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PostPosted: Tue Nov 23, 2010 5:24 pm 
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Location: Taiwan
Hey everyone!

I'm thinking there's a lesson to be learned somewhere in this story. Hopefully this will help someone down the road.

A while back I was looking for advice on what to put beneath my vocal booth. I was worried that unwanted noise from the neighbors would make its way into the booth from the floor.

I came across advice from John Brandt, John Sayers and others about how to build a poor man's floating floor. Essentially having a layer of rockwool, then two layers of plywood screwed together.

One such post:

viewtopic.php?f=1&t=14618

I never had any delusions that this would 100% take care of any problems. But now that I've got one and I'm hoping that it was my fault in the building process, and not just a "there's nothing that can prevent it" problem.

The Problem:

I'm getting a lot of low-end 'rumble' inside the booth when the neighbor's kid jumps off the bed onto the floor. I would guess and say it's very sub bass, below 70hz. I can filter it out of voice recordings, so it's not a major issue...but still...why do that when I can kill it at the source?


Some info on my house:

I have the vocal booth in a mostly-empty room. It's located on the 3rd floor. Control room is on the 4th floor. The building is a 4-floor townhouse(rowhouse) made from concrete and rebar. We share one wall with a neighbor. I'm assuming their floor and ours was poured at the same time. Actually it must have been.


Location of booth

It's located about 5 1/2 feet from the shared wall; 2 feet from the directly opposite wall; 4 feet from another wall; and about 9 feet from the windows at the front of the house.


[EDIT] The size of the booth is 6' x 6' measured from the outside. Not great dimensions for a booth, but I got an amazing deal on it b/c is was a return. The floor I built is only beneath the booth. I didn't cover the entire room with it. So essentially I made an 'island'.[EDIT]

I'll post up some pictures to help visualize this. (at 'work' now)


How I built the floor

This is probably where the problem lies. I screwed up on the rockwool part. When I was buying it, I was also researching broadband absorbers (4" thick). So I ended up using 4" of rockwool 100kg/m3. That's twice as thick as what people are saying to use.

Is this my problem?

With the plywood, I had a bunch of 1/2" OSB lying around. In total, it says I need 1 1/2". So I used three layers of OSB, seems staggered, and screwed together. Vocal booth on top of it all.

I'll also put up pictures of this before I put the booth on top.


Assumptions

I've made the assumption that my problem is coming from the floor. Is it possible that it's not? Perhaps it's coming through the wall or flanking? Maybe some basic treatment on the walls would help if this is the case?

You know what? I just now thought of a way to test this. Really should have thought of this before. (darn I'm dense). I should jump up and down on my floor and see if there's any noise in the booth. Will try that when I get home...

Thanks for your suggestions on this. Eagerly awaiting your replies! Please let me know if I missed anything important.

Best,
Glenn


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PostPosted: Wed Nov 24, 2010 2:45 am 
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Floating floors have a resonance where the Transmision Loss (TL) is worse than the bare floor. It sounds like you have made a flaoting floor with the resonance right where the noise is.

Andre

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PostPosted: Wed Nov 24, 2010 7:33 am 
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agreed with Andre - and it might also be that the float floor is somehow coupled to the actual floor? or the walls of the booth are not on the floating floor and therefore transferring from the floor through the walls. i'd try some tap testing on the floor around the unit to see if you can identify any spots where the booth is coupled to the floor or ceiling. i'd run some 70hz test tones to see if your wall structure has the resonance problem as well just as the floor. and finally as Andre pointed out, the compression of the rigid insulation may not be enough to where the floor is still buoyant and operating at sufficient low resonances. one option would be to add additional mass to the floor - 2" of MDF or cement board on the inside of the booth floor might help assuming the underlying floor can support it and your have enough space on the rigid insulation to compress.

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PostPosted: Wed Nov 24, 2010 3:36 pm 
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Location: Taiwan
Very good. Thank you both for the input. I'll take a look at what you suggest and go from there.

One thing you mentioned gullfo, "or the walls of the booth are not on the floating floor":

The walls are sitting on the booth floor itself, but I never actually screwed them into the booth's floor. There are metal rails bolted to the booth's floor, and the walls bolt to the rails. I was waiting to see if everything worked out alright before doing this last step. I'll start with that and see what happens.

Thank you


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PostPosted: Sun Nov 28, 2010 5:48 am 
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What is the weight of the iso-booth you put on the base?

The reason I ask this is because if the insulation has either to little or too much compression it will tend to act as a transmitter rather than an isolator...

Rod

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PostPosted: Sun Nov 28, 2010 4:05 pm 
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This is a good question. The shipping bill lists 1,451 lb (658kg), which would be the weight of the booth AND all of the included packing materials & crate.

The crate consisted of (1) sheet of 4x8 3/4" OSB, and about (4) sheets of 4x8 1/2" OSB. From what I read on the Internet, those would be around 290lb of that weight. The rest of the packing material was mostly foam-based materials, so not much to subtract there. There's a few other odds and ends of weight....

Final guess would be around 1,100 lb, give or take. (499kg) (plus the weight of one or two adults; but I'm getting that low rumble even when nobody's in the booth)

What do you think?


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PostPosted: Wed Dec 01, 2010 12:31 pm 
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can you determine how much the floor compressed when you load on the booth? based on say 1500lb on a 6x6 platform you're about 42lb/ft2, and depending on if the booth load is actually distributed or there is more pressure on the edges, you may have compressed things too much, or too little resulting in the transmission. if you have some idea how much you have compressed the insulation it could help us understand. also, doing a measurement of the problem frequencies will help as well.

another consideration, perhaps purchasing some isolation pads for the neighbor's bed could help all parties. they don't get as much wear and tear on their floor, and you get less rumbling...

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