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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
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!
Follow Ups:
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!
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