John Sayers' Recording Studio Design Forum

I am in the design and planning stages of a small basement recording studio. I have been working with Rod Gervais' book, "Home Recording Studio: Build it Like the Pros", and reading through these forums for a while. I still have some questions.

Purpose:
The recording studio is to be used for speech/spoken word, and interviews. It will not be used to record bands. There is not a need to try and reduce noise that neighbors hear. The main design objective is to eliminate ambient sounds in the recordings (HVAC, spouce walking around, etc.), and to achieve the lowest noise floor possible with a reasonable amount of construction and expense.

Environment:
The studio will be in the basement of a residential home located on 1 acre of land. The studio will be located below a formal living room and formal dining room that are not used much. A kitchen and laundry room are on the floor above the recording studio. Home offices are located up on the second/top floor, so most day-to-day activity and movement will be separated from the studio by one level. The house is located on a dead-end street and has little traffic. A four lane road is located about a quarter mile away and semi-trucks (18 wheelers) travel on this road. A small racetrack and drag strip are about two miles away and are active in the spring, summer, and fall two days a week. A small county airport is about 5 miles away.

Overall it is a quiet environment, but I don't have ambient dB readings yet for the basement environment.

House construction:
The house is a typical single family multi-story stick built home with a concrete block basement. The blocks are 12 inch blocks. The front wall of the house is eight feet below grade. The side of the house where the studio will be located starts at eight feet below grade and tapers off to grade with a walkout sliding basement door in the rear at grade. The non studio side of the basement is below grade, but this side of the basement houses the HVAC system, well pump switch and pressure tank, water treatment systems, and sump pump.

There are two windows in the basement, one in the area where the control room will be located, and one in the office area.

The concrete slab floor is four inches thick with wire grid running through it.

Floor joists for the level above the basement are standard 2x10 joists topped with 3/4" sub-floor and 3/4" hardwood over that.

Known Problems:
There is a steel I-beam that runs the full width (left to right) of the basement. There are no support posts in the area where the studio will be located.

There is also the PVC waste drain pipe that runs a few feet from the I-beam. The waste pipe then curves and runs along the inside wall where the vocal booth will be, and exits the house through the side wall (below grade) about four feet from the front right corner of the house. On the inside, at the point where the waste pipe exits the house there is a clean out port for the waste line and one for the sump pump line. These two clean out ports cannot be permanently covered over.

There is also a refrigerant line for the heat pump that runs between the I-beam and waste line.

The HVAC unit in the basement is separated from the recording area by one interior wall with an open doorway.

Basement dimensions:
The basement dimensions are: 42 ft wide, 25 ft deep, and 8 feet tall (to bottom of floor joists above).

Studio dimensions:
I am looking to build a vocal booth in a space that is roughly 8 ft wide, 10 ft long, and 8 ft tall. I am considering single leaf construction because the recording area is relatively quiet, and what is being recorded is relatively quiet. A double wall system begins to reduce the interior space of the vocal booth.

The control room/editing room will be about 13 ft x 14 ft, will be 8 ft tall, and will contain one window and a sliding patio door.

Below is a picture of the rough layout in mind:



Question about design and building:

In order to provide access the clean out ports where the vocal booth is located, I am considering adding a second door in that location that is well sealed. While this is not ideal, it allows for more space inside the vocal booth. If I were to separate these clean outs from the vocal booth, in order to provide access I would need to build the vocal booth two feet off the front and side walls, and that begins to reduce the interior space of the booth quite a bit.

Because I am considering a second sealed door in the booth, I am also considering using single leaf construction for the vocal booth using three layers of drywall (instead of two layers) on each side of the studs, with two layers of green glue. Would moving from two to three layers or drywall make much difference with single leaf construction?

The basement will be a finished basement. In the picture above I included two diagonal lines that point to areas where a the exterior of the vocal booth wall will meet two regular finished walls. Is there a need to decouple the exterior of the vocal booth wall from the finished walls, and if so, how do you do this so that there is not a gap? I was looking at the WIC clips from Mason Industries as one solution here, but I am not sure how to cover the gap without coupling the walls back together.

The finished room needs to look nice without any gaps where concrete block would be visible.

