# Old school PPI FRX-456 crossover question



## mosk22rte (Dec 28, 2009)

This is a sanity check, and more or less a followup question to a post I made a few weeks ago about using a PPI FRX-456 crossover.

So I decided to use the PPI FRX-456 in my 98 4Runner. I am running this as follows:

Front: Bi-amped (Dynaudio MW-160s and MD-100)
Rear: older Nakamichi 3-ways (full range, for rear fill)
Sub: Illusion Audio ND-10 in sealed enclosure

I'll skip over the rest of the components as they aren't relative to the current question, which is: my front stage is two way. I have three crossover pots for the front: mid bass, mid range, and high pass. Based on this chart:










is it correct to hook the high pass output to the tweeter amp, the mid bass output to the mid bass amp, set the high pass crossover to whatever value I want, and set the other two crossovers to their smallest value (e.g., full range)? In essence, the only crossover value I set for the front stage is the high pass value, unless I want to limit the low range of the front woofers, in which case I do that using the mid bass crossover, which would essentially create a notch in the front sound?

It seems obvious and yet a part of it also seems counter-intuitive. 

Sorry in advance for posting such a n00b question, but I haz confuzion.

Thanks.


----------



## TREETOP (Feb 11, 2009)

The FRX-456 is a "tracking" crossover, meaning each output is selectable by it's own filter on one end and cuts off where the adjacent output is cut off on the other end. I'm scratching my head trying to come up with a better way to explain it, hopefully that makes sense.
Anyway, you're best off using the midrange output, as long as you don't need a crossover point lower than 80hz. If it needs to be lower than that you _can_ use the midbass output instead, I believe it's selectable down to 55hz on the highpass side but it'll only play up to the highest setting of your midrange highpass (which is also the tracking midbass lowpass) which maxes out at 1700hz. That's asking a lot from your tweeters.. 
If you use the midbass output for your midrange, and skip the midrange output, you can underlap the midbass/tweeter crossover points but since it's a 12db/octave Linkwitz-Riley filter it filters best by using the tracking controls and using midrange and tweeter outputs to your mids and tweets.


----------



## mosk22rte (Dec 28, 2009)

Thank you -- that does make a lot of sense. The manual did describe the FRZ-456 as a tracking crossover, but I didn't understand what that meant. The manual isn't as clear as it could be on how to set things up for a two-way system, and none of the examples match my system.

Follow-up question: any recommendations for crossover points for the above Dynaudio speakers? The MW-160 is spec'd with a frequency response of 55Hz - 3.5kHz; the MD-100 is spec'd with a response of 2,500Hz - 25kHz. If it matters, the tweeter amp is a Nakamichi PA-304, and front mid-woofer amp is a Soundstream Rubicon 555 (run in 3-way mode, i.e., channels 1 & 2 and 3 & 4 bridged + mono sub channel).


----------



## TREETOP (Feb 11, 2009)

Personally I'd start out with the MW-160 at 80hz-3khz and the MD-100 from 3khz up, and go from there.


----------



## marko (Jul 10, 2006)

this is the only problem with the 456, i had one and loved it but it's geared towards a 3way front end, running it 2 way means a cut off of 80hz and ideally you want to be down to 56hz like you can running 3 way.

i'm sure if you were clever enough you could actually change a few components inside and have what ever frequency you like..


----------

