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post #21 of 56 Old 11-06-06, 09:21 PM
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Re: Bass traps

Actually, if you want to emulate 703, see if you can get some Roxul RHT40.

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post #22 of 56 Old 11-06-06, 10:05 PM
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Re: Bass traps

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Actually, if you want to emulate 703, see if you can get some Roxul RHT40.

Bryan
Thanks Bryan for the tip,it should be no problem getting the RHT40.

The Roxul site states it has a density of 3.5lbs pcf.Would the product I mentioned (see link)with a density of 8lbs pcf be even better suited for bass trapping duties or is that too dense?
http://www.roxul.com/graphics/rx-na/...sh_5-12-06.pdf
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post #23 of 56 Old 11-07-06, 06:30 AM
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Re: Bass traps

Depends on how you do it. If you're going to use 4" straddling a corner then the 8lb would be a better option. If you're going thicker or even chunking it, no need to spend the extra money. As you increase thickness, you can slack on the density a bit and still get good performance.

For the same money, I'll take 8" of 4.5lb over 4" of 8lb any day.

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post #24 of 56 Old 11-07-06, 10:24 AM
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Re: Bass traps

If you're looking to eliminate unwanted bass at frequencies below 100Hz, you'll need to have some type of material that actually absorbs the acoustic energy. Obviously, right? But typically, fiberglass insulation - even dense 705 FRK mentioned in Winer's article - is acoustically transparent below 100 Hz. So you need another level of function, some type of material or process to swallow up these 10' + energy packed waves.

I've used hanging absorbers in the isolation booth of my studio derived from the formula in 'Acoustics and Psychoacoustics' by Argus. After they were built, I subscribed to Sound on Sound magazine out of the UK and discovered an even handier bass trap built by Paul White, Editor in Chief of SOS. This design is unique in that it's similar to a Helmholtz absorber, yet instead of pegboard, it uses a neoprene type material hung loosely over the rockwool (think, 'rigid insulation') barrier. This hanging sheet is what gobbles up the bottom end, not the rockwool. Between these three features; 1) the airgap between the absorber and the wall, 2) the rockwool, and 3) the hanging sheet of neoprene, you have a very effective wide-spectrum absorber.

If you're looking for a cost-effective design, these traps appear to be just the ticket as they're frequently built and added to the many home and semi-pro recording studios (think, 'poor') that are featured in SOS. If you search the last three or four issues of SOS at www.soundonsound.com there are some plans to build these using 1x4's, burlap and the materials mentioned above.

Best Regards,
TJ
post #25 of 56 Old 11-07-06, 10:37 AM
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Re: Bass traps

Fincave,

Do you have a PC setup that you could use to measure the response of the room before and after the traps? They have some free software at this site called RoomEQWizard. It'd be really neat to see how much of a difference the corner traps made.

I built some tube traps, - I'll try and measure the room without and with the traps this coming week (it might be the weekend) and I'll post a link to the results.
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post #26 of 56 Old 11-07-06, 10:55 AM
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Lightbulb Re: Bass traps

Quote:
tjschuhow wrote: View Post
fiberglass insulation - even dense 705 FRK mentioned in Winer's article - is acoustically transparent below 100 Hz ... an even handier bass trap built by Paul White, Editor in Chief of SOS. This design is unique in that it's similar to a Helmholtz absorber, yet instead of pegboard, it uses a neoprene type material hung loosely over the rockwool (think, 'rigid insulation') barrier.
Just to clarify, rigid fiberglass is absolutely effective at frequencies much lower than 100 Hz. However, its absorption is improved by the addition of a membrane. I wouldn't charactertise Paul White's bass trap idea as a Helmholtz trap, but it might work better than plain rigid fiberglass.

You can see a comparison of three densities of rigid fiberglass, without and without the FRK facing, in this report:

www.ethanwiner.com/density/density.html

There you will see rigid fiberglass only three inches thick making a small, but very real, improvement even at the room's lowest 42 Hz mode.

--Ethan

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post #27 of 56 Old 11-07-06, 12:49 PM Thread Starter
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Re: Bass traps

No progress as of yet, just more questions! Went and had a look at one store today and they have rigid rockwool panels that are 100cm X 60cm X 5cm, no mention of density on the packaging and no salesman in sight (no saleslady either). The panels are sold in packs of five though I may be able to get loose ones if I ask nicely. From the above package I would be able to get:

1) One trap with front being 78cm, sides being 50cm and 60cm and 100cm tall

2) Two traps, front of 60cm and both sides being 42cm and being 100cm tall, the second trap would have a face of 50cm with both sides being 35cm and 100cm tall

3)One trap (oblong) with sides being 60cm X 25cm and being 100cm tall

Of the above options what would be the best, options 1&2 are both triangular in shape and would fit nicely in the corner. Is option 3 being oblong a problem or not, appearance wise it would not bother me! While I was in the shop I happened to notice sacks of loose rockwool, roughly 100cm X 40cm X 30cm and weighing 20kg, these would be the cheapest, easiest and ugliest option though easy to cover in material.

I seem to be getting the hang of REW and will use it to take measurements before and after treatments, as soon as I decide on what traps to build.

Once again any and all input will be most appreciated. Thank you in advance.

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post #28 of 56 Old 11-07-06, 05:04 PM
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Re: Bass traps

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Depends on how you do it. If you're going to use 4" straddling a corner then the 8lb would be a better option. If you're going thicker or even chunking it, no need to spend the extra money. As you increase thickness, you can slack on the density a bit and still get good performance.

For the same money, I'll take 8" of 4.5lb over 4" of 8lb any day.

Bryan
Thanks , I will use the RHT40 and shoot for a 8-12"thickness.
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post #29 of 56 Old 11-07-06, 05:28 PM
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Re: Bass traps

TJ.

Yes - those can work nicely - but they'll only work for maybe a couple of octaves. That may not be what is desired. And, I can assure you that if you use 6-8" of even 703, you'll get significant absorbtion well below 100Hz. Even 6" of 703/705 straddling a corner will be pretty effective down to the low 60's/high 50's.

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post #30 of 56 Old 11-09-06, 11:15 AM
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Re: Bass traps

Here's a link that will give you more things to think about for your project. As if that's going to help! http://www.sae.edu/startpage/support.php Maybe you've already checked SAE out, but go to the 'Free Reference Material' center panel and click on '1. Audio Studies.'

You'll find clear answers related to traps, absorbers, layout, design, materials, coefficients of absorption, acoustic transparency, etc. There's even a Helmholtz Resonator Calculator - my personal favorite.

If you get information overload, I won't fault you if you chuck all the data and stuff a couple bundles of old bluejeans in the corners of the room. It worked in the '60s, right?

Regards,
TJ
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