GPA's Vintage Altec E-Zine, Jeff Markwart's Corner
Great Plains Audio 604-8H-III
The Great Plains Audio 604-8H-III is a much improved version of the vintage ferrite magnet Altec 604 family, and is currently in production. Compared to the early production ferrite Altec 604-16X discussed elsewhere in these pages, the GPA 604 exhibits very smooth and extended response. I was given the opportunity to measure these drivers some time ago, and came to the conclusion that a Butterworth 2nd order filter centered at 1500Hz with the crossover points spread 30% would both accomplish the necessary phase correction and also yield reasonably flat SPL magnitude throughout the crossover region. The drivers’ owner, and subsequent......
