By Georg Rumpf
Playing bass for a good number of years I developed a taste for having a nice sound system in my car. So a while back, I got into making sub-woofer speakers for my cars. It all started with a custom job for my car. I got married and made one for my wife. Being my second attempt, hers turned out better than mine, so naturally, I was on a mission to one up the one I made for her.
It happened that one day I ran across Daniel Wilkins. He invited me down to a maker space in Kalamazoo called Kzoo Makers that he was helping to get off the ground. The Kzoo Makers is a shop loaded with machinery and devices for people to come in and make whatever they want.. With the access I had to cool tech and manufacturing equipment, it became clear I could improve my previous designs.
Let’s start with some background and fun theory. The technical reason for having a speaker box is to eliminate the sound waves coming off the back of the speaker. The sound waves coming out of the rear of the speaker is out of phase 180 degrees ( inverted ) to the waves coming out of the front. As the speaker cone travels in and out, it pushes air in front but also draws air from the rear and vice versa, creating sound on both sides. When these sound waves meet, they cancel each other out or distort each other resulting in sound loss or change. So the enclosure separating the rear from the front seeks to eliminate this.
I started with the shape. As shown in the next picture, a sphere is a great shape for a speaker enclosure.
Access to 3D printers at Kzoo Makers made manufacturing the spherical enclosure an easy possibility for me.. The spherical enclosure I designed included bracing to fit it inside a square enclosure. This allowed me to add another layer of sound absorption to this sub-woofer, which I will detail further.
Being a sub-woofer, this speaker will generally be low frequencies. Low frequencies pass through materials fairly easy and make it more difficult to isolate the sound waves coming from the rear. We have all probably walked by that house pumping music and probably noticed what you heard was mostly bass. Oddly, human flesh makes a very good sound absorber for low frequencies. Since I couldn’t use actual flesh, I decided to simulate this with gel. The space in-between the inner sphere and outer box gave me a good place to put it.
Finally, ready to mount the front face, run the wire for the speaker, install the speaker, and mount the amplifier!
Let me just give my highly subjective opinion and state that this little sub has some serious kick. Now If I get some calls from Bose for patent infringement, I’ll know I did something right.