The first user-adjustable EQ was created in the 1930s by John Volkmann while he was at RCA (Szikla, 2022). He created it to get better sound for motion picture theatres. It allowed movie theatres to selectively boost or cut frequencies to make them movies played sound better.
At around the same time Arthur Davis from the Cinema Engineering Company (CEC) created the first Graphic Equalizer, the 7080 (Szikla, 2022). This device had six bands (63Hz, 160Hz, 400Hz, 1kHz, 2.5kHz, and 6.3kHz) with +/- 8dB for each band.
Arthur then left CEC and took a job with Altec where he designed the 9062A seven band equaliser (50Hz, 130Hz, 320Hz, 800Hz, 2kHz, 5kHz, and 12.5kHz). This is a completely passive device that remained a benchmark until the 1970s. And just look at those faders…
The biggest leap in EQ was the parametric EQ. In 1971 Daniel Flickinger invented a ‘Sweepable EQ’ which allowed a user to arbitrarily select a frequency and gain for up to three bands (Parametric Equalizer explained, 2022). However, it was in 1972 that George Massenburg and Burgess Macneal created the idea for a tuneable EQ. George wrote a paper presented to AES (Massenberg, G. 1972) that had adjustable bandwidth for each of the frequency bands. Massenburg called the a ‘Parametric Equalizer’. George’s company GML still sells them under this brand name today.
References:
Massenberg, G. (1972) AES convention papers forum, AES Convention Papers Forum ” Parametric Equalization. Available at: https://secure.aes.org/forum/pubs/conventions/?elib=16171 (Accessed: March 11, 2023
Parametric Equalizer explained (2022) SoundBridge. SoundBridge. Available at: https://soundbridge.io/parametric-equalizer-2/ (Accessed: March 11, 2023).
Szikla, A. (2022) View from the bench: Tracing the EQ path, AudioTechnology. AudioTechnology. Available at: https://www.audiotechnology.com/tutorials/view-from-the-bench-tracing-the-eq-path