Ceiling Treatment?

Posted: Sat Feb 08, 2003 8:39 pm

Hi Ethan,

the ceiling in my tracking/mixing room is only 7´. As you can see in the picture, I already installed some of your low and high basstraps but
no high absorbers yet. The acoustic improved a lot, but the room still sounds boxy and dull. So what would you suggest? Should I add even more basstraps or maybe diffusion? You often suggested to make the ceiling as absorbant as possible, but I´m afraid to make the room even more dull sounding. Any suggestions?

<img src="http://freehosting.rbftp.org/kaarroo/basement%20room.JPG" alt=" - " />

Posted: Sun Feb 09, 2003 3:41 pm

My 2 cents,
If I were you I'd only make the ceiling between you at the board and the speakers absorbtive (also on the walls between you and the speakers, sort of a live end, dead end thing). Let the rest of the ceiling reflect towards the back wall. 2 dimentional diffusors on the back wall would definately help. Maybe even 1 dimentional diffusors on the side walls directing the sound back to the 2-Ds on the back wall. You don't mention what material you have on the floor. If it's wall to wall carpeting that's going to absorb a lot of highs. If you have to use carpeting I recommend the tight woven commercial grade stuff.
Gerry

Posted: Mon Feb 10, 2003 7:10 am

John_Bob,

> but the room still sounds boxy and dull. <

To me, boxy is too much midrange caused by reflections between parallel surfaces. The sound is not unlike boosting a narrow band EQ a bunch at 400-500 Hz. My guess is the room is bright enough, but the brightness is drowned out by all the midrange. Of course, without being there I can only guess.

So you should consider adding 4-8 fiberglass absorbers as I show in my plans, if only to reduce the midrange boxiness. But what's on the floor? Carpet? A hard surface?

> Should I add even more basstraps or maybe diffusion? <

You probably do need a few more bass traps. And yes, diffusion is another option for avoiding the problems caused by parallel walls but without damping the sound further. And diffusion doesn't have to be a bunch of fancy shaped gizmos. Just lean some plywood sheets against one wall at a slight angle. If that makes the sound less boxy and doesn't then make it too bright, you can paint the plywood and mount it permanently. If reducing the boxiness reveals the sound as plenty bright, or too bright, you can add fiberglass to tame that.

--Ethan

Posted: Mon Feb 10, 2003 8:04 am

Ethan is exactly right about the boxyness at around 400 hz. A way to deal with this and not affect the high ed is a very simple panel absorber that is made from very easy to find materials. All you need is R-19 faced insulation that you can buy at Home Depot. Build a box (2' x 4' x 6" or whatever size will work in your room). Make sure that you seal the back of the box. Put the fiberglass in facing out sealing the edges and using a staple gun. Build a frame and wrap fabric over it to put on top. Make sure the fabric does not touch the facing.

This set up targets the frequencies between 250hz and 500hz. This will take care of the "boxyness" of the room.

Start out with about 4 of theses, but be careful where you place them, do not put them in a position where you can get a reflection from your speakers because they reflect more than they absorb above about 800hz and this can seriously affect your stereo imaging.

You can also use the same set up for a broadband absorber above 250hz by turning the fiberglass the other way around.

Eric

Posted: Tue Feb 11, 2003 8:06 am

Thanks for your posts. Surprised

When I took away
one 1" panel the boxi/boominess was still there. :confused:
Now can anyone tell me which the problem frequency is?
I guess you were right Ethan that the brightness is drowned out.

So would you try to tame that frequency with a panel absorber, or should
I just hang some 3" from the ceiling? Where would you put these thingies?

@Eric
What is R-19 insulation? Why does it only affect freqs up to 500 Hz?
I thought fiberglass would absorb almost anything from a certain freq upward?
:confused:

Posted: Tue Feb 11, 2003 8:43 am

OK, here goes if this doesn't make sense let me know. R-19 insulation is standard house insulation, not rigid. It comes with paper facing on one side. This paper facing is heavy enough that it will reflect higher frequencies, but the lower ones will go through and be absorbed. It works very well on that range.

If you flip the insulation over in the box, it will just act like broad band absorber down to about 250hz.

What you could do since you already have rigid fiberglass (which is very difficult for me to find) is cover the front of the box with slats to create a helmholtz resonator to target those low midrange frequencies. Formula for calculating slot width and depth can be found here. Spend a couple of days reading the information here, it will be worth your while.

Did that make sense?

Eric

Posted: Tue Feb 11, 2003 10:21 am

John_Bob,

> When I took away one 1" panel the boxi/boominess was still there. :confused: Now can anyone tell me which the problem frequency is? <

I dunno - maybe 200-400 Hz.

> So would you try to tame that frequency with a panel absorber, or should I just hang some 3" from the ceiling? Where would you put these thingies? <

Panel absorbers are most useful for flattening the low frequency response of a room. Although I'm sure you need that kind of treatment too, it's really not the same as the midrange boxiness problem you're describing. To treat those low-mid problems you should attach as many 3-inch thick panel bundles as you can manage.

The ceiling could be covered completely, and I'd hang the fiberglass from little strings or wires so there's an air gap between the fiberglass and the ceiling. The larger the gap - up to about one foot - the better they'll absorb.

For the walls I would not cover them completely with fiberglass. Better is to alternate hard and soft surfaces in either floor to ceiling stripes two feet wide [hard, soft, hard, etc.] or use a checkboard pattern. The goal is to cover 1/4 to 1/2 the wall surfaces with fiberglass, but not have any one large area all live or all dead. Again, if you space the fiberglass away from the walls, they'll absorb to a lower frequency.

--Ethan

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