I'm setting up a converted garage to record voice. The room dimensions are 22'9" x 23'2", with an eight-foot ceiling.
I live near an industrial property that produces noise. In particular, there is the sound of a piece of industrial machinery at around 240Hz, and the back-up warning beeping of construction vehicles.
To block outside noise, I made some window and door plugs out of 3/4" MDF. The door plugs have EPDM rubber seals to seal them against the french door surfaces. The window plugs have felt around their perimeters which is compressed into the gaps when in place. In one window, I have an air conditioner which was admitting quite a bit of sound so I built a box out of MDF to put over that, under the full-window panel.
To control reflections I put (a lot - 224sf) of OC703 on the walls and onto the plugs when in place, and an additional 4'x4' panel over the desk where I record.
I attached a photo that shows these modifications.
I made a recording of the room tone while the industrial machinery is in operation. The microphone (Rode NT1A) recording level was set to the most sensitive setting which I'm likely to use (for quiet voice).
I attached an image of the spectrum analysis of this file, indicating the spikes of known origin - the industrial machinery and the back-up warning tones from construction vehicles. I believe I have these sources of noise under control.
What I'm curious about is the low-end, which seems focused around 60Hz. Could this be related to line current somehow? Or perhaps resonance within the room (dimensions already given)?
Your room dimensions on the length and width are not ideal, since they are nearly identical. A quick check of the room mode calc here shows strong support around 60hz. So it could be the room modes.
Is there any bass trapping?
It could be line noise too from the Air conditioner, or a ground loop.
I suggest you download REW free room testing software and test the room. This will help identify room resonances.
Like K said, not ideal, but you can make it better. You need to put absorption treatment that can affect lower frequencies. Drapes will only reduce high frequency reflections, flutter echo maybe...
When starting, you should avoid Foam because 1 or 2 inch foams only affect higher frequencies and will throw off the frequency balance of your room even further..
I'b be thinking of building myself some panels made of 4'' thick rockwook and place them near the corners first and measure again. . .
How your external walls are made will influence the result greatly, low frequencies from outside do not only come from the windows, I'm sure...
No bass trapping at all yet. My room is not entirely rectangular - there is a small L-shaped "nook" with partial-height walls that forms a shelving/storage area (image attached - the chair/desk show where record, either with overhead boom shotgun mic or the Rode NT1A on the desk).
The AC is always turned off when I record.
Glad to see there is a Linux version of REW, I will check it out.
I read an article on bass traps that suggests ideal placement of porous bass traps for 60Hz is four feet (!) from the corners...