CV Raman on drums

The Tabla or the Mrudangam, to be more correct. I found this paper by (Sir) CV Raman from Nature, December 1920. It’s brilliant!

Advertisements

ResearchBlogging.org The Tabla or the Mrudangam, to be more correct. I found this paper by (Sir) CV Raman from Nature, December 1920 December 1919 – January 1920. It’s brilliant!

The premise is the following. Vibrating membranes don’t produce harmonic overtones; i.e, they don’t produce integer multiples of the fundamental frequency. They, in fact, produce fairly broadband noise (don’t ask me what I mean by ‘fairly’). What that means is that vibrating membranes cannot be used as musical instruments.

But wait, you say. The Tabla and the Mrudangam are musical instruments and they do fine. Yes! The paper explains why it is that this class of Indian musical instrument can produce pure harmonics even though the basic element is a vibrating membrane. The reason, it turns out, is that black patch you see in the middle of the Tabla’s operational surface.

It will be noticed (1) that the drumhead carries a symmetrical distributed load, decreasing in superficial density from the centre outwards (this appears as a dark circle in the middle of the membrane, the load consisting of a firmly adherent but flexible composition, in which the principal constituent is finely divided  metallic iron); and (2) that a second membrane in the form of a ring is superimposed on the circular membrane round its margin.

The paper goes on to note that of the five harmonics that can be obtained from a Tabla or a Mrudangam, the first three are especially well-sustained and ‘purer’ harmonics. Expectedly, the first harmonic – the fundamental frequency – is produced by a mode of vibration that has no nodes at all. The second mode is produced by a mode that has one nodal diameter (picture a string tied at both ends with a node in the middle; now span that setup keeping the node on one diameter of a circle and that’s a nodal diameter.)

They report that the third harmonic is a combination of two different modes of vibration: one with two nodal diameters and one with a nodal circle. Both of these modes have the same frequency. They surmise that the fourth and fifth harmonics that are seen are also some combinations of more complex modes of vibration.

They also note that because the black patch is denser than the surrounding membrane, it carries more energy. This means that the vibrations can be sustained for longer.

[hr]

[/hr]

Hat Tip: Rama. The woman knows about enough things to throw one out every class. This one came up when she was telling the class about Bessel functions. I, being me, had to do the read-paper-blog-about-it bit.

End. Fini. Kaputski. Drums.]

RAMAN, C., & KUMAR, S. (1920). Musical Drums with Harmonic Overtones Nature, 104 (2620), 500-500 DOI: 10.1038/104500a0

9 thoughts on “CV Raman on drums”

  1. Interesting! Reminds me of a talk I gave in school many years ago. I repeated Raman’s experiments of sprinkling some talcum powder on the head of a Mridangam and striking the membrane. When the membrane is struck with one hand, and another finger is positioned on its periphery, a nodal line forms at the location of the stationary finger. The talcum powder moves to this nodal line, giving some very beautiful pictures! A similar concept is shown for example at

    PS : I must thank my good friend Achudhan for allowing me to experiment with his dear Mridangam!

  2. Percussion instruments that do not have harmonic frequencies have been used as musical instruments because they are expected to keep rhythm and not play the melody/harmony. Like the cymbals.

    That part of the video also explains your meaning of ‘fairly’, i guess.

    On the other hand, the tabla/mridangam (like some other percussion instruments including can play even the melody/rhythm.

    Nice informative bit about the 5 harmonics.

  3. I see that you have started naming your commentors yourself :P. Btw, the discrepancy is because, somehow, my office computer and home computer have different spellings for my name.

  4. Hi,

    I’m a mridangist by training. I have played the tabla and the western drums, and also some middle eastern/Central African/South American drums such as the bongo, the darabuka and the djembe and the congas . I find from personal experience that the repertoire of sounds that the mridangam produces is far richer than that produced by the Tabla and most other drums. This article explains why.
    http://chandrakantha.com/tablasite/articles/mridanga.htm.
    I wish to clarify here that I’m not talking of rhythmic complexity. That depends solely on the skill of the musician. I’m only talking of the tonal richness in the sounds produced.

    Talking about the repertoire of sounds, the RHS of the mridangam (assuming I’m a right handed player), produces very ‘dense’ sounds. Let me explain ‘dense’. By that I mean, a trained ear can discern a much richer tonal quality in every stroke whereas in the tabla, the sound seems to be ‘flat’. This effect is accentuated in the ‘Dhi’ sound in the mridangam. This I believe comes from the fact that the right and left membranes of the mridangam are coupled inextricably due to a single resonator, while in the tabla you have two resonators, so the feedback is negligible. Also, the beauty of the mridangam can be exemplified in one stroke, called the Chaapu. You can hear that sound at 0.03 in the following video: http://www.youtube.com/watch?v=-DDG1KpgjA4
    You can hear that sound at many points in the video, for example again at 1:39.

    There is absolutely no equivalent to that sound in any percussion instrument in the world. The Chaapu is basically one stroke where you can feel the effect of even the left membrane as you play it! It takes time to master a Chaapu. The Chaapu is the single most beautiful sound I have heard emanating from a percussion instrument. When I was in kindergarten, my elder brother had created a scrap book containing articles/newspaper cuttings from The Hindu which had Raman’s researches on the musical instruments of India. I lost that scrapbook, but a few years back, thankfully for me, RRI decided to make its Raman-archive public. Raman was indeed a genius to sprinkle powder on a membrane and study its nodal structure.

    You’ve written a very nice article. I’m trying to find this other paper by Raman, which is more detailed. I’ll post it here as soon as I find it. Thanks again!

    Arun.

    ps: I have seen Raman’s 6 volumes facing the Principia volumes of Newton in the JNC library. 🙂 Do check out vol 2 on Acoustics if you haven’t already. That should have all the papers on the subject.

  5. Ha, What a serendipity! I too land up here after Rama’s lecture on Bessel’s function – she just mentioned it remotely; but, of course, gave this example without fail! I just love her gumption; the way she reacts, derives inspiration looking at our perplexed faces!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s