Equalization

One of the most powerful tools for increasing the potential acoustic gain of a sound amplification system is the production of a "mirror image" filter to level the frequency response of the system. The process of equalizing an auditorium also improves the fidelity of the sound. The process of leveling out the frequency response of the sound system removes the peaks which will ring the system before sufficient gain is achieved.

Equalization Process

The basic idea of room equalization is for the sound system to produce in the room exactly the same signal which is put into the system. So if you put pink noise in and get pink noise out, you are close to that goal. A real-time analyzer can be set so that a pink noise input produces a straight horizontal line on its display. With pink noise input, the equalizer is then adjusted to get a straight line output. The sound system is then equalized to the room.

White Noise

For processes of testing and equalizing rooms and auditoriums, it is convenient to have broad-band noise signals. Typically, white noise or pink noise is used. White noise is noise whose amplitude is constant throughout the audible frequency range. It is fairly easy to produce white noise - it is often produced by a random noise generator in which all frequencies are equally probable. The sound of white noise is similar to the sound of steam escaping from an overheated radiator. The ear is aware of a lot of high frequency sound in white noise since the ear is more sensitive to high frequencies. Since each successive octave of frequency will have twice as many Hz in its range, the power in white noise will increase by a factor of two for each octave band. Twice the power corresponds to a 3 decibel increase, so white noise is said to increase 3 dB per octave in power.

Pink Noise

For processes of testing and equalizing rooms and auditoriums, it is convenient to have broad-band noise signals. Typically, white noise or pink noise is used. Whereas white noise is defined as sound with equal power per Hz in frequency, pink noise is filtered to give equal power per octave or equal power per 1/3 octave. Since the number of Hz in each successive octave increases by two, this means the power of pink noise per Hz of bandwidth decreases by a factor of two or 3 dB per octave.

Since pink noise has relatively more bass than white noise, it sounds more like the roar of a waterfall than like the higher hissing sound of white noise.

Pink noise is often the choice for equalizing auditoriums. Real-time analyzers can be set up so that they display a straight horizontal line when they receive pink noise.