I saw an online article recently where someone's procedure for estimating the acoustic center offset between his drivers was to measure the speaker, model the XO, then increment driver offset in the model until the predicted result matched the measured result. I was wondering if there was a different way to do this. Could we measure the impulse response of both drivers, plot them on the same timeline, and then measure the time difference between the two impulses? Then multiple that by the speed of sound to get the distance/offset between the two drivers?
Would that work? I think Speaker Workshop uses an MLS signal for the impulse response - does that mean it's computed? Would it be better to actually measure this with a real pulse input signal? Should one compare the point where the impulse starts, or the peaks of the impulses? Would the HF response/rise time of the drivers affect this?
Right now I'm using a rough estimate for the driver offset. I picked the midpoint of the magnet as the acoustic center for the cone midrange, and the ribbon's location as the acoustic center for the tweeter. This works OK, but the calculated response from my crossover is still somewhat different from the measured response. And it looks like it's mostly a phase/offset error, because it predicts peaks and dips in the XO region that don't exist in the measurements. Outside of the XO region, the two plots match quite well.
This was just something I was thinking about last night. I know people here design speakers with vertical front baffles. So as general guidelines/advice, how do you measure the offset in the drivers' acoustic centers? I think this would be an important step, because once you have this and have the driver measurements on the actual baffle, you could go off and work on the XO on the computer, and not actually build one until you had something that looked good on paper. Right?
Thanks,
Saurav
Would that work? I think Speaker Workshop uses an MLS signal for the impulse response - does that mean it's computed? Would it be better to actually measure this with a real pulse input signal? Should one compare the point where the impulse starts, or the peaks of the impulses? Would the HF response/rise time of the drivers affect this?
Right now I'm using a rough estimate for the driver offset. I picked the midpoint of the magnet as the acoustic center for the cone midrange, and the ribbon's location as the acoustic center for the tweeter. This works OK, but the calculated response from my crossover is still somewhat different from the measured response. And it looks like it's mostly a phase/offset error, because it predicts peaks and dips in the XO region that don't exist in the measurements. Outside of the XO region, the two plots match quite well.
This was just something I was thinking about last night. I know people here design speakers with vertical front baffles. So as general guidelines/advice, how do you measure the offset in the drivers' acoustic centers? I think this would be an important step, because once you have this and have the driver measurements on the actual baffle, you could go off and work on the XO on the computer, and not actually build one until you had something that looked good on paper. Right?
Thanks,
Saurav
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