12" driver passive band pass L & C

[batty]

My son has dropped a 12" driver into a pre-built ported box and is feeding the full signal to it, so what I want to do for him is to put a low pass filter in line to get rid of the non bass.

I was thinking 5.6mH and 100 microF to filter below about 220 Hz.

any help appreciated.

[mdocod]

That would pretty well and do it. Might not be perfect but it'll knock down a decent amount of the HF from the driver. I assume it must be a 4 ohm driver.

You can improve on that by making a zobel network for the driver (real cheap). The zobel will correct for the impedance rise that the network would normally see and give you a more prominent roll-off of higher frequencies for very little added cost. Also, by reducing the resistor value in the zobel below the driver impedance, you can actually cause the 2nd order network to act even steeper than the normal 12dB/octave slope.

Without the zobel, you'll get less than 12dB/octave, with it, you'll get almost exactly 12dB/octave or better with tweaking.

Normally it's best to try to deal with x-overs this low at the line level with active electronics. Large value inductors are not ideal to have in the signal path.

Eric

[batty]

Sorry I forgot the speaker is 8 ohm. It's for his bedroom not a car. and the amp is only a 12 watt chip amp. (1875 chip)

[djk]

Does the LM1875 run his other speakers too?

If not, you can use a couple of resistors and caps to build an active filter with the 1875.

[batty]

Yes, it's the only amp he has. I do have some spare LM1875s, could build a separate channel I suppose.