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Because all watts are not created equal

By Roy Johnson, loudspeaker designer, Green Mountain Audio, Inc.

A separate power amplifier is controlled by the preamplifier or the home theater control center. All it does is deliver a much higher-power signal to the speakers. Compared to the preamp, this takes a much larger, heavier power supply and either several vacuum tubes or high-power transistors to deliver the juice. So the first rule of owning an amplifier is because it needs ventilation, never place it on the bottom of a stack of gear. In this article, we explain amplifier power and describe the differences between vacuum tubes and their solid-state cousins.

How much power?

The answer depends on the speakers' sensitivity and your music, personal listening preferences, and how far away you are when you listen. Our speakers have medium-high sensitivities of 88dB or more. This means that most people will seldom need any more than 15 Watts of power if the stereo is not being played LOUD.

However, as the volume increases, power demands will also quickly increase. When playing music or soundtracks fairly loud, expect to need at least 30 Watts from an amplifier when listening inside of 10' (3m). At 12-15' (3.5-5m), expect to use at least 50 Watts. To reproduce the largest symphonies, grandest piano solos, and to reach true nightclub levels on jazz and well-recorded rock, 70-100 Watts are necessary at 12-15' (3.5-5m).

Now, the better your entire stereo system, the less loud you will tend to play it. This is because the emotions in the music or soundtrack are more easily felt, to the point that they are subconsciously felt.

The power output from an amplifier quickly increases because of how we hear. 'Twice as loud' does not require twice the power, but nearly 10 times the power. To raise the loudness by 'a little bit' would measure 3 decibels (3dB) on a sound level meter. This takes twice the power, even though the volume control was turned perhaps 10 degrees. Thus, 5 Watts quickly becomes 10, 20, 40, 80, then 160 Watts. Sounds judged 'twice as loud' or 'half as loud' show up as a change of 10dB (+ or -) on the sound level meter. A 100W amplifier can play 20dB louder (four times louder) than a one-watt amplifier.

We have been extremely pleased with the sound from all of our speakers using a well-built, 3W vacuum tube amplifier while sitting 10' (3m) away. To answer the telephone, we needed to reduce the volume on this particular amplifier while playing acoustic guitar recordings. We have enjoyed an acoustic jazz album using less than 10 Watts. If we were at your house, say, in the kitchen preparing dinner, 20-30 Watts would be required for the same music.

We have also enjoyed the sound from all of our speakers using the best 300W solid-state amplifier we have heard, when sitting only 10' (3m) away. The peak sound pressure levels achieved happened to equal what is experienced by a conductor on stage or from a nightclub's front row with only a small dance floor between us and the band. On rock music, the loudness reached was quite close to concert levels without hurting our ears. Amazing!

On any music, you may find that your body reacts differently to the live sound level of any instrument, compared to what is heard at concert-distances of 15-100' (5-30m). You will more deeply feel the emotion and power of the performance, which is what the musicians are feeling and responding to onstage.

Solid-state power versus tube power

Over the years, many people have asked us, "Is 'vacuum-tube' power louder than the same 'solid-state' power?" The answer is dependent upon the music being played and the behavior of the two different amplifiers as they approach their peak limits.

A solid-state amplifier generates sharper, harsher-sounding distortion when it begins to run out of power on the peaks, compared to a tube amplifier. This makes you aware of its limits rather quickly.

On the other hand, a tube amplifier softens the peaks before the sound becomes audibly harsh, so it seems to play louder than it should. Overall, audiophiles usually consider a solid-state amplifier to deliver more impact on music that is compressed (its peaks having been limited in the studio). This would include all rock, hip-hop, and electric jazz. A tube amplifier is usually considered to sound more 'graceful' and more musical on acoustic music and voices. The best amplifiers will combine both characteristics. In this regard, we have been consistently impressed with power amplifiers and integrated amplifiers from Almarro, Art Audio, Ayre, Blue Circle, Edge, Electrocompaniet, Leben, LFD, Manley, Pathos, Pass Labs, Jeff Rowland, VAC, and Viva.

How to audition an amplifier

Trust your ears, first. Think about your favorite music and soundtracks. The best amplifier will not only play everything in your library loud enough, it will be the one to reveal the subtle shifts in dynamics and rhythm -- even on rock music. A superior unit will reveal the small inflections in guitar and piano, a singer's voice, and the smaller details of a soundtrack.

With our speakers, the truly musical amplifiers clearly stand out, whereas too many well-reviewed amplifiers make an acoustic string bass sound like an electric bass. The lessons we learned were to 1) play a wide variety of music; 2) relax so that the attention is on the overall feel of the music or soundtrack, and 3) remember that a reviewer's advice is a guide and also an opinion based on past experiences, beliefs, values, and biases.

Whenever you can audition any product at home, at some point simply allow the stereo to play at a moderate loudness level while you go on about your activities. After a few afternoons or evenings, you will subconsciously recognize if the amplifier is 'boring' or really allows your music to swing. For movies, instead of intently listening to the soundtrack, assess whether your favorite movies are more satisfying and engaging. Your subconscious mind always notices something about the sound sooner than your conscious mind -- so relax and play everything you can!