Ah ok, 2nd order sounds a lot better.

1. sounds a bit like bridging both outputs of hte amp into one channel. Too low an impedance coming from the speaker and the amp will get very hot!

i am just beginning with pd, so cannot offer much about tricks, but have done sound system engineering for years and years. fir filters are nto typically used for subs because of latency times. 24 dB/octave linkwitz-reiley filters are the most commonly used and probably the best starting point.

how well do the tops integrate at the crossover frequency?

@je305 said:

I've been running a two speaker setup for a while, but fancied a bit more punch, so I bought a passive subwoofer. My amp doesn't have a special subwoofer output so it's a bit tricky to separate it, and I can only pass signals between my PC and the amp using a 3.5mm (stereo headphone type jack) to phono cable.

What Pd is doing for me is inverting everything <100Hz on one side so that the bass signal is out of phase between left and right. Then I can get my bass separation to the sub in one of two ways:

1. wire the sub between the positive terminals of L + R speakers (L+ to Sub+, R+ to Sub-). Only out of phase signals will cause a potential difference, so the bass signal will pass through the subwoofer because I made it out of phase.

2. Read up on how Dolby Surround works - basically the rear channel is encoded in a very similar way to how I've encoded the bass. By plugging my subwoofer into the rear output of my amp (which has only stereo inputs but dolby pro-logic and surround outputs) I get the bass signal through the sub.

Both of these worked in practise, but number 1 was more successful - it sounded brilliant, the sub giving it some punch and all the higher frequencies through the smaller left and right speakers. I'm going to be fiddling with setting for a while yet to optimise it, but really happy at the moment.

One thing I need to do is learn how to use Jack, because I currently have to use a wire from out->in on one of the soundcards to make it an input in Pd. That should cut a bit of noise and latency out, although I can't hear any noise and the latency is 50ms, but it might help.

*edit: I have no idea if this idea has been incorporated into commercial sound systems or not - does anyone know? After reading how Dolby worked it seemed the obvious solution.

It's different to bridging both outputs of the amp into one channel (which I did do at one point, it triggered the overload cut-out). All the connections between the terminals go through a speaker, so no short-circuiting is possible.

I've been running it with Linkwitz-Riley filters for a few weeks now and it's performing really nicely, so I'm not going to dabble any more (I have a degree to be doing instead now!)