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Hi guys,
As some as you now I recently got my hands on two tractrix horns with a Fc of 220Hz. I'm planning to use them from 500Hz upwards, crossing over to a 15inch Ciare Woofer. There are several compression drivers that could be interesting, I'm sure some 1.4 and 2'' drivers will go down to 500hz, but I figured that 1'' most prob. will have better HF extension. So, What about the Altec 902 (or GPA 902 or 909), can it be safely crossed (2nd order) at 500Hz for home use? Or maybe some other 1'' drivers that can pull this off without a problem?
cheers,
Jacob
Follow Ups:
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.
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
Greets!
What is its throat size? Anyway, a 220 Hz tractrix long enough to mate to a 1" will beam big time, so a narrow 'sweet spot', and the poor flare match up will probably roll off some of the small driver's top end, defeating the point of using it.
GM
Loud is Beautiful if it's Clean!
This is a measurement from the horn with the BMS 4590 both axial and at 30degrees. It extends well over 20kHz so it is not completely clear to me why other drivers like e.g. the Altec 902 should also not extend enough. (btw the measurement was done by somebody on a german message board that owns this combo. )
For the simple reason that Altec, JBL, etc., are single element drivers relying on well controlled diaphragm/suspension break-up modes for their HF BW while the BMS is a coaxial, so an apples n' oranges comparison. The others can be made to extend this high, but must have a horn designed to do it and even then CD horn EQ is required, at least on the Altec/GPA units if horn loaded for other than tweeter apps.
Anyway, it will be interesting to see how an Altec/GPA, JBL, or similar driver measures on these somewhat compromised 'rubber throat' tractrix horns. From what you've presented though, seems like it's been optimized for the 2" BMS or similar, so apparently the one to buy if extreme HF SQ is a major issue.
As always though, YMMV. ;^)
Loud is Beautiful if it's Clean!
Hi,
the 30degrees off axis measurements with the BMS and my horn do somehow show not so much beaming? is this the driver? or is the it the horn that makes this possible? I always thought the horn would cause the beaming, not the driver?
Jacob
Greets!
No it doesn't. It's a function of either or both, though a single diaphragm driver will always beam some. Anyway, my remarks were about a big tractrix run all the way down to a 1" throat, which doesn't apply to the 2" BMS coaxial horn combo.
GM
Loud is Beautiful if it's Clean!
Well, it is better then to stick to 2'' drivers in my case I would say. And seems like the BMS together with my horns makes a very nice combo when it comes to extension and beaming I would say. And there are quite some fans around when it comes to BMS 4590, also some people that do not like them of course.
Jacob
30degrees
Well, The diameter of the horn is 52cm, which whould translate into a Flare cutoff freq. of ~220 if I'm correct. The horn length is 33cm and the throat entry is made for a 2'' driver.
for a 2" dia throat and Fc = 220. The mouth dia seems right.
Jim N
Hmm, I get a ~52.56 cm axial length with a 26 cm mouth radius down to a 2.54 cm throat radius and ~70.54 cm for a 1.27 cm throat radius, making it ~ the horn equivalent of a 'pencil neck geek' ;^).
Loud is Beautiful if it's Clean!
mmmm, I think that it is not a Tractrix then?
The horn appears to be a tractix except with possibly a short transition throat section, but can't tell for sure, and it looks like the adapter preserves the driver's wall angle and accept a glitch in the expansion higher up at the adapter/horn junction.
The bottom line is the horn needs to be carefully matched to each driver size/type for best performance since the first few inches represents the entire HF BW, which they appear to have done, so probably is fine, though it will beam excessively by my standards due to the slow overall expansion.
As always though, YMMV. ;^)
Loud is Beautiful if it's Clean!
What are you using for sonic velocity?
Jim
- http://cgi.ebay.ca/Tractrix-Horn-2-140-Hz-Lowcost-Version-without-BMS_W0QQitemZ9718926978QQihZ009QQcategoryZ14980QQcmdZViewItem (Open in New Window)
Something like that. Just imagine the taper continuing down to 1", the driver will be basically firing into a pipe, choking it somewhat.......
I use 1130 ft/sec.
Loud is Beautiful if it's Clean!
Are you doing 5-way horn system?? If not how are you going to integrate tweeter with 220 Hz behemot? Regards
No no, I want to build a 2 way. The tweeter doesn't need to go down to 220Hz(Fc of the horn) but to 500Hz, or maybe another higher suitable freq. But I understood that 500Hz is a good XO point. The 15inch woofer will go into a MLTL or a BR.
Jacob
.....and has been implemented down towards 500Hz by some.
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