PA speaker X-0VER

[oquela]

hello. I'm new here, and I hope this is the right place for my question. If not, admins please move to the appropriate sub-forum (electronics??)

I've built my own speaker box w/a 15" and a horn (both 8-ohm) , and I'd like to build my own x-over to cutoff @ 2k. Yeah, I know, I could buy it pre-made, but this is DIYaudio, right?

Question: I've heard that in MOST high power (200-400 watt) PA speaker system ( typical 8 ohm, 2-wayspeaker: a woofer and a horn tweeter,) the woofer has a 6db (first order) crossover, but the horn (tweeter) has a 12 db (second order crossover)

IF this is indeed true, how is it wired? I've seen charts where both speakers are either first-order, OR both are 2nd order.

thanks.

 

[Inductor]

X-overs. Time Alignment by Lenard Education
http://www.lenardaudio.com/education/06_x-over.html

Yes indeed. You can have a first order on the woofer and a second or third order on the horn tweeter driver. That's because of usually high resonance Fs on the speaker driver and the xover frequency have to be over it. If you use a third order as stated please always invert polarity on the speaker horn connectors to start with, for perfect phase alignment.

 

[oquela]

Thank you for the link and quick reply. Just a thought: didn't phase shift happen / 2nd order crossover design ONLY? I seem to remember reading that in a few places.


just for clarification: I would wire as below:

+++++++++++COIL+++++++++
amp WOOFER
---------------------------------------------

Will the 2nd order for my tweeter xover "wire-in" after the coil (before the woofer), or back to the amp?

 

[krytar]

Thank you for info.
Lenard Audio site is one of the best site on audio.

 

[Inductor]

Just a thought: didn't phase shift happen / 2nd order crossover design ONLY?

A second order plus a second order = phase shift (180º),
a first order + a third order = phase shift (180º).
(a first order (45º) + second order (90º) = more or less reversal depends on the frequency you are looking at, case by case, it is possible or maybe not). See that your magnet of the compression driver must be almost on top of the magnet (center of coil) of your woofer, just my guess.

 

[oquela]

BTW: which 2nd order slope is prefered on a PA box (I can always use an L-pad to attenuate the horn)

linkwitz-riley, butterworth, or bessel?

I've done a search, but no real answer.

 

[oquela]

for post #3 above, my schematic didn't come out as planned....sorry.


1 more question: if I do flip polarity on the tweeter, is an L-pad still necessary?

 

[Cal Weldon]

Yes, the reverse polarity simply cancels the 180 degree phase shift. It does not attenuate the circuit. It realigns the drivers so there is no dip (phase cancelation) at the XO point.

12 dB (second order) is fine for both ends, unless you want to consider a 6 dB on the woof and an 18dB for the top for better power handling. Only problem is you aren't cutting off the cone breakup very well with a 6 dB.

Six in one, half a dozen the other.

 

[Inductor]

Only problem is you aren't cutting off the cone breakup very well with a 6 dB.

oquela what speakers do you have, and what xover (schematic) do you have?

 

[oquela]

I don't know the model # on the woofer, but the specs are the following:
15 inch, 8 ohm impedence, 98 db sensitivity, freq resp: 50Hz-3.5khz, 250 rms/ 500 Peak, 54 oz magnet.

the tweeter is a Fostex 025M01D; on the back of this compression driver, it also says 120W max, 8 ohm; I don't know the range, but I believe it goes from 2k - 20K