[Audio Empire]

On Sun, 7 Aug 2011 07:13:14 -0700, Charlie Bonitz wrote
(in article ):

Am 07.08.2011 01:36, schrieb Nikki Thuillier:
I have blown both tweeters and the resistor on one side also! My dealer
wants $2,600 to replace them!!!

Nikki

Make shure to have your amp(s) checked if you don't know the reason of
the failure for sure.
Otherwise the tweeters might blow again next time you try.

Charlie

Good point. There are generally two amp conditions that can blow tweeters.
One is that the amp is ultrasonically oscillating, and the second is that the
amplifier that you're driving the speakers with is too small for the
listening level to which you are driving the speakers and the amp is clipping
- a lot!

In the first case, the amp itself is faulty, and a high-level oscillation is
being produced, that while you can't hear it (it might be higher than 20
KHz), it is nonetheless being pumped into the tweeter. Unable to handle that
much power at those frequencies, the tweeters simply overheat and burn-out.
This condition is unlikely to appear in BOTH channels at the same time,
though, but it is possible. It's also possible that the oscillation is
occurring UPSTREAM of the amplifier. Are you playing music from a computer
sound card? If so, you might want to start there. You'll need an oscilloscope
to see the oscillation, as you usually can't hear it.

The second problem occurs when you couple an inefficient speaker system with
a solid-state amplifier that's too small to drive it adequately. If you
listen very loudly, and drive the amplifier beyond its power capabilities,
the amp will "clip". That is to say, that the amplitude of the waveform
feeding the speakers exceeds the amplifier's power supply limits. When this
happens, the tops of the music get cut off flat. This means that the signal
to the tweeter becomes, instead of occasional high-frequency content, a
steady-state high-amplitude "square wave". Because it's a steady state
signal, the voice coil in the tweeter doesn't have time to cool-off between
peaks and it's 'duty cycle' (the length of time that the voice coil can be
energized before it overheats) becomes exceeded. Since tweeters are small,
with small voice coils and not much mass to dissipate any heat that builds up
in them, they can't carry much power. Normally that's OK because there isn't
much power in the normal high-frequency content of music and the speaker
system's crossover network keeps the low frequencies (where the power is) out
of the tweeter anyway. However, all bets are off if the amp is defective and
oscillating supersonically at high volumes, or if the system is being played
loudly enough to clip the amplifier pretty consistently.

Most speakers have a fuse in line with the tweeter to protect it against both
of the above conditions. Some manufacturers eschew this practice because they
believe that the fuse acts as a nonlinear resistor and introduces distortion.
On the other hand, more often than not, the tweeter ends up protecting the
fuse by "blowing" first, in which case, the idea of fusing the tweeter ends
up being more like wishful thinking than having any real, practical value.