Analyzing Resonant Frequencies?

B

Bushice

New member
Spotted this quote in a link on a bass trap thread:

Analysis of the studio’s resonant frequencies indicated that energy around 100 Hz was giving the room its “boomy” quality, while parallel walls reinforced other resonances and generated flutter echoes. The room’s 100 Hz “honk” was our first target.


Have any of you done this? It seems like an expensive proposition, determining the resonant frequencies.

Any thoughts on this? How do you determine if you need to analyze room freqencies? Any ideas on how to do it inexpensively, or is it necessary to even do it at all?

Here is the article link:

http://www.musicplayer.com/CDA/Player/Main/1,2228,Lessons-Engineer_Producer-5000542,00.html

Bushice
 
Well let me put it another way. For those of you who have built studios, how did you deal with the odd frequencies in the rooms?

Bushice
 
Thanks for that Link, John. That is certainly a lot cheaper than buying an oscillator and a couple of expensive mikes!

Next question - now that I know what my resonant room frequencies and harmonics are, how do I go about managing them correctly so they don't screw up my room sound?

Bushice

PS

If they let off a gun shot, wouldn't the resulting hole alter the rooms sound characteristics? ;)
 
you will find that the room modes fall ionto two areas - those below 100Hz and those in the low mids. You can tune slot resonators to the frequencies in the low mids. The ones below 100hz will need panel absorbers tuned to the freq.

cheers
John
 
Wow, that is pretty easy to do!

That was the one link on that site I didn't click on :)

Didn't realize how important it was!

Thanks, John. Everyday I get a little closer to getting this project on its feet. I still need a few more weeks of research though.

Bushice
 
I've been thinking about this recently - any room is going to have modes based around it's dimensions. The calculator and the reverb calc are based around square rooms so they don't really apply when you start putting angles in.

The way I see it is that the sound of the room is like background noise. It has colourations in it. The aim of acoustic treatment is to lower the background noise so you hear more of your speakers and less of the room colouration.

cheers
john
 
So those calculations at SAE don't even deal with rectangular rooms well? Dang. I'd think that since the general recommendation is to NOT have a square room for recording, the calculations would support at least that.

Outside of those calculations, I think it would take a bit of money to get it right with equipment.

You have a point about colorations, but given the expanse of studio designs ( or rather the odd bits of house you have to work around :) ), it would be nice to count on a few standards, at least to not have to worry about standing waves or frequencies that make your sound all weird, or maybe an easy inexpensive way to work around it all and still end up with a killer sound. :)

Bushice
 
I remember a link to a virtual test tone oscillator, it was pretty cool. Looked like a little handheld device and you could switch frequencies.

Anyone remember the link?
 
Bushice said:
So those calculations at SAE don't even deal with rectangular rooms well?
Click to expand...

No they work with rectangular rooms. John was saying if you angle the side walls of your room to cut down on flutter echo and other standing waves, the calculators don't know how to figure out modes then. Just for angled walls. That's ok for me though, I don't have angled walls, space just didn't allow for it... not to mention resell of my house would have been impossible.
 
it would be nice to count on a few standards, at least to not have to worry about standing waves or frequencies that make your sound all weird, or maybe an easy inexpensive way to work around it all and still end up with a killer sound.
Click to expand...
Forget calculations. Low frequency and broadband bsorption is your friend. Modal resonances terminate in the corners. You can count on that. Treat the corners with stacks of diagonally cut RIGID FIBERGLASS such as Owens Corning 703. These are typically called "Superchunks". Here is a pic of one laying on the floor for testing. Yes, these have been tested which have verified their LOW FREQUENCY absorption. They work.

chunks3.jpg


Since rigid fiberglass typically comes in 2'x4' panels in thickness's from 1/2" to 6", with 4" usually available at most insulation companys. Using 4", cut the panel into (2) 2'x2' pieces. It cuts very easy with an electric knife, or table saw. Now cut these panels diagonally like so:
Superchunk elev cut.gif


Here is the plan


superchunk plan.gif



Nail some wood strips to the wall as shown here. Now stack the the diagonals floor to ceiling. It takes around (6) 2'x4' panels per corner with ceilings at 8'.
Then staple fabric to the strips as shown, and nail trim to the backer strips as shown here. There are all kinds of trim variations.

superchunk det1.gif


Or you can build fabric covered frames instead. One other suggestion. Treat the fabric with a spray on fire retardant.

superchunk det2.gif


superchunk det3.gif



And then you can use full panels around the room for broadband absorption. There are tons of threads here. Do a search. In fact, patchwork use of these on the walls increases absorption, due to diffraction at the edges, and exposed edges ALSO increase absorption. Use of patchwork patterns also contributes to diffusion. Be sure to space the panels about an inch off the wall, as this will lower the bandwidth of absorption since resistance absorbers work on the 1/4 wavelength principle. The thicker the panel, the longer the 1/4 wavelength.

But your not limited to the typical rectangle or square type designs. Use DIAMOND THEORY to use diagonals in UNLIMITED patterns. Heres a few ideas. :)


Compare1.gif

Compare2.gif

Compare3.gif

Compare4.gif

Compare5.gif


fitZ :)
 
"*cough*4 year old thread*cough*"

You're right, ALL the laws of physics have been re-written since then; DAMN, 25 years of study down the fucking drain...
 
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