Converting a walk-in closet to a iso booth

[brianw]

Hello everyone, I’ve been hanging around the forum quietly for a awhile and finally decided to register, this is my first post

Anyways, what I have is roughly a 4' Deep X 6' Wide walk in closet that I want to convert into a iso/vocal booth. I haven’t done anything yet and wanted to get some of the boards opinions on what would yield the best performance etc. The one concern that I have is that the closet shares one common wall with a neighbor (apartment complex), I don’t care to much about sound leaking out into my apartment (the other 3 walls) but I do want to take some care in keeping the peace. I am really only planning on using it for vocals and possibly light guitar amp room (w/ power break). I guess my question is should I blow my load and go all out on that one common wall (as in get it as sound proof as possibly) or if I have the singers facing the opposite wall (interior wall of my place) when they perform and if the room is acoustically dead, how much work to I need to do on that common wall to get relatively decent results (daytime recording)? Or should I do equal work on all the walls?
The neighborhood and my apartment are very quiet during the day so im not extremely concerned about sound leaking in from my 3 walls. my current plan is to do what I think is decent, if the neighbor rags on me, do a better job, and so on. but any tips up front would help :D

Since it is rather small 4'X6', I was thinking of making the room completely dead, is this a decent plan? or would something else suit the room better?

Any suggestions are most appreciated.

Thanks,
Brian

[Kurt Foster]

I think the first thing you should do, provided you are on decent terms with your neighbor is find out if any noise you will be making would be bothersome to them. It would seem that another closet would be on the other side of the wall in question. If this is the case I don't think that any noise you might make would be an issue unless it was ungodly loud.

I guess the best way to eliminat transmission noise from your closet into the neighbors area would be to use some type of sheet block, limp, dense mass vinyl on all the walls and ceiling. You would have to treat all the surfaces, walls and ceilings and be sure that all the seams of the sono matt / sheet block are overlapped and sealed. You could then cover that with treatments of your choice, foam or fiberglass, some bass trapping and diffusion.. Even if you make the booth completly dead, you need some real diffusers in there to help handle the comb filtering effects.. Absorption and bass trapping do nothing to eliminate comb filtering.

Kurt Foster

[brianw]

Thanks for your input, i didn’t think of the diffusers and I will defiantly implement that into the design.

I guess what I'm really getting after is, would it be of any benefit to treat only the common wall initially (trying to stay on a budget) and then as time/money permits treat the other walls? (by treat I mean soundproof, I’m planning on acoustically treating the whole booth immediately.) Or would only treating the one common wall be a complete waste since the sound would vibrate through the adjoining walls? I would rather put money into material that makes a difference on tape (absorption, diffusers, bass traps) rather then unnecessary modifications.

You see I’m new to the complex and just moving in so I really don’t know my neighbor and how he/she will react to living next to a project studio I also don’t want to press my luck. I talked to the manager and they basically said do what you want noise wise and if its a problem we'll let you know, but I do want to be a courteous tenant cause I know what its like to live next to Mr. Subwoofer/Hip Hop fan (previous housemate).

BTW, has anyone else had any experience/tips with apartment studios? I'm moving out of a house (never lived in an apartment) where noise and my studio was never really an issue.

[David French]

Absorption and bass trapping do nothing to eliminate comb filtering.

Kurt, what do you mean by this? This is how I understand it:
Comb filtering can be created when a strong reflection is combined with the direct sound. If the reflection is within 18dB of the direct sound, audible comb filtering will result. The reflection will lose power by the inverse square law when travelling through the air according to the formula dB Loss = 20Log(total path length in meters) + 11. If the remaining dB are made up for by absorption, about 6 more dB in Brian's case, the reflection will be 18 dB down and there will be no audible comb filtering.

As for tips on apartment audio, a couple of things you can do to reduce transmission from your speakers to the other apartments: 1) use speaker spikes. This greatly reduces them ammount of energy transmitted through your stands which in turn goes through the floor into your neighbor's place. 2) use a bass cut on your speakers if you have it. The lows are most likely to penetrate the walls.

[z60611]

I used to be 100% sure that comb filtering was a bad bad thing.
That there was nothing to do about the inter-speaker comb filtering, but first reflection points had to be killed dead.

The below are a bit out of the context of this thread, but spin my thoughts now about Comb Filtering.

from http://www.avsforum.com/avs-vb/showt...ht=comb+filter

Comb filtering

1. What is it?

It's a frequency response aberration caused by adding a signal (e.g. sound from a driver) with a delayed version. Here's the math :

<snip forumulas>

2. What causes comb filtering?

Any signal plus a delayed version : 2 drivers playing the same frequencies, but not the same distance from your ear, or a driver plus a REFLECTION (really indistinguishable from 2 separate drivers ... real plus image).

3. Why is it bad?

Although it is a frequency response aberration, it's very difficult to equalize for at least two reasons :

a. response is very position-sensitive
b. those frequency response nulls are like black holes ... pouring more energy in (boosting EQ gain at the null) won't help.

Dick Pierce wrote:

The ONLY way possible to avoid comb filtering effects is to have a
single loudspeaker placed in an anechoic chamber.

As soon as you introduce multiple sources, whether real or virtual,
you WILL have comb filtering. (A "virtual" source is a reflection
of a real source. For example, place a loudspeaker 2 feet above the
floor: at frequencies where the floor is reflective, which is most
frequencies, there is an apparent or "virtual" source 2 feet BELOW
the floor, giving a doublet source with a separation of 4 feet).

That means that ALL stereo systems, ALL home theater system in ALL
rooms suffer from pretty massive amounts of comb filtering due to
path length differences to multiple coherent sources. It is completely
unavoidable in practice.

That being said, it can be argued that the more real sources you have,
especially sources that are placed different distances apart from room
boundaries and each other, the more evenly distributed the nulls of
the comb filtering will be and thus the smoother the overall response
due to comb filtering will be.

I think it can be argued, that, at its WORST, and additional center
channel speaker will NOT make things worse, and may potentially make
things better.

The arguments of the people you cite might be strictly true in a
first-order analysis but fail or at least loose much of their strength
when the entire boundary and multiple source considerations are taken.
One can further suggest that two competely coherent sources, placed
vertically, restrict radiation in the vertical plane, but not in the
horizontal plane, and thus can arguably REDUCE comb filtering effects
due to interference effects with the virtual sources under the floor
and above the ceiling.

Another point: the demon "comb filtering" itself is something of a red
herring in reality. Comb filtering can only occur if the size of the
radiating sources are very small compared to the wavelength while at
the same time the separation between them is large compared to the
wavelength. For something like the dual center-channel approach,
the ONLY frequencies where this is relevant is high frequencies, and,
within the listening window, the path length differences are simply
not big enough to cause the problem AND where they are big enough,
you're sufficiently far enough off axis that you don't care.

I believe the comb-filter argument against using dual center-channel speakers is specious and unsupportable