Crossover: IIR or FIR?

[thumb5]

If I understood it right, Waiski's post is about designing a cross-over comprising a high- and low-pass filter. In particular, how to set the relative corner frequencies of the two filters to achieve the flattest overall response, which depends on the filter order.

[Waiski]

Correct. More info later today.

[Waiski]

Okey, so some data.

Under you see the measurement taken from pre out of D250 Pro. We did check and also speaker output crossover does work the same way.
Measured is fullrange and 250hz 1-4 order crossovers, high pass and low pass.

You can see from the measurements that 1st order crossover does give -3db on crossover freq, 2nd order -6db, 3rd order -9db and 4th order -12db.
So basically Devialet does multiply 1st order crossover 1-4 times. This means that you can use same filter order for high pass and low pass only for 2nd order crossover. Other crossover filters need to be build with calculation I sent earlier.

Order
LP=>-6dB ... -6dB=>HP
HP=>-6dB ... -6dB=>LP
1st 1.733 ... 0.577
2nd 1.000 ... 1.000
3rd 0.765 ... 1.307
4th 0.643 ... 1.556

So for 2nd order crossover you can use this without adjustments. 1000hz is 1000hz crossover point.
But for example 1000hz 1st order crossover point are... low pass is 577hz and high pass is 1733hz.

[zdenes]

I'm trying to understand this for practical application in my system. I have two active subs (ELAC SUB-2090) where I set the crossover frequency at 80Hz. I believe it's second order but the manufacturer doesn't specify. The Devialet is set for high-pass at 80Hz / second order at the speaker level.

Given the data above, would I be on safer grounds just setting both the low pass (at pre-outs) and the high-pass (at speaker level) on the Devialet and use the subs 'full range'??

I would appreciate any help on this as I have a feeling that I haven't fully managed to integrate the subwoofers.

Zoltan

[maxijazz]

Im general, in electronics, cut off frequency is the one where there is 3dB fall (or raise) in signal power.
It would mean that 1-st order filter is properly implemented (-3dB fall at 250Hz). The other filters no so well. I have to admit that different types of filters could have different definitions of cut-off

[Waiski]

If your sub has 2nd order crossover, then you can leave sub out to be full range. And speaker output 2nd order 80hz.

[Waiski]

No, it is at -6db.

[watchnerd]

Im general, in electronics, cut off frequency is the one where there is 3dB fall (or raise) in signal power.
It would mean that 1-st order filter is properly implemented (-3dB fall at 250Hz). The other filters no so well. I have to admit that different types of filters could have different definitions of cut-off

Not -3 dB.

Crossovers are -6 dB/per per order / per octave.  So 1st order is -6 dB per octave....4th order is -24 dB per octave.

Here's what I don't get:

Why would Devialet implement this in such a non-intuitative way?

[watchnerd]

You can see from the measurements that 1st order crossover does give -3db on crossover freq, 2nd order -6db, 3rd order -9db and 4th order -12db.

Okay, you're referring to the null point.

[Waiski]

Im general, in electronics, cut off frequency is the one where there is 3dB fall (or raise) in signal power.
It would mean that 1-st order filter is properly implemented (-3dB fall at 250Hz). The other filters no so well. I have to admit that different types of filters could have different definitions of cut-off

Here's what I don't get:

Why would Devialet implement this in such a non-intuitative way?

Same here. I don't get it. They don't even inform us how to use the crossover... This is pure stupidity.

I've been wondering already long time why does the crossover give horrible sound. This is the reason. When properly configured the crossover does work really good.