Chapter Excerpts

Chapter 15: Sound System Equalization
15.1 System Criteria

Equalization can’t solve loudspeaker coverage problems. Equalization can’t signal align loudspeakers. Equalizers can’t raise acoustic gain unless the system has adequate power available to support the gain increase. Equalizers are of no use in controlling reverberation, discrete echoes, etc.

Careful practice can minimize aggravating these problems via regeneration through the sound system. An equalizer can adjust the direct sound pressure level of the loudspeaker’s minimum phase output frequencies. This is accomplished by providing the conjugate amplitude and phase response to any minimum phase aberrations in the loudspeaker’s direct sound level, LD.

Proper equalization adjusts both amplitude and phase to a more uniform response. A delay in microseconds is introduced by the insertion of the filters.The measurement of both amplitude and relative phase is essential in the process of equalization. Group delay for a phono record can be years. The delay through some adaptive digital filters can be appreciable, +30 ms.

The triumvirate of proper equalization, signal synchronization, and seamless coverage are very powerful tools used to create extraordinary sound quality.

If the system is designed to be capable of benefitting from equalization, constructed and installed so that coverage is of the proper density, the electrical power is adequate and matched to sufficiently efficient transducers able to absorb it, and the entire system is free from hum, noise, oscillations, and RF interference, you are ready to equalize this system in its acoustic environment to ensure the specified tonal response and acoustic gain at each listener’s ears. To do this requires insertion of the necessary filters into the sound system and the taking of meaningful acoustic measurements.