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Multi-Way Conventional loudspeakers with crossovers

Question about wiring of second order crossovers
Question about wiring of second order crossovers
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Old 8th December 2016, 07:38 PM   #1
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Default Question about wiring of second order crossovers

I assumed it was standard operating procedure to reverse the polarity on the tweeter in a 2 way second order crossover? But doing a google search on hookup for second orders resulted in diagrams with both drivers wired both ways. (+ to+, + to -). What is the determining factor on which is works best?
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Old 8th December 2016, 08:11 PM   #2
TudorTurtle is offline TudorTurtle
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Not being flippant here; the determining factor is how it sounds. Sometimes reality doesn't match the theory/design and reversing the design polarity sounds better.
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Old 8th December 2016, 08:31 PM   #3
Scottmoose is offline Scottmoose  United Kingdom
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No matter, one of the mods will move it.

There isn't a short version or simple answer to this unfortunately, but FWIW:

It depends. Electrical transfer functions and the actual acoustical slopes are not always (usually are not) synonymous, since the driver's natural responses usually come into play unless you're crossing drivers with a flat response out to ~2 octaves past the nominal XO frequency. IOW, if the driver is already rolling off 2nd order by itself & you stick a 2nd order electrical on it in that general vicinity, you've got a 4th order acoustic slope, of xyz type (LR, Butterworth, Gaussian or whatever).

The assumption of flipping the polarity for 2nd order filters is based on symmetric filters (2nd order has 180 degrees phase rotation) and coincident acoustic centres. Usually not the case on a flat baffle, since the midbass units will usually have their VCs a good 20 - 25mm (or more) behind that of a normal dome tweeter. Less of an issue with cone tweeters of course, although even then there is likely to be some offset in the z (front - rear) axis.

If you've a flat baffle, you'll usually need some form of ladder delay network on the tweeter when using 2nd order acoustic slopes. You can physically move the tweeter back with a stepped baffle, although the diffraction can be a problem, and that only works optimally when directly on axis -as you move off, it can be more of an issue. Neither of these are necessarily inevitable -you can sometimes get away without them (although not often); that is circumstance dependent, e.g. the precise slope Q and driver positions etc.

Which is a bit of a long winded way of saying there isn't a single answer as there are too many variables involved.
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Old 8th December 2016, 08:50 PM   #4
AllenB is offline AllenB  Australia
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There is a right way to do it. The issue is there is more to it than the text book behaviour of filters calculated with standard values. They will interact with the speaker impedance and response to produce something other than intended unless designed with these things taken into account. Further, changing polarity is a matter of a 180 degree step, whereas phase rotates continuously around 360 and can be different at different frequencies.
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Old 8th December 2016, 08:51 PM   #5
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Thanks for the explanation Scott. I started a second thread in the correct forum. Might get put in the bin by the mods
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Old 8th December 2016, 08:54 PM   #6
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yeah, I was wondering what considerations would vary the textbook approach.
Thanks for your input.
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Old 8th December 2016, 11:46 PM   #7
gabdx is offline gabdx  Canada
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a microphone and a response curve will determine easy the correct way to wire your cross over.

A second order cross over is things of the past for tweeters btw, now the standard is 3 way cross overs for tweeters.

You can get good results if your tweeter is more than 30 mm wide and can cope with some midrange to pass through it.
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Old 9th December 2016, 03:41 AM   #8
eriksquires is online now eriksquires  United States
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Take a look at this discussion and scroll down to Driver Phase Matching:

https://speakermakersjourney.blogspo...crossover.html

The LM-1 crossover simulation files are available over in the software section here, so you can play with alternatives.

Best,

Erik
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Old 9th December 2016, 07:37 AM   #9
Bob Richards is offline Bob Richards  United States
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Any passive crossover is pretty likely to be way off if you just do the math and build it (even if you've used published impedance graphs of the drivers) . The final result should be verified with pink noise or a slow swept sinewave, at which point you can switch the phase of the tweeter and see which way gives you the less damaged frequency response.
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Old 9th December 2016, 10:23 AM   #10
Scottmoose is offline Scottmoose  United Kingdom
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Quote:
Originally Posted by gabdx View Post
A second order cross over is things of the past for tweeters btw, now the standard is 3 way cross overs for tweeters.
Eh? According to whom? I assume you're talking about 3rd order electrical (T section) filters? That's news to me. The electrical filter topology on the tweeter depends (or should depend) on what you're doing, i.e. XO frequency, power-handling of the drivers involved, impedances, phase-matching and a host of other factors. 2nd order electrical is as useful now as it ever was, and still regularly employed in many, many designs, just as 3rd order is.
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