I've been playing around with Altec drivers for almost 20 years and have only listened to aluminum diaphragms until now.
Altec Aluminum Diaphragms
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| Altec 20275 Aluminum voice coil DCR = 9 ohms |
The 16 ohm Altec 20275 is the original diaphragm fitted to my cherished green hammertone 802D. This is the Altec diaphragm I am most familiar with and to my ears its tonal balance favors the midrange more than the later 34852, which is known for better high frequency extension.
I speculate that late 40s to 50s wrinkle charcoal gray/brown and late 50s to 60s hammertone green 802s, 804As and 806As command premium prices IF they are fitted with original and intact 20275s, which are now unobtainium. By early to late 70s, black 802s and 806s were fitted with either the 16 ohm 34852 or the 8 ohm 34647.
I speculate that late 40s to 50s wrinkle charcoal gray/brown and late 50s to 60s hammertone green 802s, 804As and 806As command premium prices IF they are fitted with original and intact 20275s, which are now unobtainium. By early to late 70s, black 802s and 806s were fitted with either the 16 ohm 34852 or the 8 ohm 34647.
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| Altec 34852 Copper Clad Aluminum Wire voice coil DCR = 12.5 ohms |
My Altec 605B Duplex should have been originally equipped with a 20275 but by the time I acquired it, this 34852 was already fitted. Maybe that's why I still got it cheap ;)
As previously noted in my 605B experiments, I hear a significant sonic difference between a 34852 and a 20275, so much so that I cannot recommend their use as a stereo pair. Jeff Markwart has more 20275 vs. 34852 info if you scroll down to the bottom of this page.
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| GPA 34852 Copper voice coil DCR = 11.5 ohms |
AFAIK, Great Plains Audio is the only source for Altec diaphragms made to original Altec specifications. Even if they have a website, they prefer to do business the old fashioned way. I always call Bill Hanuschak to place an order and never had problems.
I haven't had a chance to compare this GPA 34852 to the Altec 34852 because the 605B Duplex was left behind in the attic;( But there's no doubt that this GPA is the real thing - very dynamic, with clean and clear harmonic overtones up the wazoo!
Altec Clone
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| Chinese Aluminum Diaphragm Clone Copper voice coil DCR = 11.9 ohms |
For kicks, I made an offer to one of the Chinese vendors on eBay and got this pair of 16 ohm diaphragms for about $24/pair, shipped. These clones will tide you over in a pinch. However, even a casual comparison to an Altec original or GPA diaphragm revealed smeared harmonic overtones and compressed dynamics.
Spot the fake
Left picture (clockwise from left) - older version Altec diaphragms used screw terminals on a raised platform, later Altecs and GPAs have tabs, Chinese clones do not have a raised platform for the screw terminals.
Right picture - The raised platform in the Altec uses tapped machine screws whereas in the Chinese copy the screws are self-tapping.
Altec Symbiotik
I recently acquired a couple of unloved 70s era 802 and 808 drivers, some fitted with Symbiotiks.
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| Two abused Altec diaphragms: Symbiotik on the left and aluminum on the right |
The Symbiotik was Altec's initial response to the 60s demand for a higher power handling diaphragm. As pictured above, due to the rigidity of the aluminum suspension, it can shatter when overdriven. I can only surmise that the Symbiotik diaphragm, which uses a polyimide/mylar type suspension, evolved from a research and development project at LTV by John Hilliard and Jonas Renkus.
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| Early + Later Symbiotik diaphragms |
In early Symbiotiks, the abrupt 90 degree angle voice coil termination (left) also caused failures in the field due to metal fatigue. I repaired this early Symbiotik by carefully flowing solder between the broken ends with a low temperature soldering iron. This issue was rectified in later production Symbiotiks (right).
