It is a collection of sensory cells that form a crest (hence the name) on top of the hollow tube (the foreleg trachea) behind the hearing membrane (tympanum) on the legs of the insect.
Their cells are attached to the tube in the legs of the insects (the trachea, "trah-key-ah").
Since these organs are sensitive to vibrations (due to changes in pressure.
[3] It turns out the cells closest to midline are the largest and sensitive to the lowest frequency (low frequencies having the largest wavelength), and the cells further out (distal) are smaller and sensitive to higher frequencies (since high frequencies have shorter wavelengths).
This orderly arrangement of sensory cells gives the insect the ability to discriminate frequencies, much like the inner ear of mammals.