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Thread: What is the function of the body?

  1. #51

    Default Re: What is the function of the body?

    Some medium is required and since air is what we have around us that particular question probably results in arguments where the distinction is without a difference. The simple answer is that the sound box provides the bass. The top of the sound box provides the treble.

  2. #52
    The Amateur Mandolinist Mark Gunter's Avatar
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    Default Re: What is the function of the body?

    Quote Originally Posted by billhay4 View Post
    I am still not sure that air is required for sound to be made (I think not but some medium is).
    Bill, I think you may be missing the point about air. Air is not "required for sound to be made"; that is, vibrations which produce sound do not have to originate in air. Air is generally required for sound to travel to the eardrums. The eardrums could be vibrated by other means, for instance hydraulically (for example, if you are underwater and your outer ear canal is filled with water with no air captured within it) - but the primary most efficient means of exciting the eardrum is pneumatically (via the air). So, whether we are discussing strings on a plank with no soundboard, or a mandolin that has a sound chamber, it is the effect of the string or the soundboard vibrating against air that enables you to hear the resulting sound. So I'm not sure what you mean about air not being part of the equation.

    Concerning the air in a soundbox as of a guitar or mandolin, that enclosed air does have an effect on the sound that is produced. According to T. D. Rossing in his introduction to The Science of Stringed Instruments,
    Guitar researchers have paid considerable attention to the resonances of the
    guitar body, and how the low-frequency resonances can be regarded as being due to
    the coupled vibrations of the top plate, back plate, and enclosed air. Luthiers have
    experimented with different bracing patterns, especially in the top plate. Unlike the
    violin, which has changed very little for many decades, the guitar is still evolving.
    It would be good if you could explain what you mean exactly when you say that you are not sure that air is required for sound to be made.

    As a side note, I observe that most people can play air guitar or mandolin much better than they can play the real thing. I include myself in that group.
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  3. #53
    The Amateur Mandolinist Mark Gunter's Avatar
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    Default Re: What is the function of the body?

    An addendum, rather than an edit: The human ear has been created (or evolved, take your pick) to specifically process sound carried by air. A simple experiment will teach the young child that he or she can process sound vibrations with their head in open air and no breeze much better than with their head under water. Sound waves can travel through steel rails, water, string, virtually anything that can vibrate within frequencies conducive to human hearing, but such vibrations are normally transferred to and travel through the air before you hear them with your ears.
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  4. #54
    I may be old but I'm ugly billhay4's Avatar
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    Default Re: What is the function of the body?

    Mark,
    I understand all of that and have from the first post. However, it is not technically accurate to insist that vibrations have to be carrier by air to be heard. I understand how sound is normally made and how it is normally heard by humans, but it can also occur elsewise as I have stated.
    I can understand how, in the context of mandolins, people would insist that we consider air as the medium and I agree. But what if I were designing a mandolin to be played under water, or in space?
    I'm not but that doesn't mean I won't try. My first exolin is almost ready to be shown. Here's a hint:
    Click image for larger version. 

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    IM(NS)HO

  5. #55
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    Default Re: What is the function of the body?

    Quote Originally Posted by Mark Gunter View Post
    Increased amplitude of sound waves = amplified, in the way I used the term. I can tell by what you've written that you understand that. In the interest of clarity, the sentence above needs to be explained: The basic use of electronics for amplification in audio devices uses electricity to strengthen a signal, which is delivered to an output device like a speaker. The moving cone of the speaker then disturbs the air creating sound waves. The distinction is that the sound is represented within such an amplifier (e.g., transistor tube or solid state transistor) by pulses of electronic current (weak signal) that is used to modify a strong current, which is then used to drive the speaker. In the case of such an audio device using electronic amplification, the "sound wave" is what actually goes into the air; the part that is affected by electrical energy is a "signal" that represents the sound wave.

