| Where's the Voice Coil? [message #71915] |
Mon, 26 March 2012 06:09  |
Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA
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Illuminati (2nd Degree) |
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I'm looking at an Alpha 10A and measure approx 2" from the spider to the front of the speaker frame.
Is it reasonable to assume that the spider is roughly centered on the coil and it's about 1 1/2" to the front?
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| Re: Where's the Voice Coil? [message #71920 is a reply to message #71918] |
Mon, 26 March 2012 10:09  |
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Wayne Parham
Messages: 18791
Registered: January 2001
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Illuminati (33rd Degree) |
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Measurements at a large distance make small shifts in acoustic center have less effect on SPL, but they don't change the effects on phase. If you have two sound sources that are a half-wavelength apart, you'll still have cancellation, no matter what distance they're at. So distance won't help with that. But if the goal is to get accurate measurements of SPL, then measuring at a distance helps, because it makes the smal shifts in acoustic center less relevant. For example, if the acoustic center is one meter behind the face and you measure one meter from the face, then you have actually measured two meters from the source. But if you measure ten meters from the face, then that's eleven meters from the source. One is a factor of 2.0-to-1.0, the other a factor of 1.1-to-1.0. See the difference?
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