EIGENTON or EIGENTONE
(Ger.: eigen = belonging to; ton = tone) The fundamental RESONANCE mode of a room or enclosure. Parallel surfaces in a room reinforce, by REFLECTION, the waves of sound having a WAVELENGTH equal to twice that of the dimensions of the room. Also called the natural frequency of free vibration (see OSCILLATION), and the FREQUENCY of STANDING WAVES.
There are at least three modes of resonance in a room, which are not necessarily HARMONICally related (i.e. simple multiples of each other) since each dimension may be of different size. Bathrooms, for instance, have bare, highly reflective surfaces, and dimensions roughly equal to that of half wavelengths of frequencies in the human voice range. These frequencies will therefore be reinforced or amplified, but for a given room only certain frequencies will be affected in this way, depending on the particular wavelengths which fit it best. The room, then, is a natural AMPLIFIER of these frequencies. For large rooms, REVERBERATION is more important than these resonances.
Compare: HELMHOLTZ RESONATOR, SYMPATHETIC VIBRATION.