music / Science

The Hammond organ

Did any of you know that the most famous instrument used in Jazz and Blues was… a church organ?

I’m talking about the famous Hammond organ. Well, it is not exactly an instrument designed for churches: just imagine that it was masterly adopted in bands of international level such as “Pink Floyd”, “Deep Purple” or “Emerson, Lake & Palmer”. But where does it come from?

It all started back in the ’30s, with the genial mind of Laurens Hammond. He was a prolific inventor who also got the idea of the first automatic transmission system for gears in a motor vehicle (though it was refused at first). He was a great clockmaker, too. His experience and skills, along with his interest in music, allowed him to project and build up this particular example of “electronic organ” that would have replaced the classic wooden “pipe organ”. Since he was not a musician, Mr Hammond took advantage from the help of a friend, an organist, and after a long and hard period of work the completed instrument took the name after its inventor.

An earlier model of an electronic instrument of that kind was the less famous “Telharmonium”, but due to serious mechanical issues and also to its “gargantuan” proportions (it almost reached 200 tons of weight!), the Telharmonium quickly disappeared from the musical scene.

But how does the Hammond organ actually work? Since we are talking about an electric machinery, the sound is produced through metallic tonewheels (very similar to cog-wheels) which are activated pressing the keys on the organ keyboard. Those wheels, when activated, start rotating next to a magnetic bar and in this way, thanks to the teeth on the wheels, the magnetic variations produce particular signals, whose frequency depends on the speed and number of teeth of the tonewheel associated to a specific key. In the end the signal is sent to an amplifier that expresses the final sound.

But there’s more (oh no please!…)

The classic Hammond organ is always associated to a peculiar type of amplifier: the Leslie speaker (from the name of its inventor, Don Leslie). As the saying goes, “there’s no real Hammond without a good Leslie speaker”. This curious engine creates the well-loved vibrato or “rotary” sound utilizing the Doppler effect, that is the dynamic variation of the waves’  length caused by a shift of the sound font position (…what?). It is composed of a rotating system of two wheels, each with a pair of sound “trumpets” on them (for the higher and lower pitches of sound, respectively called “tweeter” and “woofer”) that can also be regulated in speed. There are two basic speeds: Chorus and Tremolo. In the first case the wheels rotate slower and the sound seems pretty flat, but when we speed the machine up we put a stronger vibe on the sound, which becomes more “scratching”. More recent Leslie speakers can also be stopped, just to reproduce the older pipe organ feel, though this amplifier was introduced as a solution for the boring flatness of the earlier models of that organ.

There’s more information about this fantastic instrument to be shared, but we’re going to see it in the next post.

Everybody, for now, just relax and listen to a few pieces. Enjoy!

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