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simple question about tweeters...


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I have been looking st speakers for quite a while now, (not too long though) and it seems as though most speakers I see have a cross (or an X whichever you prefer to call it) over the tweeter. My new KG's have it, and my PM's, and my old Altecs didn't have a cross, but some other odd design. Is there any reason there is always something in front of the tweeter?


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My JBL HLS's have them.

Polk Audio tweeters have somthing like them.


They are harder to poke is the plastic is in the way!!!


Receiver: Sony STR-DE675

CD player: Sony CDP-CX300

Turntable: Technics SL-J3 with Audio-Technica TR485U

Speakers: JBL HLS-610

Subwoofer: JBL 4648A-8

Sub amp: Parts Express 180 watt

Center/surrounds: Teac 3-way bookshelfs

Yes, it sucks, but better to come. KLIPSCH soon! My computer is better than my stereo!

For JBL related subjects and more fun, click: http://www.audioheritage.org

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I thought the phase plug was behind the protective screen or dome.

I have wondered the same thing about some of the speakers I have.

They have this plastic cross on the outside of the screen.

I figured it to be a guard, like the ones they put on JBL bass ports.

John, how does the phase plug minimize phase cancellation?

Does it somehow alter the length of the waves coming from different areas of the diaphram?

I've been curious how it works.


You should of heard just what I've seen.

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Reality---There are a couple of different kinds of phase plugs. That which more hornies are familiar with is the type you mentioned inside a compression driver. It's a device between the diaphragm and throat that equalizes the path length from all areas of the diaphrahm to the throat, thus preventing cancellations and smoothing response. Some are a series of small concentric horns such as with JBLs and old Altecs, the later Altecs used the radially slit "tangerine" and Tannoy used one pierced with holes called a "salt shaker".

A second type is seen on direct-radiators. Most familair is the long snout or "doorknob" devices jutting from the center of Lowther drivers and some other cones. This prevents high frequency cancellations by blocking short wavelengths from opposite sides of the cone colliding. The little buttons in front of some domes work pretty much the same way; dome tweeters do not move as a unit at most frequencies but are subject to break-up modes and may actually act as "ring-radiators" with a ring shaped area above the voice-coil doing the radiating at high frequencies.


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Thanks, Mr.Brennan.

I didn't know there was many types.

I've been focused on compound flare rates.

Part of my ongoing horn research.

I've been working my way inward, from horn design to horn mechanics, so your info on phase plugs is very helpful.

Couple more questions, if you don't mind.

Does the plug design relate to throat size or diaphram diameter? Or both?

Is turbulence at the throat allowed for in plug design?

Do lens minimize turbulence or just help dispersion rates?

Also, on the small button type plugs, do they have a predetermined resonating freq?

Is that what you mean by "break up modes"?

I appreciate the info.

My kids think i'm taking this too seriously.

I'm finding it fascinating.

And all the while, I've got some type of klipsch speaker emminating enveloping sounds.

You gotta love it.


You should of heard just what I've seen.

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