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Started by The Real MC, March 19, 2007, 06:40:42 PM
QuoteA tone-producing mechanism of the Rhodes is shown in the drawing. When a key is depressed, a hammer hits the wire-shaped tone bar, which then vibrates like a reed. The motion of the free end induces a signal in the pickup coil. Three processes of interest to us occur as the tone decays. First, at the beginning of the tone, the tone bar vibrates simultaneously in many modes, or patterns. The faster modes die out more rapidly than the slower ones. The tone bar is shaped and mounted in such a way that these higher-frequency modes result in a pleaseing bell-like attack that decays much more rapidly than the 'sustain' portion of the tine. Second, the amplitude of the tone bar's motion at the pickup coil is much greater at the beginning of the note than at the end, and is greater for loud notes than for soft notes. When the tone bar motion stays within the range of the pickup coil's pole piece, the coil output waveform is a reasonably accurate replica of the tone bar's motion. However, on loud tones when the tone bar swings outside the pole piece's range, the coil's output waveform is 'distorted' in much the same way an overloaded vacuum tube or transistor amplifier distorts signals, and its harmonic content is thereby greatly increased. Thus the beginnings of the notes have more harmonic content than the ends, and loud notes have more harmonics than soft ones. These relationships appear to be desirable in any polyphonic instrument that produces percussive (piano-like) timbres.The third process in Rhodes tone production has to do with the way the tone bar is mounted. The mounting post is not entirely rigid. Vibrations can pass from the tone bar up through the post to the resonator bar. The resonator bar is also a reed-like structure, free to vibrate at the end opposite that which is fastened to the post. Nothing strikes the resonator bar, and no pickup is located near it. It serves only to store vibrational energy. The resonant frequency of each resonator bar is tuned to be very near that of the tone bar to which it is attached. As soon as the tone bar is struck, it begins to vibrate the resonator. The resonator vibration builds up, literally sucking vibrational energy out of the tone bar. At one point, nearly all the fundamental frequency energy is in the resonator, from which it then begins to flow back to the tone bar. If you have access to a Rhodes you can actually see this happen, especially on the lower notes; remove the top of the instrument, strike a low note, and watch that note's tone bar and resonator. First the tone bar will be vibrating and the resonator above it will be still. After a second or so the resonator will be vibrating and the tone bar will be almost motionless. This exchange of energy will keep on going for several seconds. Of course, the pickup coil signal doesn't null out (disappear) because the tone bar is never completely motionless, as long as the key is held down.From a musical acoustics point of view, this energy flow out of and into the tone bar has an effect which is similar to the flow of energy from one harmonic to another in an acoustic piano string. The sound is always moving. The energy interchange imparts complex envelopes to the sound's overtones and introduces phase shifts that slightly detune the fundamental with respect to the overtones.The 'Rhodes sound' thus has three features that contribute greatly to its aural appeal: (1) a bright, bell-like attack, (2) velocity-dependent brightness that decreases as the sound gets softer, and (3) a warm moving quality. Each of these is closely related to specific elements of the instrument's mechanical design. The ultimate success of any instrument depends not only on the existence of features such as these, but also on the care and taste with which the instrument designer proportions and adjusts the instrument's design parameters.Bob Moog, April 1980, Contemporary Keyboard
Quote from: The Real MC on March 19, 2007, 06:40:42 PMThe third process in Rhodes tone production has to do with the way the tone bar is mounted. The mounting post is not entirely rigid. Vibrations can pass from the tone bar up through the post to the resonator bar. The resonator bar is also a reed-like structure, free to vibrate at the end opposite that which is fastened to the post.
Quote from: orangefizz on April 04, 2022, 06:33:51 AMWhere is the "resonator bar"? I don't see this on any diagram I've come across. The hammer strikes the tine/spring, which is attached to a post that connects to the tone bar. Is the resonator bar part of the tone bar?