Tag Archives: Power Amplifier

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Peak power

Our system’s power amplifier is almost always bigger than needed. Or is it?

We know that headroom, the reserve amplifier power we hope not to use, is important. But how much is enough? Do we have to acquire a scope and meter and dust off our engineering degrees to measure the peak power our system demands? I think there might be an easier way.

With the understanding it’s not hard amplifier clipping we’re talking about I think we can safely make a few observations about the amount of headroom we have by simply listening.

The need for headroom has to do with perceived compression of music’s dynamics. The more headroom the lower the compression we experience.

For listening evaluations of peak power, I prefer orchestral music for several reasons: its acoustic instruments and fixed proportions. We know what those instruments should sound like and we can imagine the proportions of an orchestra easier than we can a rock band or jazz ensemble.

What we’re hoping for is a lack of compression when the entire orchestra’s playing loudly. It’s rare, but with enough headroom and the right speakers, an orchestra’s loudest crescendos should scale in image size and tonal qualities to it’s quietest levels. Anyone that’s ever heard our Infinity IRSV system knows exactly what I am referring to. Scale without compression.

Most speakers don’t scale all that well so separating out the headroom issue of the amplifier chain vs. the speakers can be problematic, but easier than trying different loudspeaker combinations. A friend’s higher power amplifier is a relatively easy swap to see where your system stands on dynamic compression.

Amplifier power is almost never enough when we consider headroom in the hopes of reducing compression.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Life’s not fair

In my earlier post, I mentioned the emergence of some angst by fellow audiophiles in response to our upcoming PS Audio 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 close to a whisper.

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.