It looks like it is loosely related to the mass breakpoint frequency formula:
f = BL^2 /(Pi*Re*Mms)
This is the frequency above which the SPL will rolloff at a 6dB/oct rate if a constant directivity is maintained.
It is typically around 3kHz for a compression driver, and in the realms of 500Hz for midbass woofers.
It only impacts high frequency response though (think 2234H vs 2235H)
Hi Ruediger ( Pos ),
The dynamic indexing formula ( as I see it ) is a product ( of sorts ) for displaying potential energy transfer ( & really, it's not very different from simply using Sensitivity ) .
I use this formula ( as well as the EBP product, ie; mass break point ) to identify & compare different woofers to the known entities that I've used for decades( such as 2225 & 6s ) .
I realize that for most, these numbers might be meaningless / but for those of us with a few decades experience ( with specific Pro products ) the numbers help me relate to how JBLs' competitors ( such as all those Italian speaker manufacturers ) might perform ( if purchased ).
Futzing about with EBP & this DPI index, also allow me to quickly execute a bunch of "what if scenarios" ( for altering a systems over-all voicing ).
Running these numbers do show ( for instance ) why someone ( GT ? ) bothered to create separate 2108 ( and 112 transducers ) as well as the 2 distinct classes of Le5-x, 5" mids ( I'm sure you can guess which have the lower dynamic numbers ) .
I will have to re-read this formula thing a few times. It seems intriguing.
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