properties of higher order crossovers

[Brendon Wright]

<span class="Apple-style-span" style="font-family: 'Times New Roman'; font-size: medium; "><div style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; background-color: rgb(255, 255, 255); padding-top: 8px; padding-right: 8px; padding-bottom: 8px; padding-left: 8px; ">

</p>

Howdy lads, most of this is pasted from a post in the Hammond section</p>

At the mo I've got a really fat spanking bass on my T500 spinet (since last night's deliberations) but it's a smooth deep bass, no, er, ..ahhh... farty rumbly resonances.</p>

It'd be fun to get some of those in. (I'm meaning to ask here about tweaking those boards...)</p>

Interestingly I've tweaked everything so the midrange compression drivers don't crackle even with a full chord played at reasonable volume in the bottom octave of the upper, then adding a full chord deep in the lower, there's just a hint of unrest, but plug a nice thumping pedal and the poor old drivers crackle.</p>

I thought the crossover would filter out every single part of the pedals but this is clearly not so. </p>

I figured the 12dB crossover would have to GO.</p>

I built first a 24dB 4th order Gauss high pass to knock out twice as much volume below 800Hz, and instead every single note rasps and protests in distortion.</p>

The recipe is very obviously in error. </p>

I cut back to an 18Hz cutback with a 3rd order butterworth, again, full distortion in the compression drivers.</p>

This is weird! The plain old 12dB filter seems to work best.</p>

I don't know what the biz is with these filters, but perhaps the higher order filters have some sort of odd property like a sharper crossover curve so you're getting a whole bunch more volume right at the crossover point. It's like the driver was getting everything though...</p>

What's up with the shameful performance of these "better" filters?</p>

I followed the formulae onhttp://www.diyaudioandvideo.com/Calculator/XOver/</p>

Cheers.</p>

-B</p></div></span>

[Brendon Wright]

Re: properties of higher order crossovers



Aheh, aheh, ahuh...</p>

My pollygies!</p>

An inductor coil used in both had a break in it, even though the meter measured it's mH for me...
</p>

[redoctoberff]

Re: properties of higher order crossovers



Brendoon,</P>


I read your updates on the compression driver thread and will respond shortly, but I thought this might be a good place to ask about the crossovers. How does putting an inductor inparallel with the upper driver double the crossover rolloff in a first vs. second order butterworth filter? Or is it the capacitor in series with the woofer that does it? I tried just using the series capacitor and parallel inductor to test my upper driver and it only cut out the highs. The leads on the coil were touching the wires running from the positive and negative terminals on the driver, respectively. Am I wiring them wrong?</P>


I was also wondering how those third and fourth order filters sounded once you figured out the break in the inductor. Lots more rolloff? How are the drivers sounding?</P>

[Brendon Wright]

Re: properties of higher order crossovers



Hi Red!</p>

I really don't know how it works, but it knocks off a good deal more of the offending frequency. Each formula has a slightly different effect, like one has a spike at the crossover point while another has a more gradual slope resulting in a hollow point at the crossover.</p>

I tried out the 3rd order one briefly, but it cut the overall volume of the whole treble and there was still a little crackle when both manuals and the the pedals were played, I can't tell if it's the drivers or at some point in the amp though. It used some of the same components that the 4th order used, so I dismantled that to build the 3rd. Might give it another go, but with the crackle still there in the 3rd and the overall drop I'm not so sure...</p>

I dropped it and went back to the 2nd order cos it was pretty good, as long as I was careful to tailor the output volumes right. I AM disappointed though that 50W of compression driver doesn't allow me to turn the 35W amp up to full, meaning while I've got it loud enough to bother neighbours, I'm certain that it's not loud enough for a stage. a 90W amp should really be able to do it.... (the bass has a 55W amp on it)</p>

The standard leslie crossover (no idea really what the formula is called) has a 7.8uF (or 8) cap on the + line and a 3.2 mH coil bridged across the +/- before the treble driver, while on the bass it has a 5.2 mH on the + line and a 12.5 across the +/-. Those are all 16 ohm speakers.</p>

To go to, for example, 8 ohms you halve the coil and double the capacitor.</p>

The problem with the 3rd and 4th order crossovers I tried is I don't know their particular personal quirks and I don't REALLY know how well the drivers cope with 800Hz. They certainly SCREAM in the upper end of the manual while seeming more sedate at the lower end, the 2' drawbar starts to scream after the 2nd or 3rd octave, and that's NOT with any manual taper on it. It just seems to be where the driver goes into its "power band". </p>

All I can say is keep battling, it's possible we might be able to get things performing better, and we're going to learn a lot from experimentation...</p>