Home Theaters

These days, ask anyone about active equalization and they are likely to show a look of complete incomprehension. Most people have no clue what you might be talking about, as they have not seen an equalizer, or if they have, they had no clue what it was.

An equalizer is a device to enable flat frequency response by electronic means. The tone controls found on most receivers are equalizers, chosen with control of the lowest and highest parts of the sound, leaving (hopefully) the midrange unscathed.

The well made speaker crossover will be an equalizer, smoothing out response near the crossover point between the drivers. It will not, however, usually be adjustable, nor will it usually employ any active circuitry to achieve its ends. The equalizers I am speaking of now are active devices, using either ICs or tuned coils to obtain changes in a band of frequencies.

There are two types of equalizers, fixed frequency and parametric. The fixed frequency equalizer will work at one specific frequency, and have an effect other frequencies on either side of the chosen frequency only because the designer decides that the ‘Q‘ of the circuit will allow for it.

Generally fixed frequency equalizers are what people have seen, with a number of them ‘ganged’ together for each channel. Usually the frequencies are chosen at musical octave centers, so most will have 10 ‘bands’ for each channel. These are aptly named ‘octave band equalizers’, there are also equalizers that choose to affect a larger band of frequencies at once. These are sometimes two-octave controls, for five bands, or 1.5 octaves, giving 7 bands. Lots of people have seen these in car audio - not that these are usually good examples. Car equalizers tend to be of very low quality, and are used to make things sound subjectively better, but the results are usually far from good.

an inexpensive octave equalizer, with a display of dubious usefulness. However, it’s better than nothing.

Parametric equalizers generally are more expensive, less used in the home, and much easier for the knowledgeable person to get good results with, while at the same time making it much easier for disastrous results when the novice uses them. In a parametric equalizer, there will be, for each group of frequencies, two controls. One control will control the amplitude of the changes made, while the other will affect how wide the band is that is acted upon. It makes getting flat response easier, provided a method of calibration is used. Otherwise, very strange results are possible, and likely.

As price goes up, the quality does as well, but sometimes the ability to do finer tuning of the response is also included. The most familiar of the higher end equalizers is the 1/3 octave model, with three controls for each octave of music. This means that there will be that many more control sliders on the front of the unit, and that much more to mess with.

 a one-third octave equalizer, for stereo, with no display for calibration - not a total loss, as other methods can be employed to achieve good results.

I use the words ‘mess with’ because the inexperienced user will almost immediately go to extremes with the controls, trying to emphasize certain ranges, whether or not those ranges need any change. Equalizers are made to repair flaws in the sound, not become toys of the tinkerer. The equalizer can make up for poor recording tonal balance, speakers that are not placed effectively in the room, oddities of the room itself, and defects in the response of the speakers. It must be remembered that this is not a panacea.

Since the primary purpose of an equalizer is to achieve flat frequency response in the listening room, there must be some way to calibrate the system. The very best units will have a noise generator and microphone to get each band equal in volume. This is often incorrectly referred to as ‘white noise’ which if used, would not be good, both for your equipment and your ears. We don’t hear in a linear fashion, and so having absolutely equal energy in each frequency band can hurt our ears at high volumes, and can destroy the speakers, by causing the amplifier to clip at lower frequencies, by causing too much excursion of the woofer,  or by sending too much energy to tweeters at high frequencies. What is used for calibration in home stereo is shaped or ‘pink’ noise, which simulates the way our ears hear, so it is less destructive to equipment, and easier on our ears.

The next installment will include techniques for usage, and some currently available models.

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