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Old 31st October 2012, 08:07 PM   #1
OMNIFEX is offline OMNIFEX  Jamaica
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Default ARTA LIMP & VAS Conflictions.

Hi.

For those who measure their own TS Parameters, have you received conflicting reports in terms of VAS? I’ve encountered nearly 2100 litres in LIMP from an 18-inch driver that offers a specification of 279 litres. QTS is fairly the same as the manufacture states however, the fs is nearly10 Hertz lower (23 measured versus 32 stated). Surely, a 10 Hz differential would not equate to 1821 litre increase in terms of VAS.

How accurate is LIMP in terms of estimating VAS?
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Old 1st November 2012, 01:20 AM   #2
VaNarn is offline VaNarn  Australia
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I am reasonably familiar with L.M.S. and the CLIO systems and I learnt that the delta compliance method is to be preferred over the delta mass alternative as it is usually quite difficult to rigidly attach a known mass to a cone assembly and avoid unwanted suspension effects.For a confirmation of the accuracy of the ARTA readings you may have to resort to the methods of the past,providing you have suitable test equipment.A lower resonance freq than the spec. value(although the 23 Hz figure is reasonable for an aged speaker) will give a significantly larger VAS but your reading appears incorrect.Perhaps,incorrect values have been used when filling in the boxes; the effective speaker diameter is a an entry to look at.
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Old 1st November 2012, 04:24 AM   #3
OMNIFEX is offline OMNIFEX  Jamaica
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Cheers VaNarn.

It appears I may have solved the problem. The impedance rise at the fs was nearly 150 ohms in which, I was using a 100-ohm resistor. The frequency shift was below 20 Hz, which I had the frequency starting point @ 20 Hz. In addition to the above the grams was too little (30 Grams) to make a significant shift.

Once I added a 200-ohm resistor, lowered the frequency starting point to 10 Hz, and added 60 grams of weight, the VAS offered similar results to the manufacture. The previous driver only required 15 grams and did not exceed
40 ohms in terms of fs.

This is one out of ten, nineteen-year-old, 18-inch drivers retired sitting in its original carton. So they would be classed as very old in the sound reinforcement world.
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Last edited by OMNIFEX; 1st November 2012 at 04:27 AM.
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