What is the difference between 908 and 902 drivers?

[BillWojo]

Picked up a set of 511b horns with a set of drivers on them, no markings on the drivers at all. I sent pics of the drivers to GPA and he replied that they were 908 drivers. There is no aluminum caps on them and no rubber ring, just bare drivers with the plastic loading caps and the tangerine plugs. The diaphragms are Symbielik.
I would like to cross these in an OB design at 500Hz.
I'm new to the world of Altec and have been reading up on them the last few days but I can't find out what the differences between these 2 drivers are. From the pics I have come across they look the same. Do they perform the same? Should I add new diaphragms from GPA? Should I get different drivers altogether? I'd like to use these if possible, I still need to get my 921 speakers reconed as 416 and figure out a cross over. I don't have buckets of money either.
Any and all help will be appreciated. I have a suspicion that this setup if done right will smoke my Klipsch Heresy's.
Thanks

BillWojo

[bowtie427ss]

for hifi apps @ 500hz XO you want an annular slit(non-tangerine) 802 with proper wool felt damped rear covers.

511 horn provides marginal acoustic load at 500hz, and has a 1 inch throat opening.

902/908/909 have a 7/8 inch throat aperture, for hifi apps you really don't want that step in the throat.

[BillWojo]

Thanks bowtie427ss. Is that the only issue, the step? I could machine a 1" thick adapter with a taper to match the throat aperture to the throat of the horn. I take it by your name that your a BB Chevy fan, well I guess this is like airflow in an engine where any step or transition will cost you. I see that when working with the airflow bench at the race shop.
So if I made the adapter, would that load the horn to get me down to 500Hz? It seems that most folks with the 511b horns like to cross down there.
Thanks, I'm learning more and more every day from this site.

BillWojo

[Elitopus1]

The older 802D/808A and earlier drivers had a annual slit metal phase plug. Those drivers are decently happy being crossed over at 500hz. Anything newer with the tangerine phase plug likes a 800hz or 1200hz crossover. The benefit of those drivers is they give up some low end to get more top end HF response.
It just depends what you are looking for.

[mah]

This thread states that not all 90x have 7/8" exits and raises the possibility of 11 and 13 slit tangerine phase plugs being used.


What consitutes the diference between the 902-8a andb? [Archive] - Lansing Heritage Forums


Phase plug:

http://www.hostboard.com/forums/f700...ug/index2.html


13 slit plug in large format driver:

Another Altec Build


The more, the better?

Rank 379 driver:

Beyond the Ariel - Page 419 - diyAudio

[bowtie427ss]

Please post a photo of a 1 inch aperture 900 series driver body with a ruler clearly demonstrating the 1 inch dimension.

Until that happens i'm calling internet lore. So far, every individual that has claimed to have a 1 inch throat 900 series driver that took the time to measure carefully and report back, has measured a 7/8 inch aperture.

13 slits governed by patent.

11 slits = GPA current production, avoids infringing on the 13 slit patent currently owned by Altec Lansing Technologies.