Time aligning planar tweeter and 15". Help please! - diyAudio
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Old 12th August 2009, 11:36 AM   #1
SAC is offline SAC  United Kingdom
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Default Time aligning planar tweeter and 15". Help please!

The tweeter (BGneo 3 pdr open baffled) is crossed to the 15" (alpha 15a OB) just below 2khz with a first order Xover. I read that time alignment at 2khz is worthwhile to within 4.5cms at this frequency.

1. Is it worth the bother?
2. At what point in the 15" driver should I aim? The acoustic centre or thereabouts?

Admittedly, I will incur diffraction problems in the event I move the tweeter back although your answers may help me weigh up the pros and cons.

Thanks
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Old 12th August 2009, 12:26 PM   #2
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My method which seems to work:

1. Measure woofer on-axis 20cm. Get impulse and record gated phase

2. Measure tweeter on-axis 20cm (exactly!) same thing.

3. Compare phase, build delay circuit then play around until the phase matches (0 deg if LR4) at the xo point. (physical offset is a good starting point)

You'd find out that the acoustic centre is *not* the voice coil.

You're crossing alpha 15 at 2kHz? ... very brave
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Old 12th August 2009, 01:11 PM   #3
SAC is offline SAC  United Kingdom
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Gainphile, your method is way beyond my means. I use a test CD with frequency sweeps to get an idea of the flatness. It is a rough design as you noted. I am relying on Audyssey auto-eq to resolve as many problems as possible. Emerald physics CS2 do a similar thing.

With regards to alpha 15 at 2khz;
I had the B200 crossed to a single and also two alpha 15s.
Also had neo3 pdr crossed with the same cross over to the B200. The four remaining alphas acted as a sub.
In conclusion, the best sound was when I crossed the tweeter to the single alpha in an experiment. Realistic treble and soundstaging for the first time. I have to give up on the B200s perhaps due to my inability with crossovers, the necessary chokes, and so on. Wooden phase plugs didn't even help much with that uncomfortable high end response.
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