On Magnet Phase Plugs

[auriches]

Hi,

does anyone here what effect the phase plug has if it is mounted not on the cone but on the magnet or frame? are these ones just for looks or do they serve some other purpose?

[CLS]

http://www.planet10-hifi.com/pp-info.html

[John_E_Janowitz]

We use phase plugs on all of our TD series woofers, mounted to the top of the pole piece. They serve 2 practical purposes. First, they eliminate any resonance of the dustcap and/or resonance from the chamber of air under the dustcap. This typically extends the high frequency limit of the driver. Secondly they act as a large heatsink to pull away from the pole and help to radiate it to the outside world.

John

[John Sheerin]

To the original poster, I've never seen a phase plug mounted to the cone of a speaker. It's typically suspended in front of the cone in some way - mounted to the frame or pole piece.

Heatsinking only works if the phase plug material is thermally conductive. The typical fullrange driver plugs people add on are wood, so they wouldn't do that much for power handling.

Another effect if the plug was electrically conductive (copper, aluminum, etc.) would be to change the Le vs excursion curve, ie, change the distortion characteristics. In a typical ceramic magnet driver with no shorting ring, this would typically make distortion worse. If the design already had a properly designed shorting ring, it would also make it worse. Iow, it should be part of the design.

[auriches]

wow, thanks guys, this is all complicated stuff.

i'm sure my b&w's (the old cm4's) have the phase plugs glued directly to the cone and i thought that this was for hf improvment. then i saw some with the phase plugs on the pole piece and hence my first thought was how this would help the hf.

are there any books or websites i could learn more about driver design? it's not talked about a lot here, probably because most drivers are off the shelf. by the way, are there any companies that make custom drivers?

[planet10]

Originally posted by auriches
i'm sure my b&w's (the old cm4's) have the phase plugs glued directly to the cone

Those aren't phase plugs, just fancy dustcaps. They will help with cross-cone standing waves, but will still leave the cavity resonance.

dave

[auriches]

Originally posted by planet10


Those aren't phase plugs, just fancy dustcaps. They will help with cross-cone standing waves, but will still leave the cavity resonance.

dave

ah, they are fancy.