The Combfilter Effect

In addition to sound that comes directly from the source, a microphone captures sound that is reflected by surrounded surfaces as well. Direct sound and reflected sound are interferring. As the reflected sound had a longer travel, it is not in phase with the direct sound. This leads to cancellations of several frequencies/frequencie ranges and therefore a noticeable coloration of the sound: the comb filter effect. To reduce this effect it is advisable to either keep the travel of the reflected sound as close to the travel of the direct sound or let it attenuate as much as possible. Attenuation can be achieved by a very long travel, by absorbing, by choosing a microphone pattern that attenuates sound that arrives at the angle of the reflected sound.

Height of sound source m

Height of microphone m

Vertical angle of microphone °
Microphone pattern

Ground distance betw. sound source and mic. m

Absorption of the ground

fully effective at/above frequency Hz

absorbing factor (1=fully absorbing)

Frequency response, that results of interference between direct signal and first reflection. The flatter the curve the better. (The spectrum is normalized, so it is independent from the distance to the sound source.)

Audio simulation with brown and white noise

Currently this audio simulation does not consider absorption and the frequency dependence of polar patterns. This is especially an issue for omnis.
The volume is normalized, meaning, that attenuaten by greater distances and direct sound arriving at non-centre angles are balanced.

play original sound

Brown noise:

White noise:

Height of sound source	m
Height of microphone	m
Vertical angle of microphone	°
Microphone pattern
Ground distance betw. sound source and mic.	m
Absorption of the ground
fully effective at/above frequency	Hz
absorbing factor (1=fully absorbing)