The use of Swell boxes of this vastly increased efficiency permits the employment of larger scales and heavier pressures for the pipes than could otherwise be used, and enormously increases the tonal flexibility of the organ.
It also does away with the need for soft stops in an organ, thus securing considerable economy. Where all the stops are inclosed in cement chambers (as in the case of recent Hope-Jones organs) and where the sound-trap shutters are employed, _every_ stop is potentially a soft stop.
Prior to the construction of the above-named organ at Birkenhead, England, it had been the custom to obtain or regulate the pressure of wind supplied to the pipes by means of loading the bellows with weights. Owing to its inertia, no heavy bellows weight can be set into motion rapidly. When, therefore, a staccato chord was struck on one of these earlier organs, with all its stops drawn, little or no response was obtained from the pipes, because the wind-chest was instantly exhausted and no time was allowed for the inert bellows weights to fall and so force a fresh supply of air into the wind-chests.
In one of Hope-Jones' earliest patents the weights indeed remain, but they merely serve to compress springs, which in turn, act upon the top of the bellows.
Before this patent was granted he had, however, given up the use of weights altogether and relied entirely upon springs.
This one detail--the substitution of springs for weights--has had a far-reaching effect upon organ music. It rendered possible the entire removal of the old unsteadiness of wind from which all organs of the time suffered in greater or less degree. It quickened the attack of the action and the speech of the pipes to an amazing extent and opened a new and wider field to the King of Instruments.
In the year 1894 John Turnell Austin, now of Hartford, Conn., took out a patent for an arrangement known as the "Universal air-chest." In this, the spring as opposed to the weight is adopted. The Universal air-chest forms a perfect solution of the problem of supplying prompt and steady wind-pressure, but as practically the same effect is obtained by the use of a little spring reservoir not one hundredth part of its size, it is questionable whether this Universal air-chest, carrying, as it does, certain disadvantages, will survive.