Radial phase plug vs concentric ring phase plug

I have always thought my old Altec 802's with the concentric ring phase plug sounded better than my newer 802 G with the Radial phase plug. If i had to describe the difference i am hearing i would say the concentric ring style just simply sounds better & smoother. I have read before the radial phase plug Altec developed was just a way to cut production cost and actually was not a improvement in the sound. This should not be surprising at a time when audio gear was advertised in every magazine and so many companies were fighting for their share of the market.

Altec engineer Clifford A. Henricksen reported on the differences between radial and "circumferential" types of phase plugs at Audio Engineering Society conventions in 1976 and 1978.[12][13] The radial design is easier to produce, but it does not differentiate between sound waves from the perimeter of the diaphragm and sound waves from the center. At high frequencies, the diaphragm does not act as a perfect piston; instead, it displays rippling, modal properties related to its stiffness and density. Because of the speed of wave propagation through the diaphragm material, the center of the diaphragm moves slightly later than the perimeter. Radial slots in the phase plug do not correct for this small time difference, which affects the highest frequencies. Concentric circular slots are able to correct for the diaphragm's rippling behavior but the positioning of the slots is critical.

Clifford Henricksen has 9 patents including the patent for the radial phase plug. So it looks like all those old timers that did not like the radial plugs had actual reasons not to and people that thought they disliked them because they were made from plastic were wrong. Some of the best sounding drivers made Western electric , JBL , TAD , Yamaha etc all use the concentric phase plugs. Looks like the adds Altec used from 1976 to 1980 for the radial phase plugs in model 19's & 604's worked well and are still working considering most Altec fans want the radial phase plugs drivers.
 
As in the link, it seems to need eq :
"lower total “Q” responsible of the 1.2dB efficiency lost around 9-10kHz. Despite this the variable flow path is desirable in order to avoid the severe notch at the high end typical of single path phase plug."
It seems a interesting compromise...even if 1,2db lost and on only around 9-10khz seems optimistic seeing response chart of drivers using it.
Don't know it there is really often notch problem, as it can't be seen in datasheet smoothed responses...
 
What I have found is as your wavelenghts get longer the, the non-piston behavior of the diaphragm becomes less relevant. This makes the radial phasing plug very applicable to cone driver loaded horns. The advantage the radial phase plug has for cone drivers is the tone of the driver is retained. You don't have entire concentric areas of the cone being blocked from directly radiating. The radial slots allow for infinite circumferential paths so no particular frequency is inhibited. In the the radial phasing plugs I've made for cone drivers, they've measured smoother and had less ripple. Reading and understanding Henricksen's AES paper is a big help in seeing where the radial phase plug should be used. However, when it comes to metallic dome compression drivers I fully understand what the original poster was saying.
 

djk

R.I.P
2001-02-04 4:23 am
USA
The Altec 288 with the Tangerine phase-plug is not THX approved, it has a bad dip in the upper midrange.

The 902 is acceptable (just barely).

Look at the Faital Pro graphs on their 1" drivers, the annular is always smoother than the radial type.
 

djk

R.I.P
2001-02-04 4:23 am
USA
Altec had to switch early on to the radial phase-pug due to patent infringement on the annular phase-plug.

After they beat the patent they went back to the (superior) annular type.

In 1978 they 'discovered' the radial type again, with less than stellar results.
 
Altec had to switch early on to the radial phase-pug due to patent infringement on the annular phase-plug.

After they beat the patent they went back to the (superior) annular type.

In 1978 they 'discovered' the radial type again, with less than stellar results.

Thats very interesting do you know what year? I want to say i vaguely remember reading about a law suit with Altec yearly in the companies history but i can't remember what it was about.
 
The Altec 288 with the Tangerine phase-plug is not THX approved, it has a bad dip in the upper midrange.

The 902 is acceptable (just barely).

Look at the Faital Pro graphs on their 1" drivers, the annular is always smoother than the radial type.

I can agree in high range, from 8 ohm curves set.But adding 16ohm versions HF10AT to HF10RT and HF10RK to HF10AK curves set, radial versions compare very well to annular and are always smoother in low-mid.
A big plus argument for radial shape for cone phase plug horn loaded.
Am i wrong analysing ?
 
I can agree in high range, from 8 ohm curves set.But adding 16ohm versions HF10AT to HF10RT and HF10RK to HF10AK curves set, radial versions compare very well to annular and are always smoother in low-mid.
A big plus argument for radial shape for cone phase plug horn loaded.
Am i wrong analysing ?

I would agree for cone loaded horns the radial phasing plug is more ideal. However, it has to be done correctly. Following Henricksen's AES paper is a must. I normally shoot for a Lt/H ratio of 1.26, a compression ratio around 6.5:1 and always use a prime number of slits (i.e. 11, 13, 17, 19, etc.) in my designs.
 
I would agree for cone loaded horns the radial phasing plug is more ideal. However, it has to be done correctly. Following Henricksen's AES paper is a must. I normally shoot for a Lt/H ratio of 1.26, a compression ratio around 6.5:1 and always use a prime number of slits (i.e. 11, 13, 17, 19, etc.) in my designs.

Correction: I incorrectly wrote Lt/H ratio of 1.26, I meant K=1.26. The actual Lt/H ratio would be more like 0.583
 

djk

R.I.P
2001-02-04 4:23 am
USA
"That's very interesting do you know what year?"

"When the Shearer system was introduced, Western Electric objected to Lansing’s use of an annular slit model 284 high frequency driver, since they had already been issued a patent on that basic design. As a result of this John Blackburn and Lansing designed a radial slit high frequency driver, the model 285, as an interim step in the evolution of the Shearer system. While reviewing the patent literature, Blackburn later discovered prior art for the annular slit design in the work of Bell and Tainter, dating from their work on the acoustical phonograph in the early years of the 20th century, so Lansing was able to reintroduce the traditional phasing plug in the high frequency driver."
 
"That's very interesting do you know what year?"

"When the Shearer system was introduced, Western Electric objected to Lansing’s use of an annular slit model 284 high frequency driver, since they had already been issued a patent on that basic design. As a result of this John Blackburn and Lansing designed a radial slit high frequency driver, the model 285, as an interim step in the evolution of the Shearer system. While reviewing the patent literature, Blackburn later discovered prior art for the annular slit design in the work of Bell and Tainter, dating from their work on the acoustical phonograph in the early years of the 20th century, so Lansing was able to reintroduce the traditional phasing plug in the high frequency driver."

Thanks i was able to find the story on Lansing heritage site. So now i am 100% convinced that in 78 when the radial aka tangerine plug was introduced it was a way to cut production cost five years later in 83 Altec was sold. The best sounding drivers JBL,TAD,Renkus Heinz,Radian,Yamaha older Altecs all have concentric plugs. I just sold a couple pair of 802 G so now i am going to give the Radian 745neopb a try.
 

djk

R.I.P
2001-02-04 4:23 am
USA
" it was a way to cut production cost"

It also had an adjustable height.

Alnico magnets had to have the depth of the iron return pot structure carefully trimmed to the magnet slug height. Altec was issued a patent on their new system which eliminated the need for trimming.