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In The Studio: Fixing Small Room Acoustical Problems

Overcoming the challenges of a dedicated studio in a small room
This article is provided by Audio Geek Zine.

 
Recently I moved my home studio from one room to another. From a nearly 200-square-foot living room to a 100-square-foot bedroom.

It’s been a long time since I’ve thought about room acoustics and because this is a common situation for home studios, I thought I’d share my experience.

This article will help you understand and overcome the challenges of a dedicated studio in a small room. It will be most helpful to those with symmetrical rooms (no weird angles) and to those that don’t need all the usual bedroom stuff, at the very least it will be a starting point to making the best of the situation.

The Problems
Small rooms are more likely to have acoustic problems than larger ones, primarily flutter echo, room modes and early reflections that are too short. In my room, I knew there was a very bad flutter echo problem and room modes may be a problem but were predictable.

The room is symmetrical which was an advantage the old room didn’t have. The measurements are approximately 11 feet long x 9 feet wide x 8 feet tall. There is a door and a closet on the back wall and 6-foot x 4-foot window on the front wall.

Flutter echo happens whenever there are parallel reflective surfaces. The sound repeatedly bounces off each wall and creates a series of bright echoes. In this room it was almost like a spring reverb. I was getting it off the side walls, floor and ceiling and from the window and back wall. When this was used as a bedroom the flutter echo was unbearable, I actually had treatment in here just to be able to sleep, but that might just be me being weird. Luckily this is easy to fix.

Room modes, also known as standing waves, are again when sound bounces between parallel surfaces. When the wavelength is a multiple of the room dimension, you will have a standing wave. It’s an acoustic phase problem. This frequency will be amplified twice as loud close to the walls and cancel out completely in the center.

Corner bass trap and broadband absorbers plus foam above.

For example, the wavelength of 60 Hz is 18.83 feet. If the width of a room is exactly 18.83, the exact center of the room will have complete cancellation of 60 Hz. If we multiply the frequency by 2, then there are two dead spots at 120 Hz, and four dead spots at 240 Hz. The dead spots are called nodes.

There are three types of room modes, each with more complex calculations, but the worst kind, and easiest to calculate is the axial mode. Axial modes are calculated: Half speed of sound (1130/2) divided by room dimension (length, width or height in feet).

Calculate all three dimensions and multiply each result by 2x, 3x, 4x until above 300 Hz. Room modes are only a problem in the low frequencies below 300 Hz.

Small rooms tend to have the worst standing wave problems, and not enough room to treat them effectively. Axial modes happen across the entire surface of the wall, and bass tends to accumulate in corners.

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Early reflections are the first bounce off a wall to your ear. So when the sound comes out of your speaker, goes past you, reflects off the wall and back to your ear. There is a certain acceptable time range for early reflections in a mixing position called the Haas zone, 5-30ms. Longer early reflections are OK because our ears and brain can separate them from the original sound, but if they are too short, like in an untreated small room the sound is blurred by the echo. Btw, leather chairs with headrests can also be a problem.

Symmetry
You might think that because there are all these problems with parallel surfaces bouncing sound around that we should avoid rooms with them. Perfectly square rooms are the worst. Two dimensions the same is bad and anything else can be treated. The benefit of parallel surfaces is that we can easily predict what the problems will be and more easily set up a balanced room. A room with one wall that angles out will prevent flutter echo in one dimension, but will make perfect stereo imaging from the speakers much more difficult. You can still get standing wave issues with non-parallel walls, it’s just way harder to predict and measure.

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