Hi Jean
- Here are a few reasons for obtaining lower SPL figures in your UHF gear.
- Review to see if one or more match your particular experience .
(a) The replacement diaphragm is very easily "twisted" in the gap when the central phase plug is removed/reinstalled . This happens if the phase plug is tightened ( or loosened) without being firmly held as the central bolt is turned.
YES THIS IS THE REASON I CHANGE MY OLD BECAUSE I TWISTED FOIL IN SEARCH THE %$?&? HIDEN SCREW..
BUT I'M SHURE I NOT TWIST CAP.
(b) The usage of aftermarket diaphragms. ie non - JBL diaphragms .
THIS IS A BRAND NAME FACTORY OLD IS BLUE AND NEW IS YELLOW
D16r2405 2 x 150$$ cnd each
(c) The installation of the heavier 075 (2402 ) diaphragms instead of the 077 ( 2405 ) diaphragm . With a high crossover point this combo would measure less loud .
(I HAVE A LITTLE EXPERTISE IN THIS AND I CLEAN GAP , VERIFIE, ALIGNEMENT, AND NO PROBLEM IN THERE... THE MOTOR IS 2405 16 OHMS AND THIS IS A ORIGINAL DIAPHRAM...
(d) The replacement diaphragm is "binding ( or touching )" in the gap resulting in a loss of efficiency . ( Proper setup of a diaphragm requires a tone generator.)
WHAT IS METHOD FOR THIS TEST PLEASE ???
(I RUN WHITE NOISE AND MIC IN NEAR FIELD : RESULT RELATIVELY flat response just around 20K is really higher (6 dB))
I GO TO OPPORTUNITY TO MY SPEAKER IS OPEN FOR CLEAN-UP THE GAP OF THE 2420 AND CLEAN CONTACT OF INSIDE SCREW POST. WOW BIGGER DIFFERENCE IN RESULT... BUT NO LOOSE SPL...