Changing Crossover Frequencies

Hi. I'm new to this forum and have a question about crossovers. I have a pair of celestion passive crossovers in my home built speakers. The crossover frequency is at 3k. Is it possible to modify this so it is at 2.4k or will I need to buy new crossovers?

Cheers.

Speaker combos are built so the upper woofer frequency and the lower tweeter frequencies overlap slightly. Shifting the tweeter frequency will cause a dip in the midrange responces. Passive crossovers are usually a capacitor coil combination that match the responce of your drivers. If you have the Fq responce of your drivers and the values of the components in the crossover you can key those values into a number of online calculators or charts and come up with new values. Weather the woofer you have now can extend up above 2.4k so the 2 still overlap is whats going to be your problem. You will most likely need to get higher frequency woofers as well as different crossover caps to have an overall linear Fq responce.

For parts and charts try "Parts Express" first. They should have all the info you may need. They also have crossovers that arent much more expensive than the individual components.

2.4k is not very different from 3.0k anyway. It's only four semitones! Why do you need to change it? The difference between the two crossovers (assuming 12dB/octave) is less than 4dB over the cut band, which isn't very significant when you still have the passband belting out at the same volume.

But in short, caps are dirt cheap to change, but coils much less so. You can change the frequency by changing only one of these, but changing one and not the other will change the filter phase characteristics near the crossover point.

Short answer: Don't bother.

Long answer: Without the proper test equipment, you're just guessing at what's really happening. Since speakers aren't anywhere near "ideal", the canned formulas for determining crossover frequencies almost never provide real world results. The natural rolloff of the drivers combined with the impedance profile of the drivers creates a much more complex situation than what's accounted for in equations.

There's also the issue of what impact a lower crossover will have on the tweeter. Most consumer grade (i.e. non "audiophile grade") speakers use cheap drivers. A cheap tweeter usually has very poor distortion qualities at lower frequencies, which necessitates a higher crossover frequency to avoid a brittle, harsh sound. I've found that this can be easily heard in systems and recognized most often by siblance in vocals. "Sssssss's" that will make your ear hair melt.

A brittle, harsh sound, or a dead tweeter.

Cheers for the advice. I think it's gonna be easier to buy new crossovers!

That's not necessarily going to be any better. Any new crossover you buy won't be designed for the drivers and cabinet you have, and would likely sound worse than what you have.

Why are you so set on new crossovers, anyway?

The speakers were plastic moulded cabs with the drivers and crossovers upgraded to celestion. The horns are compression drivers and can handle down to 2k. At the minute the speakers seem much louder in the next room rather than the one we're playing in and I was told this would help.

I don't see why it would, but let us know how it works out for you.