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Multi-Way Conventional loudspeakers with crossovers

phase shift of second order filter
phase shift of second order filter
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Old 11th September 2019, 03:01 PM   #11
AudioEngineer is offline AudioEngineer
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Quote:
Originally Posted by bondo View Post
im having a hard time figuring out my crossover design for a 2 way system im building, which includes a 6.5" tangband driver along with a fountek ribbon crossed at 2.8k with a second order butterworth filter. ive read that second order filters have 180 degree phase shift, and i am wondering if this is corrected by switching the polarity(positive and negative connections). im asking this because i read that phase and polarity are different but i do not now why. also one of the calculators that i looked at showed that the wiring for the tweeter was switched but not the woofer, why is this?

Car Audio - Butterworth 2nd Order Crossover Network Design Formulas & Calculator
In a second order crossover you have to switch the polarity of either the tweeter or the woofer i.e. swap the positive and negative terminals. A 180 degrees phase shift means the tweeter and woofer are working in opposition to each other instead of in harmony. By swapping the terminals you get them working in harmony.

Last edited by AudioEngineer; 11th September 2019 at 03:06 PM.
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Old 11th September 2019, 07:12 PM   #12
Dave Bullet is offline Dave Bullet  New Zealand
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When we talk about target slopes - we usually refer to them as follows:

crossover + driver response = acoustic target slope.

A textbook "butterworth" crossover won't give you a textbook acoustic target slope. This is because the driver itself has it's own frequency response peaks, dips, rolloff and impedance changes.

To combine all the above - you might find you need a 3rd order filter (3 components) on the tweeter (plus attenuation padding) with 2nd order on the woofer (2 components) to get a 4th order acoustic XO.
The on-line calculators assume:
A perfect flat frequency response from 1Hz to 20Khz
a perfect flat impedance.
time aligned voice coils (= slanted or stepped baffle putting the tweeter behind / further back than the woofer)

Now look at the FR curve and impedance curve for your drivers....

The impedance curve changes with frequency.

the closer you are to the natural driver roll off (top or bottom end) and /or resonant peak (where the impedance "spikes") - the more worthless the on-line calculators become.

May I suggest you review the sticky in this forum "designing loudspeaker without measurements" or google the same.

Using a XO simulation tool is extremely useful - infact essential.... or you are shooting in the dark.
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Old 11th September 2019, 07:54 PM   #13
turk 182 is offline turk 182  Canada
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it's good to know that no matter how old a thread is some people need to share their knowledge...no questions will go unanswered....i've done so, as well...
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Old 12th September 2019, 11:43 AM   #14
waxx is offline waxx  Belgium
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Quote:
Originally Posted by tinitus View Post
Problem is that "6db" doesnt really exist, or at least hard to achieve with ordinary drivers
1st order only works in a 2 way or a 3 way where the mid has a very broad spectrum (like when using a FR driver as mid). You need to count 2 decades for the slope on both sides of the cr point to make it work.

I use a 1st order at 180Hz in my Mark Audio Alpair 10M gen3/Scanspeak 26W/8534G00 WAW setup, and there it works as the 10M goes rather flat untill +/- 40Hz and the scanspeak is useable to +/- 800Hz, so at both sides i have + 2 decades space.

But on a classic 3 way this does not work as the bandwith of each driver is to small to have this kind of space, a 2nd or higher order is needed.

But when possible to do it right, a 1st order sounds the best to me.
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Old 17th September 2019, 03:09 AM   #15
Oabeieo is offline Oabeieo  United States
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Isnít 12db LR only -180 on the lowpass so reverse the polarity on the lowpass should put everything back in proper phase


As far as BW filters go they shift at 90deg IIRC (correct me if Iím wrong)
So itís not needed in a BW alignment and only on a LR configuration
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Old 17th September 2019, 01:34 PM   #16
AllenB is offline AllenB  Australia
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Each order is 45 degrees at the crossover. Second order LP + HP is 4*45=180.

The difference is that LR only comes in even orders. Butterworth is more interesting in odd orders. It is the odd order that makes the polarity work either way.,

LR2 reverse polarity. LR4 same polarity.

Filters aren't always this simple in practice.
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Old 17th September 2019, 02:07 PM   #17
steveu is offline steveu  United States
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If the two drivers had the same gain/sensitivity and were placed at the same acoustic distance from the listener then a pair of 2nd order LP+HP filters would cancel at the crossover frequency being +90 deg and -90deg. So 2nd Order crossovers often call for one of the drivers to be wired inverted.
However, the tweeter is usually mounted on the same baffle as the woofer so it is a couple inches closer to the listener giving the tweeter sound a significant phase lead. And that phase lead varies with the listening position. In any case, most drivers have peaks and troughs that are similar amplitude variations.

Of more concern is the different impedance at certain frequencies that different filters have at the driver. Woofers sound much smoother with a single inductor in series than with a shunt capacitor because the undesirable cone resonances are more pronounced when driven by a low impedance. Likewise, the Q of the tweeter resonance is higher when shunted by a choke.
So unless protecting a driver like the tweeter from harmful low frequency energy is a priority, a simple first order filter usually produces the best sound. Third order on the tweeter only, would be my next choice. 2nd order on the tweeter is not usually a problem because the tweeter also requires an attenuator, which dampens the cone by presenting a ~matching impedance.
In the final analysis, just try it and use whatever sound the best.
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Old 17th September 2019, 05:48 PM   #18
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by AllenB View Post
Each order is 45 degrees at the crossover. Second order LP + HP is 4*45=180.

The difference is that LR only comes in even orders. Butterworth is more interesting in odd orders. It is the odd order that makes the polarity work either way.,

LR2 reverse polarity. LR4 same polarity.

Filters aren't always this simple in practice.

Thatís right. Gosh itís been awhile since Iíve had to think that through. I havenít used BW in so long I forgot what they do. I just remembered never to use them because I never had a reason to.
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Old 17th September 2019, 06:31 PM   #19
Oabeieo is offline Oabeieo  United States
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Something is still telling me the order is based on the number of poles (or reactive elements) I am not entirely sure it’s just 45*4 to get there

I thought each electrical order added 90deg and not 45

As 45deg is as 1rad at cutoff , 45deg on each side of the reactive element not each order


So a 1st order BW Q.707 would be at quadrature at cutoff. 45deg on each respective side of the time constant. The sum is 90deg (or something like that it’s been awhile not quadrature because that is 1/4th of 360 it’s 1/8th so it’s someth else I can’t remember)


Please correct me if I’m wrong

Last edited by Oabeieo; 17th September 2019 at 06:38 PM.
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Old 17th September 2019, 06:51 PM   #20
Oabeieo is offline Oabeieo  United States
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Pi/4 1st order
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