3" or 6" 703 in the corners for a full range trap?

Tom_Mc · Post by **Tom_Mc** » Tue Feb 17, 2004 2:51 pm

I found some 3" 703 in my area. I am planning on putting it across the corners of my studio. Does anyone know what frequency I could get down to by doubling it up to 6" in the corners? I have heard that 4" flat on a wall is good down to 125 hz. I figure 6" in a corner should get me well under 100HZ, or am I missing something?

Thanks for the help,
Tom

Fresnog · Post by **Fresnog** » Wed Feb 18, 2004 12:06 am

Sorry, no solution from me, only a question....

What area are you in? I am in Central California and am having a heck of a time finding 703.

Just wondering....

GJ

Tom_Mc · Post by **Tom_Mc** » Wed Feb 18, 2004 11:47 am

I'm in Chicago. I only found one place that had stock. No one else I called wanted to deal with 703 sales.

bcarron · Post by **bcarron** » Thu Feb 19, 2004 1:32 pm

I'm in Chicago as well. What place did you find that sells 703?

B.

Tom_Mc · Post by **Tom_Mc** » Thu Feb 19, 2004 2:30 pm

I got it from Central Acoustic Supply. They have 3" in stock. Call Kevin at 630-629-3356. He was real nice to me, no attitude. I think he works in their Lombard office, but he had it shipped up to their Schumburg shop for me. Apparently, someone ordered a lot of 703 from him and cancelled the order, so he's will to give a good price on it.

Hope this helps,
Tom

knightfly · Post by **knightfly** » Sat Feb 21, 2004 5:37 am

tom, doubling the thickness when the stuff is across a corner mainly only increases the AMOUNT of absorption, not the frequency. Frequency is largely decided by the depth from the front of the absorbent to the solid barrier wall, so if the stuff is diagonal across a corner you have a variable depth, which would cause a more broadband (and deeper ) frequency response.

Depth from face of absorber to wall is calculated by taking 1/4 wavelength of the frequency in question - wavelength(in feet) = 1130/freq (in hZ) so, 300 hZ would have a full wavelength of 1130/300, or 3.766 feet - 1/4 of that would be .942 feet, or 11.3 inches. This means that if you place an absorbent away from the wall so that its front surface is 11.3 inches from the wall, it will absorb at full efficiency down to 300 hZ.

Placing 48" material across a corner results in a maximum depth of 24" approximately, so that would absorb effectively down to 150 hZ - in actual use, it will go lower than that since getting even CLOSE to the 1/4 wavelength will have some attenuation/cancellation effect.

Hope that helped... Steve

Tom_Mc · Post by **Tom_Mc** » Sat Feb 21, 2004 12:32 pm

Thanks for that info Steve. I really need to pick up a book and learn this stuff. Right now I have 6" of 703 across the corners; 2'W x 8'H. If I filled the gap in back of the 703 with more 703, would that decreace the frequency? I did some sine wave tests on the room last night. Many of the problems frequencies I had are a bit more even around the room. I still have a real problem with 77HZ. Do you think I need to go with panel traps to smooth that out?

Tom

knightfly · Post by **knightfly** » Sat Feb 21, 2004 5:22 pm

I wouldn't get too excited about buying an acoustics book just yet - one of the most prominent ones, Everest's Master Handbook of Acoustics, is kind of under attack right now on a couple of bbs's for being frought with errors.

As to your 77 hZ question, it's kind of like me telling my mechanic "my car makes a funny noise, what will fix it?" without telling him what make and model, when the noise happens, whether I have done any modifications to the engine, whether the noise only happens when I have the radio on loud while going downhill....

If you could post a scaled sketch of your room including ceiling height and at least general construction, location of openings, etc, maybe we could get an idea of what to do... Steve

Tom_Mc · Post by **Tom_Mc** » Sat Feb 21, 2004 5:37 pm

Thanks Steve,
I'll work on that and post something when I get it done.

genericperson · Post by **genericperson** » Wed Feb 25, 2004 10:15 pm

I just read this today in an Alton Everest book. Here's the basics:
3 inch 703, 3 inch airspace behind it, then the wall
6 inch 703, flush against the wall.

he said not much difference at all, since the total cavity is 6 inches. also went on to say that mounting that much 703 thickness would be a hassle and advised to go with an airspace solution.

that's the gist of it. you must feel relieved!

cadesignr · Post by **cadesignr** » Thu Feb 26, 2004 4:01 am

I really need to pick up a book and learn this stuff.

I won't comment about Everests book, as I already have got myself WAY over my head, even though I have had one since the 80's, but I DO know this. Do yourself a favor. Take a ride in plane. You'll learn aeronautical engineering to the same degree, but at least you'll come back to earth.

...just kidding. I will say this, I've come to the conclusion, that its ok to dabble in learning some of this stuff, but if you THINK you will LEARN it like you learn the guitar, or bowling, or things that have RATIONAL sense, then you do have something to learn

I found out the hard way, but then again, I'm hardheaded. And stubborn. However, here is a little something I picked up along the way.....

Here is a list of important things where our grasp of the truth is not firm enough to make reliable predictions:
inflation, unemployment, stock prices, love, acoustics,
influenza, and speciation.

fiTZ