# Sound Proofing With An Acoustic Panel

I recently took a crack at improving the sound proofing between the main floor of my house and the basement using acoustic treatments. As evidenced by a quick Google search, about a million people have done this before. The idea is simple: construct a rigid wooden frame to house some type of absorptive material (such as stone wool insulation), and cover that in a porous fabric (such as burlap) to hold it all in. The effectiveness of such a contraption (we’ll call it the panel) is frequency dependent – thicker panels are needed to block lower frequencies, which have longer wavelengths and can penetrate through and around objects more easily than high frequencies.

### The Build

It seemed as though the majority of sound leakage was happening via our stairwell and basement door, so this is where I concentrated my effort. I used 1” x 6” pine boards to construct the frame, Rockwool Safe’n’Sound insulation, and burlap fabric. The material cost was about $120 CAD here in Newfoundland (fun fact: the Rockwool I bought is about$30 cheaper in Ontario than it is here owing to freight costs). A pretty minimal set of tools is needed for the build: a mitre saw to cut the frame pieces and supports, a cordless drill to fasten them together, and a stapler to attach the burlap. I borrowed most of my tools from the St. John’s Tool Library.

I fastened the edges of the frame using wood screws and L-shaped brackets. I added some extra angle supports to each corner for additional strength. I used two layers of Rockwool battens in order to fill the 6” deep frame. Here’s a picture of the panel mid-construction:

And here’s a picture of the finished panel fitted in front of the basement door:

### The Measurements

I decided to evaluate the effectiveness of the panel by measuring the frequency response between the upstairs of my house and the basement both with and without the panel in place. I decided to use Farina’s log sine-sweep method1, which is particularly affective at rejecting loudspeaker distortion introduced during the measurement phase. Given that I needed to drive my loudspeakers quite hard to ensure adequate sound propagation through to the basement, I expected distortion would be an inevitable by-product in my measurements.

After making recordings of the sine-sweep both with and without the panel in place, I deconvolved the measurements using the inverse sine-sweep, and removed the distortion by-products which appear at the start of the response (see Farina’s paper for more on this). I performed the deconvolution using fast partitioned convolution (you can read more about convolution in a previous blog post). Below is a plot of the 13 octave smoothed frequency response I computed from these measurements:

As can be read off the graph, the panel is effective at frequencies of 200 Hz and higher (note the x-axis is on a log frequency scale). At the peak frequency (approximately 1000 Hz), there is a 16dB reduction in the acoustic energy transfered between floors. That seems pretty good to me. I also made a few informal tests, for example, I recorded myself singing and playing guitar. Without the panel in place the sound transfer was clear enough that I could make out what lyrics were being sung; with the panel in place, my playing was just barely audible. Overall, I’m quite happy with the performance of the panel, and would consider building more (e.g., for acoustically treating a studio space).

1. Farina, A. (2000). Simultaneous measurement of impulse response and distortion with a swept-sine technique. In Audio Engineering Society Convention 108. Audio Engineering Society. [return]