Can anyone tell me what effect a coil across the + and- of a tweeter has.

I would guess that if you put it in parallel with the tweeter you are going to change the filter freq

Essentially it forms a divider network with the cap in series. The coil has higher impedance with higher frequencies and cice versa so an AC current for a low frequency signal will go proportionally more through the coil rather than the tweeter. Net result is that the tweeter will only have higher frequency signals going through it.

Thanks i think that helps.

The formula I always remember from training was, (say it as a rhyme)

â€śone over two pi root LC gives you the resonant frequencyâ€ť

Formula for a high pass is (I think) one over 2 pi RC

Itâ€™s all very hazy now as it was 32 years ago

Actually just checking and you can use â€śR over 2 pi Lâ€ť for an inductor

A first order tweeter crossover is a capacitor in series. A second order adds an inductor (coil) across the tweeter. You can add further components for higher orders.

Thanks for all answers very helpful now have a better understanding .