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Phase plugs...

post #1 of 10
Thread Starter 
I am currently reading a speaker review over my work lunch hour and the reviewer keeps raving about a budget speaker with a true phase plug in its midrange driver. Can someone explain what a phase plug is and what it means, in terms of sound quality?
post #2 of 10
Quote:
Originally Posted by Elihawk View Post

Can someone explain what a phase plug is and what it means, in terms of sound quality?
Unless the driver is horn loaded it's pretty much eye candy, and probably not a phase plug at all, but rather a pole piece extension.
post #3 of 10
Quote:
Originally Posted by Elihawk View Post

I am currently reading a speaker review over my work lunch hour and the reviewer keeps raving about a budget speaker with a true phase plug in its midrange driver. Can someone explain what a phase plug is and what it means, in terms of sound quality?

There's a lot of misinformation out there. Bill got it right.

In practical terms, what is falsely called a "phase plug" does nothing but lower the driver's efficiency a bit. And maybe arguably help it handle more heat/power.

It's a cosmetic, not a performance, choice for the most part.

A real phase plug has to cover substantially all of the driver's radiating surface to make a material impact. Funny thing is, actual phase plugs are often mis-named "waveguides" in "hi-fi" company propaganda.
post #4 of 10
Thread Starter 
Well, the guy who reviewed this speaker was pretty adamnant that it was rare FOR a speaker under 1000 dollars to have a true phase plugs. (BTW, this review was of the EMP E5ti). Exact quote from the article
"There are two 6.5″ poly-matrix woofers, a 5.25″ aluminized poly-matrix midrange (with a true phase plug), and a 1″ fabric dome tweeter under a dedicated screen. The driver compliment alone belies the price of these speakers. Usually, at sub-$1000, phase plugs are for show only and move in and out with the driver. This, however, was a real phase plug. "
http://www.reviewboard.com/05/183/e5ti-speaker-review
Okay, Bill knows his stuff, so lets rephrase the question- What is a pole piece extension and what it means in terms of sound quality?
post #5 of 10
Thread Starter 
Thanks Bill and DS!
post #6 of 10
Quote:
Originally Posted by Elihawk View Post

This, however, was a real phase plug. "
The reviewer is mistaken. That's a direct radiating cone driver, and it does not have a phase plug. Phase plugs are used in the throat of a horn, to equalize pathway differences from the various points on the diaphragm to the throat:
http://www.centauriaudio.com.au/diy/plugs.html

Cone drivers typically have a dust cover (dome) over the pole piece. Some drivers omit the dust cover and rather than leave a gaping hole they use a pole piece extension, which visually resembles a phase plug. But it doesn't re-route the passage of sound waves coming from behind it, so it doesn't work like one.
post #7 of 10
Quote:
Originally Posted by Elihawk View Post

Well, the guy who reviewed this speaker was pretty adamnant that it was rare FOR a speaker under 1000 dollars to have a true phase plugs. (BTW, this review was of the EMP E5ti). Exact quote from the article
"There are two 6.5″ poly-matrix woofers, a 5.25″ aluminized poly-matrix midrange (with a true phase plug), and a 1″ fabric dome tweeter under a dedicated screen. The driver compliment alone belies the price of these speakers. Usually, at sub-$1000, phase plugs are for show only and move in and out with the driver. This, however, was a real phase plug. "
http://www.reviewboard.com/05/183/e5ti-speaker-review
Okay, Bill knows his stuff, so lets rephrase the question- What is a pole piece extension and what it means in terms of sound quality?

Oh, it's an audioholics "review." (I searched for the first sentence, and it came up as a reprint from AH.) Not surprising. They must have some undisclosed conflict of interest with that speaker company's parent, RDL or something like that, because any BS that company's propgandists feed AH instantly gets lapped up and regurgitated over and over again. (They have an article that's allegedly about "identifying high fidelity drivers" that has some good parts but also a fair bit of claptrap (including the stuff written about "phase plugs.")

AH does some good stuff. Hiring Josh Ricci to do sub testing was a stroke of inspiration. And they're right about wires (for the most part, except when someone gives Gene a badly-designed $60k speaker and he brags about the wires in it). But anything from this particular company is not going to be reviewed, but rather deified.
post #8 of 10
Can the lack of a dust cover reduce compression under the cone?

Is there any wave-guide function at all of having a big piece of metal in the middle of your cone?

Won't that thing radiate heat and, in doing so, help cool the driver?
post #9 of 10
Quote:
Originally Posted by JerryLove View Post

Can the lack of a dust cover reduce compression under the cone?
Yes, but so will a porous dome or a vented pole piece.
Quote:
Is there any wave-guide function at all of having a big piece of metal in the middle of your cone?
None. And seldom are pole piece extensions more than an inch diameter anyway.
Quote:
Won't that thing radiate heat and, in doing so, help cool the driver?
It can, but a vented pole piece works much better. With midranges and midbasses where you see them used there's usually not enough heat for it to be an issue to begin with.
Edited by Bill Fitzmaurice - 11/20/12 at 7:34pm
post #10 of 10
Quote:
Originally Posted by JerryLove View Post

Can the lack of a dust cover reduce compression under the cone?

Is there any wave-guide function at all of having a big piece of metal in the middle of your cone?

Won't that thing radiate heat and, in doing so, help cool the driver?

There is a good discussion of these polepiece extensions by serious home audio heavyweights (both "AndrewJ" and "speaker dave" have, I believe, designed loudspeakers rated "Class A" by Stereophile) starting here.
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