    @peter.coombe, Cringe and groan away at what I write. I'm not impersonating a physicist, claiming infallibility or even claiming to be able to express these ideas as a scholar in the particular field, I'm expressing my opinion here and trying to learn. Sorry if I don't fit in the right box for y'all. I have plenty of respect for the experts here, but can't say I take everything they write as gospel, and really consider myself no more pompous than the establishment is. In fact, I'm a pretty good guy once you get to know me, pomposity and all.
    Mark, as several folks have pointed out, physicists and engineers tend use the word "amplify" in a subtley different way than you tend to do. By "amplify", they mean that energy in the radiated sound has been increased. And they reserve the word for an energetic increase, not an apparent loudness increase (and this makes a big difference, it turns out). "Amplification" is what an electronic amplifier does to the sound signal in, say, a phonograph needle moving over a record, or in a radio signal obtained from a broadcast over the air. But with an acoustic instrument like a mandolin, once you've plucked the string to sound a note, that's ALL the energy that particular note will ever get! Put differently, there's no way for an acoustic mandolin to amplify it: there is no additional source of energy beyond what you put into it when you plucked it. But that does not mean that you can't make the string sound louder to someone's ear on the other side of the room. Someone else pointed out a great analogy, here: the old-fashioned megaphone. Singing or speaking into such a megaphone will not amplify your voice; it's just a passive device. But using the megaphone WILL direct the vibrations of your voice into a narrower cone in the forward direction. So less sound energy escapes to the back and sides, and more heads straight out toward a listener in front of you. Put another way, it changes the sound radiation field and focuses more energy towards the front. So your voice is louder to the folks in front of you (and softer to those behind you; energy is conserved!) The resonator on the back of a 5-string bluegrass banjo (not an older open-back model) plays a similar role. And that's also one role (of several) played by the soundboxes and soundholes found on guitars, violins, mandolins, etc. There have been LOTS of discussions here on the MC about how different mandolin soundhole shapes (ff-holes, oval holes, and even side ports) affect the radiated sound field. It comes down to a matter of efficiency (what you do with limited energy) and not to a matter of amplification. And, as you probably know, designing a mandolin to be louder for a listener sitting in front does not often make it louder for the player sitting behind the instrument. On the contrary: there is only so much sonic energy to go around.

    The other point that's been raised in this thread, and it's a vitally important one, is the role played by the soundboard or soundbox as an acoustic coupler. The energy in a vibrating string couples very poorly to the surrounding air, and it moves little air. The body of an acoustic instrument is designed to couple the vibrational energy from the string better into sound waves, in addition to focusing those waves in the radiated acoustic field (a "megaphone effect," if you will). With good coupling, less of the string energy is dissipated as heat (this is acoustic damping), or even as infrasound or ultrasound, and more of the string energy appears as sound you hear, with frequencies and overtones in the range that we can best sense (20 Hz to 20,000 Hz). So it's not just where the sound goes, but what goes into making up the sound! And here is exactly where things like acoustic resonances play a big role. When the fundamental frequency of a vibrating string, or one of its stronger overtones, happens to match one of these resonances, the acoustic coupling becomes much stronger between the string and the instrument, and the energy tends to be transferred more quickly. The timbre of a note (mostly, its overtone series) is hugely affected by the frequencies and physical properties of all these resonances.

    Of course, the vibrating string energy should not just go into making the instrument body or its air cavity vibrate! It then needs to get coupled into the air surrounding the instrument, and get radiated efficiently towards the listener. One good way to do this is with a wooden soundboard over an air cavity, and have sound hole(s) -- like a mandolin, violin, acoustic guitar, etc. A time-tested approach! But there are other ways, like the Stroh violin (Google it), which uses not a conventional body, but a horn instead -- much like a megaphone or an old gramaphone. See here:

    Click image for larger version. 

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    Or the Dobro, which uses a speaker-cone scheme (and the open-back banjo is not so different)

    Anyway, this is a vast and complex subject. The Stroh violin makes it clear that the roles of (1) shaping the radiated sound field, and (2) efficiently coupling the vibrating string energy into sound in the surrounding air, do not have to be played by a conventional instrument body. But SOMETHING has to serve these twin roles! So when you inquire, "what is the function of the body?" that's my attempt at a simplified answer. It turns out that it's not about amplification at all; it's all about acoustic efficiency in coupling the limited available energy into sound that will reach the listener's ear.

    I hope these words have been helpful. I am sure you're a good guy.

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  7. #56

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    It should be said that not all vibrations are equal.

    An object can oscillate side to side, like the pendulum of a clock or the tines of tuning fork. Call that a transverse wave or vibration.

    Or an object can oscillate along its length, like repeatedly pulling on the end of a long spring (like a Slinky toy), so the motion of one end is transmitted along the length of of the spring. Call that longitudinal wave, or a compressional wave, because the spring is being compressed and expanded by the motion of your hand.

    Sound travels through air by compressional waves, by repeated compression and rarefaction of the air molecules, with the molecules vibrating back and forth along the direction of sound travel. Sound can travel through any medium that carries vibration, but our ears and brain usually process compressional waves in air, so that is how sound is usually described.

    Plucking a mandolin string causes the string to vibrate from side-to-side, in a direction perpendicular to the length of the string. That is a tranverse motion. It does cause compressional waves in the air, but they don't sound loud to us because a string has a small surface area; it doesn't move much air.

    However, when the string's vibration is coupled to the soundboard via the bridge, the board has a much larger area and can set up more and larger compressional waves in the air, so it sounds lounder to our ears.

