View Full Version : 3145 crossover woofer section

05-11-2018, 05:57 PM
Hi there!
I would like to understand the bass setcion of 3145 crossover that, as I presume, it is something between 290Hz and 320Hz 2nd order.
The thing is that I want to make a new crossover for the 2245H fo the 4345 with Mundorf Aronite inductors and Solen caps but my calculations gives me a 5.6mH and a 47uf capacitor followed by a Zobel network for the 1.4mH coil of the 2245H woofer with a 22uf capacitor and a 8 Ohms resistor.
Everything is fain untill I read de original crossover schematic to find 4 20uf capacitors (80uf total) followed by the zobel (20uf + 7.5ohms) and then followed by a 10uf capacitor!
Can someone explain me what the 10uf cap is doing? and why is a 5.4mH with 80uf for the woofer?
Thank you in advance....

Ian Mackenzie
05-11-2018, 10:29 PM

Firstly the original schematic is difficult to read.

There is actually 90 uf in total in the low pass filter. All the capacitor are in parellel.
The conjugate circuit is 7.5R and 20 uf

As to why it’s different is because under real loudspeaker load conditions the 2245H loudspeaker has inductance in the motor and when placed on the actual baffle the engineer had to adjust the L and C values to obtain the desired low pass filter response.

The low pass and the high pass filter on the mid range drivers sum flat using this modified 2nd order filter. The dcr of the inductor in the stock network is about 0.5 ohms

Why are you not Biamping the loudspeaker?

The low pass filter is very expensive to make and you can get a better outcome Biamping with an descent active crossover assuming you have a second stereo amp available.

The designer has previously indicated the 320 hertz passive crossover compromised the performance of the 4345.

Tell me more about your project and what you are trying to do?

05-12-2018, 02:48 PM
Ian, thank you for the information!
I had no idea the variation of the inductance would be so great when loaded and hence, never had a clue why the original crossover was double the capacitance that of my calculations (some +/- 10% was expected but not double)... thank you again enlighten me ;-)
I will try both (47uf and 90uf) to hear the difference (Mundorf inductor is the same value but with 0.33 ohms)

About biamp, no second amp available by now and already have the components for making the crossover.
I will check and come back soon with my apreciations.


05-12-2018, 05:08 PM
Your efforts will be in vain if you donít biamp. Speaking from experience here for many years. Biamping will unlock the true potential of these monsters.

Ian Mackenzie
05-12-2018, 11:54 PM
We would love to see a pic of your 4345ís

Ian Mackenzie
05-13-2018, 04:36 AM
I note you have also re built a stock 3143 crossover (Jbl 4343) recently.

The 3143 and 3145 crossovers are designed for different drivers used in the respective systems.

Just so my comments are appropriate can you advise if you are upgrading a 4343 and a 4345 separately or are looking at combining aspects of both designs?