Are radial phase plugs really that good?

[Richard C.]

Hello all,
I have been reading all I can find on 1" drivers for 2 way systems. Most Altec specs indicate a usable response to 20 or 22 kHz, and this is before the radial phase plug came along! I think that most 1" drivers are reasonably flat and then roll off above 3.5 kHz or so. How much better is a radial phase plug over the older style? And was there more than one style before that? Does anyone know where I can find actual test data showing the difference? There are many different Altec 1" drivers on eBay and I would like to know what people think of some of them. I know the older drivers aren't junk! A quick reply with "get the ones with radial phase plugs" is not what I am after here.
Thanks,
Richard C.

[cclark65]

I think I read somewhere that different phase plugs were designed for the mantaray style horns because the older ones weren't working right with them. I can't remember the specifics, maybe somebody else can fill you in, but the older drivers without the "tangerine" phase plugs worked great on the radial horns, but not the CD horns, so they use the tangerine ones on CD horns. Remember, this is just something I read a long time ago, and cannot remember the specifics!

[Don McR]

I had a chance to meet with the former Altec Lansing product manager responsible for the development of Model 19 and 802-8G last April. He stated that the development of Tangerine phase plug was strictly a cost reduction exercise. The circumferential phase plug it replaced is a complicated assembly of numerous, precisely machined, metal parts. The goal was to replace this with a single cast plastic part.

He went on to state that there is no question that the response of this driver was superior to the 802-8E that it replaced, but he said that it had nothing to do with the phase plug. As he explained it, the 802 diaphragm had been modified over the years to meet the ever increasing demands for power handling. The aluminum grew thicker in gauge and gap between the diaphragm and the phase plug was increased to allow greater excursion without slapping into the plug. All of this conspired to restrict high frequency response.

The 802-8G used a completely redesigned diaphragm that this person stated was a back to basics concept. In other words, it was similar to that used in the very first 802. It used a very thin and light diaphragm that had the minimal clearance necessary to safely function in a home speaker. He said that the same extension could be achieved with this new diaphragm using the older circumferential phase plug. Testing revealed no significant differences in response.

BTW, the Tangerine pre-dated the Mantaray horns and its development was not related to that product.

[sfogg]

" I think that most 1" drivers are reasonably flat and then roll off above 3.5 kHz or so. How much better is a radial phase plug over the older style? "

I can't compare against the older units but this is a FR of a 902-8B on a 511B.

[IMG]http://forums.klipsch.com/idealbb/files/902-8b.JPG/IMG]

Shawn

[thevott]

Side note: My Model Nineteen drivers have black tangerine phase plugs. I wonder if the black ones sound better than the orange ones or if the orange ones just taist better.

MP

[thevott]

Pardon me, what I meant was "taste"

MP

[Todd W. White]

Phonetic spellings are always allowed here...

[RonSSS]

"I had a chance to meet with the former Altec Lansing product manager responsible for the development of Model 19 and 802-8G last April. He stated that the development of Tangerine phase plug was strictly a cost reduction exercise. The circumferential phase plug it replaced is a complicated assembly of numerous, precisely machined, metal parts. The goal was to replace this with a single cast plastic part.
He went on to state that there is no question that the response of this driver was superior to the 802-8E that it replaced, but he said that it had nothing to do with the phase plug. As he explained it, the 802 diaphragm had been modified over the years to meet the ever increasing demands for power handling. The aluminum grew thicker in gauge and gap between the diaphragm and the phase plug was increased to allow greater excursion without slapping into the plug. All of this conspired to restrict high frequency response.

The 802-8G used a completely redesigned diaphragm that this person stated was a back to basics concept. In other words, it was similar to that used in the very first 802. It used a very thin and light diaphragm that had the minimal clearance necessary to safely function in a home speaker. He said that the same extension could be achieved with this new diaphragm using the older circumferential phase plug. Testing revealed no significant differences in response."

Many years ago Jim Dickinson told me that the diaphragm in the 802-8G was special, lightweight and no longer available. So "don't blow them up" he said. I still have that letter......
Your note here is the first time I have heard this confirmed. Glad I still have those drivers.

However, this doesn't make the owners of these drivers feel too awful good about repalcing the diaphragm if needed huh? GPA pretty much make a "fits all" diaphragm...right?
And, I guess Altec chose the "feature" the radial phase plug instead of admiting at the time it was simply a cost reduction excersize.

I have measured the freq response of the 802-8G, as well as a pair of 806A and 902-8A. The later radial phase plugs were clearly superior above 10khz in my tests.

Ron

[Steve Schell]

If you guys want a real treat, go to the uspto.gov web site and look up US patent #2,183,528. It was granted to Dr. John Blackburn on Dec. 19, 1939. By then he had left the employ of Lansing Manufacturing Company, but he was working there when the patent application was filed on August 4, 1937. This patent is for the radial slit phasing plug, and it predates Cliff Henricksen's patent on the Tangerine phasing plug by about forty years.

Blackburn's design was a beautiful thing, a 20 section radial slit plug machined from brass. There is a bit of intrigue to the design. Apparently, Western Electric was unhappy with Lansing's use of the circumferential phasing plug in his 284 driver, as used in the Shearer Horn System. W.E. insisted that Lansing cease the manufacture of this design. Dr. Blackburn designed the radial plug to avoid any patent infringement, and Lansing continued to produce his driver with the radial plug as the model 285. I own several 285 drivers, and the phasing plugs are impeccably machined, and look exactly like the drawings in the patent.

Before long, Lansing was able to invalidate W.E.'s infringement claim, by showing that there had been prior art in circumferential phasing plugs in the acoustical phonograph era. He then resumed the manufacture of the 284 driver, grandaddy of the later Altec 288.

John Hilliard states in an article of the era that the radial phasing plug had been produced as a cost saving alternative to building the circumferential plug. This may have been true in a way, as the early Lansing circumferential plugs were welded together from hand machined parts. Later 284, 287 and 288 drivers made use of die cast parts, which no doubt brought costs into line.

[Todd W. White]

In his book "Motion Picture Sound Engineering" (I have his personal copy), Dr. John K. Hilliard did, in fact, state that the circumferential "acoustical transformer" (phasing plug_ WAS superioir, but (in those pre-WW2 days) it was cost-prohibitve to produce. Therefore, the radial design was developed.

IMHO, it is very likely that Hilliard stated it this way due to the patent infringement issue with WE on the circumferential plug, even though the radial of the day was, admittedly, inferior.

HOWEVER - the TANGERINE radial phasing plug is NOT the same as the radial of the Lansing/Hilliard era. Without going into all of the differences (I don't have time right now), it is noticeably SUPERIOIR to the earlier version. I will mention that the most obvious difference is the fact the Lansing had to cut the metal for the radials with two cuts - the thinnest one first, which went nearly all the way to the center, and the thicker one second, which only part of the way up. This created a "shoulder" which adversely affects the HF response. Each slit in the TANGERINE is smooth, thus eliminating this problem.

The TANGERINE radial phasing system does work better, AND if you get everything else right (diaphragm mass, material, compliance, magentic flux, etc.), I think you'll find the small-format 902-style driver IS superior sounding to even the best circumferential Altec made. Even if the only difference were the phasing plug, I think the radial works better, because Henrickson & his crew did way more to it than just copy an old design...

By the way, there IS a phasing plug design that IS superior to ALL of them, but it's not in production.

Yet.