Uncovered: Altec > Emilar
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| Top = early Emilar with brown mylar suspension Bottom left = later Emilar with gray mylar suspension Bottom right = Altec Symbiotik |
I have written favorably about Emilar and Renkus-Heinz compression drivers, and noted that their extreme top end was a bit reticent compared to Altec drivers with aluminum diaphragms. Let's see how the earlier Symbiotik technology stacks up.
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| Top = later Altec Symbiotik with tabs and improved termination DCR = 6.7 ohms Bottom = early Altec Symbiotik with screw terminals DCR = 7.5 ohms |
In retrospect, Altec aficionados may have been hasty and/or unkind in their initial reception of the Symbiotik. Even if the Symbiotik rolls off earlier than its aluminum brethren, it still reproduces proper harmonic overtones. It sounds very sweet, airy and open, with none of the smearing and compression I hear from the Asian clones. A Symbiotik equipped 802/808 sounds more organic than its descendants from Emilar and Renkus-Heinz. To my ears, the Symbiotic diaphragm has a niche in Hi-Fi and may well be the antidote to those who find the aluminum diaphragm a bit aggressive.
Unfortunately, there are no modern replacements for Symbiotik diaphragms. You'll have to find original units that did not suffer catastrophic meltdowns. Although it's just a hunch, the Radian replacement diaphragm for Altecs should have Symbiotik DNA because of the Emilar/Plus One connection.
Octave RTA by Onyx
Since affordable audio measurement apps have become available, I got this $5 app for my iPhone as suggested by my buddy J-Rob.
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| Test set-up |
The Altec 414A housed in a 3.5 cu. ft. repurposed Madrid (861) bass-reflex cabinet is driven full-range, J-Rob style, while the Altec 32A metal horn + driver combo is protected by the crossover + EQ below.
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| Crossover + EQ |
I was quite surprised to see pretty decent RTA results since I've been building/tweaking crossovers for over 20 years without a computer simulation program or an RTA.
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| Altec 802-8D + GPA 34852 |
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| Altec 808-8A + Chinese 16 ohm diaphragm |
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| Altec 808-8A + Symbiotic |
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| Emilar EA175-16 (alnico) |
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| Emilar EC175-8 (ferrite) |
These graphs pretty much represent how these driver/diaphragm combinations perform except the Chinese clone which looked good but sounded rolled off, compressed and smeared as mentioned above. Unlike human ears, an RTA will measure sound waves but will not discern unmusical harmonic overtones. Even my wife thought the Chinese diaphragm sounded muffled. Although she argues that if I can afford only a $12 diaphragm, I better be happy with it ;(
It goes to show that it is much easier to satisfy audio measuring equipment than human ears.
Update
Check out HifiTown's Altec 808-8A video!
I tried a pair of the Radian diaphragms on some 15" Urei co-axials which had JBL HF drivers, they were a big improvement over the stock titanium JBL diaphragms. Probably worth the price of admission just to compare them to the rest of what's available in the current market...
ReplyDeleteRoscoe
That's good to hear Roscoe! Ti and Be diaphragms are controversial to those weaned on classic Altec/JBL/WE designs ;)
DeleteMy only problem with the Radian 1228-8/16 (Altec replacement) is, they cost the same as GPA aluminum diaphragms ;(
JE
I’m in the process of testing the Radian diaphragm on my UREI 815A, the new diaphragm arrived Thursday, will let you guys know how it goes. I’m particularly curious how IMD performance will change.
ReplyDeleteSo I'm disappointed in the results from the Radian, and I'll be reaching out to the manufacturer for their perspective. One unexpected difference from the old to the new driver however, was that the UREI A-series still had the loading cap on the HF driver...I was expecting that to have been gone, and the back cap to have the damping material in it, like I've seen in other ceramic Altec coaxials...and given the differences in the diaphragms, I could not use the loading cap with the Radian diaphragm. I did place a fiberglass disc inside the loading cap however during the test. I found sensitivity was less than the Altec, and ran an IMD test with 2 tones at 2KHz and 3KHz and examined the IM products, and unfortunately found 3rd order products at -56 dbc (1KHz) and -49 dbc (4KHz)...the Altec diaphragm showed 3rd order products at -72 dbc (1KHz) and -57 (4KHz). The higher order products were all elevated as well.
