Grant Bunter wrote:From what I've seen here so far, the more common driver failure in Bills designs is tearing. That may suggest over excursion is the cause, as generally, voltage has been exceeded.
I apologize for discussing this so extensive. I'm a nitpicker who's just trying to learn
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If overexcursion is to blame, overexcursion being driving the cone beyond Xmech, and limiting at 60V prevents that, it may suggest that the coil already left the linear magnetic field of operation and is already playing in its non-linear area where Xmax < cone travel < Xmech
before the voltage reaches 60V, meaning power compression has already set in quite severe even before hitting the 60V limit, right? In this case it would be safe to say it's mandatory to limit at 60V. So far it's obvious
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But if one were to assume that the 60V limit is set according to
Xmax and NOT Xmech, which I believe would be the right parameter to specify the maximum allowable voltage by, one
could argue there's a little safety margin built in, namely from 9.6 mm of cone excursion (Xmax) to 17 mm (Xmech or Xlim). Right?
So this lead me to think about that 60V limit: If it is Xmax that dictates 60V, then in my opinion, the cone being strong enough to withstand the high air pressure occurring in the horn, it would be safe to say
musical peaks above 60V are allowable, as long as thermal heating of the coil and magnet structure stay in the safe zone. I.e. the coil, surround or spider would
not be damaged if excursion stayed < 17 mm. Thermally the drivers spec sheet allows for this (450Wrms (~60V) and 900W Peak (~85V) (EIA 426A noise source)).
But if it is Xmech (Xlim) that dictates the 60V (give or take a few safety-volts), than there's simply no headroom left and 60V is the brick wall beyond which the magic smoke is released from the coil.
Grant Bunter wrote:Why try to squeeze an extra (maybe) 2-3dB from what you have (which is roughly equivalent to 1 cab), with a possible consequence of driver failure, when you could build 2 extra cabs and add 6dB?
Practical as well as musical: using the amps limiter would offer a little more headroom and a cleaner sound (while still limiting continuous RMS power). Other than that, it triggered my thoughts on the limiting factor, as I've been trying to explain.
At this point I think only Bill (or anyone who has the correct software and horn model of the T48) can help out...
Awaiting the
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P.S., I must say I like to discuss this kind of things on a forum like this, where contributions make sense and not just bash the OP or any other comments
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