Colorations caused by acoustical anomalies of studios , monitoring rooms, listening rooms, and other small rooms are particularly devasting to speech quality . Gilford states that axial modes spaced approximately 20 Hz. or more, or a pair of modes coincident or very close , are frequent sources of colorations. He also states that colorations are likely to be audible when an axial mode coincides with a fundamental or first format of at least one vowel sound of speech, and are in the region of high-speech energy . Speech colorations below 80 Hz. are rare because there is so little energy in speech in that part of the spectrum. There are essentially no speech colorations above 300Hz.
Modal colorations are more noticeable in speech than in music.
The bandwidth of room modes , measured at the -3db points, increases as reverberation time is shortened. Modes in ordinary studios have bandwidths on the order of 5Hz. In order to control these unwanted resonances that occur in our listening room environment, diaphragmatic absorption must be used. Diaphragmatic absorbers provide the maximum amount of absorption in the smallest amount of space. A non-perforated panel of mdf with a calculated air space between each panel,will respond to sound energy hitting it by vibration.