Infinity crossover coil value
in [Repair]
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From: Peter Larsen on 25 Jan 2007 15:31 BOB Urz wrote: > I had a customer bring in an Infinity KPX00 crossover > for a 6.5" car unit. Surely the customer has stereo in the car, so one avenue would be to ask for the other cross-over as a source of comparison. > Coil L2 has burnt marks on it, Its a 24db linkquitz riley filter > (or so the spec sheet says). OK. You know the target response, and implicitly it is the tweeter cross-over slope this is about. Tweeter response is reasonably easy to measure, so if you replace the coil with a guesstimate coil it is possible to determine in what way the replacement coil is incorrect. CALSOD comes with a lil' util called inductor.exe, it is quite possibly not the only software on the planet for calculating inductors, and its existence suggests that the4 coil geometry can get you a close estimate of the inductance of the coil. > Strange, this seems to be a 3rd order filter rather than > what the tear sheets says. It would be good design practice to design a cross-over that fits the units so that the number of components can be reduced. > Only one coil on the high pass with two caps. > Minus the pad, it looks like the 3rd order 18 DB filter here: > http://www.apicsllc.com/apics/Misc/filter2.html > and these calculated 3500hz values are (4 ohm nominal) > C=7.5 ufd > L=0.1364 mh > C2=22.7 > standard replacement coil values are .1,.13,.15,.20,.27,.33 and etc. > Thoughts? You know the coil geometry, you know the wire diameter, it should be possible to get an estimate of the lenght of wire in the coil. That should make it possible to calculate a probable value for its resistance. Determining the actual resistance and comparing may provide correction data that can be used to convert the measured impedance of the coil to what it should have been. > Bob Regards Peter Larsen
From: Arny Krueger on 25 Jan 2007 16:11 "Peter Larsen" <SPAMSHIELD_plarsen(a)mail.tele.dk> wrote in message news:45B90E56.130D0584(a)mail.tele.dk > BOB Urz wrote: > >> Strange, this seems to be a 3rd order filter rather than >> what the tear sheets says. > > Nothing strange here, a 24 dB L-R filter can only be > claimed implemented if the acoustic output from the units > actually have the proper acoustic slopes when combined > with the filter. Agreed. Furthermore, the crossover drives a reactive load, not a resistive one. So, the crossover is unlikely to have an 18 dB/octave response that its electrical configuration suggests. I suspect that it drives the tweeter just above its resonance, where the tweeter is more like a capactive load. The 14 uF cap is then acting a bit like a member of a series capacitive voltage divider. This nets out to more like a 12 dB/octave high pass filter, which would combine with the 12 dB/octave high pass acoustic characteristic of the tweeter to provide a 24 dB/octave filter.
From: Peter Larsen on 25 Jan 2007 15:38 BOB Urz wrote: > Thoughts? Passive network transfer function, as I understand it when loaded with actual loudspeaker load, is available in the .pdf you linked to. A few trial and error substitions should lead to the correct coil value. You really have to verify that the units are OK anyway. > Bob Regards Peter Larsen
From: TimPerry on 27 Jan 2007 22:44 > Why is it that all anybody wants to discuss is ring tests rather than > suitable coil replacement values? > > When i get some time, i'll have to find the equations and try to solve > for the inductor value and get the closest standard value. That's what > this thread was all about. > > > > > > Bob bob, are you sure the schematic you drew at the first post is correct? i ask because i have found that tweeters usully have a series capacitor rather then an inductor. can you load the remaining portion of the crossover in such a way as to determine the crossover frequency by sweeping with a signal generator?
From: TimPerry on 27 Jan 2007 23:15
TimPerry wrote: >> Why is it that all anybody wants to discuss is ring tests rather than >> suitable coil replacement values? >> >> When i get some time, i'll have to find the equations and try to >> solve for the inductor value and get the closest standard value. >> That's what this thread was all about. >> >> >> >> >> >> Bob > > bob, are you sure the schematic you drew at the first post is > correct? i ask because i have found that tweeters usully have a > series capacitor rather then an inductor. nevermind... i see it now. > > can you load the remaining portion of the crossover in such a way as > to determine the crossover frequency by sweeping with a signal > generator? how come those bozos could give you the thiele small peramiters but not include a simple schematic? |