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In the Forum: Horn-Loaded Speakers
In the Thread: Altec radial phase plug vs concentric phase plugs

Post Subject: Altec radial phase plug vs concentric phase plugsPosted by Sean19 on: 3/28/2016

I have always thought my old Altec 802's with the concentric ring phase plug sounded better than my newer 802 G with the Radial phase plug. If i had to describe the difference i am hearing i would say the concentric ring style just simply sounds better & smoother. I have read before the radial phase plug Altec developed was just a way to cut production cost and actually was not a improvement in the sound. This should not be surprising at a time when audio gear was advertised in every magazine and so many companies were fighting for their share of the market.

Altec engineer Clifford A. Henricksen reported on the differences between radial and "circumferential" types of phase plugs at Audio Engineering Society conventions in 1976 and 1978.[12][13] The radial design is easier to produce, but it does not differentiate between sound waves from the perimeter of the diaphragm and sound waves from the center. At high frequencies, the diaphragm does not act as a perfect piston; instead, it displays rippling, modal properties related to its stiffness and density. Because of the speed of wave propagation through the diaphragm material, the center of the diaphragm moves slightly later than the perimeter. Radial slots in the phase plug do not correct for this small time difference, which affects the highest frequencies. Concentric circular slots are able to correct for the diaphragm's rippling behavior but the positioning of the slots is critical.

Clifford Henricksen has 9 patents including the patent for the radial phase plug. So it looks like all those old timers that did not like the radial plugs had actual reasons not to and people that thought they disliked them because they were made from plastic were wrong. Some of the best sounding drivers made Western electric , JBL , TAD , Yamaha etc all use the concentric phase plugs. Looks like the adds Altec used from 1976 to 1980 for the radial phase plugs in model 19's & 604's worked well and are still working considering most Altec fans want the radial phase plugs drivers.

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