Tubular bells - Construction
Tubular bells are housed in a stand about 180 cm high (90 cm wide and 70 cm deep) and consisting of a base with wheels, a frame and two suspension rails. The chromatically tuned tubes are arranged in two rows in keyboard fashion and hung on straps from the two suspension rails.
The back row is composed of those tubes that correspond to the black keys of the piano and is set about 20 cm higher than the front row, so that the tubes can be reached easily by the musician.
Depending on the range, a set of symphonic chimes consists of either 18 tubes (1½ octaves: C4–F5) or 25 tubes (2 octaves: F3–F5).
The tubes are both vibration generator and resonator.
The frequencies of tubes, plates and bars are in inverse proportion to the square of their length. For example, the frequency of a tube that is 70.7 cm long is theoretically roughly half that of a 50 cm long tube of the same thickness. At the same time the frequencies are in direct proportion to the square of the thickness; the thinner the plate or the wall thickness of the tube, the lower the pitch. The pitch (of the striked note) is therefore dependent on the diameter, wall thickness and length of the tube. On a standard 1½ octave set of chimes the tube lengths range from about 75 cm (shortest tube, pitch F5) to 155 cm (longest tube, pitch C4). The corresponding tube diameter is 3.8 cm, the wall thickness 1.5 cm. If one of these parameters changes, e.g. the wall thickness, either the length or the diameter of the tube must change, too. As a rule, the tubes’ diameter is between 3–4 cm and their wall thickness between 1–2 cm.
On short metal tubes the fundamental dominates, so the sound is not bell-like. The sound of long metal tubes, on the other hand, contains a great many partials, so that their sound is similar to bells.
At the base of the stand there is a damper pedal which is connected to the damping system by means of rods. Operating the damper pedal effects all the tubes simultaneously.
The damping pedal works in the same way as on the piano: a depressed pedal allows the notes to rensonate and when released dampens the tubes. The mechanism is as follows: if the pedal is not depressed the damping system is in the upright position and does not touch any of the tubes. If the pedal is depressed, the damping system turns to the horizontal position along with the damping material and damps all the tubes.