What causes a harmonica note to drop in pitch (AKA bend)?

manpreet Best Answer 2 years ago

I understand how I can lower the pitch of any note on my trumpet, regardless of the volume, by slowing the rate of vibrations of my lips. But how is it that I can lower (AKA bend) the pitch of a reed on my harmonica, regardless of the volume, by altering the way I draw air through my throat?

Can you suggest one or more household experiments that I could conduct to demonstrate the harmonica note bending phenomena?

I have read past information relating to this subject (below). I was wondering if I was somehow creating a change in air pressure, verses velocity, within the resonant tube of the harmonica reed chamber and or my oral cavity.

Additional information that may be helpful: I did not want to over complicate the question. But yes, regardless of key, the low notes in holes 1-4 and 6 can be bent down using a unique inhaling technique and the higher notes in holes 8-10 can be bent down using a unique exhaling technique. The note in hole 5 does not respond well to either technique.

However these observations are only true with blues harmonicas (AKA Richter tuned). Harmonicas other than common blues respond differently. So there is a contributing factor at work here that I was not pursuing.

To keep this simple: I have conducted my own experiment and found that I can bend down the pitch of most any harmonica reed when it is the sole reed present in a single reed chamber. The reed chamber naturally includes one reed slot for said read.

Related past posts:

The basic model for the harmonica is an open tube as a resonator and an oscillating free reed as a driving mechanism.

The free reed could be modeled in the first (and pretty good) approximation as an oscillating cantilever beam. Which opens and closes the tube - hence the pressure and velocity variations. The frequency (or frequencies - there would be more then one peak in frequency domain) of such an opening mechanism is given by the cantilever paratemetrs such as stiffnes, mass, surface, length etc. (see the link) and intensity of the excitation mechanism: the velocity of blown air.

These frequencies are provided to the resonant open tube in which some of them are attenuated and some amplified based on tube parameters (where the length and cross section area are the most decisive parameters).

By a combination of many free reeds and resonant tubes the diatonic harmonica is given. More to that: these instruments usually posses a posibility to chose between two resonant tubes: one for the inspiration and one for the exhalation.

Note: In fact, almost all of that is valid for all reed pipsef with free reeds (e.g. for some parts of organ as well), i.e. for all the Hornbostel-Sachs class 422.3

shareciteedit answered Dec 12 '15 at 9:35

Victor Pira 2,0711732 add a comment

Each tube in the harmonica is an open tube. The frequency that is produced in any open tube depends on length, speed of sound and n, using f=(nv)/(2L). The base note is where n= 1, which is the usual note you hear. If you blow a bit harder, you can hear the first harmonic, where n = 2. Here the frequency is double what was heard earlier (when n=1), and sounds an octave higher. There are more, higher harmonics that can be produced, so the answer is, yes, the physics calculations do predict higher sounds.