Life's not fair

In my earlier post, I mentioned the emergence of some angst by fellow audiophiles in response to our upcoming AN Series of loudspeakers. The fact that each pair is internally amplified with a servo woofer system means that your main power amplifier will only be responsible for the midrange and tweeter, not a very glamorous job for big and expensive amplifiers. Will these new speakers relegate our amps to the position of unnecessary overkill? I am going to argue no, they do not. Not when high-performance audio is at stake. Bass frequencies consume the most power in a speaker but that's only a portion of what's required to adequately reproduce music's dynamic contrasts to listeners seated in a room. From several hundred Hertz and above, the demands of proper reproduction in an average size room might surprise you. The way we measure sound is through the acoustic decibel which has a relationship to amplifier power measured in watts. That relationship is a very unfair system called "logarithmic" which means your amplifier must deliver ten times as much power to merely double the subjective loudness (I know, it sounds neither accurate nor fair). Between 6dB and 10dB is double the volume level and 6dB is four times the power and 10dB is 10 times the power! (not fair either) You might think this is not a big problem because you've read your speakers are capable of producing 90dB with only one watt (and 90dB is a good starting point for loudness). But, this is measured at only 3 feet (1 meter) in front of the speaker. Unfortunately, sound doesn't diminish with distance in a fair way either. Here, we get mired in yet another unfair logarithmic type problem called the "inverse square law": when the distance from the source is doubled, the sound pressure weakens by 6dB (and remember we need 4 times more power for every 6dB). So at a 6-ft distance, our 90dB speaker only produces 84dB (really quiet). Now let's double that distance again to 12 feet, a fairly common listening distance. The speaker now produces a mere 78dB, which is quite low. Since classical music can reach peaks of 120dB, you see the problem. If we were to start with a 50-watt amplifier (which is certainly enough to play our new speakers loudly) we'd quickly run into trouble if we wanted to honor dynamics. But wait. Dynamics are only the tip of the iceberg. There's more which we will cover tomorrow.