Atlas 12" and tc2+ a few measurements... - diyAudio
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Old 31st January 2005, 04:29 AM   #1
npdang is offline npdang  United States
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Default Atlas 12" and tc2+ a few measurements...

I'm a bit curious. What causes the hump around 60-80hz that most 12" woofers exhibit when measured using a close mic technique?

I've always assumed it was inductance given the various threads I've read over the years, but I've also heard that it's a nearfield artifact of some kind. Any clues? According to Joe D's book on "Testing Loudspeakers", he quotes a rough upper limit as 4311/ cone diameter in inches... which is around ~350hz for a 12". He makes no mention of any other issues with nearfield measurements.

Some recent plots of the Ascendent Audio Atlas 12" using a xbl^2 motor, and a good old Tc Sounds tc2+ 12" overhung motor w/ copper ring.

Tc2+ green
Atlas blue

Click the image to open in full size.


Sine sweep taken nearfield, 21Vrms, unbaffled. Small note, the Atlas exhibited rather large mechanical noise during testing. The Tc2+ was very quiet, as shown in Mark's testing. I'll let you draw your own conclusions

tc2+
Click the image to open in full size.

Atlas
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Old 31st January 2005, 02:24 PM   #2
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In short: K2 for the TC2+ is about 5dB lower than that of the Atlas, whereas the Atlas' K3 is roughly 3dB lower than that of the TC2+.

Mechanical noise, you say? What kind?
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Old 31st January 2005, 03:56 PM   #3
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Isnt the atlas more efficient that the TC? not to point out the obvious, but if theyre measuring distortion with given power input, and the atlas is say 1.5 db more efficient, its still moving a fair bit more than the TC sounds is.
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Old 31st January 2005, 04:48 PM   #4
npdang is offline npdang  United States
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I'm not quite sure what the noise is, only that it's rather loud and sounds like a small motor. Keep in mind this is only audible with the driver unbaffled, in free-air.

As for differences in sensitivity, looking at the two distortion plots I don't really see >1db difference between the two drivers, although I will concede they are not matched exactly.

I also forgot to mention the Atlas was run with the small voice coil shorted, for a "low qts" configuration.
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