Helmoltz-Resonator vs panel traps

[bubblefish]

hi I,ve noticed on the most of the studio designs i have seen here that, people generally favor the Helmoltz-Resonator bass traps.

see link for example:

http://www.johnlsayers.com/HR/index1.htm

although it mentions that the traps in this design are effective from 150hz -500hz.

I played with the Helmoltz-Resonator calculator sticky to see what i would need to construct to deal with the 3, 1st modes of my (hopefully soon to be new) room

length 1st: 49.49hz

width 1st: 58.96 hz

hight 1st : 67 hz

but i ended up needing something like 49" x 1" slats spaced 10" off the wall with a slot gap of 0.25" for the first mode

And i certainly didn't see any of those i all the picutres on this site.

where as i calculated the depth of panel trap needed using this equation below:

............ ( 28,900)
d= _______________________________
.......... ( f squared M )

d = depth of required air space, inches( distance from back of panel to rigid wall)

f= fundemental absorbing frequancy of bass trap, Hz

M= surface density of panel, lb./ft squared

using the formula above, assuming an average weight for 1/2" plywood @ 1.375lb./ft squared. (from jeff coopers book :building a recording studio) I calculated the individual distances needed.

in the hope someone will correct me if I,m wrong heres an example:

length 1st : 49.49hz squared = 2449.2601 x 1.375 = 3367.732638

28900 / 3367.732638 = 8.581441316

thus space required for room length mode = 8.58"

width mode= 6.04"

hieght mode= 4.68"

so i guess I,m asking what am i doing wrong with the slot resonator calculations?

is there a reason the folks around here go with slot resonators over panels, or is that not actually the case in the first place?

and finaly can use aim for higher harmonics to treat low end modes, and is that why the traps in john plans above are only aiming at 150hz -500hz

anyway thanks for getting this far down the post

[famous beagle]

Don't expect an answer to this. It seems that these folks don't really like to give answers to people who are still learning. I've asked several questions on this site and have gotten basically nowhere.

good luck.

[drfrankencopter]

The key to getting an answer, Beagle is to have a detailed question (at least from what I've noticed). It's really more like guided discovery as opposed to getting spoon fed an answer.

Regarding the Helmholz question, why not tune the trap an octave up, and stuff it with insulation to make it a broad Q trap, instead of a narrow one working only on the fundamental mode?

I think I'd be inclibed to do a panel type treatment in the corners, with a broad Q, so you touch all modes and offer some damping. Then, shoot the room with an RTA, and use helmoltz to treat any remaining offending frequencies.

I think the the slat traps are used often here, because John Sayers is pretty familiar with them, and they look nice, plus with the angle to them they deal with flutter echoes too.

Cheers,

Kris

[John Sayers]

Bubblefish - you can't work on frequencies below 150 hz using slot resonators. They only work on low mid frequencies which is why I use them all the time as that is the area most rooms have a major problem.

Panel traps are designed to work below 150 hz and the best diagrams for building them are at Ethan's site.

http://www.ethanwiner.com/

cheers
john

[bubblefish]

Bubblefish - you can't work on frequencies below 150 hz using slot resonators. They only work on low mid frequencies which is why I use them all the time as that is the area most rooms have a major problem.

Panel traps are designed to work below 150 hz and the best diagrams for building them are at Ethan's site.

http://www.ethanwiner.com/

cheers
john

thanks for the feed back people and thanks for clearing that up john . its all appriciated