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In the Forum: Horn-Loaded Speakers
In the Thread: Midbass Horns and Real Estate.

Post Subject: Circumferential phasing plug problemsPosted by JLH on: 8/7/2009

I understand your position on compression and not wanting to screw up the tone. The Community M4 driver is the perfect example of how NOT to build a 4” exit compression driver. First, the cone/dome material is garbage. Neither the sandwiched aluminum nor the carbon fiber cone/dome has anything interesting to offer in tone. In addition the phasing plug is all wrong in design. The circumferential phasing plug is a huge offender of tone if not implemented correctly. Funny enough, Vitavox is the only one to get it right in the S2. All others are compromises which do not have interesting tone.

The problem can be seen in the design of the circumferential phasing plug. Various different frequencies launch off of a cone or dome where the frequency’s wavelength is equal to circumference. So, if you have a 15” woofer and play an 800Hz tone through it, you will find that most of the acoustic energy is coming from the area of the cone that is 5.38” in diameter. The higher the frequency, the closer the sound emits from the dust cap area and vise versa.

Now knowing this, you see the inherit flaw of the circumferential phasing plug. The rings that form it block several diameters across the dome. This also creates reflections and resonance problems. The radial phasing plug on the other hand does not suffer from these problems. Since the radial slits start at the center and go to the edge of the done or cone, all diameters have a clear path straight forward and all tones are represented. They are not impeded or forced to wiggle around a ring. This means that all tone gets through the radial phasing plug and is better preserved. No it doesn’t exactly sound like the cone without a phasing plug, but it is very much closer to not screwing with the sound.

http://www.nutshellhifi.com/library/Altec&Henrickson_Tangerine.pdf

Another advantage to the radial phasing plug is the slit width and dome spacing can be changed to shape the high frequency response. The circumferential phasing plug dies quickly at high frequencies, but the radial phasing plug has a useful high frequency tail.

http://www.nutshellhifi.com/library/Henricksen_1978_Tangerine_PP.pdf

Rgs, John

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