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Rapid
08-03-2003, 03:14 PM
Hello!
I'd like to know if a JBL 2240 would work to cross at 500Hz? It would be crossed to a JBL 2445 driver on a 350Hz horn.

Would you use the same slope for the highpass and lowpass filters, or is 2nd order highpass and 4th order lowpass better?

Mattias

Rapid
08-05-2003, 03:12 AM
Since 42 persons have read it but nobody answered, I guess I've expressed myself bad. The 2240 is flat to 1Khz, while the horn drops quick below 400Hz. That's why I wonder if I should use a different crossoverslope for the horn, like 2nd order, and 4th order lowpass for the sub. The idea is that the horn+crossoverslope would give 4th order response together.
I don't want to crossover higher because 500Hz is already too high for an 18" speaker.

Earl K
08-05-2003, 09:49 AM
Hi Rapid

- What horn are you going to use ?
- Do you already own the mentioned components ?

As far as crossover slopes; if it was me, I'd just wing it and add the necessary extra crossover elements ( poles 2, 3 & 4 ) as I went along . Listening and analyzing with an RTA ( Real Time Analyzer ) will show you whether you need to increase your passive crossover slopes from an initial 6 db to as high as 24 db . I'd likely stick with 12 db per octave myself . If you go to 2 pole ( 12 db ) consider a Bessel style filter instead of the usual ButterWorth. The reason ? - you'll need all the extra transients you can get in the area of your chosen crossover point. The Bessel has superior transient and group delay qualities at the expense of equal power summimg in the crossover region. You need to essentially "pick your poison" .

Your particular arrangements of components is a bit out of the norm - so it's understandable why you haven't had any responses.


regards <. Earl K

Rapid
08-05-2003, 02:49 PM
Thanks Earl for replying!
I was going to use a 12" EV speaker in a 80Hz exponentialhorn but one of the speakers are broken so I can't. This setups is probably a temporary solution until I can find other speakers.

The horn is a 350Hz round tractrixhorn, designed by me. (http://hem.passagen.se/sajberrapid)
I've got all the components:
JBL 2240 300l sealed box (might port them later)
JBL 2445
Fane ST5022 for 10Khz and up

I just need to paint the bassbins and solder some crossovers :) I've got a behringer DEQ2496 with RTA, if that'll help.

I think I'll build an active 4th order linkwitz-riley lowpass for the 2240s becuase the X-over frequency is already to high. Then I'll make a 1st order active highpass/lowpass filter 500Hz/10Khz. I'll also add a 33uF cap to make sure the amp doesn't fry the compressiondriver. This will totally make a 2nd order highpass at 500Hz (I think). For the Fanes, I'll have a 2,2uF cap to make a 1st order highpass at 10Khz.

Is this a bad idea?

Cheers,
Mattias

scott fitlin
08-05-2003, 03:14 PM
You can in fact use the 2240 crosswed over at 500Hz. However, this wouldnt be my choice of doing things! 500hz is into the midrange, and the 18in cone is just too large and heavy to really have quick, and open sounding response. The 2240 will definitely go up to 1K though.

Using a 12 between the woofer and the horn IS a good idea!

Another thing to point put is xover choice! You ( if your going to use said 18 up to the horn ) should listen to earl K.! 12db slopes will have a more natural sound and allow some overlap that your definitely going to need! 24db slopes will not have as much overlap and as i said before, the 18in woofer is not really lightweight and fast enough to reproduce the critical lower midrange frequencys properly. Jus my .02 cents.

Rapid
08-06-2003, 02:38 PM
Scott and Earl. Thanks for your replies!

Earl K
08-06-2003, 03:57 PM
Hi Rapid

- How are you going to pad down the 2445 to match it to the lower sensitivity of the 2240 ?
- What's the AC impedance of that Fane ST5022 around 10K ?
- Do you have an impedance curve for that Fane ?

regards <. Earl K

Rapid
08-07-2003, 01:42 AM
Hello Earl!
I'm going to use two amplifiers so I'll pad in the active crossover.

This is the first time I'm makeing filters :) . I just thought 8ohm, so 1/(2*pi*8*2,2uF)=9Khz, but now when you say it, maybe I should have looked at the curve because it's probably not 8ohm at 10Khz. hmm....

I can't find any impedacecurves for the fane st5022. :(

Cheers,
Mattias