Twice in the last month I have been at someone’s house, servicing their turntable, when they asked whether they should be considering a new phono preamp that offers additional playback equalization curves besides the standard RIAA. My usual reaction is to thumb through their record collection, where, more often than not, I find that they don’t own a single record that was cut using a curve other than RIAA.
Phono playback EQ is one of those audiophile topics that stokes some people’s passions, with plenty of disagreements about how important it is. I have seen grown men get into heated discussions about the history of record EQ curves, but in truth, the subject is only likely to matter if you listen to a lot of 78s or original mono LPs pressed between the late 1940s and the mid-1950s.
Going well back into the pre–World War II 78 era, the engineers who designed record-playing systems realized that there could be two big benefits to applying some equalization to the signal before it reached the cutter head that creates the lacquer master disc. The reasons are complicated. For one thing, the energy in music peaks in the 50–100Hz range, depending on genre, and declines at higher frequencies. For another, loudspeaker drivers couple to the air less efficiently when the wavelength of the waves they’re producing exceeds the transducer side by a lot.1 Finally, a vinyl-record cutter head, with an electrical signal that is flat with frequency, results in a groove size that declines with frequency at a rate of 6dB/octave (see sidebar).
The result is that when you are cutting the squiggly grooves for a record, bass energy results in big, wide swings of the groove while high-frequency sounds produce microscopically tiny