Thank you for your time.

Hi "Birds", and welcome to the forum! Great first post, by the way!

Do you have a particular level in mind? There's a "standard" way of defining and measuring how quite a studio should be, described by NC curves. Take a look at those and find the one that you think you'll need, then set that as your goal. That will help define the amount of isolation you need, how to deal with HVAC noise, etc.

How noisy is the HVAC system, the water in that PVC pipe, and the noise of your souse walking around? You should measure those with a sound level meter, in order to have objective numbers to work with. Also check other typical problematic things, such as phones ringing, TV, radio, vacuum cleaner, doors opening and closing, toilet flushing, wind, rain, thunder, etc.

You don't have much choice here: it is automatically a two-leaf system: the outer leaf is the basement wall, and the inner leaf is what you are going to build to create the vocal booth. The only way for you to have single-leaf construction, is to not build anything at all, since it is already single-leaf!

It's really hard to read that tiny text: maybe you could post a link to a larger version?

That's not a single-leaf! That's a two-leaf wall, where the leaves are coupled. It would be single leaf if you had drywall on only one side of the studs.

If it really is single leaf (in other words, two layers on drywall on only one side of the studs, vs. three layers on drywall on only one side of the studs), then the answer is no, it makes practically no difference at all: Maybe 2 dB or so. You wouldn't even notice the difference at all. The reason is that single-leaf walls are governed by mass law, which states that you get an increase of 6 dB each time you double the mass.

But if you are talking about adding an extra layer to each side of a two-leaf MSM system, then the answer is yes, it does make a worthwhile difference. Depending on various factors, it could be around 10 dB more isolation, which would make things sound about half as loud, subjectively.

No part of the booth can touch any part of the basement: it must be totally separate. Not even a single nail can bridge the gap between the basement and the booth. In other words, imagine that you are building a box in there, that just sits on the floor and does not touch anything.

There has to be a gap. If you want isolation, then the booth must be decoupled from the basement, so there MUST be a gap there, and it must be sized correctly to give the wall the amount of isolation that you need, at the frequencies that you need it.

One thing you can do is to wrap a piece of 703 in acoustically transparent cloth, and use that to fill the gap.

Another possibility is to build it with a two-leaf system, where the outer leaf of the booth will be the wall that is visible from the rest of the basement, and can therefore be connected to the other basement walls and ceiling, while the inner-leaf of the booth itself would be hidden behind that, and would not touch anything.

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Stuart,

Thank you very much for your detailed reply. I also appreciate you correcting me on single leaf vs double leaf. I now understand that a leaf refers to the layers of drywall on a single side of the studs, and does not refer to the drywall on both sides.

You also answered one of the big questions I had about walls - that on a two leaf MSM setup with an air gap between leafs, the exterior wall can be coupled to other existing walls and ceilings in the building and in doing so eliminating gaps, while the interior leaf is decoupled by the air space. I have more questions about this but I will wait until later when I have numbers to share and talk about.

I will pick up a sound level meter and look at the NC curves so that I can develop that target amount of isolation that is needed. When I get those numbers should I follow up on this thread, or start a new one?

Question about meter measurements and NC curves:

I am guessing that the way to approach establishing a baseline for how much isolation is needed in the space is to do the following:

- take ambient sound level measurements of the space with a meter at various times to be sure to capture a range of levels and frequencies "heard" in the space (silence, HVAC noise, lawn mowers, house noises such as toilets, phones, etc.)
- use the NC charts to figure what dB level is needed at certain frequencies for the desired NR rating (example: an NR 30 would require a maximum of 40 dB at 250 Hz)
- subtract the NR dB level at the frequencies from the maximum dB measurement recorded in the space at those frequencies, this would establish how many dB the construction needs to attenuate at those frequencies.

Is that the correct process?

Thank you very much for your time,
Chris

It's probably better to keep all your posts about your studio together in one single thread, otherwise you start to lose track of what you asked where, very quickly.

That's pretty much it, yes. Of course, the curves are idealized, so the real curve for your actual studio probably wont match very well, but as long as you are mostly under the ideal curve, you should be OK. The idea is to get all your readings at all frequencies under the curve you decide on, but that might not actually happen in real life.

