How to tame 50hz with a 1' depth

[johndykstra]

Hey guys, I could really use some help.

I've got a control room being built, and at this stage, the room is entirely engulfed in insulation. It was a concrete room, measuring 14'w X 17'd x 9'h.

We've constructed an inner wooden shell, with a 6 degree sloped ceiling, and both walls slanted towards the front. THe entire cavity between the concrete and studs is filled with insulation 16kg rockwool. The shallowest depth of rock wool is at the front and back walls which is at 1'. Where the walls and ceiling slope to the front, there's over 2' at the very front of the room.

The idea was to install a combination of slats and drywall over the skeleton to tune the response.

The problem is a very pronounced 50hz ring... not in frequency response, but in the waterfall measurement. Response actually looks really good... but with all theat insulation I guess it should.

After manipulating the slat wall calculator, I came up with a ridiculous 3' wide slat and .2" wide slot to get down to 50hz. giving me what... maybe 3 slots on the back wall and 2 on the front... to try to curtail this frequency. (It is a length mode I'm dealing with I think, as an SPL meter reveals these two walls as the highest in sensitivity.

I'm wondering, is there a different method... one that will fit between 16"oc studs, and maintain a depth of 1' that will help me hit this 50 hz problem?

[AVare]

First of all congratulations on doing things right, as in measuring the actual response of the room.

If I am understanding your post correctly, you have installed the insulation but not the covering drywall and slats. Is this correct?

If this is, bear in mind that as you add the reflective surfaces, the waterfall will become more ragged. Addressing your slat design question directly, one option is to use 2x4s or some other form of material in front of teh drywall to increase the depth of the slots.

Good luck!

Andre

[John Sayers]

john - you aren't going to treat 50hz with a slot resonator - as you discovered, you don't have the depth.

can you post some pictures so we can see what you have?

[johndykstra]

hey guys, thanks so much for the quick response. Here is a sketch file of the room in it's current state... minus all the insulation. We added a wall on the right side to attempt to enforce better mode spacing. This wall is 2x4 constructed, filled with VERY dense rockwool, and sheathed with 2 layers of 5/8" mdf... all joints and seams caulked.

amit new.skp.zip

and here is a waterfall plot of what we have after insulation is in place. we've since been able to attribute much of the tiny razor rings to a fan in an adjacent space.

waterfall 4_6.jpg

[johndykstra]

slats2.jpg

here is a rendering of what i want aesthetically from the slats and fabric. My slat spacing was not figured mathematically at this point in the design... this is the stage I am currently working on.

[johndykstra]

setup3.jpg

here's a shot of the testing process

[johndykstra]

Hi Andre.

I'm expecting the introduction of reflective surfaces to create new anomalies in the waterfall.

What I am hoping to do, is tame the existing problem....

I'm thinking, if I were to build mdf boxes that can be mounted between the stud cavities, and utilize a perforated panel... though I'm unsure if this design will yield any lower frequency targets than the slats can.

[johndykstra]

50-150 .skp.zip

Here is an additional sketchup file. This time with numbers indicating spl readings of two frequencies.

50 hz is in red

150hz is in blue

speakers were emitting sine waves of these pitches, and the spl meter was walked around the room and thresholds recorded.

[John Sayers]

John - this is a mistake I keep seeing - you have wasted all the space behind your walls where you can use the depth to get decent traps and low frequency slot resonators to function. You've misinterpreted the design of control room shapes completely. I'd pull it down and start again. Sorry.

[amit monga]

John - this is a mistake I keep seeing - you have wasted all the space behind your walls where you can use the depth to get decent traps and low frequency slot resonators to function. You've misinterpreted the design of control room shapes completely. I'd pull it down and start again. Sorry.

hi mr. sayers
WITH RESPECT

real world situations are different. as we can see and interpret that the room is dead now with good frequency graph there is only some liveliness to bring out and some specific frequency tuning. so in spite of what could be done it is better what can be done taking into account the current situation. so as expected from you, you should give advice with what already had. sorting out things is real result of your life time experience not discouraging.

[Ethan Winer]

here is a waterfall plot of what we have after insulation is in place. we've since been able to attribute much of the tiny razor rings to a fan in an adjacent space.

That 50 Hz resonance looks like AC power line hum because it never decays and doesn't seem to have an associated peak. Are you sure you don't live in Europe?

--Ethan

[johndykstra]

Hi everyone.

Well now that we're all here...

Amit is the actual owner of this space. He had started a thread on a different forum looking for advice on his control room... which is in India... perhaps the ac problem is there as well Ethan?

John,

Is there any improvements that can be made given the shell of the space? Meaning, if we remove some of the insulation and employ a better thought out trapping system within?

Initial thought had been given to a different shape of the shell. One in which splayed surfaces could take the place of 1st reflection absorption... Amit and I did not trust our abilities to predict a final speaker placement at the beginning of the design phase.

Humbly, if there is any directions you can point me in to help Amit get the best room possibly, I'd really appreciate it.

Thanks,

John

[AVare]

In India? The continuous spikes are 50 Hz hum. It would be good to see the waterfall without the hum.

Andre

[johndykstra]

Well,

that's good news... right?

What needs to be done to clean the power up and get rid of this interference?

[John Sayers]

John and Amit - yes I was being a bit hasty in making my judgement. It appears that your 50hz problem is what has been mentioned. i would imagine the room sounds very dead and lifeless.

try this

John_1.skp