I'm probably just adding more detail then really needed (again) but...
Speaker/
Amplifier Question:
Ahhhhh... the old
speaker/amp terms struggle. In an industry in which these terms are not well standardized (sometimes not at all) and in which one manufacturer often uses the same term as another, but with altered meaning - its difficult for
anyone to decipher at times.
I agree that it can be quite confusing.
Generally speaking, the "continuous"
rating describes how well the
speaker can withstand long term average demands often measured by playing steady sine waves or some sort of weighted noise input. This type of signal, even at lower
power ratings, causes the
speaker to do "continuous" hard work and thus, this
power handling figure is the lowest of the three.
The Continuous
rating is the one that is the most standardized and has the most meaning, primarily because it is typically the only
power rating that is actually measured. It is also the
rating that most closely relates to long term use and thermal failures. There are two general areas where things get confusing. First, there are a number of standards that define different test signals and time periods. Manufacturers use the various standards based on their own engineering and/or marketing perspective. Second, while the Continuous
rating is based on failure, you have no way of knowing what defined the failure; was it something that the
speaker could recover from after a period of rest or was it flames and cones flying across the room? The tests and ratings also do not indicate whether the sound of the
speaker or
driver changes significantly before reaching the failure
point. You sometimes see Continuous
Power referred to as
RMS Power which is technically incorrect, but because it is
power calculated based on
RMS voltage and
impedance this terminology has become quite common.
"Program" is typically based on a test signal that simulates "real world" music conditions - such as - perhaps - your band and vocal group. Obviously, this type of sporadic (both in amplitude and frequency) signal does not require the
speaker components to work as hard as a steady-state signal (of similar wattage) and thus the increased allowable "program" wattage figure.
Literally, the Program
rating is a made up number. The logic is indeed to represent some 'real world' signal, but since there is nothing limiting how the
speaker is used or the type of signal it will reproduce, it is pretty much just a made up number that is usually halfway between the Continuous and Peak ratings.
"Peak" is usually based on an instantaneous
spike of signal (usually no more than 1/10 of a second), and is a signal that the manufacturer is indicating should not be exceeded without expecting damage to the
speaker (just as in the previous examples). Thus the
power handling capability is higher - but only for that brief "instance of time".
Actually, the Peak
rating is based solely on the fact that the most common signals used for the Continuous
power rating tests are defined to have a 6dB
crest factor, thus the peaks in the test signal are 6dB above the average
level. Based on this it is assumed that the
speaker can handle peaks 6dB above the continuous
rating, so the Peak
rating is almost always simply 6dB above, or four times, the Continuous
rating and is not an actual measured value.
In a nutshell, the terms/ratings described above are merely ways of expressing how much
power input the
loudspeaker can withstand as it experiences different forms of amplified signal input.
What is really surprising to many people is that the tests rarely actually measure the
power applied, they measure the
voltage applied and the
speaker impedance and from those values calculate the
power. There is a committee in
AES working on new
speaker testing and
rating standards that would report both the actual
voltage and
impedance measurements and would be based on when the
speaker exhibits an audible difference in response (+/-3dB at any frequency) rather than requiring actual failure. Some people will resist the new standards as they will likely result in much lower, but much more accurate and valuable, ratings.
Though there is no absolutely "right" amout of
power - a reasonable rule of thumb for powering a
loudspeaker is to provide
amplifier power that has a
power rating of 1.5-2.5X the
speaker's continuous
rating. More is possible with care and with proper utilization of peak limiting.
That rule of thumb is for when you have no specific performance goals and for an average user. For installed systems the process is typically quite different and involves working back from the desired performance at the listeners, including
headroom, through the room to the
speaker and then using the
speaker sensitivity to derive the
power required. Only then does the
power rating come in and simply as a verification that the
speaker can support the
power required. So different approaches for different applications.
