It's suggested that this text supersede paragraphs 2-5 of the current article. The article would begin with the 1st and 6th paragraphs of the current text, then the following text, then the list. Comments / suggestions / edits welcome. I'd like to put it up in a couple of weeks if all goes well. Adrian Pollock (talk) 03:37, 2 January 2008 (UTC)Reply

I really like what you wrote, and made some edits and cuts throughout. My concern is that this is exclusively historical. I'd like to put in sections about fundamental concepts, applications, and possibly research areas. I'm having trouble completing the list of fundamental concepts and applications. Your thoughts? I'll draft some material for my vision of the fundamental concepts and applications before Sunday. Also, I was looking around for pictures, and there are some good ones already available on the German site. This is the Google translation of German site. Is this how you wanted to edit the material, or should I put these comments on the talk page? Joe056 (talk) 18:14, 2 January 2008 (UTC)Reply

Good going Joe. I haven't studied your material in full detail yet, but I see that you are fixing to make the article more substantial across the board. I'm up for that; I had confined my ambitions to the introduction before, but certainly, its kinda stubby to have just a historical review and a list of subfields. Also, your organization of the subfields into groups is constructive and likely very helpful to newcomers. It had crossed my mind to try that but after noting that the previous list was close to a referenceable list from elsewhere, I said ok enough already. About the German article, it looks good, the one thing I didn't like was the way in the second paragraph it gave such pride of place to one particular subfield so early in the overall article. First time I saw anything from an other-language Wikipedia article.

So, looks like we have some good things going. I'm real new to Wikipedia, just one article written very recently (Lamb waves) and a few minor edits here and there, how about you ? A question that comes up for me is: how long do we use this space to build material and develop consensus - do you have any good explicit criterion for when to come out of the cupboard and change the article itself ? This kind of system savvy I'm just trying to learn as fast as I can, I was lucky to have a good mentor getting started on the Lamb wave article. I'll come back for another bite over the weekend if not sooner and see if I can do something with your specific questions. Adrian Pollock (talk) 03:40, 4 January 2008 (UTC)Reply

I've been making minor edits on wikipedia for a few years, but nothing as large as this. This is an outline of how I'd like to organize our efforts:

1) Fill out sections that are clearly incomplete. Address all comments that we've made (aka very rough draft).

2) From there, we can rewrite some stuff, and expand or shorten as necessary.

3) Insert images, fix up citations, make it look prettier, put in wikilinks, and copy edit.

4) Be bold! Put it up onto the main page.

I don't know if this is standard, but it seems like a good plan. As far as consensus, we seem to be the only two working on this, so a consensus should be easy to reach :). The Wikipedia community can edit other details as soon as we post it. Where else did you see the list of divisions? Joe056 (talk) 06:20, 4 January 2008 (UTC)Reply

I wrote some things that got accidentally erased before I save them. Still struggling with how to structure this thing. So I decided to tabulate short descriptions of what's actually there in the existing subfield articles. That was quite interesting, you can see it at User:Adrian de Physics/sandbox. For me, the absence of a physical acoustics article is a glaring hole and I'm wondering whether we should take some of the things you have written and put them into that - considering this as one of your "1. ...sections that are clearly incomplete".

There was a nudge from a nameless IP number who wanted to make acoustics a branch of applied mechanics. I didn't agree, it's too broad for that. Trouble is though, I can hear someone saying "well if it's too broad for applied mechanics, isn't it too broad for physics too?" Being a physicist I hate to hear that but must admit he has a point unless you go for the broadest definition of physics. So I'm wondering whether we should advertise it as an "interdisciplinary field" or suchlike. That of course aggravates even more the difficulty of identifying just what are its fundamental concepts ! I think we have to hang loose and let this become clearer, if you ever read "Stranger in a Strange Land" you'll know what I mean. Meanwhile work on smaller pieces that we can solve.

