The Drum Bubble - Leaks in my space

Ekimtoor1

Member
In theory, a good plan, but in practicality.... The low end on those speakers is mfr-rated at 50Hz (at what dB drop off?), and low frequency transmission is really what you want to be looking at in this test.
Thank you. If I could do it over, I would pay more attention to that. I expected that the pink noise test would include 50hz. I can say that going by my ears, low end bleed into the house is equally offensive for mounts and stands.
 

Ekimtoor1

Member
My process of elimination continues.

I’ve now got a good door with a tight seal and it works well, so I’m checking that off.

I now know that chopping a hole in the wall for a window AC doesn’t work and I undid that. My space is now near air tight, so a portable AC will not work and would also require cutting substantial holes in a wall. So a mini split is really the only choice.

Thanks to Rob, I’ve got a better understanding of wall construction and how rigid fixtures might affect transmission. I can’t practically change what I’ve built and I would build a do-over much differently, but it is what it is and it’s not bad.

The enemy all along has been low end bleed into an adjoining BR. Everything else is very acceptable. So that’s what I’m chasing.

Following the principle of try the easy, inexpensive things first, I could add mass between my room and the adjoining BR wall, which forms a triple leaf (not good). There is a 2” air gap there. I have a quantity of 2’x8’ scrap pieces left over from the build, enough to create almost two more layers of 5/8” drywall between the room and the BR wall. But that would reduce the air gap to less than an inch and the drywall pieces would be loose, not screwed or glued. So I’m wondering if that will actually get me anything.

After that, there is the concrete slab floor. From what I’ve read, a slab is good at blocking impact noise, of which I have very little, and is vulnerable to airborne noise, of which I have a lot. I see there are good solutions for both, but are expensive to do something that actually works.

The last resort option is to move the entire structure further away from the BR wall. I have about another foot to work with. This is actually possible because the plate is not bolted to the slab. I did this once during the build by raising a corner with a wrecking bar enough to get a 1” piece of pipe under the plate. Repeat at the other three corners and the entire room can be rolled to a new position. But I’m afraid of damaging the structure and the electrical would be disturbed. It’s a scary option.

The bleed seems to be coming through the wall and not so much through the floor.

Thank you for any input you might offer.
Mike
 
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rob aylestone

Well-known member
If you have the sheets, a temporary fix would let you assess any difference. If your tones are playing via a speaker that's a bit bass light, have you got a bass guitar amp/cab. They go low - much lower. My guess is the spill through to the bedroom will be obvious once you find a big oomphy speaker. With the pink noise, you can use an app on your phone to help locate the leak. The low end bleed - if you are hearing it, but your speakers aren't that brilliant at reproducing it, where is it being generated?
 

Ekimtoor1

Member
If you have the sheets, a temporary fix would let you assess any difference. If your tones are playing via a speaker that's a bit bass light, have you got a bass guitar amp/cab. They go low - much lower. My guess is the spill through to the bedroom will be obvious once you find a big oomphy speaker. With the pink noise, you can use an app on your phone to help locate the leak. The low end bleed - if you are hearing it, but your speakers aren't that brilliant at reproducing it, where is it being generated?
Actually the speakers produce enormous low end for their size. And I’m not after solving that kind of low end, just unamplified drum strikes. But I am testing with that sort of low end thinking if I can solve some of that, then the drums will also be more blocked.

As for the sheets, the thing I’m afraid of is making things worse. While I could get them out, getting them in will be physically extreme, maybe even injuring myself. Getting them back out will be near impossible. What are your thoughts on the consequence of reducing the air gap?

I’m pretty certain the bleed is coming through the wall. Very little doubt of that.
 

rob aylestone

Well-known member
I'm sceptical that reducing or increasing free space transmission through the air does very much, compared to sheet material. I think you just need to find out where the sound is getting through - should be doable.
 

Ekimtoor1

Member
I’ve started doing some real world tests on my space. The results are not unacceptable, but not nearly close to my vision.

I set up my kick-snare and got a base line by striking the kick-snare medium hard and used its max of 104db as my reference point.

I then set up mics and recorded some strikes. I adjusted my mixer and speakers to reproduce the strikes at 106db.

