This article is provided by Bartlett Microphones.

 
Some time ago I decided I wanted to find out how the location of a microphone near a banjo affects the tone quality you hear.

To make these tests scientific as well as subjective, I measured the spectrum of the banjo in several different mic locations.

The spectrum of a musical instrument is its output vs. frequency.

It affects the tonal balance or timbre. It is the relative levels of the fundamental frequencies and harmonics, and can be measured with a real-time analyzer.

As an experiment, I measured the spectrum of a Chuck Lee open-back banjo in several different mic locations to find out what the differences were.

I also compared the sound by recording the mic signals and listening to the playbacks at equal listening volumes.

For example, this screen capture shows the frequency spectrum of a banjo picked up at 1 foot (green) and at 3 inches (yellow).

The 3-inch placement sounds bassy (more low frequencies than the reference) and dark (less high frequencies than the reference)

I placed a flat-response omni measurement mic 1 foot from the center of the banjo head as a reference. Compared to the reference, the spectra of other mic positions exhibited the following differences:

Green curve: Spectrum measured 1 foot from the center of the banjo. Yellow curve: Spectrum measured 3 inches from the the center of the banjo.

Six inches from the center
Warmer or thumpier than the reference. +8 dB from 100-180 Hz.

Comments: The closer the mic is to the banjo head, the more warmth or bass you get. That’s not due to microphone proximity effect in this case, because I used only an omnidirectional mic, which does not have proximity effect.

Instead, the banjo’s bass is weak at a distance because the low frequencies from the front of the head are partially out of phase with the low frequencies from the back of the head, so they partly cancel out at a distance.

The same thing also happens with an open-back guitar cabinet.

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