Ethan, question on treatment...

Posted: Sun Feb 09, 2003 1:33 pm

Hi Ethan,

One question I always wanted to ask (but were afraid ... :c: )

When applying some broadband absorption to help me with problematic frequencies, what I'm doing is flattening out the bumps in my room's freq response right but at the same time reducing overal reflected sounds, right ??
What I'm trying to say is: together with attenuating the bad freqs I'm attenuating the 'good' freqs too, right ?
So, what I understand is the more broadband absorption I add, the flatter my room freq resp. will be, but as a drawback the deader it will be.

Now, when treating this room, is there a way to predict how much treatment I'll need, or would it be a matter of experimenting? (I'm talking near square room here, very bad conditions)

Thanks for your time,
Herwig

Posted: Mon Feb 10, 2003 6:59 am

Herwig,

> together with attenuating the bad freqs I'm attenuating the 'good' freqs too, right ? <

Not at all. Bass traps do absorb bass frequencies, but the net result is an increase in low frequency content in the room. I know this sounds strange!

Your loudspeakers are probably fairly close to flat, and play low frequencies at a relatively even level if you put them outdoors. But when you bring the same speakers into a room, reflections from the walls, floor, and ceiling combine with each other in the air, and cause the peaks and dips in the room's response. Depending on where the speakers are in the room and what frequencies they're playing, the reflections - called acoustic interference - cause some frequencies to be boosted by as much as 6 dB. while others are reduced by 15 dB. or even more.

> the more broadband absorption I add, the flatter my room freq resp. will be, but as a drawback the deader it will be. <

Yes, and no. We usually think of "dead" as a property of the midrange and higher frequencies. So if you put in too much absorption that affects those frequencies, the sound will be too dead and unnatural sounding. So you never want to cover all of the walls with fiberglass or foam. But you probably can't absorb the low frequencies too much, and the low end is what improves by adding more and more absorption. Not so much because of the liveness or deadness, but because of the improvement in low-end frequency response as described above.

> is there a way to predict how much treatment I'll need <

As a starting point, you could cover about a third to half of the wall surfaces with material that is absorbent at mid/high frequencies. I prefer a hard floor and fully absorbent ceiling, but that's a matter of taste and there's no rule.

--Ethan

Posted: Mon Feb 10, 2003 7:46 am

deadpoet
I'm not Ethan, but I will give it a shot. You can predict what the treatment will do to your room. There is a spreadsheet program on the site
studio tips
that you can use to predict the reverb time at frequencies from 125hz to 4000hz. Go to calculation tools and download "excel sabin and mode" Also download "absorption coefficients to go with calculators"

Play with this for a while, to figure out how it all works. Add treatment until the RT60 at all frequencies are fairly close.
The frequencies that bass traps work on aren't covered by these calculations, but the general rule of thumb is in smaller rooms the more bass trapping you can do the better.

Hope this helps.

Eric

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