[Peter Larsen[_3_]]

Phil Allison wrote:

I'd just replace the bulb with a soldered in polyswitch,

** Bad idea.

Incandescent bulbs provide a better solution for live sound apps.

They allow all transients and normal levels through and rapidly
compresses ( without distortion ) exceptional levels - like
feedback howls - to a tolerable level for the HF drivers.

It is less bad, agreed.

OTOH, a Polyswitch cuts the sound almost right off ( without any
warning) and takes quite a while to re-set after tripping.

The result of playing something with unexpected 40 Hz content on Celestion
RS1220 is a gunshot-like sound that scares horses.

Relative comparison of voltage sensitivity for all units:

8 ohm 9135815 4 ohm 9090530 4 ohm 9090546

treble -16.78 treble -21.62 treble -24.73

mid -34.77 mid -43.36 mid -48.2

bass -41.61 bass -42.87 bass -43.22

Input signal to box: white noise, bass units has mic 1 cm from center dome,
mid horns has mic far enough away to be clear of box edge reflections and
treble units has mic once cm away. dB values are "average loudness" with a
300 ms window as determined by CE2k. 2 conclusions are obvious: bass unit
voltage sensitivity is as predicted by Dick Pierce and both 4 Ohm boxes need
service. So this seems to have been the end of a very long winnning streak
in buying second hand equipment, win some, loose some, now gain knowledge to
offset loss.

Finally got feedback from Yorkville. Both 4 Ohm boxes suffer from
deteriorated x-over or midrange driver or mis-mounted midrange drivers or
dirty midrange drivers or "all of the above". Midrange driver gasket is
visually misplaced - protruding 3 mm into the horn - in one of them.

Next to do:

1) measure output frequency response directly from x-over
while loaded with units

2) remove midrange drivers and measure frequency response sans horns on

3) expected result: get a new version eminence screw-on and just remove the
piezos.

Voltage sensitivity of 8 and 4 ohm bass loudspeaker versions is near
identical, which is what made me not simply put the 4 Ohm PL315's in a
dumpster and move on. Midrange output from 8 Ohm box is basically linear, 4
ohm boxes are differently unlinear.

.... Phil

Kind regards

Peter Larsen