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In Reply to: RE: GPA/Altec 902 all the way down to 500Hz? posted by Jacobusje on August 04, 2007 at 03:48:53
I use the Altec 902 with a 2nd order 800 hz crossover on Edgar 650 hz horns, which have a Tractrix flare. This is the best high frequency speaker system I have had in my home. The 802 (alnico magnet version) is often mated with the Altec 511 horn, and commonly crossed over at 500 hz.
Follow Ups:
Interesting. What are in general good XO points (with slopes) for 2 way systems with a horn and a 15inch woofer for the bass section. I often read 500Hz, 900Hz, 1200Hz? all with 2nd order? I guess my questions is what are the best XO points ans slopes to get the best integration between the horn and the woofer?
There are a few considerations when choosing a crossover point.
1: Directivity-- For a 12" woofer 1200Hz-- 15" woofer- 700Hz
2: Distortion--- A 1" driver distorts sooner than a 2" driver.
Best fit is 1" 1.5kHz to 2kHz--- 2" driver 700Hz and above.
Note this parameter is also power dependent. You can crossover a 1" driver at 500Hz as long as you do not exceed 1w/1m.
Note also that this means total program power. About 30% of lets say 10 watts, what hits the HF driver is 3watts.
This is 106dB 1w/1m ( 10 watts) if the system is 100dB 1w/1m ..pretty loud.
The fabulous RCA LC9 crosses over at 500Hz--sounds terrific, with a JBL 2410/D175 driver ( 12 dB per octave). The radial horn with it's 20 degree x 90 degree dispersion is why this is possible.
PS the Altec 802 has an underhung voice coil. The JBL D175 voice coil is .125" longer-meaning better power handling at 500Hz. ( same size as .250” gap)
You must have at least 12-18dB per octave network to protect driver. 6db is OUT!
Hope this helps, Bill
hey bill-
why would a first order on a comp driver be out-- especially given the other things you were saying-- e.g. matching directivity and distortion capacities to the driver?
if you're crossing over a 1" driver to a 12" woof-- since you're already limited to what's possible with what you have-- you'd probably need to cross over pretty high, right? assuming to get the best characteristics out of your compression driver, you're going to need to knee it at about 1800hz-- so if you're already rolling off that high-- the driver will still roll off naturally too-- and a well chosen horn'll also help lift the load. in theory- you'd still be down at least 12 db by 450hz-- but the horn and driver'll run it down a lot faster to boot.
not to say you'd want to run 250 watts through it-- but it's not impossible to use a 6db/octave slope.. i think a lot of folks ask too much of their drivers!
yrs
d
"why would a first order on a comp driver be out-- especially given the other things you were saying-- e.g. matching directivity and distortion capacities to the driver?"
Unless you are crossing over above 1500Hz or so, there is just too much energy hitting the diaphragm. Especially at 700hz or below.
The distortion level of most compression drivers i 1-2% even with one watt.
The power handling drops dramatically below 1500Hz as well.
The diaphragms are very fragile- it only takes one party to wipe out your TAD at 6 dB.
Also using a steeper slope with a notch filter will help with the acoustic phase.
I would say, you could get away with a 4.6 uf, or 6.8uf if you are careful.
Finally, horns unload fast, so you want a horn with the right Fc if you do use a 6dB.
But, I come from the P.A. world, many a sad story to tell- perhaps I am over cautious.
Bill
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