604 horns

[selmerdave]

Apart from the other differences, can someone confirm that the 604B HF horn is larger than the later ones? It appears that way in pictures, I suppose that would account for the 1000hz crossover point. My 604E horns measure around 2 5/8" x 5 1/4" at the sides.

Dave

[joyspring]

The 604B did use a larger horn with cells that extended further back to the horn throat as well.

Subsequent horns were smaller and the cells did not extend all the way back to the pole piece.

I'm not certain why the horn was changed (Todd? Don?) but I imagine that it may have been to offset the horn `shadowing' the output of the cone LF driver, especially closer to the crossover frequency.

BobR

[jmarkwart]

Dave,

I measured my 604B's horn mouth area and it's approximately 4 by 6 inches, or 24in^2. That area would theoretically support throat loading down to 782Hz. The 2 5/8 by 5 1/4 inch area (13.8in^2) you reported for later horns would provide loading down to 1030z or so, which raises the later horn cutoff about 1/3 octave. (See some great pictures of the two on Todd's Website at http://nleinternet.net/alteclansingu...al/Duplex.html

When I measured the on-axis magnitude response of my 604B's woofers they were both +/-2dB from 500 to 1000Hz, so I doubt that was the reason for the horn change. One thing I did discover was that the 604B horn response had a major dip in output (-9dB!) at 1100Hz. You can clearly see this in the old Altec plot of 604B fullrange output, although with the network inserted it is reduced to about -6dB. This looks like a better reason to change the horn to me - but even that could have been avoided by simply raising the compression driver's crossover frequency. Maybe Altec eliminated the 1100Hz dip, saved materials and fabrication costs by going to a sectoral horn, and improved off-axis response all in one shot with the new horn design.

Jeff