The PIPE ORGAN

One very important consideration in a pipe organ winding system where there is a tremulant is how the tremulant is connected to the winding system. For best results, the tremulant should be connected by a length of rigid pipe and not a flexible hose. Also, the length of this connecting pipe is important. It should not be too short. If the tremulant is not too big, a two inch diameter line is sufficient, but it should be at least 7 feet long. If the tremulant is larger, the pipe to the tremulant should be 3" in diameter and at least 10 feet long. A tremulant that is connected to a pressure regulator with a short length of flexible windline is very unlikely to work at all, or if it does, the effect on pipe tone will be weak and choppy. When the tremulant is in use, there should be a smooth and very regular vibrato effect in the pipe tone. The wrong length or type of windlines can cause among other things, irregular or unreliable operation; very weak vibrato; Choppy vibrato; or worse, a double-beat vibrato that sounds twice as fast as it should.

Even though the pipe organ tremulant is a device by itself, the complete "tremulant" really consists of four things: the tremulant device, the associated pressure regulator, the windline or piping that connects the tremulant to the pressure regulator, and the windchest on which the pipes to be affected stand. In setting up a pipe organ and in adjusting the tremulant to produce a nice vibrato effect in the tones of the pipes which it controls, it's necessary to take all four of these items into consideration.

In most classical and concert organs, the tremulant is usually connected to the regulated side of the pressure regulator for a particular section of the organ, and provides a vibrato effect to all pipes that are supplied from that particular regulator. Another very common arrangement in classical and concert organs is to connect the tremulant to the inlet distribution manifold (or stop action assembly) which is usually an integral part of a multi-rank windchest. In theater organs, however, there are frequently specific regulators and tremulants for specific ranks of pipes. Often in theater organs, the tremulant will be connected to a specific single-rank windchest on which the pipes stand, which usually significantly increases its effect on pipe tone. Regardless of the particular application, the connection should be made with a suitable length of rigid pipe for best results.

There are a number of different types of tremulants that have been used, but the most familiar is the bellows tremulant which you will find in theater organs as well as in many church and concert organs. The bellows trem is a large valve that opens and shuts at the desired vibrato rate and it is powered by the organ wind. Another type which is finding more and more favor on new instruments is a simple fairly big electro-pneumatic valve which is powered by a signal originating from a solid state oscillator with a square wave output whose frequency you can vary between 6 to 7 Hz. When there is an output from this oscillator, the tremulant valve opens, and when the output goes to zero, the valve closes. The advantage to this method is that it's very easy to control both the intensity and the rate of the resulting vibrato by varying respectively the duty-cycle or time on for each output cycle and the oscillator frequency.

On a typical bellows-type tremulant, you can also vary both the rate and the intensity of the resulting vibrato, but it's much less easy. There are three important adjustments which are fairly critical, and to make matters worse, are somewhat mutually dependent. The first is the inlet valve right at the point of entry for the tremulant connection pipe. The second is the positional relationship of the internal tremulant valve to the top of the tremulant bellows, and the third is the outlet opening on the bellows top. The most import function of each of these adjustments is as follows. Inlet valve: tremulant intensity or depth. Position of internal valve relative to the top: actual performance or operation. Top outlet: tremulant rate. However, closing the inlet valve will reduce the intensity and also the rate. Closing the top port will increase the rate and reduce the intensity. Incorrect adjustment of the internal valve relative to the top significantly impacts reliable operation including starting and stopping and also affects the rate and intensity, but has more of an effect on the rate.

The correct operation of the bellows-trem is much more dependent on the length and type of connector between the tremulant device and the pressure regulator that it affects. The oscillator-controlled dump valve's cycling is entirely controlled by the settings of rate and duty cycle, but proper connection to the regulator will improve its effect on pipe tone. Still another type consists of a weight at the end of an arm that rotates at the desired tremulant rate, powered by a small motor. This device mounts on the top of a pressure regulator. Because the weight is mounted eccentrically, when it turns it produces a severe wobble and bounces the top of the regulator up an down which affects the instantaneous pressure in the regulated side of the pressure regulator. In my opinion, which is based on having played a number of instruments, both classical and theater, the effect of the rotating weight tremulant is not all that special. Plus it has a noticeable "spin-up" and "spin-down" effect whereas the others start and stop almost instantly.