I have a 3” hole in the wall facing the garage door which will eventually be filled with a line set for a mini split AC. I was curious how much leak the hole would create.

So I split the test into hole open and hole patched. The patch is filling the hole with rockwool and taping two layers of 1/8” mass loaded vinyl over that on both sides. Both tests were done with the recorded strikes maxing at 106db. Here are the results:

Hole in the wall test

Inside kick-snare, medium hard
Max 104

Recording of same inside
Max 106

6’ from the hole inside the garage
Max 71

Inside BR 6’ from wall
Max 54

Outside garage door 6’ away
Very faintly audible

Outside block wall 6’ away
Very faintly audible

Hole patched test

6’ from the hole inside the garage
Max 73

Inside BR 6’ from wall
Max 54

Either the hole made no difference or this thing I made is simply a poor build. I was hoping to see improvement after patching the hole, but I may as well have not even bothered.
 

mjbphotos

What?!?
Was your speaker directly facing the hole? A 2dB difference is probably within the error tolerance of your meter. Move around with the meter, the level may be greater in other positions, and you may have a partial null where you were standing.
 

rob aylestone

Well-known member
There is some physics around the wavelength - remember that microwave energy is very harmful to health and 800W of it in your kitchen is quite capable of heating your eyeball content making you blind, maybe even dead. However - it doesn't and weirder on the surface, is you can see into your oven when cooking. 800W of microwave energy inside and a bit of perforated metal in the door letting the light out, but not the microwaves. It's because the holes you can clearly see are still a barrier to the microwaves which are longer wavelength than light. Your hole is the same as the microwave - but scaled up. The wavelength of the bass cannot escape through a small hole, like the microwave energy, but of course higher frequencies can escape. Clearly sound travels differently, speed wise than microwave energy, but your kick might have a wavelength 8m long which would have to be aligned quite well to let the sound out.
 

Ekimtoor1

Member
Was your speaker directly facing the hole? A 2dB difference is probably within the error tolerance of your meter. Move around with the meter, the level may be greater in other positions, and you may have a partial null where you were standing.
There is some physics around the wavelength - remember that microwave energy is very harmful to health and 800W of it in your kitchen is quite capable of heating your eyeball content making you blind, maybe even dead. However - it doesn't and weirder on the surface, is you can see into your oven when cooking. 800W of microwave energy inside and a bit of perforated metal in the door letting the light out, but not the microwaves. It's because the holes you can clearly see are still a barrier to the microwaves which are longer wavelength than light. Your hole is the same as the microwave - but scaled up. The wavelength of the bass cannot escape through a small hole, like the microwave energy, but of course higher frequencies can escape. Clearly sound travels differently, speed wise than microwave energy, but your kick might have a wavelength 8m long which would have to be aligned quite well to let the sound out.
That makes a lot of sense, especially the microwave analogy. This would account for no significant difference with or without a hole. An acoustic Faraday Cage?

I suppose I could further test by cutting holes of various sizes all over the structure to see more broadly what the effect is.

Nah, I don’t think I’ll do that.
 

Ekimtoor1

Member
Was your speaker directly facing the hole? A 2dB difference is probably within the error tolerance of your meter. Move around with the meter, the level may be greater in other positions, and you may have a partial null where you were standing.
The speakers are 90 degrees to the hole. I think you may be right about the null but I’m probably going to move on to the next thing. I can always come back to it.
 

Ekimtoor1

Member
Still chasing improvements.

If I were to hang a curtain of two pound mass loaded vinyl on a wall facing a bedroom where sound is getting through, would it work? What would be better, inside or out?

Thanks
Mike
 

mjbphotos

What?!?
The 'mass' absorbs some of the sound energy, so it will dampen the soundwaves that were directly impacting the wall. Whether this makes a noticeable difference in sound transmission .....
 

Ekimtoor1

Member
The 'mass' absorbs some of the sound energy, so it will dampen the soundwaves that were directly impacting the wall. Whether this makes a noticeable difference in sound transmission .....
Right. So much of this is a crap shoot as to whether I actually get any improvement. Kinda frustrating. But thank you very much for the input.

Mike
 
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