Impedance vs Sensitivity

[Guido]

This is posted in "technical help" although it deals with aftermarket components simply because it might be interesting for JBL components too.

Here is my prob:

I had time last weekend and an aftermarket dia for testing purpose on hand so I tweaked around with aftermarket and original dias on my 2416H (4425s).

As we all know the JBL 8 Ohm dias are 4 Ohm Dias in reality as they have a DCR of 3.2 Ohm.
My aftermarket Dia have a DCR of 4.3 Ohm and is the closest possible substitute.

What I did was:
I switched the aftermarket dia in the 2416H of one 4425 and left the other 2416H original.

What I expected was:
As the aftermarket dia have a slightly higher impedance the sensitivity of the 2416H will be slightly reduced.

What happened was:
The 2416H with the aftermarket dia had an appr. 2 dB higher midband sensitivity.

Huh??

Could this be because the aftermarket dia have a "longer" wire inside the gap and therefore a higher BxL?

Who can explain this to me?


Final Result: Don't mess around with aftermarket components!

[Guido]

I did know it: Nobody can explain this but it happened :(

[Steve Schell]

Hi Guido,

It is hard to make generalizations as there are so many factors playing against each other in a particular case. The BL will not necessarily be higher with a longer conductor in the gap, as BL really needs to be considered as gap flux X length of conductor X current flowing in the conductor. The higher impedance coil may have more length, but will draw less current.

The 2dB higher midband sensitivity could be due to differences in coil or overall moving mass, suspension characteristics, spacing to the phasing plug, or something else. Also, that higher sensitivity may be over a more narrow band, providing a "humped" response. Actually 2dB is not that bad- I have seen worse variations from supposedly identical diaphragms.