Jerry-rigging a passive crossover

[olmie75]

I have a pair of Infinity Kappa 693.5i speakers and I am missing the external passive crossover units. I called up Infinity and they don't carry these replacement parts anymore. Any ideas of how I can jerry-rig a decent crossover? (without having to dedicate a 4-channel amp w/ active crossovers to these speakers)

There are 2 sets of speaker terminals; I checked them with a multimeter, and the resistance is 3.5 Ohms. I have a Kicker KX650.4 amp (2 channels to dedicate to these speakers) that is stable at 2 ohms. Therefore, I can't wire the two terminals as-is in parellel since it would reduce my resistance below 2 ohms. So in addition to crossing over the frequencies properly, I need to get a managable resistance from the speaker system.

Please advise.

[enzowho]

You can go here to determine cap/inductor values you need to build a crossover. From what I found, the crossover point is 3500kHz at -18db/oct. I personally would not recommend building them though. First off, it isn't cheap (figure 6 inductors at $4-12 a piece, 6 caps are $.50-3 a piece, several L-pad resistors at $1 a piece, soldering iron $10....) Also, if you have never soldered before, they might be prone to breaking.

I would personally recommend instead searching for another pair of crossovers on forums/ebay. I would not recommend picking up a random crossover, but one that is made specifically for your driver (if there's a 6.5" or a 5.25" version that might work too). The reason for that is (1) you can blow tweeters if they are crossed over too low (2) it could sound pretty bad if its at a bad crossover point and (3) crossover points are dependent upon the resistance (so you might think you are getting the right crossover point when you aren't). The other option is going active, but as you mentioned above you don't want to do that. Good luck, hope you can find something.

[olmie75]

Checked on ebay, and all I could find was reference series crossovers (not sure if these would work) - Where did you find the specs on the Kappa crossover? (I checked their website & called tech support, and they couldn't give me any answers).

I've never built a DIY crossover before, but it seems like it could be an interesting project (nothing to lose except a pair of $200 speakers I can't use anyways). So I have a few basic questions on building a crossover:

1) should I try to keep it simple and just do a first order crossover? (How did you determine that I needed a 3rd order crossover?)

2) how is the resistance issue accounted for? (in the diagram, the drivers seem to be wired in parrallel which takes the resistance for the speaker system too low; how does this work? I'm guessing it has something to do with the L-pads you mentioned, but I don't understand how determine the correct values to acheive the correct impedance)

3) where do I get capacitors, inductors and L-pads for the specific values I need? (Radio Shack was my only guess, but they don't have inductors)

4) Is there a resource that provides some basic instructions on the process of fabricating the crossover circuit board?

[helotaxi]

Your crossover will keep the amp from seeing the actual parallel load of the two coils. That's what the crossover does. It increses the apparent load on the amp in the out of band region for the driver it is wired in series with. The basic result is that in the freqs that hte tweeter plays, you have the coil of the tweeter wired in parallel with what ammount to a load heading for infinity as the frequency goes away from the crossover point. The final load seen by the amp is the impedance of the driver that covers the frequency at which you are testing the impedance.

Something to realize is that you're not measuring impedance with the DMM when you measure a coil. You are measuring DC resistance. Impedance is a resistance to AC and varies with frequency. The impedance of a driver will most always be a bit higher than its DCR. 3.5 ohms DCR is about right for a nominal 4 ohm driver.

[olmie75]

Thanks for the explanation - makes sense now. So since the resistance is not an issue, any 2-way crossover at 3500 Hz (for 4 ohm speakers) should work for my speakers, right?

I saw some Infinity reference series crossovers on e-bay which the seller states are crossed over @ 3500 Hz, would these work just as well? (sadly, the "tech support" at Infinity aren't capable of answering such a question)

[enzowho]

1) should I try to keep it simple and just do a first order crossover? (How did you determine that I needed a 3rd order crossover?)
2) how is the resistance issue accounted for? (in the diagram, the drivers seem to be wired in parrallel which takes the resistance for the speaker system too low; how does this work? I'm guessing it has something to do with the L-pads you mentioned, but I don't understand how determine the correct values to acheive the correct impedance)
3) where do I get capacitors, inductors and L-pads for the specific values I need? (Radio Shack was my only guess, but they don't have inductors)
4) Is there a resource that provides some basic instructions on the process of fabricating the crossover circuit board?

1) No, you don't want to use a 1st order crossover. That would be a very gentle slope (-6db/oct). This means the power that reaches the speaker is 1/4 when the frequency is doubled/halved. (i.e. you design a first order low pass crossover which a corner freq/crossover freq at 2000Hz. You then apply 100 watt of power. This means at 4000Hz the speaker will see 25 watts) I believe most crossovers use either second order (-12db/oct) or fourth order (-24db/oct). This helps prevent damage/overexertion of th drivers.

2) An L-pad is a combination of resistors that reduce the intensity of the tweeter. So, for instance when you buy a tweeter with 0db and -3db terminals the -3db uses a L-pad to reduce the power going to the tweeter.

3)Madisound or PE will have the stuff you need.

4) Off the top of my head Zaph's site has some good resources. Google might have some good results if that doesn't help out.

As for the the crossover on ebay, I'm not quite sure. If the midrange and tweeter for that driver are both 4 ohms then you should good to go.

[TRWANCZYK]

I have one for sale if your still interested??? trwanczyk@comcast.net

i have a pair of infinity kappa 693.5i speakers and i am missing the external passive crossover units. I called up infinity and they don't carry these replacement parts anymore. Any ideas of how i can jerry-rig a decent crossover? (without having to dedicate a 4-channel amp w/ active crossovers to these speakers)

there are 2 sets of speaker terminals; i checked them with a multimeter, and the resistance is 3.5 ohms. I have a kicker kx650.4 amp (2 channels to dedicate to these speakers) that is stable at 2 ohms. Therefore, i can't wire the two terminals as-is in parellel since it would reduce my resistance below 2 ohms. So in addition to crossing over the frequencies properly, i need to get a managable resistance from the speaker system.

Please advise.

[ramos]

I would hope to god that he's not still looking 3 years later