Another Type of Phase Plug

[joyspring]

The `pepper pot' phasing plug is Tannoy's Ronald Rackham's creation. It was used from the earliest dual-concentrics until quite recently. The System 6/8/10/12/15/15DMT and 600/800 etc. series monitors feature the `Tulip' waveguide, which on cursory inspection appears to be a standard circumferential phasing plug.

The story is that the `pepper pot' became prohibitively expensive to machine, though it would seem that a standard circumferential phasing plug would entail similarly-complex machining...

I'm quite suprised that a UREI would have such a phasing plug as all the post-Altec UREIs (series 811, 813, 815 -B and -C) utilize standard JBL 2425H compression drivers which contain (to my admittedly poor recollection) standard circumferential phasing plugs :-/

Oh, and by the way, UREI switched away from Altec when Altec production quality became inconsistent (actually, from all accounts, worse than poor).

And what's more, the switch occurred well before JBL's acquisition of UREI; in fact, the B series (811B, 813B, 815B) used a PAS (Professional Audio Systems, Carlsbad, CA) 15" coax with a JBL 2425H mounted on its back.

After JBL's acquisition of UREI, the C series (811C, 813C, 815C) finally featured an all-JBL driver complement.

Robert

[martyh45]

Hello,
I don't know when tannoy was building drivers like this but RCA used this type of phase plug on the 9458. the later 9584-a used the radial plug.
HTH,
Marty

[thevott]

The Stephens Tru-Sonic Coax used a 'pepper-shaker' plug as well. I remember observing that feature the day I tossed one in a dumpster. That was pre-Ebay. Darn!

[Mirrophonic Sound System]

Further to the recent excellent discussion on Phase Plugs,
how many have seen the unusual phase plug in Tannoy speakers ?

I took a Tannoy apart once and was surprised to
see that the phase plug was accomplished by simply
boring about a dozen converging holes of,say, about
1/8". This seemed like an elegant solution compared
with the complexity of fabrication of the Western Electric.

Does anyone know if/when this method was patented
and by whom ?

I used to work on recording studios and took apart
a UREI Coaxial speaker once. This was the driver
made by JBL after they bought out the UREI Co
so naturally they didn't want to use an Altec.
Anyways, I was shocked to see that it had the
"Tannoy"-type phase plug with the converging bored holes

[joyspring]

Yes, UREI (JBL) also manufactured a smaller 800-series monitor line, the 809 and 809A. These were comprised of a 12" coax with a scaled-down 1" screw-on titanium-diaphragm compression driver (JBL 2416H?). They also featured a Time-Align(tm) network as well. In any event, the 809/809A was an all-JBL affair.

Never having repaired an 809, I'm not certain which type of phasing plug is in these drivers.

JBL used the 2416 in other lower-end MI and sound reinforcement lines as well (MR-series, for example).

In addition, I believe Eminence also manufactures a very similar driver as well - in fact, I understand that it may be diaphragm-compatible with the JBL line.

BobR

[Mirrophonic Sound System]

Regarding the JBL-UREI, it was the late 80's I think
and they had a number of models and I'm sure they had
a 'half pint' version using a 10 or 12" coax with the
"blue UREI 'trademark' horn" . This may have been the
one with the pepper pot phase plug - but it did appear to be of Northridge origin

[Steve Schell]

I have seen the drilled, or pepper pot style phasing plug in several RCA compression drivers of the WWII era; they were used on the U.S. Navy ships. Also, all of the Stephens Tru-sonic compression drivers I have seen used this type of phasing plug. Hal Cox has mentioned that Bob Stephens discussed this with him in the late 1940s, and said something like " Those holes should really be tapered, but people like my drivers the way they are, so I'm going to keep making them that way."

[Todd W. White]

The pepper pot was, indeed, used in the RCA models - I've seen that, too.

That's interesting that Stephens would say that - the radial design shown in Hilliard's book, and also used in the TANGERINE shows tapering away from the dome of the diaphragm. It also shows tapers in the slits themselves, something the TANGERINE does not have.

Maybe we'll get a new TANGERINE someday - one that has the best of all worlds...

[Xhorxhi]

I'm new so as an aside; what does a tangerine phase plug look like? Anyone have pictures. The 808-8A drivers have a bullet shaped plug inside the slotted dome shaped machined pole piece. Am I looking at the right spot, inside the throat, to see this bullet shaped plug? Does the pole piece come apart or out? Is the tangerine plug better? I've removed the symbiotik diapragms and I'm considering putting the "good" 34647 diaphragms in.
Do I have the right idea here to get these 808's sounding sweet?
Thanks in advance?
-Chris-

[Todd W. White]

The acoustical transformer (phasing plug) of a HF compression driver is the thing you see when you remove the diaphragm - it lies right beneath it.

The TANGERINE phase plug looks like this:

Altec Literature - 1978

Here's how it goes together:

Altec 800-Series: Exploded View

Here's how a compression driver works:

Altec 800-series: Cutaway view

The only part that should come off (aside from the rear cover) is the diaphragm.

I think the TANGERINE does, in fact, work better than the older style, but there are also ways to improve it....

I would put the 909-series diaphragm in your driver. Get them from Bill at Great Plains Audio