ReplyDeleteAFAIK, Radian diaphragm technology evolved from the research done by Jonas Renkus and John Hilliard when Altec was still owned by LTV in the early 60s, which resulted in the Altec Symbiotik diaphragm. Thus, the Radian diaphragm is quite different from the Altec/GPA aluminum diaphragm.
DeleteJE
Hello,
ReplyDeleteI've discovered my old set of Altec Valencias (846B) have the diaphragms with the right angle bend in theleads. Both are broken at the bend in one speaker and I suspect both speakers.
Can you give me some advice on repairing the breaks? I considered one forum poster's method but that included extra wire and a blob of solder which I think will load the diaphragm, reducing the frequency response.
My second thought was a conductive epoxy, but the mass of what would probably be a 'blob' of epoxy woud probably, also, load the diaphragm.
You're method seems the best and would last the longest.
I asked Midwest Speaker Repair about servicing mine and they declined saying they had had bad luck wth the repair or the longevity of the repair.
Thank you,
Jim
Hi Jim,
DeleteI have no experience with conductive epoxy. The only repair I've done is flowing solder to bridge the gap between the broken leads as pictured above. I don't hear a difference between that repaired Symbiotik and an intact sample. I've also never repaired an aluminum version.
I've had no issues with any of my repaired diaphragms but then I only use flea powered SET amps and crossover above 2 kHz. I can understand why speaker repair centers won't take on this job because there's a good chance that it will break when over driven especially at lower crossover frequencies which is beyond their control.
I published this repair tip for those who want to try it on dead diaphragms since GPA's prices have risen significantly in the past couple of years.
Just like anything in my blog, try it at your own risk.
Good luck!
JE
Hello,
ReplyDeleteI forgot to ask. Do you make such repairs?
Thank you,
Jim J.
Sorry I'm not accepting repairs. I'm still busy teaching and performing. I was out of town for rehearsals and concerts, that's why my replies were delayed.
DeleteJE
Hi JE, great job recapping Altec diaphragm types and still very useful, thanks!.
ReplyDeleteHence I hunted 1 early 20275, happiness turned to disapp't as DCR=1 though seller claimed he enjoyed listening to it(BS). Opening Dia revealed dirtiness/marks under Dia dome n driver circumf. was told aluminum VC wire is fragile and the debris killed it! Could IT be said?
I've only had experience with 2 pairs of 20275 and they are all clean. I've yet to encounter severely oxidized voice coils. But I've heard from others that, that is the result of poor storage.
DeleteUnfortunately, as these things become more sought after buyers also have to watch out for less than honorable sellers.
Sorry about your bad luck!
JE
Thanks for quick reply. My last sentence s/be: Could it be saved? Mine might have severe oxidization(wish I could att. pics) therefore, KAPUT!
ReplyDeleteSevere oxidation is probably the reason why the DCR reading = 1 Ohm. I wish I could help but this is beyond my experience.
DeleteHi JE,
ReplyDeletesuper helpful blog. Currently in the process building an altec two way with a 416A woofer and 811 horn.
It's been incredibly difficult to find 802s or 806s with original parts and it seems that original altec diaphragm's actually have not printed the part number you refer to i.e. 20275 or 34852 on there. At least that's what I can see in the pictures of yours and the ones I found. Is there a way or place I could check if the diaphragm's I got or want to get are original ones?
Thanks a lot.
Philipp
Through the years, I've handled a little over a dozen of original Altec diaphragms and have only encountered one which didn't have the part number printed. The main thing to avoid are the Chinese copies which are pictured above. Other than that I've uploaded everything I know. Good luck!
DeleteJE