Gongs, Tubes, Parsifal Bells A flattened major seventh below the tap tone is generally found to give the best results in a deep bass bell. The hum tone is governed by the relative proportions of the shape given to the bell. Construction and Production of Sound Quality of Tone
In some dramatic works composers have wished to imitate the sound of church bells. It is evident that in the case of larger bells, a deeper sound is necessary. This effect is somewhat difficult to attain satisfactorily. Large bells of a very low pitch are too cumbersome and heavy for the orchestra; the notes are often impure and obscured by the dissonant harmonics, and bells large enough can overpower the orchestra with their volume of sound. Various substitutes have been tried, but of course no other instrument gives a tone in the least similar to that of the bell, which independently of the harmonics has two distinct simultaneous notes. The first is the tap tone which gives the pitch. This is dependent on the bulk of the metal used in casting the bell as well as on the quality and proportions of copper and tin. The second harmonic is the hum tone or lower accompanying note, whose interval from the tap tone varies in different bells according to pitch.
The Parsifal bell instrument has been constructed somewhat on the principle of the grand piano; the massive frame is shaped like a long dining table and rests on four solid feet; the soundboard is of spruce fir strengthened underneath by belly bars. There are thirty strings in all, mostly covered with copper wire; six to each note, of which three are in unison and give the fundamental note, and three an octave higher. The mechanism is simplicity itself. There is no action; the strings are struck by large wooden hammers, thickly and loosely covered with cotton wool, which the performer sets in motion by a strong but elastic blow from his fist. The hammers are fastened to arms about 22 inches long, fixed by screws to a strong wooden span bridge, placed horizontally above the strings at about two-fifths of the length from the front. On the front of the arm is the name of the note, and farther back the green felt ledge struck by the fist. To control the rebound of the hammers, a strong wooden bar on two arms, fastened also to the span bridge, overhangs the notes. Two belly bridge and two wrest plank bridges, one set for each octave, determine the length of the strings and the belly bridge, as in other stringed instruments, is the medium through which the vibrations of the strings are communicated to the soundboard. The strings are fastened to the thirty equidistant pegs at the father end of the instrument and to give groups of wrest-pins firmly set in an iron wrest-plank in the front of the instrument. The back of the instrument is strengthened by an iron plate and four iron pillars to resist the tension of the strings.
The quality of tone is rich, powerful, noble an carries well. It is clearly a good substitute for church bells in the orchestra, since is preserves the dignity of the atmosphere, which is destroyed by the triviality of all Glockenspiels and tubes. There have, however, recently been much larger and deeper steel tubes placed upon the marked, and these give both the clangor and solemnity of the large bell very satisfactorily.