Since I was positively impressed by some of the HF qualities of 4" diaphragms in a 2" exit driver and following my attempts to get the most UHF extension out of a 2445 - see http://www.audioheritage.org/vbullet...n-reverse-mode - I'm pursuing my investigations into this area.


It is well known that one of the decisive factors influencing the UHF extension is the distance between the diaphragm and the phase plug (the lower the air volume between the two i.e shorter the distance, the better the UHF extension - see for instance John Eargle's book on Loudspeakers).

I'm now wondering whether:

1) does anyone know what the current distance is in those 4" core drivers - it being understood that due to diaphragm curvature, it is presumably the least at the tip of the diaphragm dome? Since i've managed to implement various types of diaphs in my 2445 drivers (JBL D16R2445, D16R2441, aftermarket ribbed/non aquaplased model normally meant for other JBL drivers etc.) I would assume the core and diaphragm geometries are basically the same throughtout the product range and years (some isolated exceptions ???).

2) provided the driver is not used at too low frequencies (but in the range 2kHz-16kHz area as in my case) and is not used for extreme levels as in PA equipment, it would theoretically be possible to reduce the distance between diaph and core, and if so by how much ?

3) has someone tried a modification ? one that seems feasible would be to remove the lowest of the two metal rings (provided they are not glued too strongly together and it would not distruct the two signal leads) underneath the plastic diaphragm support ring, and to replace it with one or several layers of bristol disks/spacers down to the desired heigth.