View Full Version : Diaphragm screw torque requirements
05-08-2003, 11:00 AM
Just out of curiosity, is there any data available on torque requirements for the mounting screws on JBL diaphragms used in any of their compression drivers?
When I repaced may domes? on my drivers I just tighten them to a point I felt ok. Before that I sent a signal to the drives from 300-1500Hz with the bolts very loose (don't remember the power..Robert knows) to center them. After that it was ok, and they play good.
05-08-2003, 02:35 PM
3-4 volts at 550Hz for 1" CDs and 350Hz for 2" CDs during the centering process. Frequency sweep and voltage differs according to specific CD. There are some generalities but enough exceptions to negate posting a sweeping statement.
05-08-2003, 05:50 PM
I torque until the screw has "just become" firm or positively seated, if that makes sense .
Quite recently I found a way to eliminate that pesky "buzzing" that comes from those rare diaphragm/driver combos, that just refuse to center and be "cleanly" torqued down ( no matter what order/amount of torqueing is applied to the screws ).
I now use a very small (@ 1/2" x 1/2") paper gasket, cut from normal 20 to 24 lb stock, placed below the diaphragms plastic holding rim, directly underneath that one screw that seems to be the cause of all the tuning grief. The screw (bolt) goes through the paper. It seems something in the manufacturing process isn't perfectly flat and this solves that. The (screw) needing the treatment usually reveals itself quite soon into the trial & error portion of the torqueing procedure. I'm still waiting for one of these drivers to go " Kazoo" on me . :D
Old RCA drivers ( cheaper type PA ) used to use a gasket method like this except the gaskets were full circumference , very thin, and a quantity of 2 to 6 used. The quantity of gaskets could raise or lower the coil into the gap for maximum output ( centering ). That much paper to work with does create a bit of compressability "or give" that helps snug up the screw without warping the diaphagm holding ring. I'm not sure what build tolerances RCA were trying to adjust for. :p
regards <. Earl K
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