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Old 10-21-2006   #4 (permalink)
007
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Default Re: dB per Watt Ported

Quote:
Originally Posted by Raven
Any thoughts on the outrageous difference between the Dayton and every other woofer?

This is a bit misleading and should be called db/watt at manufactures recommended RMS Power handling, but in reality is sort of bogus if you look closely…

For instance, in the extreme case of the Fi BLT which clearly has a much higher sensitivity rating than many of the drivers, it actually did worse in this quasi dynamic sensitivity measurement. The reason is that 2000 watts clearly puts this driver into either a power compression state, a bl limitation state or a compliance limited state or other or a combination. Either way, you can keep putting more power into the driver and not get much more output relative to what you can get going from 100 watts to 200 watts for example. At 1000 watts or 500 watts, the BLT would probably walk away with the db/watt title with ease. Sure, its loudest at 2000 watts, but you’re clearly beyond linear limits observing its baseline sensitivity. That, or you have low voltage amplifiers that can’t deal with back EMF.

Secondly, and probably more pertinent, the db per watt ratio is completely ambiguous anyway. The first db gives you the sensitivity which can range from 80 to 90ish dB among those drivers. Hypothetically speaking, if a manufacture rated their driver at 1 watt RMS, then the db/watt ratio would be off the charts. Even if the driver maintained a perfect linear excursion up to infinity which is impossible, the db/watt would eventually drop to 0 because if you take the limit of (3x)/(2^x) as x goes to infinity, you get zero. 3x/2^x would be the ratio of perfect linearity as the dB increases. If you look down the line, the watts decrease from high to low perfectly, so it does tell you much at all, lol.

Sigh…

Therefore, I quickly derived a different formula to use which compensates for Thiele small sensitivity and gives a number more or less like db/watt. Call it the dynamic sensitivity rank. Its more or less some bull**** I just made up, but at least it works.

[ ln( 1 / RMS watts) ] / [ ln (2) ] + ((Measured SPL at RMS power) – (Sensitivity at 1 watt)) / 3

That will just give you a number much like db per watt. (it may be negative depending on the type of box)

The formula resides around the fact that doubling the power gives you 3 more dB if you are within linear limits.
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