Radial(Tangerine) versus the regular circumcerential phase plug

[Baaronj]

Cool. I'll plan to do it this weekend.

As to the differences I hear between the two speakers in a stereo setup, in short, the older circumferential driver sounds louder in the ~2-8k range by ~1-3db (I'm guessing at these values). The output differential is enough to be noticeable during stereo playback. Because the circumferential driver is louder in the midband, I can't really tell if the radial/tangerine driver is more extended above 15k or not.

If the radial/Tangerine driver IS more extended in the highest octave, AND is indeed down a db or two in the ~upper-mids like I think I'm hearing, it would sort of correlate to the predictions/findings of Altec engineer Clifford A. Henricksen in his presentation to the Audio Engineering Society at the 1978 convention ("Phase Plug Modeling and Analysis: Radial Versus Circumferential Types" - http://www.nutshellhifi.com/library/...ngerine_PP.pdf).

Henricksen's model on page 17 predicts a ~1.2db loss in efficiency in a radial phase plug vs. circumferential at ~9.2k (but with some efficiency loss seemingly extending back into the midband based on the chart on page 17). He also predicts a ~5db gain at 20k for the radial/Tangerine vs. circumferential. He tests his predictive models in the same paper and validates them.

So the difference I've been hearing between the two is significantly more output/information in the ~mid/upper-midband in the circumferential driver vs. the Tangerine driver. The Tangeringe'd driver sounds like it has less gain and midrange energy than the older driver, and sounds polite by comparison.

Are there other factors I'm not thinking of that could cause these two 604-8gs to sound so different, remembering I've swapped crossovers/diaphragms/room position/room orientation, etc? I'm using 23744 diaphragms with the simplified Markwart 604-8g crossovers. I went through four 23744 'phragms to find the two with the closest output.

As to measuring equipment, I'm afraid I only have The Studio Six Digital RTA app for my iPhone. It does apply a calibration curve to my iPhone's mic. I can also take measurements with a another RTA app I have for a separate Android phone.

Question: The iPhone RTA app lets me choose Flat/A-Weighted/C-Weighted SPLs as well as Flat/A-Weighted/C-Weighted Plots. Any thoughts as to which I should set it to for these two settings?

I plan to run a digital pink noise file at approx 90db and measure on-axis at 1 meter. I'll use the same crossover and diaphragm on both speakers for testing.

Anything else I should be thinking of?

Anyone else here ever had GPA put a new phase plug in an older driver?

[rogerh113]

Just curious - how do you know how 'flat' the rest of your system is? Or is that a concern?

It would seem that there is a response curve stacking starting at the source component, and to one degree or another happening at every component along the way, including cables. The speaker and crossover are only the last item in the chain. It would seem that the differences you are hearing are different ways the plugs are compensating for the other components, as well as their own character.

[GM]

Cool. I'll plan to do it this weekend.

Anything else I should be thinking of?

Anyone else here ever had GPA put a new phase plug in an older driver?

Thanks!

I can't speak to the 604, but between the 802/808-8A Vs 802-8G the latter's entire BW is shifted a bit higher, i.e. compare responses on a 511 and why the Tangerine is a poor choice unless at least a 700 Hz XO and preferably 1200 Hz where Altec ultimately wound up, which basically bypasses the 511's horn gain BW and its attendant 'honk' if CD horn EQ isn't used plus has a flatter response out to ~10 Hz with some peaking in the 10-20 kHz BW for more top end 'air' than the earlier drivers, so guessing that there's this fundamental difference in the two 604s, which for a given XO design it should in theory sound different in the ~800 - 3200 Hz based on a 1600 Hz XO point as it can't be optimized for both, so might be enlightening to BW limit/audition this region.

Still, your basic impressions mirrors mine except that the difference is more extreme due to my comparisons were on a huge DIY 500 Hz WG and only as a super tweeter from 5 kHz-up where the 8G's top end 'air' really stands out once EQ'd flat to the same pass band SPL. Note these were the so-called 'ultralite' diaphragms which I imagine further skews my results somewhat.

Not me nor recall ever reading about it.

GM

[Earl K]

Baaronj,

A couple of things come to mind here ( the following assumes the 11-slit radial phase plug is NLA, so please bear with me ).

(1) Consider having GPA replace both of your 604's phase plugs with their 9-slit radial type.
- You currently have the 11 slit type ( and from the response traces that I've seen ) there's enough of a difference between these 2 radial types that I would personally want both to be the same..

(2) Also, ( IMO ) never send to GPA drivers loaded with ones precious ( NLA ) 23744 diaphragms ( unless they are being sent to be centered-up ).
- If that describes your situation then make sure you have included written instructions taped to each driver about your expectations of service ( & who owns what ).
- If you send your drivers to GPA loaded with diaphragms, just be prepared to see them disappear and then go through the angst of having GPA locate and return them to you.

(3) Still on the matter of diaphragms, while your 604's are at GPA consider having them install 2 new 34647 type diaphragms ( since the 9-slit phase plug was optimized around the 34647 and that combo offers the most linear response above 1K ).

