Our Objective and First Steps: Our main goal was to find a way to make sound travel through solids without a muffled sound. There were two angles we went at to find results; hardware speaker design and software equalization. Besides being able to seal to the wall, the speaker design proved to be less important than sound modification with software. After using Autodesk Inventor to design a speaker that would effectively seal in sound, we began to play around with Adobe Audition and Avid Pro Tools to find audio settings.
Hardware Design: We quickly learned that we needed to make the audio "cut" through the surface. Our test surface was a baseboard with a thickness of 15mm. When experimenting with speaker cone designs, we found that a narrower and sharper bass cone helped to make the high sound cut through the surface. This let the bass come through, but not overpower frequencies above 300 hz (mid to treble) and level off distortion. To offset the vibration, which contributes to distortion, we decided to mount the hardware of the ring surrounding the speaker on a set of springs separate from the speaker. At this point, we used a curvature comb analysis to check how and where sound would move off of the speaker.
Software Design: We realized that the design of the speaker, while important, was not going to do the job alone. We needed a strong, custom audio processor that would create sound powerful enough to go through solids. The <20hz range had to be lowered drastically, as those sounds are not heard in the human ear, but felt through vibration. from 20-300hz, we lowered the levels and added some compression to save quality. From 300hz on, we had to compress and add a hi-pass amplifier and de-muffler to get the sound we needed. Despite the massive amount of compression and filtering, the audio coming through the baseboard we tested on was coming through a lot cleaner and less muffled than our baseline test.
Conclusions: While we were unable to get the audio to sound identical to uncovered audio, we did improve upon the issue greatly. We tested the prototype module with the audio software against similarly sized speakers, and found that our design worked far better for the purpose than anything on the market. After some revised designs, including the more durable isolation housing seen in the picture, we began work on a product that would use the hardware and software developments we had found. This product can be found here, or by clicking the picture below.