Phil Jones Bass M-500, Руководство пользователя, Страница: 17 / 25

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The above chart quotes the minimum power available from the M-500. In reality
amplifier power can vary somewhat due to variations of the AC voltage supply.
(Variations can occur due to supply and demand of the region. For example, on a hot day
it is possible that voltages drop dramatically due to mass usage of air conditioners in the
region.) Also no such speaker has true constant impedance. The impedance of a speaker
will vary with frequency. PJB speakers are rated at their minimum impedance load.
Power measurements on PJB amplifiers are done with constant ‘sine wave’ signal at full
power across a static load resistor. This is the harshest environment for the amplifier and
in real circumstances it would not be subjected to such a hard workout.
Although the M-500 can work on speaker loads down to 2
Ω , it is not advisable to do so
on a continual basis at high power levels, since there is more heat generated. If the
weather is hot, there may not be enough cooling from the internal fan so the amplifier
could momentarily cut out as the amp’s heat protection circuits kick in.
A Note on Amplifier Power and Speaker Power Handling
Very often loudspeakers and amplifier power ratings are totally misunderstood by the
non-technical user for good reason. This is a complex and involving topic that will only
be touched upon in this manual.
First the ear is not capable of telling how much power is going to a loudspeaker.
Secondly loudspeakers have different power ratings at each and every frequency. The
amplifier will produce different power levels if the frequency changes, even if the volume
is the same. Finally, we hear sound based on a logarithmic scale. So in order to perceive a
note twice as loud, in theory we need 10 times the power to produce the perceived
doubling of volume. In reality another parameter comes into this already complex
equation. It’s called “Power Compression” which are losses in the loudspeaker units due
to heating up and reducing efficiency of converting the amplifier’s electrical power to
acoustic energy.
Loudspeakers are complex devices and very inefficient converters of electrical energy
especially when it comes to reproducing bass frequencies. More than 90% of amp power
goes to heating up the speakers and that is why the “Power Compression” factor is a
major one.
Two limiting factors determine the power handling of a bass speaker. One is the ability to
withstand the heat buildup before the unit goes up on smoke. The other is the excursion
capability of the cone. The cone will move in and out further not only with volume
increase but also as you play lower notes. An open B or E string will cause the cone to
move more than an open G-string at the same volume level. Also boosting the bass EQ
will cause greater excursion on the speaker cones.
PJB bass instrument speakers were developed with a focus to overcome the problem of
power compression, and this is one of the reasons they outperform competitive products