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Moondog55 16th July 2012 11:15 AM

Rock and Roll speakers, is a Chebyshev bass XO going to give more "Kick"??
I know that Chebyshev crossovers are not used much and there are probably a dozen reasons why. but what effect does using one give?
As it isn't used much in passive cross-overs I have never seen or participated in a discussion on their use.
I did however notice the use in a cheap passive sub from Tandy that I rebuilt as a 1st order a while ago.
Would using such a XO give more "Kick" for want of a better word when building a set of R&R /Party speakers?

Moondog55 16th July 2012 11:31 AM

Second part of the question.
how would you implement the XO?
Set a Chebyshev alignment on the second of a 2 woofer system an octave below the nominal XO frequency? or where a kick drum has most of its energy around 120/150 Hz???
What would this do to the complex impedance of the whole speaker?

bear 16th July 2012 01:21 PM

In practice it won't make as much difference as "everything else". That being the amps, the speaker system (what it is) itself, and the venue, position of the speakers.

The Chebyshev merely gives a bit of a bump before rolloff and in return you get a slightly steeper roll off slope, and a bit of ripple in the passband. For bass in a PA you can pretty much ignore the ripple in the passband.

For a PA/SR situation, I'd prefer an active xover. That assumes that I have control over the unit. Or that it is locked.

The impedance of the speaker is going to be dominated by the stuff going on lower in frequency where the LF rolloff and whatever loading method there is causes the impedance to rise. At the high end, a passive xover looks like a rising impedance as well, as the frequency increases... with an electronic xover you have only the natural impedance of the speaker.

But what matters is the acoustic response. Say you have a speaker that rises from 125Hz up to 500Hz at >6dB/octave. If you put a crossover at 250Hz, it may not actually roll off AT 250Hz. because of the rising response.

For example a bass bin that has a front loaded horn will be rising in response assuming a nominally flat driver was used.

Of course you can use passive components and a speaker level crossover. In that case you would start by following the usual formulas or online calculators.

It is best to actually measure the speaker's response, the good part is that you can use freeware and almost any halfway decent microphone for what you are trying to do. Total accuracy and precision isn't required at all, just a halfway decent visualization of the frequency response.

One thing to note is that "nearfield" and "farfield" are likely to be rather different. Test for the xover in the nearfield. That would be 3-6ft in front...


Moondog55 16th July 2012 11:20 PM

Thanx Bear
It seemed like a good question at the time. I was looking through my box of bits and found a few cheap 300uF caps and I thought it might be worthwhile finding a use for them.
These would be a relatively cheap set for my mate the builder ( long story and long time coming) home use and totally passive

bear 17th July 2012 12:16 AM

The true answer goes farther - the way an xover is implemented when done passively will effect the subjective presentation.

Speakers that are run direct from amps seem to sound somewhat different than those run via passive xovers...


PeteMcK 17th July 2012 12:49 AM

I used this alignment once with a 4" woofer that wouldn't go as low as I wanted otherwise, it worked quite well, for party speakers the bumpy response probably doesn't matter that much. As for part 2, an interesting idea, be interesting to see how it works out in practise.

Moondog55 17th July 2012 11:03 AM

Trouble is 300uF is way to low, what would you call a CL configuration where C=2x and L=x/2? Reverse Linkwitz??
Honestly Pete with the cheap Jaycar woofers it would probably throw the voice coil out of the gap, almost as much fun as hooking one up to the AC and throwing the switch.
Something in between tho may work.

bear 17th July 2012 03:24 PM

Whoa - there is a difference between a C4 "alignment" which relates to the tuning in a ported box at the LF rolloff point, and a crossover using a C4 filter for the LP (low pass) filter. Or for that matter as a HP filter electronically, below the F3 tuning point of the driver + box + port. Very different things...


Moondog55 17th July 2012 08:59 PM

Well aware of that Bear.
Might be an interesting experiment tho.
The trouble with C4/EBS alignments is simply the huge size of the boxes needed and the resultant poor WAF, so getting small boxes can become the priority sometimes

bear 18th July 2012 12:02 AM

ummm... well I have no clue what you are actually trying to do!

I thought you were going for a PA/SR thing??


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