Greetings,

WRT. passive x-overs, Assuming that's what we will use and assuming proper design for application in both cases, would we rather have a 12db w/poly or mylar caps; or 18db w/ electrolytics? Can we hear the difference? How about as box "work" increases?

Thanks so much,
regards,
J.K.C

Reply posted by Tom Young on June 25, 2000

Selecting the slope of a crossover involves consideration of where the crossover frequency is going to be, power handling and sensitivity of each driver but specifically the HF driver, and awareness (or the ability to measure) the lobing and phase effects of the slope. And this must be weighed against the application (FOH or stage monitor) and you should conduct listening tests to determine the best crossover frequency and type for the specific woofer and HF driver (plus horn).

Then there's a host of other considerations including crossover parts quality ncluding their power handling. Electrolytics are generally not as good sounding as higher quality plastic-film caps and they may cause problems due to their polarization. In live sound, nuances of how crossover parts sound may be lost in the noisy environment that they are used in.

For the question you posed, I'd base the decision as much on crossover frequency as anything else. If the crossover frequency is high enough, the 12 dB per octave slope will work and will have less phase shift and lobing than with the 18 dB per octave slope, plus it has better quality caps. But how good are the inductors ?

Tom Young

Reply posted by Jeremy Johnston on June 26, 2000

Guys:

One capacitor represents one pole in your filter (eg low pass or high pass filter of a crossover) as such a single capacitor is only worth 6db/octave rolloff. No matter how you slice it. The slope of the filter is defined by the order and type of the filter such that a 3rd order filter has an 18db/octave slope.

Capacitor types aside, no single capacitor will give you a slope of 12 db/octave or 18db/octave. The construction of the filter, including capacitors, inductors and sometimes resistors for impedance compensation, determines what its response will be. You need to take all these things into consideration when designing a crossover (either passive OR active). Check out a good filter design book or a speaker design book for more help.

Jeremy Johnston

Reply posted by j. nelson on June 27, 2000

Sure as you make a blanket statement some joker comes along and contradicts it. Yes, one capacitor does make one pole. Yes, you can have a one capacitor crossover with a 12db slope. Its a special case (wish I could draw a schematic here) The amp drives a series combination on one cap, one inductor.

The woofer is across the cap and the the tweeter across the inductor. In this configuration, the slope is 12 db/octave at the crossover point and 6db/octave from then on. This is sonically a very pleasing filter. I built some monitors using this design with Peavey 4 ohm 15" speakers and and the Peavey 1" driver.

The horn driver almost didn't didn't have to be attenuated at all because the 4 ohm 15" speaker was soaking up so much power. Surprisingly, even with the low slope, blew few horn diaphragms in the long haul. Some of the best cheap monitors I ever owned.
J.

Reply posted by Alan Wheeler on June 26, 2000

Jeremy, you're Absolutey correct! The cap itself doesn't determine the slope. It's the circuit.

Wheels

Reply posted by peter m on June 25, 2000

why not 18db with poly or mylar???? the cheap bipolar electrolytics have a tendency to blow up and the better ones are priced very close to poly/mylar caps.

peter m

Reply posted by J.K.Constantine on June 26, 2000

Hi Peter,
This question is in regard to manufactures x-overs, not "home built", But your additional advice is well taken. thanks

regards,
J.K.C.