Types of Harmoniums
There are two general types of Indian portable harmoniums: Delhi Style harmoniums which are most widely used in chanting and kirtan, and in Western playing, and Calcutta Style harmoniums, which are more commonly used in Indian classic music. Harmoniums can also be distinguished by collapsible/folding or non-collapsible cases and one or two piece key mechanisms.
Delhi Style Harmoniums
Delhi Style harmoniums use a soft wood like pine, for the reed board and usually have just two banks of reeds. They have a one piece key action. When you press down on the "key end" the back end of the key moves up on a vertical pivot pin. This uncovers the holes above the reeds which are mounted on the bottom side of the keyboard tray. Air passes through these holes causing the reeds to vibrate. The picture on the right shows the keyboard with one key removed. The two reed holes are plainly visible. The vertical “pivot pin" below the reed holes fit into a hole in the key and allows the key to pivot up and down.
Springs for each key press down on the back of each key so when the key is released, the key returns to the normal position and the reed holes are covered preventing them from playing.
Calcutta or Kolkata Style Harmoniums
This style of harmonium use a hard wood for the reed board which gives a different tone compared to the Delhi style. Calcutta harmoniums often has more stops and up to three banks of reeds. To save space, the male and female banks of reeds may be mounted vertically.
They may also have a scale changer feature to allow the pitch of the keyboard to change by half steps. The keyboard is moved up or down by half steps relative to the reeds. So you could play the C key but the pitch could be Bb or E for example. This requires a two piece key mechanism. This is described on the Calcutta Coupler page.
Most harmoniums used for kirtan have two banks of reeds, called 'bass' and 'male'. The bass reeds are the lowest octave with the low C on the keyboard usually being C2 (65.41Hz) with the male reeds being one octave higher than the bass or low C having a frequency of C3 (130.81Hz). Calcutta style harmoniums often have three banks of reeds, which can be two male reeds banks and a female bank. Others will have bass, male and a female bank. The female bank would start on C3 (261.63Hz). This can vary between manufacturers.
This information can be useful when ordering replacement reeds to make sure you get the right one!