I have just built a really simple amplifier based on an LM386:

Circuit diagram of amplifier

And I am now looking to design a crossover to go with it. What is the most appropriate type of crossover design to use here? I am looking at driving two 8Ω speakers; a tweeter and a midrange/woofer. I don't need anything really fancy, just a basic inductor/capacitor low/high pass filter.

EDIT: Please look at the links for specifics on my speakers!

EDIT: I would also like to know; What kind of capacitor should one use for the high capacitance values required by an audio crossover? I have been yet unable to find any that are suitable.

  • \$\begingroup\$ The 1st part of the question about the design of crossover is okay. The 2nd part is about sourcing, so it's off-topic on the EE.SE board. I took a liberty to edit the 2nd part out. If you still need to talk about sourcing, you can ask sourcing question in the EE.SE chat. \$\endgroup\$ Feb 19 '14 at 21:02
  • \$\begingroup\$ Have you considered an active crossover? - i.e build a second amp to handle the second speaker and split the common input audio signal with a simple RC network (one high pass, one low low pass) \$\endgroup\$ Feb 19 '14 at 22:21

A cross over needs to seperate bands of frequencies so that you are not wasting power feeding bass to a tweater and possibly damaging it. Firstly the bass crossover. I've chosen a cross over frequency of 500Hz but this needs to be considered in light of the speakers you wish to use. I've gone to this website and plugged some numbers in to the online calculator: -

enter image description here

The R in the circuit I've chosen to be the impedance of the speaker (8 ohms) although strictly speaking I should check to see that it is largely 8 ohms resistive at bass/middle. I've used 30uF and 3.3mH for the cap and inductor and this gives a 3dB cross over at 505Hz with a damping ratio of about 0.7.

See the graphs for predicted overshoot and passband - overshoot is about 1.07 (7%) and there will be an almost unnoticable peak in the spectrum. At 1kHz the signal level will be reduced by about 12dB. It is performing as a low pass filter.

The nice Mr. Okawa (the site I used) has got a similar page for a high pass filter using a series C and L//R down to ground - you should be able to follow the link and have a go yourself.


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