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. This vibration results in a flexing of the fibers where frictional loss results in absorption of this energy. The mass of the panel and the springiness of the air forms a resonant system. The peak of this absorption occurs at the resonance frequency. If this curve is inverted , a transmission curve results.