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Passive Crossover

Posted by KCHANG (A) on February 21, 2007 at 19:52:13

In Reply to: Are You Using Passive Crossovers? Re: TB v. FX120, and PLUTO posted by Dr Deville on February 21, 2007 at 14:09:58:

Hi George,

I think it is reasonable to suspect that a sharp change in the response of a mechanica/electrical/acoustic system means that it is going through a resonance or mode transition of some sort.

I don't know how "bad" the peak in the response of the TB driver really is. It doesn't look too bad compared to the peaks and valleys in the repsonse curves of many famous FR drivers, but I agree that it would nicer if it could be avoided.

As to cone break-up modes and resonances, are you thinking that a 5" paper cone like the FX120 will maintain pistonic motion all the way to 20KHz? There are break-up modes, and the question is how well the resonances are controlled. In this regard, I wonder how the response curve of FX120 will look like without smoothing.

I used first-order speaker-level crossover in the PLUTO clones because it was easy to put the speakers together quickly that way. Nevertheless, the first-order crossover was selected also because I thought that it should be relatively benign in terms of phase rotation as compared to a 4th-order active. I was shooting for a crossover frequency around 1200Hz. Even though the crossover was in the midrange, I was hoping that the transition was not be as objectionable as it would be with a 4th-order crossover.

With my OB projects, I normally do not use any speaker-level high-pass filter (i.e. a cap) on the FR driver. In some projects, I run the FR driver wide open, and add bass using a powered subwoofer with a 2nd-order low-pass. In other projects that use separate woofers, I use a 4th order active crossover and biamp the FR and the woofer. When I played with the Audax PR170MO with a tweeter, I did use a cap on the tweeter.

You are right that there are so many variables in designing a speaker system, and the problem is that the effects of some variables are not well understood, let alone well-controlled.

Best,

Kurt

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