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View Full Version : What consitutes the diference between the 902-8a andb?



leifchristensen
12-14-2009, 10:58 AM
I can see that the drivers seem identical except that the b can be crossed lower..500 versus 1200hz ..is it only the use of different dia.that seperates them?
best
Leif
Norway

stephane RAME
12-14-2009, 11:26 AM
http://www.altecpro.com/pdfs/vintage/SpeakerAndMics/drivers/902-8A%20902-16A%20902-8T%20HF%20Drivers.pdf

http://www.altecpro.com/pdfs/vintage/SpeakerAndMics/drivers/902-8B%20HF%20Driver.pdf

Stphane :D

leifchristensen
12-14-2009, 11:30 AM
ha-ha
Ive been through those a couple of times but I cannot see the difference except the frequency and I want to now what makes them perform differently
best
Leif

Earl K
12-14-2009, 11:31 AM
Info gleaned from Todds' forum :


Sunday 5th of January 2003, 11:33 PM

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Hi this is Jim D, I'm over at Steve's and his computer is faster than mine.

The 902-A has no loading cap and no centering ring below the voice coil which effectively allows the diaphragm to vent into the magnet cavity.

The T is an A with a loading cap to prevent the diaphragm from moving too far at higher power input.

The B has the centering ring which prevents venting into the magnet and a loading cap.

All As amd most Bs have a 7/8 exit. About 1989, Jerry Hubbard then cheif engineer of acoustics at Altec, changed the 902s and 908s and the new 909 to a 1" exit.

To complicate matters further the last production of 902Bs, 908Bs and 909As once agin were built without the centering ring.

Yes they sound better without the loading cap and centering ring, although they may handle slightly less power.

Jim

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<> :)

leifchristensen
12-14-2009, 11:51 AM
thxs

ok so the A sounds better due to the lack of loading cap and centering ring at the price of being more restricted down towards the "upper midrange" and poorer power handling capacity
does anyone have a technical drawing maybe in "exploded view" where I can see the details
I have one of each driver and the 811B horn
maybe I should get another B?
since I planned to potensially run it with 515ghp in 416as , 1200 hz x/o seem slightly too high?
best
Leif

Earl K
12-14-2009, 12:30 PM
- More info from Jim D , ( gleaned from Todds' place )

- Original (OLD) thread is located here ! (http://www.hostboard.com/forums/altec-users-board/54863-mr902-hf.html)


Monday 9th of December 2002, 11:17 PM
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What you have are basically 902s.

The only way to tell which mark is to remove the diaphragm and then push a piece of bar copper #22 wire down the gap and see when it bottoms.

If it only goes in about 1/4 inch, these are B's.

If it goes in 1/2-1" they are A's.

Felt and screws can be obtained from GPA or locally. The felt fits snugly inside the cap and is about 3/8" thick. Get it from a fabric store.

The screws can be cut-off with a cutting tool like that on some wire strippers or get phillips head stainless 6/32 screws the right length.

No, there are no pins in the 902s, you center them the best you can, I always use an oscilator on ours.

The mounting studs are steel and are 12/24 on the driver side and 1/4/20 on the horn end. GPA might be the only place to get these.

You could use 12/24 all-thread with 1/4 sleeves in a pinch. Good listening,

Jim

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ok so the A sounds better due to the lack of loading cap and centering ring at the price of being more restricted down towards the "upper midrange" and poorer power handling capacity.

- This seems to be the commonly held POV ( group wisdom ) though I've never seen any response studies to support this view-point .


Does anyone have a technical drawing maybe in "exploded view" where I can see the details

- I've never seen an "exploded view" published, for the 902 .


I have one of each driver and the 811B horn, maybe I should get another B?

Since I planned to potensially run it with 515ghp in 416as , 1200 hz x/o seem slightly too high?

- Many people consider 1200 hz the correct crossover point for the 902/811 combo ( regardless of the 902-8x suffix ) .

<> :)

ps ; Here's the exploded view for the 808-8B driver . I've pointed to the centering ring within it's construction .

Earl K
12-14-2009, 02:20 PM
What consitutes the diference between the 902-8a & the 902-8B?

- Another possible difference between the two models is the number of radial slits in the tangerine phase plug .

- My pair of 902-8B have an eleven slit phase plug ( like the later 909-8a model ) whereas the Altec literature for the 908-8a & (early ??) 902-8B stipulate 13 slits should be present in the phase plug . Maybe the original 902-8a phase plug has 13 radial slits .
http://www.lansingheritage.org/images/altec/specs/components/902-8b-16b/thumbs/page1_small1.jpg (http://www.lansingheritage.org/images/altec/specs/components/902-8b-16b/page2.jpg)http://www.lansingheritage.org/images/altec/specs/components/thumbs/908_small.jpg (http://www.lansingheritage.org/images/altec/specs/components/908-8b/page2.jpg)http://www.lansingheritage.org/images/altec/specs/components/thumbs/909_small.jpg (http://www.lansingheritage.org/images/altec/specs/components/909-8a-16a/page4.jpg)

<> :)

leifchristensen
12-15-2009, 12:29 AM
Fantastic thxs
from junior member to senior member:applaud:
best
Leif

leifchristensen
12-23-2009, 05:18 AM
hello again
after setting up an excel spreadsheet with a matrix of my different 1 inch HF drivers and checking all available pdfs, I start to get the picture:
If I take out the loading cap and adds felt in the back chamber of the 902-8B it essentially becomes a 902-8A with respect to powerhandling,efficiency and frequency respons, OR ?
best
Leif
Norway