I see the subfield list comes from the American Physical Society. Maybe it got edited since. I'm in a quandary whether we should aim to hold rigid to a list from an authoriatative source like that, or whether we should consider it up for grabs and anyone can have a go at it. Do you know what a good Wikipedian would think about this ? Adrian Pollock (talk) 04:50, 7 January 2008 (UTC)Reply

So I think I just wrapped up the rough draft (1). Now we need to revise the parts that need help. Watch out for weasel words. Instead, cite a source. Joe056 (talk) 06:20, 4 January 2008 (UTC)Reply

I take that back (about finishing draft 1). I'm really unhappy with how the "fundamentals" section was looking, so I drafted up a new outline. Still, I'm a pretty awful writer. If you can write it down better than I can, please do. --Joe056 (talk) 01:12, 6 January 2008 (UTC)Reply

I came up with the diagram added below, which may do useful service as a unifying fundamental concept. Your emphasis on transduction helped me to come up with this. Transduction is indeed of fundamental importance. Adrian Pollock (talk) 04:21, 8 January 2008 (UTC)Reply

I finished studying the enumeration of subfields (a) in the article, (b) in PACS as referenced in the article, (c) based on the names of the ASA technical committees, (d) googling to get a crude idea of size / recognition of the subfields (e) noting status of subfield Wikipedia articles. This is all in the table in User:Adrian de Physics/sandbox. Conclusion: we are basically in good shape. It was a very good decision of someone to use PACS, it's an impressive resource. Let's stick with those 18 PACS subfields (this also means mergeing back the small, non-PACS "biomedical acoustics" is it) and aspire to get each one covered with an article (many are already). Also I'm all in favor of discussing in the main article a higher-level breakout, a smaller number of broader categories, such as you started in your table. It'll make the subject more approachable. Maybe some refinements, I still haven't dug real deep into your table but am starting to catch up and look at it more often now. Adrian Pollock (talk) 06:10, 9 January 2008 (UTC)Reply

I think that the article is starting to shape up. All we really lack now are some pretty pictures and references (imho). Let's shoot to finish on February 15th. After that, I will publish this on the main site and we can let our fellow wikipedians have at it. What say you? Joe056 (talk) 00:07, 2 February 2008 (UTC)Reply

Good diagrams Joe ! I resequenced the beginning; below is the draft as it looks today. Also I undid the capitalization in the titles in deference to Wikipedia preferred style. May be a few more things to add but I would have no problem putting it up in the form it is in right now (just delete internal refs to the edits). It's a good step forward. After that we could see about getting the clean-up label removed ? Adrian Pollock (talk) 00:45, 6 February 2008 (UTC)Reply

Thanks. I was amazed at how much of a difference the pictures made myself. I will keep making small changes preparing needed citations, but foresee no need for major changes. I'll put up the site on February 15th. I agree about the cleanup label.Joe056 (talk) 00:00, 8 February 2008 (UTC)Reply

Joe, I made a few small changes. Just two remaining things stick out at me now. One is the reference to Biel at the bottom, it's typographically odd. The other is: I wonder whether the long list of "see also" items could be arranged into columns for better appearance and readability. I'm not very sure/skilled about doing either of these. Are these in your skill set ? If not, I can work on them or ask my adopter for advice. Also, I posted on a higher page our intent to "go public" shortly. Adrian Pollock (talk) 06:34, 12 February 2008 (UTC)Reply

The Biel reference is typographically odd, but I felt that an inline citation was necessary for the table of pressure values. It would be less awkward if we cited more stuff, so we should work on that after the article is put up. Joe056 (talk) 18:12, 15 February 2008 (UTC)Reply

It's up! Joe056 (talk) 19:25, 15 February 2008 (UTC)Reply

Acoustics is the interdisciplinary science that deals with the study of sound, ultrasound and infrasound (all mechanical waves in gases, liquids, and solids). A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers.

Hearing is one of the most crucial means of survival in the animal world, and speech is one of the most distinctive characteristics of human development and culture. So it is no surprise that the science of acoustics spreads across so many facets of our society - music, medicine, architecture, industrial production, warfare and more. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge.

