909s are 1"

[Phil-G]

here's a pair for sale on ebay. there's a picture of the gasket side without the gasket and screen. I copied the pic and resized it till the studs were on 3" centers at the base. the outlet measures 1". check for yourselves

One Pair of Altec Lansing Model 909-8A High Frequency Drivers | eBay

[GM]

True, what's this about?

GM

[bowtie427ss]

what's this about?

900 series drivers have a 7/8 inch throat.

There is an ongoing debate that they made 900 series motors with 1 inch throats. Perhaps they did, but i will need more than scaling a digital image for proof positive.

It wouldn't make sense. The 900 series drivers are all shown to be the same depth.

If there was a variation in throat diameter with a constant depth dimension, then there would have to be a variation in throat angle, no?

I understand that the marketing department is a whole other ball of wax. But, would the Altec engineering dept have done that?

[IMG][/IMG]

[Phil-G]

One thing I noticed when i pulled the gasket off, was the throat insert on my 902 has a 1/16 lip inside a 1" hole.
Check the photo yourself.

[Elitopus1]

I would bet that all the 900 series were at one time 7/8" and then later (or earlier) 1". It would make no sense for only the 909 to be that way. I'm sure if you looked at enough of them you could find 1" 902 and 908 also

[GM]

At least the few I had any 'hands on' experience with, the 902, 908 are 7/8", hence have a frequency BW shifted somewhat higher than the 802-8Gs, which in turn is slightly higher by design than earlier 800 series, with 909 switching back to 1". Don't recall doing anything with 906s, but assumed 7/8", so anyone know for sure what size it is?

GM

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I would bet that all the 900 series were at one time 7/8"........

Inretrospect, by the time the 909 came out, Altec was already down to 'making do' in some cases with what they had/could afford according to the local distributor, so no telling what they actually shipped out, especially if it was a panic replacement order for a prosound app.

Frankly, the 802-8G was the last Altec small format driver of interest to me, so recommend using more modern drivers if the older, pampered [or at least GPA rejuvenated] ones aren't in the budget.

GM

[BillWojo]

I have been reluctant to remove the screens from my 908 converted to 902 drivers (new GPA aluminum diaphragms). I did how ever make 3/4 inch thick adapter plates from 4" diameter aluminum barstock that taper from 7/8" to 1". I may still remove the screens, these will not go into an outdoor installation.
I'm just wondering what the transition from the two tapers looks like. I suspect that they are fairly close.
Where the drivers bolt to the horns is interesting. There is no machined taper, just a hole that rapidly changes shape. I really don't think that a small difference in taper from either the 802 or 902 or even my adapters would matter much. Heck, the hole is not machined, you can feel the imperfections at the seams.
BTW, I arrived at the 3/4" thickness of my adapters by calculating what I needed to still fit them inside the HeathKit AS101 enclosures if anyone wants to know.

BillWojo

[Elitopus1]

I have been reluctant to remove the screens from my 908 converted to 902 drivers (new GPA aluminum diaphragms). I did how ever make 3/4 inch thick adapter plates from 4" diameter aluminum barstock that taper from 7/8" to 1". I may still remove the screens, these will not go into an outdoor installation.

I have taken the screens out of my 802D and 802G drivers. They sound much better without them. Just curiously why are you keeping them in your 902/908? I am not familiar with the ferrite Altec drivers and how the screen is installed.
I have also been using wax paper gaskets too. It makes the transition much smoother

[GM]

Hmm, 7/8" = 0.875" and ~1130 ft_sec = ~13560"_sec. and circumference/pi = dia. of a WL, then:

13560/pi = ~4316.3" dia. for a 1" exit and /0.875" = ~4932.9 Hz = ~616.6 Hz shift in BW, acoustic impedance mismatch, so acoustically not what I'd consider as 'fairly close', but I'm not an expert, so just IMO/E.

Using a common reference [2 pi f], this theoretically shifts the HF up by ~3874 Hz, though the horn's mass air inductance [reactance?, can't remember ATM] will knock down much of this, though still an audible gain IM[limited]E before I lost my top end 'air' hearing.

Re ideal adapter length, no clue without my Excel spreadsheets or drawing it to scale, though as you noted, any ambiguities in the path-length will reduce usable hi-def HF.

GM

[BillWojo]

GM, could you break that down for us mortals to understand please. If building the tapered adapters is going to screw something up, what does keeping the 7/8" to 1" transition do? Altec thought it was ok to do this, I thought blending the transition would be beneficial instead of an abrupt step.
I see I have a lot to learn, and you seem to know a lot, can you dumb some of this down, I'm sure a lot on this board would benefit.
Thank you

BillWojo