Comb filter effect is the effect that is created for example when two exact same sound signals are added and one of them is just a bitÂ delayed. Signal a and b. Signal b hits the down-phase of signal a:s waveform with an equal “up-phase” and “turns off” frequencies which creates this effect. This effect is mostly auidible in higher frequencies.
For example, when you listen to a mono-recording through stereo speakers, this effect will emerge as soon as you are moving from side to side and not sitting right in the middle of the two speakers! Another example of comb filter effect can emerge from loudspeakers. Loudspeakers have eq filters between the different speakers (In different frequency-bands) within the same “box” Top-speaker, (sometimes) mid-speaker and low-speaker. At these points where the eq filters is located there are two signals generated and there is a possibility of this effect.
“The principle of superposition states that every infinitesimal (hur oÃ¤ndligt litet det Ã¤n Ã¤r) volume of a medium is capable of transmitting many discrete disturbances in many different directions, all simultaneously and with no detrimental (skadlig) effect on other disturbances.///At a given point in space, assume an air particle responds to a passing disturbance with amplitude A and 0Â° direction. At the same instantÂ another disturbance requires the same amplitude A, but with a 180Â° direction. This air particle satisfies both disturbances at that instant by not moving at all.”
-Source Master handbook of acoustic 5th ed.
And since air is the bearer of sound, this explains how comb filter effect emerges. Comb filter effects is causing the air particles to stop moving in various frequencies causing these measurable dips, so called “combs” to the frequency spectrum.