Exactly. Try to think about this as one single isolated room, or a set of isolated rooms if you are going to vocal booth, control room, live room, drum room, for example, that is/are located inside the set of "everything else". Each room has only one single leaf around it, which is the inner leaf with respect to that room, and the "everything else" is the outer leaf. so between any two adjacent rooms there are two leaves, and between any room and the outside world there are also two leaves.

Here's an easier mental picture: Take a shoe box to represent the outer leaf, and set up several matchboxes inside the shoe box, sitting on the bottom such that no match box touches any other, and no matchbox touches the sides of the shoe box. The matchboxes are your individual rooms. Each matchbox is a complete single-leaf unto itself, but if you were sitting inside one matchbox then you would always find two leaves between you and the interior of any other matchbox, and also two leaves between you and the outside world.

Not sure if that makes sense!

So anything that is not part of an individual inner leaf, can and should be mechanically joined to everything else that is "not part of an individual inner leaf".

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Goal of Project:
After looking at the NR curves, I would like to work to achieve an NR 20 rating. After taking some sound level measurements I think this may be possible. I have some concerns mentioned below, and I am not sure how to build the vocal booth to best achieve the needed isolation given those concerns.

Sound level measurements:
Sound level measurements of the space were taken with a simple Radio Shack meter. The basement has some repairs being done so there is no carpet on the slab, and a lot of the concrete block wall is exposed. There is very little in the room to attenuate sound.

The measurements were taken between 2-3 PM. During the time the measurements were taken the air conditioner was running, the washer and dryer were running, toilets were flushed multiple times, my spouse slammed kitchen cabinets above and walked heavily around the level above, planes were flying into the municipal airport. Not to mention normal levels of traffic and outside activity such as lawnmowers, etc.

The following measurements were recorded using C weighting and Slow response.

Center of basement: 48 dB consistently
Corner of basement where vocal booth will be located: 43-45 dB consistently
Volume of waste pipe when toilet flushed (measured about three inches away from waste pipe at location where vocal booth will be located): 50 dB
HVAC air handler (measured 2 ft. away from unit located in unfinished area on other side of basement): 60 dB
Spouse stomping around on floor above: 50-55 dB

Peak level seen: 66 dB This level was not typical, but it was seen.

Concerns:
I mentioned that I had a concern about a waste pipe being located right next to the vocal booth. Below are two images of that pipe. The block wall was was recently treated with a commercial grade cement based epoxy to seal it against water intrusion. This coating is still drying and curing and that is why the color looks mottled. Sump pump lines are being installed below the concrete slab against the interior wall.





My concern here is that this waste pipe will be running between the two leaves that make up the side wall of the vocal booth. The studs for the vocal booth wall will be 1 foot from this concrete wall. I am concerned that the pipe running between the leaves will compromise the functionality of the two leaf MSM wall. If I were to build a two leaf MSM wall between the interior of the booth and the pipes, then this side of the booth would turn into a 3 leaf wall when the concrete block is taken into account. My understanding is that a 3 leaf wall would lead to problems.

Another issue here is that this is the clean out point for the pipes (mentioned in the first post), and it can not be permanently covered over. I was going to create a small door in the side of the vocal booth wall (well sealed and dense) so that these clean outs could be accessed if there was a need. I know it's not ideal, but if done properly my thought is that it shouldn't be much different than the booth having doors to two rooms, or one large door.

Here is a photo of the location for the vocal booth:



The soffit in the ceiling on the right side of the photo covers an I-beam support, the waste pipe, and the HVAC refrigerant line.

The control room will be on the other side of the soffit.

Floor Plan:
Here is a 2D drawing of the floor plan that includes measurements, but does not include the soffit:

Do the open air gaps in the unfinished area between the block wall and the framing need to be sealed with some type of acoustic insulation to keep sound from entering the cavity and traveling to the finished area?

(click image to enlarge)




Here are two 3D images of the plan (these include the soffit) - click images to enlarge:





Here is the skp file. It is larger than 500 KB so it was zipped. The 4" slab floor has been removed to make it easier to look into the drawing as it is rotated.



Thank you very much for your time and assistance.

Chris