cross over

[sid510]

what is the disadvantage of buying a generic cross over.
ive seen many postings telling people to build it from scratch.
if i find a generic one giving me the right frequencys for my drivers wouldnt that be simpler.....

thank you

[Centauri]

Most generic crossovers are simple low/high pass filters tuned for resistive load at "nominal" impedance. Actual impedance of a speaker varies quite considerably with frequency, and as a result these simple crossovers may give quite a horrible overall response. For a cheap and simple speaker project, fine, but for a serious speaker project proper simulation for the particular drivers is a must.

Cheers

[sid510]

sorry i am a newbie at this, ive done a lot of research but im still missing little details.
when you say "nominal impedance" do you mean the 8ohms rating.

So when i am using software to get the values of the caps and coils for the XO i should not use the 8 ohms rating,

thank you for your reply.

[Centauri]

when you say "nominal impedance" do you mean the 8ohms rating

Yes, this is an average "around-about" figure. The impedance varies due to speaker voice coils having inductance (Le) themselves. Using the published figure of Le and Re (DC resistance) of the particular speakers, you can plug these values in to simulation software to calculate the required zobel networks (impedance compensation). Some software will even allow you to use an impedance file generated by measuring software to allow better simulation.

Its all fairly involved, but can make as much difference as a correctly tuned cabinet.

Cheers

[wintermute]

Just to add to what Centauri said, the impedance of a speaker tends to rise as the frequency response rises. The crossover is designed with a particular impedance in mind (eg 8 ohms) doesn't give the same level of cut at higher or lower impedances.

The impedance compensation network basically "flattens" the impeadance curve of the speaker so that the crossover sees a constant impeadance.

So (and now I'm speculating) I guess if you added a zobel to a stock crossover then maybe (assuming the crossover freq was suitable, and the response curve didn't have any nasty peaks) a stock crossover would be ok. This of course assumes that they have used decent caps and coils.......

Just for the record I'm only going on theory here. I personally have stock crossovers in my system with no zobel, but I have been researching, and am planning on doing my own

Tony.

[sid510]

thanks a lot for clarifying that