The implementation of parallel LCR and RC circuits in crossovers
Copyright 2013 Troels Gravesen

A very common question to my crossovers is why my layout differ from schematics., i.e. why is the RC circuit turned up-side down or why is the LCR circuit components in a completely different order.

The short answer is that circuits parallel to the driver can be put together in any order, being RC or CR or LCR, CRL, LRC, etc. They do the same thing regardless of orientation.


However, they MUST be at the same spot in the signal path! Do not move an RC or LCR circuit to the other side of a series capacitor or series coil! Then terrible things will happen.

An RC or LCR circuit in parallel to the driver can be implemented in any order; it does the same thing: It absorbs energy at certain frequencies being a harmonic oscillator in technical terms.
If we have a resistor connected between plus and ground it will absorb energy in a magnitude dependent on the value of the resistor but regardless of frequency. The energy will be turned into heat and the resistor will get hot.
If we have an RC circuit this all of a sudden becomes frequency dependent, depending on the value of of the coil and the speaker impedance it sees. The coil will pass lower frequencies and at higher frequencies its impedance will rise steadily until infinite, thus will not work in the e.g midrange and treble range (R2021/L2021).

My LSPcad software always places the components in a specific order but when it comes to the actual crossover layout it may prove beneficial to change the order due to size of the components or due to wanting to get coils as far apart as possible to reduce interaction given the space constraints of the crossover board.

Hope this helps :-)  

RC circuits


Above the midrange section of the Jenzen-D speaker.
After the series capacitors we have an RC circuit smoothing the roll-off of the midrange drivers towards lower frequencies.
Below you can see the same crossover where the RC circuit has been turned up-side down.


L2021 and R2021 turned up-side down.

 

LCR circuits

Above is seen an LCR circuit, a notch filter, suppressing a peak in the treble range of the middriver.
The values of the components are tuned so that we have a smooth roll-off of the middriver towards higher frequencies.

Below you can see the same LCR circuit in different order, e.g CLR (from upside down) or LCR. It could also be LRC.
It does not matter. It does the same thing regardless of orientation.