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Old Yesterday, 01:03 AM   #1431
Ssmith3 is offline Ssmith3
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Thanks, Byrtt.

Itís just that it seems like a simple question, and the answers seem inadequate or vague. And more importantly, the difference at the crossover frequency of the 33mm difference between the two main potential ways I could see this Z measurement being defined makes a huge dip in my response curve, with a drop of 12-15dB. It isnít an inconsequential number to the results, and I donít know which number to use. Itís practically like dropping in a notch filter.

If the Z number can cause that dramatic of a notch in my crossover design, I want to make sure I am getting the right number in there and adjust before I buy new caps and inductors for my passive crossover.

But you are certainly right that I would be better off measuring the response than using predicted data. I may do that. At least then, whatever effect the Z number would have should be included in the recorded test data - not to mention the other acoustics of my specific enclosure.

Thanks.

But it would still be nice to know what physical part of the speaker is the point of reference to measure Z. But I canít seem to get a simple answer on that question. You refer to ďacoustic centerĒ. Where, physically, is the acoustic center on a dome tweeter and a woofer that would be the points you use to determine Z?

But you DID give me a simple answer for + vs - on Z. Thanks for that.
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Old Yesterday, 02:08 AM   #1432
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by Ssmith3 View Post
...But it would still be nice to know what physical part of the speaker is the point of reference to measure Z. But I can’t seem to get a simple answer on that question. You refer to “acoustic center”. Where, physically, is the acoustic center on a dome tweeter and a woofer that would be the points you use to determine Z? ...
Welcome Ssmith3 and yes seriously before ordering any components get some measurements of system in situation : )

About real acoustic center for a dome tweeter and a woofer is probably real complicated from unit to unit, myself don't care so much because i use DSP and can offset to whatever numbers and get documentation via step response or scope in measurement program, but have read some pointers about real acoustic center over time and as far as i remember its a physical point somewhere in front of center of voicecoil where the energy will start as electric signal, so probably you could estimate a point a little in front of voicecoil for your drivers and then use that numbers and their physical position on baffle to get to a close estimate to use in VituixCad simulation. Also if i remember correct real point of acoustic center can sometimes be frequency dependable onto some transducers, if that is true and two physical different drivers is alligned and sums say a 1kHz sinus perfect in cycle, then they will drift a bit in cycle at say 2kHz, for such a case of allignment for a sinus wave guess one should look for allignment of acoustic center is optimized at same frequency as one intend to slope the XO.

Last edited by BYRTT; Yesterday at 02:11 AM.
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Old Yesterday, 02:32 AM   #1433
Ssmith3 is offline Ssmith3
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Awesome. Thanks, Burt. That makes sense, and explains why a very simple answer was not easy for people to give.
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Old Yesterday, 03:56 AM   #1434
kimmosto is offline kimmosto  Finland
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Typically with unidirectional i.e. boxes speakers, difference between straight non-stepped front baffle surface and acoustic center of each driver should NOT be adjusted with Z mm parameter. Z should be 0 mm for all drivers. Adjusting with Z is legacy error in DIY scene inherited from old-fashioned tools which were not designed for off-axis response simulation. Correct parameter is Delay [us] of driver which handles timing properly also to rear sector (90...180 deg): positive delay stays positive also to 180 deg off-axis.

Using of Z mm parameter for timing adjustment is meant for stepped baffle.
Z works also with dipole radiators because positive Z becomes negative when mic/ear is rotated to 180 deg off-axis.
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Old Yesterday, 04:57 AM   #1435
kimmosto is offline kimmosto  Finland
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Quote:
Originally Posted by BYRTT View Post
..myself don't care so much because i use DSP and can offset to whatever numbers and get documentation via step response or scope in measurement program...
Basically DSP does not change anything compared to passive XO if you design with simulation wanting to simulate+visualize also power & DI and other off-axis. Both need measured timing (compared to rotation center) for each driver model, and setting of geometry parameters X,Y,Z,R,T for each driver instance.

Most of my latest designs are DSP with IIR, FIR or mixed. Only way to design with possibility to make controlled changes even in remote is making "everything by the book".
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Old Yesterday, 05:26 AM   #1436
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Ssmith3 View Post
I am really not trying to be dense here, but....first off, at this point I am not measuring, I am designing and predicting while building a crossover in software.
I see. I was in this boat, too. I took me a while to realise that Vituix is not based on the idea of "forward simulation of everything".

Think of Vituix as a data processing tool. You feed it with measured data (which is referenced to whatever z=0 you used in the measurement), and then Vituix processes this data (by considering the x-over filters and geometrical offsets between the drivers). The output is referenced to the z=0 in your measurements.
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Old Yesterday, 06:22 AM   #1437
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by kimmosto View Post
Basically DSP does not change anything compared to passive XO if you design with simulation wanting to simulate+visualize also power & DI and other off-axis. Both need measured timing (compared to rotation center) for each driver model, and setting of geometry parameters X,Y,Z,R,T for each driver instance.

Most of my latest designs are DSP with IIR, FIR or mixed. Only way to design with possibility to make controlled changes even in remote is making "everything by the book".
Thanks guidance and imagine work by the book get rocking good results : )

Will say in my own two way active DSP system i can be a bit lazy and jump over all that work because a 10F/8424 is the system dictator for dispersion in its sloped with 96dB/oct linear phase XO covering 240Hz and up, below one woofer sits within 1/8 wavelenght and cover the rest. System is on wall and guess nothing one can do about mid tweters inherent dispersion in begin to measure all the way around, what helped me enorm for realistic good room sound is set speakers exactly mounted position into room (you know relative distance numbers to bounderys and listening position etc) into one of Jeff Bagby's spreadsheet and use that curve in reverse into DSP, that got me close to exelent in room sound not to speak of with open door in nearby rooms one can hear that correction made wonders so speaker response is kind of tuned to room.
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