Considering the oft-repeated claim that the harmonica is the biggest selling commercially produced musical instrument in history, there have been surprisingly few studies into how it actually works. There have been published studies of free reeds in general, going all the way back to Wheatstone's research in the late 1820s, but only a few researchers have focused on the unique qualities of the harmonica. Fortunately, a good proportion of these studies are now available online.
One particularly influential article was written by Robert "Johno" Jonston in 1987, during his studies at Monash University in Australia. Entitled Pitch Control in Harmonica Playing, it was originally published in Acoustics Australia, Volume 15, Issue 3 and was the first formal study of the physics of bending and overblowing. A copy of the article in .pdf form is available here.
A decade later, US researchers Henry Bahnson and James "Turbodog" Antaki collaborated on some research leading to the 1998 publication of the article Acoustical and Physical Dynamics of the Diatonic Harmonica. Originally published in the Journal of the Acoustical Society of America, Volume 103 Issue 4, a .pdf copy can be downloaded here.
Additionally, Turbodog has made several computer simulations of the air flow around harmonica reeds, one of which can be viewed here and x-ray footage, boroscopic video and sonograms (some of which include internal footage of Howard Levy!) which can be viewed as Real Video on this page.
Turbodog has also had several harmonica-related patents granted, a couple of them having extremely useful information about the physics of the instrument. US Patent 6359204, issued in 2002 covers some innovations in harmonica reeds and reedplates. The patent documents can be studied online via Google Patents here. US Patent 6635814 was issued in 2003 and covers various aspect of comb design. It can be viewed online here.
The leading French researcher into harmonica physics is Laurent Millot. A collaboration with Christian Cuesta and Claude Valette lead to the publication of Experimental Results when Playing Chromatically on a Diatonic Harmonica, in the journal Acustica, Volume 87, Issue 2, in 2001. This article is not currently available online, but those interested in such things are advised to try to order a copy through the library system. The journal's ISSN is 0001-7884.
A study by Laurent Millot and Vincent Debut entitled Time Domain Simulation of the Diatonic Harmonica was published in the same year by the Mosart Workshop on Current Research Directions in Computer Music. An abstract of this article is available here.
If you read French, then you may be interested in earlier work by Laurent Millot, including Étude des Instabilites dés Valves: Application à l’Harmonica Diatonique and Étude De l’Aérodynamique De l’Harmonica Diatonique, published in the Laboratoire d'Acoustique Musicale Report of Activities 1997-2000.
Associate Professor of Physics at Coe College, Iowa, James Cottingham has done substantial research into free reeds, particularly those used in reed organs. Some of his studies have relevance for those interested in how harmonica reeds work. Theoretical And Experimental Investigation Of The Air-Driven Free Reed was published in Proceedings of the International Congress on Acoustics 1998 and is available in .pdf format here; The Motion of Air-Driven Free Reeds was published the following year in Collected Papers of the 137th Meeting of The Acoustical Society of America. It can be downloaded as a .pdf file here. The article Variation Of Frequency With Blowing Pressure For An Air-Driven Free Reed was published in the same collection and is available in .pdf format here. More recently Pitch Bending and Anomalous Behavior in a Free reed Coupled to a Pipe Resonator was published in Proceedings of Forum Acusticum 2005 and is available in .pdf format here.
Tom Tonon is the inventor of the BluesBox and hold several patents on free reed designs. His article Reed Cavity Design and Resonance was originally published in the Papers of the International Concertina Association and can be read online here. Although mostly concerned with chamber design in bellows-driven free reed instruments, some of the points he covers apply equally well to harmonicas.
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