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Old 12th October 2011, 11:12 AM   #21
alspe is offline alspe  Finland
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Haven't red whole topic, so I ask am I thinking correctly at all.

If acoustic crossover orders are 2nd, tweeter should be connected at reverse polarity because both have 180 degrees phase shift and in different directions. Is that phase shift calculated from zero or from impedance phase curve of the driver in enclosure?

So if tweeter has 3rd order slope and bass has 2nd order slope, I assume that they should be connected reversed. Although I've seen many speakers drivers are connected both positively even if drivers had 2-3 order slopes. Does that come from difference of distance of acoustical centres of drivers? 5 cm (difference) corresponds 6800 Hz so half wavelenght is 3400 Hz which usually is XO point of small speaker.
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Old 12th October 2011, 02:40 PM   #22
AllenB is offline AllenB  Australia
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Originally Posted by alspe View Post
Is that phase shift calculated from zero or from impedance phase curve of the driver in enclosure?
The frequency response and the impedance each have a phase component. The crossover works on the impedance (magnitude and phase) to alter the acoustic response... it is the acoustic phase which you are referring to.
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Old 13th October 2011, 07:00 PM   #23
alspe is offline alspe  Finland
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^ okay , really have to study this more. Just wondering what are the main priciples how to calculate or figure out ways to design crossovers that makes driver in phase. And how drivers are time aligned. What Ive seen is that woofer is in someway brought closer when 1st order slope is used (timealignimg??)
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Old 13th October 2011, 08:41 PM   #24
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Most of the information you will see on this will be for theoretical crossovers that are really just electrical filters or math functions. They will quote information such as "1st order adds in phase and 2nd order adds out of phase". A real loudspeaker is more complex than this in that usually each driver has considerable extra phase shift that adds to the phase shift of the electrical network. That is, every woofer and tweeter has a finite bandwidth and an inherent rolloff and phase shift at high and low frequencies. Those increase the rolloffs that the electrical filters inherently have. In addition there will be phase shift due to driver depth. Generally a tweeter has little or no depth and a woofer has an effective depth roughly equal to its voice coil depth behind the cabinet front. This will bend the woofer phase downwards at crossover.

A proper simulation will include all of those factors and will show if your drivers and crossovers (together) can add in phase or perhaps add in phase if the polarity of one unit is flipped.

Short of doing a full simulation any generalities (such as "second order adds out of phase") are just as likely to be wrong as to be right.

Regards,
David S.
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Old 14th October 2011, 01:28 AM   #25
AllenB is offline AllenB  Australia
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ways to design crossovers that makes driver in phase.
You can measure the drivers separately and together and note the cancellations, but simulation is a handy thing.

If you want to simulate you'll need to take some measurements. At the very least, four per driver. You'll need the impedance magnitude (level), its phase, the acoustic (frequency response), and its phase.

I agree with Dave when I suggest you not concentrate on the theory of slopes and such for the time being. Once you've measured, look at what you have and turn it into what you want.
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Old 14th October 2011, 05:42 AM   #26
alspe is offline alspe  Finland
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Yes, that I will do. Of course I have to simulate 1st crossover for drivers, listen for a while, break driver in and then do 2nd round with measurements.
I wondered if is it always good to not sink bass driver in front baffle (because its acoustical center isn't where domes is)? Or is that also depending of phases of drivers, slopes and crossover in every case?
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Old 14th October 2011, 06:24 AM   #27
AllenB is offline AllenB  Australia
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Time aligning is lining up each driver with their origin, typically their voice coil. Not doing this will affect the phase as presented to your listening position. This will not likely line up either way as many factors are already affecting the phase, however it is part of crossover design to roll the phase around to where you can make good use of it.

With regards to sinking the driver flush with the baffle, I'd be more concerned with diffraction...but I haven't found this to usually be a major issue with woofers.
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