The word "acoustic" is derived from the ancient Greek word ακουστός, meaning able to be heard (Woodhouse, 1910, 392). The Latin synonym is "sonic". After acousticians had extended their studies to frequencies above and below the audible range, it became conventional to identify these frequency ranges as "ultrasonic" and "infrasonic" respectively, while letting the word "acoustic" refer to the entire frequency range without limit.

History of acoustics

Early research in acoustics

The fundamental and the first 6 overtones of a vibrating string. Pythagoras was the first to study this phenomenon.

The science of acoustics had its beginnings in the Greek and Roman cultures between the 6th century BCE and 1st century BCE. It began with music, which had been practised as an art for thousands of years, but was not evidently studied in a scientific manner until Pythagoras took an interest in the nature of musical intervals. He wanted to know why some intervals seemed more beautiful than others, and he found answers in terms of numerical ratios. Aristotle (384-322 BC) understood that sound consisted of contractions and expansions of the air "falling upon and striking the air which is next to it...", a very good expression of the nature of wave motion. In about 20 BC, the Roman architect and engineer Vitruvius wrote a treatise on the acoustical properties of theatres including discussion of interference, echoes, and reverberation - the beginnings of architectural acoustics.

The physical understanding of acoustical processes advanced rapidly during and after the Scientific Revolution. Galileo (1564-1642) and Mersenne (1588-1648) independently discovered the complete laws of vibrating strings (completing what Pythagoras had started 2000 years earlier). Galileo wrote "Waves are produced by the vibrations of a sonorous body, which spread thought the air, bringing to the tympanum of the ear a stimulus which the mind interprets as sound", a remarkable statement that points to the beginnings of physiological and psychological acoustics. Experimental measurements of the speed of sound in air were carried out successfully between 1630 and 1680 by a number of investigators including Mersenne. Meanwhile Newton (1642-1727) derived the relationship for wave velocity in solids, a cornerstone of physical acoustics (Principia, 1687).

The Age of Enlightenment and onward

The eighteenth century saw major advances in acoustics at the hands of the great mathematicians of that era, who applied the new techniques of the calculus to the elaboration of wave propagation theory. In the nineteenth century the giants of acoustics were Helmholtz in Germany, who consolidated the field of physiological acoustics, and Rayleigh in England, who combined the previous knowledge with his own copious contributions to the field in his monumental work "The Theory of Sound". Also in the 19th century, Wheatstone, Ohm, and Henry developed the analog between electricity and acoustics.

The twentieth century saw a burgeoning of technological applications of the large body of scientific knowledge that was by then in place. The first such application was Sabine’s groundbreaking work in architectural acoustics, and many others followed. Underwater acoustics was used for detecting submarines in the first World War. Sound recording and the telephone played important roles in a global transformation of society. Sound measurement and analysis reached new levels of accuracy and sophistication through the use of electronics and computing. The ultrasonic frequency range enabled wholly new kinds of application in medicine and industry. New kinds of transducers (generators and receivers of acoustic energy) were invented and put to use.

Fundamental concepts of acoustics

The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations.

The steps shown in the above diagram can be found in any acoustical event or process. There are many kinds of cause, both natural and volitional. There are many kinds of transduction process that convert energy from some other form into acoustical energy, producing the acoustic wave. There is one fundamental equation that describes acoustic wave propagation, but the phenomena that emerge from it are varied and often complex. The wave carries energy throughout the propagating medium. Eventually this energy is transduced again into other forms, in ways that again may be natural and/or volitionally contrived. The final effect may be purely physical or it may reach far into the biological or volitional domains. The five basic steps are found equally well whether we are talking about an earthquake, a submarine using sonar to locate its foe, or a band playing in a rock concert.

The central stage in the acoustical process is wave propagation. This falls within the domain of physical acoustics. In fluids, sound propagates primarily as a pressure wave. In solids, mechanical waves can take many forms including longitudinal waves, transverse waves and surface waves.

Acoustics looks first at the pressure levels and frequencies in the sound wave. Transduction processes are also of special importance.

