Altec 902 vs 908 driver

[Blvdre]

Does anyone have any experience or opinions as far as the audible differences between these two drivers? It looks like the main difference is w/ the diaphragm materials, and I'm wondering if the 908 may not measure up to the 902 in terms of sound quality.

[cjgeraci]

Not familiar with the 908.

Are you sure that you don't mean the 909 driver?

Carl.

[Blvdre]

No, this is the 908:

http://www.lansingheritage.org/html/altec/specs/components/908-8b.htm

[Blvdre]

From what I've read, it sounds like diaphragm replacement is a good idea anyway, so my question is, could I replace the 908's symbiotik diaphragm with the 902's aluminum? I see Legacy Sound has these for $200 a pair, has anyone tried sound speaker repairs replacement, at $50/each? I'm guessing not as good, but you never know.

[PrestonTom]

Regarding the diaphragm replacements:

Part of the answer depends on what sort of bandwidth you are trying to achieve (especially how high in frequency) and how hard you are going to drive them (especially if they are crossed at too low of a frequency). The choice of material used will depend on this.

I would be wary of aftermarket diaphragms (non OEM), you sometimes get what you pay for.

It is worth contacting Great Plains Audio to get some advice on this issue.

-Tom

[Blvdre]

Thanks for the advice Tom, I'll do that. My intention is to put together a two-way using my La Scalas for low-end duty (for now), and the 511B/ 908 on top, so I'm hoping for enough high-end extension to get the job done. From what I've read, it seems 600 hz is a popular x-over point, and I won't be pushing these at high volumes.

[JohnA]

The 908 has a symbiotic diaphragm that takes lots of power and gives up highs above 10k for it.

The 902-8B diaphragm will fit and will be 3 or 4 db down at 20k.

Great Plains Audio is a bunch or old Altec guys with the OEM tooling. Their 902 diaphragms are just like the originals and perform as well. I'm pretty sure a new one costs $75.

[Blvdre]

Thnaks for the info John. I left a message with the Great Plains guys, will try e-mailing them. From what I gleaned on this forum, the great plains diaphragm is light, like the original diaphragm (type A, if I remember), more extended than the later versions.

[TBrennan]

An interesting aside. The difference between the diaphragm pf the 902 and the "symbiotic" of the 908 is not in the material of the dome but the surround materail, the 902 using the traditional folded aluminum and the symbiotic a plastic material. This plastic surround gave higher power handling because the old aluminum surround could crack under high stress.

So anyway I read online where an old Emilar guy who'd worked at Altec (Emilar was an offshoot from Altec) said the reason the symbiotic had less high frequency extension was because the diaphragm had a thicker mounting ring, thus the diaphragm was farther from th phasing plug with a resulting loss of highs. This was done for marketing reasons, the sales people for some cockamamie reason wanted a difference in performence between the two.

Note that Emilar used, and Radian uses an aluminum diaphragm very similar to the Altec symbiotic with no loss in highs. Radian was in part an offshoot from Emilar.

[TBrennan]

Thnaks for the info John. I left a message with the Great Plains guys, will try e-mailing them. From what I gleaned on this forum, the great plains diaphragm is light, like the original diaphragm (type A, if I remember), more extended than the later versions.

The GPA diaphragm is NOT the elusive and legendary "light", not that it makes any real difference. Most of the reputation of the so called "light" is based on articles and assertion by Jim Dickerson. Personally I never heard a difference nor have I seen a difference in high frequency extension documented by testing. If such a difference exists it's very subtle.

[djk]

The thinner diaphgrams didn't really go any higher, they went into breakup mode and the high distortion

seemed like high end. They handled power poorly at 500hz and were discontinued.

The 908 had a Kapton edge that absorbed a lot of fine detail and rolled the high end off a bit.

Part of this was having to increase the diaphragm to phase plug spacing to get enough output

at 500hz and not crash into the phase plug at 50W input power. The 909 also suffers a bit in the

high end for the spacing reason too.

I've bought Radian replacement diaphragms for both Altec and JBL drivers. They are unreliable

for PA. I wouldn't use them for hi-fi unless I has a tweeter. I've also had samples of their top-of-the-line

1" and 2" drivers. While reasonable in price they would not replace Altec and JBL, and I returned them.

[Blvdre]

OK, so the increased phase plug spacing of the 908 diaphragms detracted from the high-end output. It sounds like the GPA replacements would be fine, even better that they're not the light diaphragms.

I had a line on some 908 drivers, but passed on them, so that point is a bit moot. I would like to pick up some 902s down the road, though, so this info is helpful.