I love how noise-cancelling headphones work. Crammed into a narrow airplane seat near the engines, with nowhere to put your elbows and a baby crying one row back, you slip these on and press a button, and everything around you just slips away.
Noise cancelling tech exists all over the place, but this is an application I think a lot of people can relate to. To accomplish the feat, the headphones have a microphone installed, and surrounding noise is recorded and flipped out of phase and then played back through the headphones on top of your music, making the noise invisible to our ears.
Sound travels as a wave, and a wave has a shape. There's the tip and there's a trough, and a gentle wave shape between.
A drum strike will blast a wave into being, with the first movement being upwards to make a tip. Then, the strike wave quickly descends to make a trough — natural sound waves have both. When you mix identical tips and tips, the volume of the sound doubles up. When you mix identical tips and troughs, however, the positive pressure plus the exact same negative pressure equals no pressure, and you hear nothing.
The reason I'm talking about this in the middle of our DIY subwoofer project is that it will form the basis of our understanding about how subwoofers make sound inside a room. Once we understand that, we can fix the problems inherent in the most common of bass applications.
Bass sound waves are long, and they bounce back quickly. In almost every room, the waves of certain notes will bounce back and cancel out the outgoing waves from the subwoofer. And some of the notes will meet with the new waves, aligned tip to tip, and the overall sound will increase or even double.
How this happens, and which notes get affected depends on two things: the distance from the sub to the nearby walls, and the location of the listener. Bass can sound good in one part of the room, and peaky or almost nonexistent in others. With DSP, we can dial in one main listening spot, fix the holes and tame the double-ups, no matter where the sub is placed.
Our current DIY project is based around the Parts-Express Dayton 10-inch DSP subwoofer kit, and its 8-inch cousin. Dayton has created a computer program to control the DSP functions of the subwoofer amplifier, and we'll start to focus on that side of things now. If you've missed the beginning of the project you can always catch up at coloradodaily.com.
Our next step is to choose a location for the subwoofer, and after that we'll measure it.
For sub placement, I always start with it near the main speakers, about a foot closer to me than the speakers, and either between the speakers (closer to one than the other) or just outside of one of the main speakers — doesn't matter which.
If you can't or don't want to place the subwoofer in plain view like that, fear not. Place it as close to that area as you can, and we'll dial in the bass with DSP soon enough. Continued next week.