1874 - Ernst Werner Siemens patents dynamic or moving coil microphone.
Ernst Werner Siemens (1816-1892), founder of Siemens Corporation
The dynamic microphone did not become widely used at the time. Eventually, as technology improved, the dynamic microphone became the basis for most microphones used today.
1877 – “Theory of Sound” textbook by Lord Rayleigh, the 1904 winner of the Nobel Prize in Physics, is published in the United Kingdom.
John William Strutt, 3rd Baron Rayleigh, 1842-1919
Lord Rayleigh discovered “Rayleigh Waves”, the sound waves that travel on a solid surface. The acoustic impedence unit quantity “rayl” is named after him.
1877 – Third edition of “On the Sensations of Tone as a Physiological Basis for the Theory of Music” by Herman von Helmholtz (a friend of Ernst Werner Siemens) is published.
1890 Helmholtz Resonator, Source: Physics Dept, Case Western Reserve University, Image credit Wikipedia
The book describes Helmholtz resonators, which are used to amplify specific frequencies based on a volume of trapped air (like blowing over an empty coke bottle). Helmholtz used his resonators to isolate single tones of musical instruments.
1883 – The Indonesian island of Krakatoa experiences a volcanic eruption emitting what is considered to be the loudest sound ever heard in the modern world. It is heard up to 3000 miles (4800 km) away from the eruption.
Lithograph of 1883 volcanic eruption in Indonesian island of Krakatoa
Over 36,000 people are killed in the resulting tsunami, shock waves are recorded for days afterward, and the world climate was altered for years.
1924 – After approval from the “International Advisory Committee on Long Distance Telephony”, the Bell system renames the Transmission Unit (TU) into the decibel (dB). The decibel was named after the Bel, in honor of the telecommunications pioneer Alexander Graham Bell.
Decibel (dB) scale for sound level
While the decibel unit was originally used to measure the loss in power in telephone cables, it later became widely used in acoustics to describe the level of a sound.
1930 – The “International Electrotechnical Commission” replaces “cycle per second” with “Hertz” as the SI unit of measure for repeated events per second, or frequency, in honor of Heinrich Hertz.
Heinrich Hertz, 1857-1864
Gustav Ludwig Hertz, the nephew of Heinrich, later became the research laboratory director at Siemens.
1930 - The Perrin Acoustic Array appears on the cover of Popular Mechanics. The array, developed by French Nobel prize winner Jean-Baptiste Perrin, is billed as an "Airplane Finder Which Locates Ships in Flight, and Registers Their Altitude, Speed and Distance from the Apparatus".
Perrin acoustic array on cover of Popular Mechanics
1933 – Fletcher-Munson Curves of equal loudness published in the “Acoustical Society of America” journal. The blue lines, represent the dB level required to have a tone sound equally loud to a listener at any given frequency.
Curves of equal loudness - dB vs frequency. Blue lines represent equivalently loud levels
The curves of equal loudness have gone thru several updates. In 1956, Robinson & Dadson updated them using a frontal speaker in an anechoic chamber. In 2003, they were updated again as part of ISO 226:2003.
1936 – American National Standards Institute (ANSI) adopts the A-weighting curve based on Fletcher-Munson research in standards for sound level meters.
A-weighting Curve - dB of attenuation vs frequency
The A-Weighting curve is used to introduce the effects of human hearing into microphone recordings.
Stanley Smith Stevens (1906-1973) from the book “Stanley Smith Stevens” by George A. Miller, National Academies Press
The word Sone was derived from the Latin word sonus, which means sound.
1942 - Leo Beranek, working at Harvard, develops the first anechoic chamber. An anechoic chamber is used to simulate an acoustic free field. It this case, it was developed for testing loudspeakers for the US Army.
Anechoic chamber has fiberglass wedges to absorb sound so it is not reflected. Anechoic means "no echo".
Beranek also developed the metric Articulation Index (AI),which was used to understand how well speech can be understood over background sound. AI was used in evaluating different models of headsets used in aircraft to make sure instructions from the ground could be understood.
1961 - The Bark scale, used to describe the logarithmic frequency groupings of human hearing, is proposed by Professor Karl Eberhard Zwicker of the Institute for Electro-Acoustics of TU Munich.
In the bark scale, the critical bands of human hearing increase in width with frequency.
The Bark scale was named after Heinrich Barkhausen. Zwicker also developed the DIN 45631 loudness standard.
1961 – Stanley Smith Stevens publishes “Procedure for Calculating Loudness: Mark VI”.
1963 – Only an acoustician! J.C.R Licklider, a psycho-acoustician and department of defense researcher, invents the internet (it was not Al Gore!)…OK, not quite...read on....
J.C.R Licklider, 1915-1990, acoustician and “Inventor of the Internet”
In 1963, Licklider secures funding to start building the “Intergalactic Computer Network” or ARPANet for defense department, the fore-runner of the internet.
1972 – Acoustical Society of America publishes “Perceived level of noise by Mark VII and decibels” by Stanley Smith Stevens.
Want to experience sones? Head to Home Depot for the bathroom fan display
Stevens was the founder of Harvard's Psycho-Acoustic Laboratory.
1975 - ISO532 standard established for calculation of Loudness.
ISO Standards Organization logo
ISO532B outlines two methods of calculating loudness: a narrowband spectral approach and a 1/3 octave approach. It also incorporates Zwicker masking.
1981 - ANSI incorporates B-weighting as well as the A-weighting curve.
A, B, C, and D Weighting Curves
B-weighting is a flatter curve than A-weighting. This mimics how the response of the human ear flattens with increased sound levels.
1981 - The ECMA-74 Standard for "Measurement of Airborne Noise emitted by Information Technology and Telecommunications Equipment" is published.
1994 – Actors Jeff Daniels and Jim Carrey introduce the “Most annoying sound in the world” in the movie Dumb and Dumber.
2000 - Directive 2000/14/EC (Outdoor Noise Directive - OND) is adopted by the European Parliament and the Council on July 3, 2000. The directive harmonizes the laws of the Member States on 57 types of outdoor equipment referring to noise emission standards.
Layout of a sound power noise certification test for outdoor equipment
The world becomes a much quieter place as equipment manufacturers strive to meet the new noise regulations!
2008 - Fourteen year old Kyle Krichbaum correctly identifies 5 vacuum cleaners “by sound alone” on British TV show "Wanna Bet?", hosted by Ant and Dec...
2018 - The ECMA-74 standard is updated with Annex G. Annex G describes a new way of calculating the sound metric "Tonality".
Traditional tonal metrics considered only the difference between the tone and surrounding background, and did not account for loudness perception
The new method is based on the hearing model. Instead of producing values only between 0 (no tones) and 1 (all tones), it produces a wider range of values that also account for the loudness of the tonal sound.