900 series drivers

**badtoby** · March 25th, 2012, 12:24 AM

I'am trying to put together the parts I'll need for the 19 cabs I've got and have seen different versions of the 900 CD's. Are they all the same except the diaphragms ?

**bowtie427ss** · March 25th, 2012, 07:55 AM

Are they all the same except the diaphragms ?

There is some variation in motor structure between the earliest produced versions and the bulk.

One thing you might want to consider is that 900 series drivers have a 7/8 diameter throat and 811 throat is one inch.

IMO, 902 doesn't belong on 811 or 511. Those horns are designed to mate perfectly with 800 series drivers.

**Altec Best** · March 25th, 2012, 08:18 AM

One of the horns for those 900 series are the small Manta's, MR931 I think. Bowtie the MR931 has a 7/8" throat doesn't it ? Although later Model 19's came with 902-8A's with the 811 along with the change of woofers as well, the new ferrite 416's . The 416-8C.

**bowtie427ss** · March 25th, 2012, 08:54 AM

Bowtie the MR931 has a 7/8" throat doesn't it ?

Yes, making the transition area from horn to driver "smooth as a newborn baby's butt".

**Altec Best** · March 25th, 2012, 09:40 AM

Toby do you have Model 19 XO's for this ? The cabinets in good shape after inspection ?

**badtoby** · March 25th, 2012, 01:14 PM

Still looking for the XO's, don't want to build any.Its not that its over my head I just don't want to. However I have been spending time looking at the Z19's. 25 years ago I was a tech at AT&T till they closed leaving 1000 techs unemployed not long after Bendix dumped another 1500 techs that the KC market could not support. At that point I became a rural letter carrier and forgot most of what I had learned, the PO will do that to you. The cabs are OK to use for now but down the road they will be getting new veneer. All I need now is the XO's and CD's

**Earl K** · March 25th, 2012, 04:24 PM

> If I was in your shoes I'd buy new drivers ( for your M19s ) from GPA .
> Either their 802G, or their 902 variant will function well with the M19s crossover point .

> GPA's 902s do use a 1" exit ( so they'll mate nicely with Altecs legacy sectoral horns ).

> GPA re-engineered Altec's 11-Slit Radial ( Tangerine ) phase-plug into a 9-Slit Radial phase-plug and in the process achieved better UHF extension for their efforts ( at a cost of slightly reduced LF performance ) .

> More importantly ( IMO ), GPA achieved better linearity within their drivers pass-band and so were able to partially fill in some of those pesky response "holes" that plague all earlier 802s ( & 902s when mounted to 811 & 511 horns ) .

> Here's a look at the sort of response that is typical of the legacy combo ( red trace ) ;

> The legacy driver ( on 811 Horn ) typically exhibits this "roller-coastering", displaying significant dips at 3K & 7.5K .

> Keep in mind , the second capture ( shown above from Zilch on his Z19 ) uses a higher resolution vertical scale ( & size ) when compared to the other 2 sweeps .

> In a nut shell , I'd use GPAs improved small format drivers ( rather than searching out vintage Altecs ) for a project like yours .
> The response variations are about 1/2 as big as the original Altecs .

PS ; Here's another look at Roller-Coastering in both vintage combos ( the 811 is worse than the 511 / with the M19 slightly exacerbating the hole at 3K ) ;