GPA 902-8A on a 511a ( measured by Zilch ) using the Z19 network


GPA 802G on a 511b ( fr traced from GPAs measurements ) seen on a custom network

[endeeinn]

GM...You state that the band width shifted on the 802 with the tangerine driver on a 511. What are your thoughts on the 288 with the circumferential phase plug vs the tangerine. Does something similar happen with a large format driver such as the 311-90? Thanks.

[magnarc]

The absolute last thing I would do is change the phase plugs, that's just mucking up a perfectly good speaker. Sell the one you don't like and buy a match to the one you do like.

[Baaronj]

Baaronj,

A couple of things come to mind here ( the following assumes the 11-slit radial phase plug is NLA, so please bear with me ).

(1) Consider having GPA replace both of your 604's phase plugs with their 9-slit radial type.
- You currently have the 11 slit type ( and from the response traces that I've seen ) there's enough of a difference between these 2 radial types that I would personally want both to be the same..

(2) Also, ( IMO ) never send to GPA drivers loaded with ones precious ( NLA ) 23744 diaphragms ( unless they are being sent to be centered-up ).
- If that describes your situation then make sure you have included written instructions taped to each driver about your expectations of service ( & who owns what ).
- If you send your drivers to GPA loaded with diaphragms, just be prepared to see them disappear and then go through the angst of having GPA locate and return them to you.

(3) Still on the matter of diaphragms, while your 604's are at GPA consider having them install 2 new 34647 type diaphragms ( since the 9-slit phase plug was optimized around the 34647 and that combo offers the most linear response above 1K ).

GPA 902-8A on a 511a ( measured by Zilch ) using the Z19 network


GPA 802G on a 511b ( fr traced from GPAs measurements ) seen on a custom network

Thanks for your input here Earl. I spoke to Bill at GPA a few months ago, and I *think* he said he could put a Tangerine phase plug in the driver that has the older circumferential type. If he is able to do this, would matching Tangerine plugs be preferable to the newer GPA radial phase plugs?

Very interesting you mention that the newer GPA plugs were optimized around the 34647 diaphragms. I also have a pair of GPA's Alnico 802-16g, using the newer GPA diaphragms, and they've always sounded great to me.

Is there anything other than the mismatched phase plugs in my 604s that could cause the difference in output I hear between the two drivers?

I didn't get around to measuring the drivers this weekend. Hopefully I can get to it this week.

- - - Updated - - -

The absolute last thing I would do is change the phase plugs, that's just mucking up a perfectly good speaker. Sell the one you don't like and buy a match to the one you do like.

I've thought about doing this, and tbh, if I could, I probably would. The challenge is finding a single Tangerine'd 604-8g. There is an audio shop I came across online a while back that stocked a pretty decent selection of vintage Altec pro gear, and did have single drivers periodically, but now I can't for the life of me remember the name of the shop. They always had their inventory and prices listed on the website. Does that ring a bell for anyone?

EDIT: I finally found it: Jammin Jersey Music!

[Earl K]

The "Radial" phase plug that GPA markets & uses IS indeed a tangerine ( they just don't have the rights to that trade-name, so can't call it as such ).

Honestly, the 2 phase-plug types is likely not your problem ( in marked level differences ) though I don't know what it is ( it could be almost anything ).

[Baaronj]

Honestly, the 2 phase-plug types is likely not your problem ( in marked level differences ) though I don't know what it is ( it could be almost anything ).

I was afraid you were gonna say this. I'm going to at least get some quick measurements tonight of each speaker, so I can know how drastic the difference between the two really is. I've swapped diaphragms, crossovers, etc. I just hope it's something that is addressable - though since both drivers have been gone over by GPA, I don't know what else could really be done.

Someone on another forum asked if I had checked the magnetic polarity of the drivers since getting them back from GPA...they were sent to GPA before I acquired them, but I'm curious how I'd go about checking? Were they referring to possibility of the +/- getting somehow switched while at GPA? (I thought +/- on the compression drivers was determined by the orientation of the diaphragms and couldn't be changed).

Thanks again for your input....

[Earl K]

I was afraid you were gonna say this. I'm going to at least get some quick measurements tonight of each speaker, so I can know how drastic the difference between the two really is. I've swapped diaphragms, crossovers, etc. I just hope it's something that is addressable - though since both drivers have been gone over by GPA, I don't know what else could really be done.

Someone on another forum asked if I had checked the magnetic polarity of the drivers since getting them back from GPA...they were sent to GPA before I acquired them, but I'm curious how I'd go about checking? Were they referring to possibility of the +/- getting somehow switched while at GPA? (I thought +/- on the compression drivers was determined by the orientation of the diaphragms and couldn't be changed).

Thanks again for your input....

Have you made sure the phase-plug ( from the the lower level driver > which I believe is the tangerine one ) is still glued in properly?

That glue does eventually let go ( that's much more likely a problem than a magnetic polarity problem ).



Magnetic Polarity? Bowtie is referring to the magnetic polarity of the magnet in the driver ( GPA has had at least one documented "Ooops" moment in the past caused by setting their recharger to the wrong polarity setting for alnico type magnets ).

You would need something like REW and a UMIK-1 usb test mic to test for polarity ( since you need to look at the impulse of the captured sweep ) > this is gear you don't currently have I believe.