AUDIO
THE AMP RACK | Bill Gibson
The proper selection of power amplifiers for any system is not random . First of all , in this industry reputation is everything , whether you are considering who to work with or what equipment to purchase . If you find a power amplifier that seems too good to be true — its specifications are incredible , it ’ s lightweight , and it ’ s less expensive than anything else you ’ ve seen , but you ’ ve never heard of the manufacturer — be careful . There are a few good names in the professional power amplifier field , and they are worthy of consumer trust . Any brand that hasn ’ t been proven in the field and favorably reviewed is likely to add drama to your life right in the middle of the most important performance . I don ’ t know why things fall apart in the middle of the biggest show of the year , but that ’ s how it often works out .
It ’ s important that each amplifier is judged on a level playing field . Power ratings are sometimes confusing to the inexperienced buyer . Terms such as RMS , peak , +, EIA , and continuous power aren ’ t equal , but they can all be useful when considered thoughtfully and when they ’ re assessed fairly . Always combine the implications of multiple specifications . For example , two amplifiers might claim an RMS rating of 500 watts ; however , one is rated at . 1 percent distortion ( THD ) and the other at 5 percent distortion ( THD ). In this case , the amplifiers sound like they ’ re similar at first glance ; however , they ’ re quite different .
PEAK POWER Peak power is the highest instantaneous power potential in an amplifying circuit . It is essentially the absolute maximum amount of power a circuit can muster up in a mere instant in time . It far surpasses the sustainable power level . Sustained peak power levels result in circuit failure .
Peak power ratings are numerically impressive but offer little to no value in the assessment of a power amplifier .
RMS POWER RMS stands for root mean square , which is technically the square root of the arithmetic mean of the square ’ s set of values . There is a fair amount of math involved in the actual
calculation , but for our purposes we need to remember just a few simple conceptual principles . If you are mathematically inclined , look up “ root mean square ” at wikipedia . org .
Amplifiers are tested using sine waves as audio sources . The RMS value is calculated as . 707 times the zero to peak rating of the sine wave . Conversely , the peak rating is calculated from the RMS value by dividing by . 707 .
Practically speaking , the RMS rating resembles an average power rating in that it closely resembles the average metering of the typical VU meter . RMS power closely equates to perceived volume because , like the human ear , it tends to ignore instantaneous peak levels . In reference to a square wave rather than a sine wave , the RMS value is the equal to the peak value .
CONTINUOUS POWER Continuous power represents an amplifier ’ s continuous reliable power output potential and is often equated to the RMS power rating . This rating indicates the power level for continuous
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