by mozilla » Thu Jan 23, 2003 2:59 pm
Tubes produce EVEN ordered harmonics.
Music consists of musical tones or notes. A scale in its basic form has eight tones. The sound of an instrument consists of much more than single notes. Each note is a complex collection of a fundamental, overtones and harmonics.
The basic sound characteristic of an instrument is determined by the strength of the first few harmonics. Each of the lower harmonics produces its own characteristic effect when it is dominant or it can modify the effect of another dominant harmonic if it is loud enough. In the simplest classification, the lower harmonics are divided into two groups. The odd harmonics (third and fifth) produce a "stopped" or "covered" sound. The even harmonics (second, fourth, and sixth) produce "choral" or "singing" sounds.
It is generally accepted that tubes are musically superior audio devices because they produce a higher portion of even rather than odd-ordered harmonics. Transistors, on the other hand, tend to emphasize the odd-ordered harmonics. Even-ordered harmonics are musically related to a given frequency in terms of octaves, while odd- ordered harmonics are dissonant. A higher proportion of even-ordered harmonics more closely resemble the natural harmonies in music. A signal passing through a tube will be automatically altered in such a way as to be in sympathy with the normal characteristics of music. Thus, tube amplifiers are commonly called "musical" or "warm" sounding.
The second and third harmonics are the most important. Musically the second is an octave above the fundamental and is almost inaudible; yet it adds body to the sound, making it fuller. The third is termed a musical twelfth. It produces a sound many musicians refer to as "blanketed". Instead of making the tone fuller, a strong third actually makes the tone softer. Adding a fifth to a strong third gives the sound a metallic quality that gets annoying as the music gets louder. A strong second with a strong third tends to open up the "covered" effect. Adding the fourth and the fifth to this gives the sound a more "open" quality.
Higher harmonics, above the seventh, give the tone "edge" or "bite". Therefore too much edge can produce a raspy, slightly out-of-tune quality. Since the ear is very sensitive to the edge harmonics, controlling their volume is very important.
The basic cause of the difference in tube and transistor sound is the weighing of harmonic distortion characteristics. Transistor amplifiers exhibit a strong component of third harmonic distortion producing a "covered" or restricted sound when driven hard. Alternatively a tube amplifier when overloaded generates a whole spectrum of harmonics. Particularly strong are the second, third, fourth, and fifth overtones which give a full-bodied "brassy" quality to the sound. Tubes sound louder and have a better signal-to-noise ratio because of the extra subjective headroom that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. The feeling of more bass response is directly related to the strong second and third harmonic components which reinforce the "natural" bass.