Each frequency specified in Hertz has a specific wave length. Some frequencies
can be heard by humans while others cannot. There is a direct relationship
between frequency and wave length.
The fundamental frequency of a stretched string or wire is given by:
n = 1/2L (sq route of T/m) where
L = length T = tension m = mass per unit length
Knowing this, electronic pianos and other musical instruments have been
manufactured with good approximation.
Use of frequency and wave length depends on the context/discipline with whom
you are communicating. In radio, frequency is used as the center frequency of
a particular bandwidth spectrum. HD radio uses upper and lower sidebands in
a specific spectrum and may contain data and information different from what's
transmitted on the central frequency. Radars are usually specified by
wave-length. Microwave ovens are a particular type of radar.
Stan Doore
----- Original Message -----
From: Bill Hooper
To: U.S. Metric Association
Sent: Monday, January 14, 2008 9:40 PM
Subject: [USMA:40050] Re: Stuart & Sons Pianos
On 2008 Jan 14 , at 5:50 AM, STANLEY DOORE wrote:
Pianos make sound. Sound waves and frequencies (radio and TV) are given in
metric (mm, cm and m) as common practice for more than 100 years. So it seems
logical to build pianos using metric units.
The frequencies of sound waves are not usually "given in ... mm, cm and m".
Those length units could be used to report the wavelength of a wave and that
would be quite correct. However, sound waves are NOT USUALLY reported as such.
Instead, sound waves are almost always specified by their frequency (which is
related to their pitch). Frequency in metric is measured in hertz (Hz) and its
multiples. (One hertz equals one oscillation per second.)
However, many radio/TV waves are also specified by their frequency (in
hertz). While it is true that some of the lower frequency (and therefore
greater length) radio waves have been commonly specified by their wavelength
("millimetre waves", "microwaves*", "3 m waves", "quarter wave length
antennas", etc.) by far, the commercial broadcast bands are almost always
referred to by frequency**.
So, Stanley's suggestion may be good if applied to frequencies in hertz, but
not in connection with wavelengths in millimetres etc.
Regards,
Bill Hooper
==================================
Additional comments, off the main subject but maybe interesting to some.
* I believe "microwaves" is a term used to describe radio waves of
wavelengths in the micrometre range, but I am not certain of that fact. Does
anyone know the wavelength used in common microwave ovens? Such ovens all use
the same frequency, I believe; namely, the frequency which most efficiently
transfers energy to the hydrogen-oxygen bond in water and other molecules.
That's why they heat the water in a cup but not the cup.
**The AM radio band runs from about 550 kHz to 1600 kHz while the FM band
runs from 87.7 MHz to 107.9 MHz. That means the FM waves at the SLOW end of the
FM dial are oscillating about 55 times FASTER than the FASTEST waves on the AM
dial. (87.7 MHz is about 55 times 1600 kHz.) For comparison, audible sound
waves (those that can be heard by the human ear) are in the
range from 20 Hz to 20 000 Hz (20 kHz). These are not sharply defined because
they depends on an individual's ears. I mysefl haven't been able to hear above
15 kHz most of my life.
