Passive Crossover Design

ceharden wrote: Something I think is very important is chosing drivers that have a response that extends either side of the crossover point.  Passive crossovers are a long way from being 'brick wall' and the crossover region where both drivers are affecting the response could be an octave or more wide.  In hi-fi world the rule of thumb is that each driver should have a flat, or at least smooth response at at least an octave past the desired crossover point.  This is one of the reasons that things like a 15" + 1" cab just doesn't work because the crossover point tends to be at the operational limit for each driver and doesn't allow for the overlap you get on the resulting acoustic crossover.

What sort of power do you plan to feed the 10" with? A passive would be possible, but you may well run into design compromises and especially to a budget.

You don't have to necessarily use inductors either. Just a cap would give a single order roll off if you can get a result you like using a 6dB crossover slope with your LMS. It's always the inductors that get pricy the quickest.

Another option is to biamp with chipamps, maybe a couple bridged for the sub and one each for the tops. This could be a compact enclosure and you could feed each one with an actively filtered signal which is just a few more opamps and components each. There are some shops on ebay where you could buy a kit for each chipamp module, couple of crossover boards, add a power supply module, put it all into an enclosure and you have a dedicated amp unit for all the cabs. I expect you could do it for <£100 but it depends how comfortable you are with a soldering iron really. Buying the modules ready assembled would make for a minimal effort job, all you have to do it set the amp gains and the crossover frequencies then and plug it all together.

Enjoy! You might need to upgrade a few of the components on the cheaper pre-assembled modules for a quick boost in performance but chip-amps themselves can give very good results if implemented well.

There are many threads on diyaudio. com discussing improvements to the cheaper modules you can get by replacing components etc.

There are also class D modules out there that you might want to try on the bass end.

I just registered to this forum & you seem to be knowledgable so hopefully someone can answer this... I have an 8 ohm 3 way cabinet speaker w/ 3 (5 ohm) speakers inside that are blown all to crap. My question is that if I replace the 5 ohm speakers inside w/ 4 ohm speakers what will the resulting impedance be? I know that's probably not possible to answer be its something to do with the crossover but, since it magically turns 5ohm speakers into an 8 ohm cabinet what would it make 4 ohm speakers? Lol thank you for any & all advice!

The impedence quoted on a speaker is a nominal figure. When you measure the impedence with a meter it is never what it says on the label. An 8 ohm speaker usually measures between 5 and 7 ohms. A 4 ohm speaker will usually measure between 2.5 to 3 ohms. Also the actual impedence of the driver varies with the frequency being played through it. An 8 ohm driver can be as high as 30 ohms on bass frequencies.

If you replace 8 ohm speakers with 4 ohm it will completely screw the crossover points and usually leaves large gaps in the frequency response.

What you measure with a ohm meter is the coils resistance, not impedance.