Small dialog booth wall/treatment

[post78]

I’ve been asked by a good friend to help design a very small booth for dialog. Not for VO, but for clear Skype/Zoom/phone calls. Unfortunately I can’t be more specific at this time due to NDAs.
The room requirements are to be roughly 4’x7’ with a ceiling of around 8’. The initial concept was circular and I explained that they would have too many acoustical problems to overcome in a room like that, so I’ve got them on the right page with using a rectangular design and avoiding parallel walls. So far so good!

In order to keep the space sounding more neutral and less “boxy”, I am planning on incorporating slats over rigid insulation panels. I’ve done this in the past for a medium/small room and it worked out very nicely. We also have the ability to prototype this, so the experiment is worth it to me. The problem is the overall wall thickness. They want the walls to be a thin as possible (again I apologize but due to the NDA I can’t explain the reasons for this, but I understand the requirement). They would also like to have the booth be not necessarily sound proof (which is good since that isn’t technically possible anyway), but isolated enough to keep the calls private. The booth will be within an office that is already isolated from the outside world, but there might be other people in the office and they would like the calls to remain largely unheard.

Typically, i’d build a double-leaf wall filled with rock wool or fiberglass, and potentially green glue two layers of drywall on either the outside or inside wall. Then I would build my treatment on top of that. Due to the thickness requirements, I believe I *might* be stuck incorporating the treatment into the wall itself. Basically a frame with a layer of drywall (or something better) on the outside, insulation filling the cavities of the frame, and covering in slats for the side walls. (The ceiling and rear wall will likely start with simple absorption and can be slatted if necessary.)

The question:
Am I out of my damn mind?
Real question: Am I giving up far too much potential transmission loss by losing the layer of drywall? Keeping in mind that we don’t need to keep out traffic or keep in music. We just want to keep the conversation personal and private.
Also, the only builds I have done this far have been using drywall. It’s cheap. Easy to find. Easy to work with. However my client (again a friend) seems to have more of a budget for this one, so is there a material I should be looking at aside from drywall?

Thanks! Been awhile since I’ve posted here. Always a good resource!

[post78]

I forgot to add that I’ve sent them a CAD drawing of the room design and was given the go ahead. So we aren’t starting from scratch. They seem eager and happy about the potential.

[post78]

And just for additional clarification: the sound quality inside the booth is more important than the isolation. They want it as isolated as possible, but I’ve explained that without thickness, that will be difficult. They understand.

[DanDan]

Is there any real need for Isolation? Twice recently I have designed 'Caves' or Tent's of simply framed absorption.

[post78]

Is there any real need for Isolation? Twice recently I have designed 'Caves' or Tent's of simply framed absorption.

They would say “yes”. But I’m really trying to contain their expectations. If I can get the STI down to 0, i’d be happy even if there were audible “mumbles”. It’s more about privacy of conversation than anything else, although limiting interruptions as much as possible would be great. I’ve checked out some of the newer acoustical drywall on the market, but I don’t know how effective that would really be for a single leaf system.

[post78]

My hope is that the addition of fairly tight slats will help contain the mid frequencies enough to keep the transmission index down. Realizing of course that lower frequencies will probably not “see” the slats at all.
Compromising is always fun...

[post78]

Okay good news. They are now planning two versions. One will be thin and the other does not have any wall size limitations. They finally understand that the thinner walls will severely limit our ability to isolate the conversation and are okay with it.

Whew...

[post78]

Still interested in modern ideas for wall material. The acoustic drywall seems like a good single-layer option (instead of two layers with green glue). But maybe there’s something better out there these days?