Active Power Management
This abstract outlines the background and basics for the TC Electronic Active Power
Management™ introduced on the RH450 Bass amp.
What watt?
When rating an amps’ power handling there are number of factors that need to be included, i.e.
voltage, time, crest factor of the source signal and a number of other technical parameters.
However to most bass amp users the perception of power is more important than how it
measures – in other words, it all comes down to sound and loudness.
In bass amps specifically, there are very obvious differences in the perceived power handling of
the two most classic categories: Tube- and solid state- (transistor) amps. In order to understand
why this is, we need to take a quick look at the dynamics of a typical bass signal as well as how
our ears respond to sound.
Bass signals and Dynamics
The average signal of a bass has a very wide dynamics span that ranges from a short and very
high peak at the stroke of the string and quickly dropping to a significantly lower level at the
sustain of the note played. This is known as the ‘crest factor’ and describes the ratio between the
highest peak and the average energy of the signal. Typically bass signals have a high crest factor
of 10-15 dB depending on playing style (fig. 1).
Figure 1: Bass signal sample
Human ear response
Our ears, being fairly slow in response, pick up on the average level of sound rather than short
term peaks. In other words the level, or loudness, that we experience rarely has to do with the
peaks, but is tied closely to the average level, or energy, of a certain signal. In the case of bass
signals, this means that it is not the actual stroke of the string, but the sustain of the note that we
determine the perceived loudness by (fig 2).
Figure 2: Bass signal with approximated RMS marking / perceived loudness
