There is a partition between the bellows and the right-hand side of the housing. The wind generated by the bellows flows through the visible openings, which can be closed by means of a slide valve.

With closure (tremulant active) the pressurised wind flows through the two flaps on the left, which are set in motion by the periodic pressure build-up (valve closed) and supply the reeds with wind only intermittently, which produces an resulting in an ascending and descending tone.

The inertia of the keys can be adjusted with a sliding weight. Their knocking can be heard in the audible.

With suction wind (pulling the bellows), the right flap opens (only its underside is visible). When the bellows is pushed, the left one opens (the two foreign bodies serve the purpose of illustration). The result is a drop in pressure which the respective flap falls back into its original position due to its own weight and the additional and pressure builds up on it again, and so on.

The result is a periodically interrupted air flow, a vibrating volume. The tremulant of this instrument changes the sound of the right side only. A tremolo effect can also be produced for a short time without a tremulant by a trembling bellows, but this requires practice

Tremolo and tuned beat therefore describe the same tonal effect on hand harmonicas: a tone that pulsates in volume but is produced in different ways.

A tremolo is produced by a mechanical device. A tuned beat is a result of the superimposition of sound waves (interference) by a second, slightly differently tuned choir (which is more expensive).

Depending on the strength of the sound effect, the term flat or strong beat is used. Today, the latter is usually referred to as tremolo.

A strong tuned beat is difficult to distinguish from a tremulant in terms of sound.

The powerful tremolo of the tremulant shown is barely gradable. Flat beats, such as those produced by tone overlay, are not possible.

A vibrating sound is a matter of taste. It is typical of the musette from France and earlier bandonions in southern Germany, which sounded very similar to an accordion.

Photo: If the chrome-plated adjusting rail is pulled upwards, the tremulant is switched on or off by means of a driver (lower circle) of the internal locking slide rod.

A tremulant was also built into accordions in order to achieve the sound effect without doubling the number of reeds.

The picture shows a tremulant reed set in vibration by hand, which vibrates only about 3-6 per second and determines the wind waves and thus the volume waves of the tremolo tone. A tremulant reed is made of much softer material than a tremolo reed, which determines its low (inaudible) natural frequency. determines.

This tremulant is also mechanismally switched on or off. The closed stop valve can be seen at the bottom of the picture.

Tremulants were constructed in different types. The picture shows a tremulant in the bellows of a bandonion from the factory of Alfred Band in Krefeld (not part of the Collection Oriwohl).

Under the hole is the tremulant. On the left next to it a long vertical air flap, the opening of which stops the tremulant.

Behind the partition are the tuning pins.

The hole ensures a low but constant basic wind when the tremulant is active, which makes the tremolo sound softer.

A tremulant consisting of a wind chamber on which a movable flap rests.

Its own weight and the additional weight that can be moved determine the frequency of the flap's opening and thus the frequency of the tremolo tone's fluctuation in volume from flat to strong.