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View Full Version : 2402 "bullet" protection issue (please help)



DLutz
12-10-2005, 02:33 PM
I am upgrading with an ashly XR-4001 (4 way active crossover) and will be
running my 2404's direct wire from the amp.

Should I place a capacitor in line to protect the 2404 from amp pops at turn on or other unhealthy signals? Or should I just leave the passive crossovers hooked up as they are now?

If I leave the passive crossover hooked up what are the negatives?

If I need a capacitor where can I find the formulas to see what I need?

Or are there other options I am not listing?

Thanks in advance for your help

David

duaneage
12-10-2005, 02:56 PM
I would use a capacitor for DC protection. If it is 16 ohms use a 15 uf, for 8 use a 8 uf. These will provide DC protection without affecting the reponse since they operate below your crossover point by 2 octaves or more. The idea is DC protection, nothing more.

scott fitlin
12-10-2005, 03:46 PM
I would use a capacitor for DC protection. If it is 16 ohms use a 15 uf, for 8 use a 8 uf. These will provide DC protection without affecting the reponse since they operate below your crossover point by 2 octaves or more. The idea is DC protection, nothing more.Ditto!

Tom Loizeaux
12-10-2005, 04:24 PM
I would use a capacitor for DC protection. If it is 16 ohms use a 15 uf, for 8 use a 8 uf. These will provide DC protection without affecting the reponse since they operate below your crossover point by 2 octaves or more. The idea is DC protection, nothing more.

If you were concerned about getting ALL the top end to your 2402s, you could add a 1 uf and, or a .1 uf in parallel to the 15uf cap. This is called "bypassing" and is a way to ensure that none of the top gets lost in the larger cap.

Tom

Baron030
12-12-2005, 05:01 PM
Hi DLutz

I also own an Ashey XR4001. So, I completely understand your situation.

To provide protection for my high frequency drivers, I have been using the high pass section of a second order (12db / octave) butterworth crossover network installed between the amplifiers and the drivers.

To minimize the effect of these passive high pass filters, I chose crossover frequency points that were about one octave lower to what the Ashey is set at. By going an octave lower, I am changing the driverís slope rate to 36 dB per octave only after the output level has already dropped by a full 24 dB. So, the filterís impact is pretty minimal.



For example in my system: The Ashey active crossover is set to 8 KHz for driving my 2405 drivers. And to provide driver protection, a passive 3 KHz high pass crossover network section is installed between the amplifier and the drivers. The network was made up of a parallel array of capacitors equaling to 4.68uf and a 0.6mH Ė 18ga. coil.

On the Internet, you should be able to find a crossover network calculator. So, designing a network to suit your projectís special needs should not present you any real problems. When working with these calculators, it is best to re-scale your crossover design around some stock coil size, and then create the equivalent of some rather strange capacitor value by paralleling a bunch of capacitors together until the sum of their values equals the value your design needs.

And one good source for parts is: www.partsexpress.com (http://www.partsexpress.com)

Good luck with your project.

DLutz
12-13-2005, 05:49 PM
Thanks to all for the valued info...

Baron,

I have not yet received my Ashly crossover and am currently using a Rane 3 way stereo. I am interested if you have any comparison of the two? I have heard and read that the Ashly is quieter and more natural (smoother) sounding but honestly I don't have any first hand knowledge.

Also, do you have any more suggestions or comments before I hook the Ashly up?

I know I have a trillion questions, but what amp are you driving your JBL 2405 with? And any recommendations here?

Thanks again for you help
David Lutz

ralphs99
12-13-2005, 09:01 PM
Just a small correction to Duaneage's calculation.

The capacitor value should increase as driver impedance decreases to maintain a similar cutoff frequency. 15uF sounds OK for a 16ohm driver, but 8uF is a bit too small for an 8ohm 2404. 33uF would be better.

It's also worth keeping in mind that the impedance of drivers is often below the rated impedance at some frequencies, requiring a slightly larger capacitor value. Also phase shift from a filter extends a factor of 10 above and below the cutoff frequency. I prefer to to use a capacitor value that I calculate with Z/10. This needs a much larger capacitor for which I use an electrolytic and a parallel film capacitor of 1/10th the value. The smaller impedance of the film capacitor means the electrolytic conducts little current except at the lowest frequencies and is really only present to reduce the filter's phase shift. The film capacitor does the work.

Cheers,
Ralph.

Ian Mackenzie
12-13-2005, 09:26 PM
May also be worth adding a polyswitch to prevent driver burn out in the event of large signal input to the driver.

Ian

Mr. Widget
12-13-2005, 11:47 PM
For my nominal 16 ohm drivers that I actively crossover at 600Hz, I use a 47uF 400V polyester cap. (this provides a first order crossover frequency of ~200Hz) I can not measure or hear a difference with it in or out of the circuit. If the amp takes a dump on me, it will protect the driver from most low frequency or DC signals.

Widget

Hofmannhp
12-14-2005, 03:34 AM
Just a small correction to Duaneage's calculation.

The capacitor value should increase as driver impedance decreases to maintain a similar cutoff frequency. 15uF sounds OK for a 16ohm driver, but 8uF is a bit too small for an 8ohm 2404. 33uF would be better.
Cheers,
Ralph.

That's what I mean too

HP

duaneage
12-14-2005, 10:16 AM
Sorry, I got that backwards. If he is rolling it off at a very high frequency I doubt it would matter much. Another idea is to use a 2 amp fast acting fuse. Anything over 16 Volts DC hits it and it pops.

louped garouv
01-18-2006, 03:03 PM
might be an interesting read...

seems to agree with the lower uf value, right?