Why do my microphones sound hollow?

A common complaint about AV systems used in teleconferencing, presentations, and performance is that the “microphones sound hollow.”

“You sound like you are in a cave” is heard frequently on conference calls.

So, how can we get you out of the cave and right next to the person you want to talk to, sing to, or yell at?

First off, you don’t have to buy anything. You already did that. We just need to make some simple adjustments to your stuff that most anyone can do.

Most of the time, this hollow sound is coming from using TOO MANY microphones. That is right! Less is more when it comes to picking up sound. If more that one microphone is picking up the sound, the sound waves are likely at different stages of their cycle when they get to different microphones.. The waves are traveling different distances to get to each mic. When one mic pics up the sound, the wave might be at the top of it’s crest. The other mic might pick it up at the bottom. Then all that stuff gets mixed up together and makes a big hot mess…hollow sounding mess.

So we would one mic to pick up one sound. If I need more than one mic because my room is big and we can’t hear people on the ends, all you have to do is remember a couple of rules. The 3 to 1 rule is handy. Make sure the second mic is 3 times as far away from the speaker person as the first mic. The waves will dissipate enough over that distance as to not cause the hollow sound if the second mic pics them up.

Another way to fix it is to have the mics turn off when there is not loud sound present. WE call that a noise-gate. It is in almost every audio wing-dinger you have now. Just set it so that the mic is off unless someone is close to it and making noise.

The last reason for hollow sound, and the hardest to fix, is acoustical stuff. If the sound of your voice goes straight to your mic, but part of it heads over to the window, bounces off and then heads over to the mic, the waves get all mixed up and make a crummy hollow sound. WE can’t make the windows go away, or the floor. It will be there no matter what, but any other surface in the room, we try to make uneven. We want paintings, tapestries, Chuck-E-CHeeze animated animal heads, whatever we can to make the flat walls NOT FLAT. This will help redirect the sound bouncing off AWAY from the microphones, kind of like a break-water made out of concrete chunks protecting the little boats. Acoustics is fancy science with fancy scientists. If you don’t have access to fancy scientist, but you have access to velvet-Elvis posters, that will do.

Just remember to try to talk into one mic at a time. Less is more.

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John Hood – Principal – With 20 years experience as a manufacturers representative, John Hood serves the consultant and engineering community for The Farm. John enjoys bike riding, fly fishing, and scrap booking.