The celesta looks like a harmonium, that is, it consists of a case with a keyboard and pedal. The case contains the metal bars, the resonators and the complicated striking mechanism.
Sound is produced primarily by steel bars which rest on felt rails over hollow wood resonators. The steel bars are struck from above by felt-covered hammers which are connected to a keyboard by means of a complicated mechanism. Notes are played on the keyboard, as on the piano. However, unlike the piano, the celesta’s hammers vary in size and weight; the lower notes are produced using larger hammers with a thicker felt covering, which results in a particularly warm and rich timbre. This mellowness in the lower register is one of the celesta’s most cherished qualities.
The resonators, hollow boxes made of wood, are fixed below the metal bars (one resonator per bar) and fashioned to correspond exactly to the pitch of the bar above. The resonators serve to amplify the fundamental and resonance of their particular bar. This is especially important because steel bars produce a high proportion of inharmonic partials. The resonator amplifies the fundamental and suppresses the inharmonic partials which ensures a clearly identifiable pitch.
The resonators, especially the larger ones for the lower notes, require a lot of room and for this reason are arranged in two rows, one above the other, with the corresponding metal bars. To preserve a consistent timbre the pitches over the entire range are spread over both rows, for example one pitch on the top row, the next one up on the bottom etc., rather than the lower register being below and the upper above.
The pedal works in the same way as on the piano. It raises the dampers and allows the notes to resonate.
Differences between the glockenspiel and the celesta
The biggest difference between the keyed glockenspiel and the celesta is that the latter has a greater compass in the lower register (on older models C4–C8, on more recent ones C3–C8) and the lower notes possess a fuller sound.
The lower notes present some problems in terms of acoustics, because the larger the metal bar, the greater the proportion of inharmonic partials. An extension of the compass in the lower register is only made possible by the addition of the appropriate soundboxes which amplify the fundamental of each bar while at the same time suppressing the inharmonic partials. This also results in greater volume, which means that soft felt hammers are quite sufficient for the striking mechanism, thus ensuring a warmer, richer timbre with fewer overtones than the glockenspiel with its hard mallets.