knight...quick answer?

terrible_buddhist · Post by **terrible_buddhist** » Wed Mar 31, 2004 7:15 pm

Hoping you have a chance to answer this, as we are litterally building these now.

I realized I don't have the slot dimensions for the broadbands in this drawing.

for reference, this is the previous thread, http://www.johnlsayers.com/phpBB2/viewt ... c&start=15

is the broadband absorbers just supposed to be this:

terrible_buddhist · Post by **terrible_buddhist** » Wed Mar 31, 2004 7:51 pm

actually...take the rush off of this, I had them move onto a different project. Whenever you get to this...thanks!

knightfly · Post by **knightfly** » Wed Mar 31, 2004 9:53 pm

No, the broadband absorber would have no slats in front and just be a continuous wall frame with no wallboard on it, only your absorber material between studs and with a cloth cover - see the diagram... Steve

terrible_buddhist · Post by **terrible_buddhist** » Fri Apr 16, 2004 12:15 am

Hey knight, the room is coming along FABULOUSLY, we don't even have the slates on the 150/ 300 absorbers and the room sounds 100% better!

Couple questions:

1) how wide should the slats be? (I think you told me the spacing in between the slats, I need to look that up) should each slat be 5.5in?

2) for the panel traps, I was looking at Ethans Deep Bass trap, it looks cheaper to build, but will it accomplish what I need?

here was your recomendation:

3/8” plywood over a 12” air cavity will give you the 48 hZ center frequency you need for the panel traps- these, being low frequency, should have all but the front panel built from heavy MDF - ¾” is fair, 1” is better. I would build four of these, 2 feet wide and at least 6 feet tall, sealing everything - you can use standard 6” house insulation inside, make sure the insulation doesn’t touch the front panel but is within 1-2” from it. You can “trap” the insulation by using chicken wire or other lightweight “hardware cloth” and a staple gun and fastening the wire mesh to the sides of the box all around. Thin wood lath or cleats over the wire with small screws where the wire lays flat against the side walls will make things stay put. This layer should hold the insulation at least 1” away from the inside of the front resonator panel of 3/8” plywood. All joints, including the front panel, should be caulked with acoustic sealant. All construction should be glue and screw. When finished, these traps can go in all four corners of your tracking area, facing each other, and against the walls. These are pressure activated traps so they need to be against the walls, not ¼ wavelength away.

Thanks as always!

knightfly · Post by **knightfly** » Fri Apr 16, 2004 12:50 am

Kieth, since I worked out your specs it was discovered that almost ALL the helmholz calculators on the web were WRONG - there was a + in one part of the formula instead of a *. I've since corrected the spreadsheet and it's available in the acoustics forum. I'm doing extra 12-hour graveyards covering vacations, so give me a day or two and I can re-calculate your dimensions to get the right frequency ranges... Steve

terrible_buddhist · Post by **terrible_buddhist** » Fri Apr 16, 2004 2:40 am

I think you already did that for me, this is what you said:

OK, for your 150 hZ trap change the spacing between slats to 7/16", keep all other dimensions the same.

For your 300 hZ trap, change the spacing between slats to 5/8", keep all other dimensions as they were stated.

That should do it... Steve

this is the thread:

http://www.johnlsayers.com/phpBB2/viewt ... ight=#9999

knightfly · Post by **knightfly** » Fri Apr 16, 2004 8:48 am

Right, but there's a good possibility that I used the INCORRECT spreadsheet to get those values - I'll have some time Sat or Sun and will double check, don't build them before I get back... Steve

AVare · Post by **AVare** » Fri Apr 16, 2004 12:53 pm

OK, for your 150 hZ trap change the spacing between slats to 7/16", keep all other dimensions the same.

For your 300 hZ trap, change the spacing between slats to 5/8", keep all other dimensions as they were stated.

Right, but there's a good possibility that I used the INCORRECT spreadsheet to get those values - I'll have some time Sat or Sun and will double check, don't build them before I get back... Steve

I just ran the figures through on my Helmholtz calculator (writen by myself to the correct formula) and the values are correct.

Have fun!

knightfly · Post by **knightfly** » Sun Apr 18, 2004 3:34 pm

Good catch, Avare - by the wording of my comments (thanks for finding that) I agree, it means I HAD re-done the calcs... Steve

terrible_buddhist · Post by **terrible_buddhist** » Mon Apr 19, 2004 11:32 pm

your better than you thought

So how wide should the wood be?

Also, on the panel traps, could I use Ethans low bass design?

knightfly · Post by **knightfly** » Thu Apr 22, 2004 7:03 am

Kieth, I used 5-1/2" for all slat widths so you could use standard dimensional lumber - if you can check the post where I gave dimensions, the last version is correct. For those low frequencies, I most likely spec'd 2x lumber (1-1/2" thick) - but check the earlier thread to be sure, as this WILL change the frequency range along with spacing between slats (very important), depth of air space, and width of slats.

Can you post a link to the specific traps you want to build? I'll check them out and let you know... Steve

AVare · Post by **AVare** » Thu Apr 22, 2004 2:03 pm

I used 5-1/2" for all slat widths so you could use standard dimensional lumber - if you can check the post where I gave dimensions, the last version is correct. For those low frequencies, I most likely spec'd 2x lumber (1-1/2" thick)

As luck would have it, I saved my spreadsheet with the data inputs from checking the slot widths. The values I used were

Slat width: 5 - 1/2"
Slat depth: 3/4"

terrible_buddhist · Post by **terrible_buddhist** » Fri Apr 23, 2004 4:06 am

thanks knight...the link is:

www.ethanwiner.com/BTPlans.gif

knightfly · Post by **knightfly** » Thu Apr 29, 2004 3:57 pm

Kieth, the dimensions of the low bass trap won't reach down to the low end I recommended - they would result in a peak absorption point of around 100 hZ, which wouldn't be a bad thing but wouldn't do much for your lowest modal frequency.

For efficient absorption at 50 hZ with an absorbent type trap, the depth would need to be 1/4 wavelength or about 68 inches. This is why people without serious depths available for trapping usually use panel traps for the lower frequencies... Steve

terrible_buddhist · Post by **terrible_buddhist** » Thu Apr 29, 2004 11:01 pm

This is why I dip into your well of knowledge...thanks!