Calcutta Coupler Mechanism
Calcutta scale changer harmoniums need to allow for the keyboard to be shifted up or down the scale. This makes the coupler mechanism more complicated than on a Delhi-style harmonium.
An array of flat 'sticks' sit underneath the keyboard at an angle, with one end under the key and the other end sitting in the lifter mechanism one octave lower or higher than the keyboard end. When you engage the couple, usually with a push/pull knob to the left of the keyboard, the lifter one octave above or below the played key is raised to allow air flow through those reeds, creating a richer and louder sound.
Each stick has a hole in the middle and allows the stick to pivot up or down on a pin on the bottom of keyboard tray. The sticks are trapped (barely on some instruments) between pins on the keyboard tray.
When the scale changer handle on the front of the instrument is pressed down, it tilts the front of the keyboard up, and the far end down, so it can slide back and forth 'underneath' the lifter arms for the reeds.
The sticks are not very secure and can work their way free and interfere with the key, preventing it from going down far enough to make a sound.
In one case, the harmonium was turned upside down and almost all of the sticks scattered around the keyboard.
The image below shows the coupler sticks underneath the keyboard mechanism and is taken from the back of the harmonium. This coupler system activates the keys one octave below any pressed keys. The keyboard is tilted up and back and is at the top of the picture. The lifter mechanisms for each key are at the bottom of the picture.
Note the diagonal scratches on the coupler sticks which helps you put the sticks back in the right location if you had to remove several of them.
Some couplers, like the ones shown on this page, sound a note an octave below the active key. Some have the sticks going from left to right, which activates the note one octave above the depressed key.
The picture to the right shows a close up of the coupler sticks at the low end of the keyboard with the keyboard shifted up five notes.
When a key at the right end of stick is pressed, the associated stick lifts the lifter of the key one octave below the key, allowing this reeds to sound.
A harmonium with an coupler which plays the key an octave above the depressed key has the sticks running from left to right.
This picture shows more details of the coupler mechanism with eight keys and one of the lifters removed to hopefully provide a better view of the mechanism.
The lifters have springs which keep the reed holes covered when the key is not pressed.
This harmonium had four(!) ranks of reeds so the lifter 'shoes' are quite long.
The horizontal row of nails between the 3rd and 4th reed holes keep the lifter 'shoes' aligned and are not the nails which keep the coupler sticks in place.