Wave propagation: pressure levels

In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. While this disturbance is usually small, it is still noticeable to the human ear. The smallest sound that a person can hear, known as the threshold of hearing, is nine orders of magnitude smaller than the ambient pressure. The loudness of these disturbances is called the sound pressure level, and is measured on a logarithmic scale in decibels. Mathematically, sound pressure level is defined

$SPL=20*log_{10}{\frac {P}{P_{ref}}}$

where P_ref is the threshold of hearing and P is the change in pressure from the ambient pressure. The following table gives a few examples of sounds and their strengths in decibals and Pascals ^[1].

Example of Common Sound	Pressure Amplitude	Decibel Level
Threshold of Hearing	20*10^-6 Pa	0 dB
Normal talking at 1m	.002 to .02 Pa	40 to 60 dB
Power lawnmower at 1m	2 Pa	100 dB
Threshold of Pain	200 Pa	140 dB

Wave propagation: frequency

Physicists and acoustic engineers tend to discuss sound pressure levels in terms of frequencies, partly because this is how our ears interpret sound. What we experience as "higher pitched" or "lower pitched" sounds are pressure vibrations having a higher or lower number of cycles per second. In a common technique of acoustic measurement, acoustic signals are sampled in time, and then presented in more meaningful forms such as octave bands or time frequency plots. Both these popular methods are used to analyze sound and better understand the acoustic phenomenon.

The entire spectrum can be divided into three sections: audio, ultrasonic, and infrasonic. The audio range falls between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear. This range has a number of applications, including speech communication and music. The ultrasonic range refers to the very high frequencies: 20,000 Hz and higher. This range has shorter wavelengths which allows better resolution in imaging technologies. Medical applications such as ultrasonography and elastography rely on the ultrasonic frequency range. On the other end of the spectrum, the lowest frequencies are known as the infrasonic range. These frequencies can be used to study geological phenomenon such as earthquakes.

Transduction in acoustics

An inexpensive low fidelity 3.5 inch driver, typically found in small radios

A transducer is just a device for converting one form of energy into another. In an acoustical context, this usually means converting sound energy into electrical energy (or vice versa). For nearly all acoustic applications, some type of acoustic transducer is necessary. Acoustic transducers include loudspeakers, microphones, hydrophones, sonar projectors, and ultrasound imaging equipment. Most of these are an electromechanical devices that converts an electric signal to or from a sound pressure wave.

One common example is a subwoofer used to generate lower notes in speaker audio systems. Subwoofers generate waves using a suspended diaphragm which oscillates, sending off pressure waves. Electret microphones are a common type of microphone which operate using a similar principle. As the sound wave strikes the electret's surface, the surface moves and sends off an electrical signal.

Divisions of acoustics

Countless subfields have been created as we have perfected our understanding of the underlying physics of acoustics. The table below shows sixteen major subfields of acoustics established in the PACS classification system. These have been grouped into three domains: physical acoustics, biological acoustics and acoustical engineering.

Physical acoustics	Biological acoustics	Acoustical engineering
Aeroacoustics General linear acoustics Nonlinear acoustics Structural acoustics and vibration Underwater sound	Bioacoustics Musical acoustics Physiological acoustics Psychoacoustics Speech communication (production; perception; processing and communication systems)	Acoustic measurements and instrumentation Acoustic signal processing Architectural acoustics Environmental acoustics Transduction Ultrasonics

References

^ Bies, David A., and Hansen, Colin. (2003), Engineering Noise Control

Benade, Arthur (1976), Fundamentals of Musical Acoustics, New York, NY, United States: Dover.

Rayleigh, J. W. S. (1894), The Theory of Sound, New York, NY, United States: Dover.

Wilson, Charles E. (2006), Noise Control, Malabar, FL, United States: Krieger Publishing Company.

Stephens, R. W. B. and Bate, A. E. (1966), Acoustics and Vibrational Physics, 2nd Ed., London, UK: Edward Arnold {{citation}}: Cite has empty unknown parameter: |1= (help)CS1 maint: multiple names: authors list (link).

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[1] Bies, David A., and Hansen, Colin. (2003), Engineering Noise Control

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