Altec diaphragms - Radian or GPA?

[robertbartsch]

I have a pair of Altec 902 compression drivers and both have bad frams.

I'll be using these in a HT.

Anyway, should I go with the GPA or Radion diaphragms?

Thx.

[Tom Brennan]

GPAs, they're just like original Altecs.

At one time Radians were an excellent alternative but now their prices are almost as high as GPAs so you might as well use GPA. There's nothing wrong with Radians, they sound good.

[Earl K]

Hi Robert,

- I'd suggest that neither alternative is very good if you don't have FR measuring equipment to help do a proper diaphragm install .

- If you want new, properly fitted-up Altec type 902 drivers / then maybe buy a new set of drivers from GPA ( after receiving some reassurances from them about what a stock FR curve would look like ) . GPA is unfortunately, quite miserly on publishing stats that help a buyer determine FR performance .
- Then sell your current 902s for what you can get for them ( on eBay or one of its' competitors ).

- Here's a study of 3 "unEQed" drivers on a cheap Korean exponential horn ( I use it since it gives good HF-lift & has quite decent LF loading ).
- Only the B&C ( in aqua ) with its titanium diaphragm has a useful response curve ( even after 3/4 of a decade of use ) . The Radian diaphragm appears to have a significant fitup problem ( & sorry, I can't remember how much time I spent trying to get it correct ). FWIW, this driver/diaphragm comb has never seen any use / so it's "not fatigued" . Perhaps tomorrow I'll ry again to see if I can get a better result .
- The OEM diaphragm in this Altec 902 example ( in fucia ) would appear to be fatigued / likely from it's years behind a 511 horn on a A7 combo ( obviously I bought a used pair ). Hopefully ( for the sake of GPAs business ) what I've shown is not the expected response curve of a new GPA 902 driver . I've got one other 902-8b which ( also to be done tomorrow ) I'll measure to see where it comes in at .

-FWIW,I guess you can see that installing new diaphragms is not just a "Plug & Play" exercise .


>< cheers :)

[Earl K]

- For those who are wondering , here's another study .
- An unfair comparison ( I suppose ) since the Altec diaphragm is certainly not brand new / though / the study is eBay applicable ( for those who prefer to roll the dice that direction ) .

>< cheers

[Earl K]

One final comparison ;

While the B&C is very good / even though it has a slight upward tilt on this horn / the JBL 2427H is better still ( it almost seems it was designed around this horn / or maybe it was the other way around ) .

Note ; no EQ was used / & all FR snapshots are from 24" away ( on axis ) .

>< cheers

[lowpoke]

Earl,

I'm pretty new to this and am just in the process of installing new GPA diaphragms in a pair of 808's (as you probably guessed by my question regarding gluing phase plugs). As far as I can tell there are two locating pins that hold my diaphragms in position, with no other adjustments evident.

Could you explain what you mean by "a proper diaphragm install"?
If I read your posts correctly you're saying that diaphragms should be "dialed in" somehow. Do you mean via EQ, or is there something I'm missing?
(Do other model drivers differ from the 808's for instance?)

[Earl K]

Hi lowpoke,

- Truthfully, I had forgotten that all Altec drivers still had those 2 locating pins / JBL 1" drivers stopped including them back in the 1980's .
- With those locating pins in place, it means that for you (unless you have some test gear ) / you're finished with your install .

- If you do have some test gear (such as a signal generator ) one would sweep sine waves through the driver ( from @ 600 hz to 2500 hz at say .25 volts which will be plenty loud ) listening for a purity of the signal . Any voice-coil "binding" ( within the gap ) will showup as a partial buzzing or a form of distorted signal . That's the sweep test in a nutshell . If buzzing is present then the coil needs to be slightly shifted within the gap. To accomplish this shift with an Altec, one would need to enlarge the holes (found in the diaphragms plastic ring ) where the locating pins insert themselves .

- After all this , a person should take a frequency snapshot ( the driver on a horn ) to verify performance . The challenge with taking a FR snapshot is that one needs a recognizable baseline for the sake of making meaningfull comparisons . As mentioned above , I have mine ( a cheap Korean exponential horn ) .

