We can already see that it may make more sense to increase a loudspeaker’s efficiency than to increase its power handling. If less is wasted, we don’t need as much from the source. And some means of increasing the power handling of a loudspeaker actually reduce its efficiency, yielding a higher power rating but less sound production!
So it is entirely possible that a loudspeaker with a lower power rating is actually a better transducer than one with a higher rating. The only way to know is to consider the efficiency, which is something that is often neglected by equipment buyers.
Back To Sound Systems
Now, in review let’s bring it back to sound systems. The power generators in a sound system are the amplifiers and loudspeakers.
Notice that I didn’t say power amplifiers. Power isn’t amplified, it is generated. An amplifier that is rated at 100 watts continuous can do just that – generate 100 watts continuously just like the dude on the exercise bike. And while it must be measured using a load, the available power is actually independent of the load.
A greater or lesser load does not change how much power is available from a source. An automobile rated at 240 horsepower has the same available power whether it is coasting down hill or pulling a trailer. You are just more likely to max it out pulling the trailer. A light bulb rated at 1000 lumens can do so in either full sunlight or complete darkness.
Amplifier specifications do not usually describe available power, but rather how much power can be generated into a specific load, such as an 8-ohm loudspeaker. This number is always less than the available power from the amplifier to allow for stable operation, longevity and high fidelity.
Although it is often overlooked, the power that the amplifier consumes from the electrical service is also important. Some amplifier types consume less power (and run cooler) than others in the course of providing their rated power. Others may serve us well as a space heater while generating a few watts for our hi-fi system.
Loudspeaker Ratings 101
The electrical power rating for a loudspeaker is a measure of consumption. Loudspeakers consume electrical power and convert it into heat and sound via mechanical motion. Since the sound is the part we are interested in, the main parameter of interest should be how much sound we get for the applied power, not how much power we can apply.
The ideal loudspeaker would generate the desired sound level consuming no electrical power. But because this is impossible, we must rate the loudspeaker’s ability to dissipate the waste.
The electrical power rating of a loudspeaker is a measure of waste removal, not a measure of sound production. A higher wattage rating is a good thing only if was achieved by a method that doesn’t reduce the efficiency. Like the light bulb’s luminosity, the loudspeaker’s sound power is the most important specification.
And as important as it is, you won’t often find efficiency ratings on a specification sheet. Instead you will find sensitivity ratings—numbers which describe the sound levels that result from confining the sound power to smaller areas (directivity) and increasing the power transfer to the air (horns, baffles, etc.).
Hopefully this clarifies some of the relationships and terminology regarding power generation and consumption.