sheep wool has mystic properties).

B.

Here you go. The dimensions of my theater are on the top of the image below.