- Sorry I can't be more of a help / what horn are you using ?

>< cheers

ps;
- Moments ago I started a sweep on the 908 that has the Radian diaphragm installed / I haven't heard any problem so far that would pinpoint the cause of its very ragged response .
- I just took the Radian diaphragm out of the 908-8a body / & guess what ? The ferrite 908 doesn't have any locating pins . The Radians' fit has a lot of slop/"side to side play", allowing adjustments ( & mis-adjustments ) when centering the voice-coil within the gap, FWIW .

[bstleve]

Hi all,

here after, what I measured before, and after diaphragm centering on a 909-8A mounted on a multi-cellular horn :
It's worth a try !
None of mine 802, 902 nor 909 got pins...

Bertrand.

[Mr. Widget]

- The OEM diaphragm in this Altec 902 example ( in fucia ) would appear to be fatigued / likely from it's years behind a 511 horn on a A7 combo ( obviously I bought a used pair ).

-FWIW,I guess you can see that installing new diaphragms is not just a "Plug & Play" exercise .Thanks Earl... I've tried to make these points before and I don't think most people really believe or want to believe that the performance of vintage drivers is so fraught with potential problems. Yes, that coveted vintage driver may have seals intact and may still have a beautiful paint finish, but without really testing it, you have no idea what you are listening to.

As for plug and play... without a tone generator and some experience installing them, it can be very difficult to get a new diaphragm properly centered... especially if the diaphragm is slightly out of round or the guide pins are too tight.


Widget

[Earl K]

Bertrand, thanks for those "Before & After" pics. :)

- I'm sure that they'll help motivate those needing to get their OEM diaphragms realigned .

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=38832&stc=1&d=1240675775

- Above are my control curves ( to keep track of what's possible ) .

- Below are todays dismal results . :(


Thanks Earl... ,,,snip,,,,,
As for plug and play... without a tone generator and some experience installing them, it can be very difficult to get a new diaphragm properly centered... especially if the diaphragm is slightly out of round or the guide pins are too tight.

- You can say that again . I'm out of patience ( & I have all the necessary tools ). :banghead:
- I took the Radian diaphragm and put it into a remagged 802-8D.
- This driver has locating pins and the diaphragm fit onto the pins quite tightly.
- One can see the disappointing results ( below ) in "Aqua" .
- I didn't bother to enlarge the holes in the diaphragm to get a looser fit so that I could try again .

- I put the Radian diaphragm back into the Altec 908 body and did my best to align it with tone ( after looking at an RTA of it mounted on a horn ). All I achieved was a different FR curve from my first posting ( & still not acceptable ) .

- I've now given up trying to get a decent fit ( & response curve ) from this combo.
- This diaphragm was purchased 9 years ago / perhaps Radian makes a better product now / though I won't be spending the money to find out .

>< cheers

[lowpoke]

Hey guys, thanks for the explanation, I understand what you're saying now.

My diaphragms are tight as hell on the pins with no room to move. I just hope it's all centered properly, as I have no way of testing them.
Thanks for spoiling my day :(

(Oh, almost forgot ... I have 511B horns Earl.)

[junker]

Hey guys sorry to bump this necro thread, but I recently went over to Radian in Orange, CA and they were even nice enough to give me a complete tour of the facility. I picked up four of the 1228-16 ohm diaphragms for me and my friend's Altec Flamencos. We both agree that they are clearly better then the OEM diaphragms, and anyone who is buying new diaphragms definitely need to consider these. The build quality is better, and the Al-Mg alloy is stiffer and lighter than the stock diaphragm material. The frame is beefier and has an extended metal platform. It also has copper plated aluminum voice could wire (square). The mylar surround is also lighter than the stock Al surround. We both feel there is improved clarity - my friend described as being more articulate. It may also have less edge and more smoothness, while possibly being slightly more extended on the top end. It certainly wasn't a mistake. GPA is an awesome company and I'd support them at every turn but these Radian diaphragms are the real deal and I at least need to put this out there for others considering replacement diaphragms. Thanks!