    The ear functions by sensing compression waves in air (or water, whatever). "Sound" can come from any vibration source which causes the air around it to move, but we only call it sound when compressional waves impinge on our ear drums and the auditory nerves tell the brain "Hey, we hear something."

    That's not a physicist's explanation; that's the explanation of a guy who took a few quarters of physics 30+ years ago, but I think it's generally correct.

    Ed

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  9. #57
    The Amateur Mandolinist Mark Gunter's Avatar
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    Default Re: What is the function of the body?

    sblock, I'm sure that is a helpful post; it has told me nothing I didn't already know; if you'll read my posts you'll see that I well understood from the start the difference between electronic amplification and the volume increase that is gained when a soundboard/soundbox is used, the problem is that I was using the word "amplify" to describe the increase in the volume of the soundwave - the actual output that reaches the ear. I also understand that this increase in volume which I referred to as amplification is due to the efficiency of transferring the vibrations to a soundbox and soundboard. I readily nod to the fact that the experts are using the word amplify in a much narrower sense than I was. I have pointed out numerous times that I used the word in reference to the amplitude of the actual sound wave reaching the ear as compared to that of the corollary sound wave that might be produced by the same action on a similar instrument without the soundbox. I don't know how much more clear I can be on that. I will happily refrain from using the word "amplify" in the future in that manner in order to avoid confusion. I'm not suggesting that we should use that particular term in the way I used it. The point I was making about the function of the body still stands, in that one function of the body of the instrument is to make the instrument sound louder. My interest in this discussion is the reason for a soundbox on a stringed instrument, an invention that predates modern science and even the historical record. The first instruments must have been crude, but when a soundbox of some fashion was used there was an increase in volume that was desirable. As these instruments have developed through history, they have been refined through experimentation and of course there has been study and experimentation that continues today in order to understand the complexities involved. It remains that the soundbox increases the volume and affects the tonal qualities. This increase in volume, which is somewhat directional, is one of the main reasons that soundboxes exist on musical instruments.

    As to the other note I've been sounding here: Sound waves travel through air . . . I have been beating that horse because I do not understand Bill's point, or his anxiety, about it. I have not insisted that sound waves must be carried by air to be heard, but I've pointed out that that is the normal mode of hearing. I've not heard of a musical instrument that is not meant to be heard by the human ear via the motion of air in the outer ear canal, yet that is not to say that some do not exist. We have sonic devices designed specifically for transmitting very low frequency waves through water; sea creatures may communicate via sound in the water; perhaps someone has made musical instruments intended to be felt rather than heard - in other words, I am not spouting absolutes on that point, but if we are discussing common sound boxes of stringed instruments it would not be easy to discuss how they make sound and music without reference to sound waves in the air, so I'm a bit confused still about what Bill is getting at there.

    By the way Bill, interesting shape to that body, can't wait to see the finished product.
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    Default Re: What is the function of the body?

    Quote Originally Posted by billhay4 View Post
    I posed this question precisely in hopes of a "messy" discussion like this one.

    Finally, I would like all the scientists among you to recall the each individual learns differently and incompletely (even you). Some learn by reading Red Books (I have read these articles), others by listening, some by making fools of themselves (my way), and some simply by being superior human beings. All of these methods are valuable IF expansion of the mind ensues.
    Bill
    Bill, I was a professor for 34 yrs before retiring. I am well aware that everyone learns differently. The problem for me with the "messy discussions" on these fora is that you are asking the scientists here to essentially give you an IEP (individualized educational plan) at their expense. In academia, we are paid salaries to do that sort of thing. The goal of higher education is ultimately to teach the learner how to learn for him/herself. Once we get past secondary education, there are limits on how much time we have per student. While we provide as much guidance as possible, at some point, the student has to take some responsibility and do the homework. Without that, no amount of support we can provide will ultimately do any good.

    Scientists (at least physical scientists) tend to be visual thinkers, because the problems to be solved need to be visualized. One of the first things we teach students about problem solving is - draw a picture or sketch of the system before doing anything else. The students find that once they are able to draw a sketch of the system, the problem is just about solved. That is why I referenced the articles in the Big Red Books; they have pictures, sketches, diagrams, and graphs. With that in mind, if you go back to the pictures, & etc. in the articles, then look in the text for the descriptions associated with the pictures, you will doubtless still have questions. The difference is that those questions will be narrower and more specific. Then, if you bring those specific questions to someone who can help you, you will get the specific answers, one by one. Science is reductionist. We do not get the big picture by looking for the big picture; we only get it by reducing the big picture to its' component problems that are manageable, solving those problems, then putting them together for the big picture. And unfortunately for some learning styles, learning science is also reductionist.

    What was the pint of all that? Learning the function of the (instrument) body is likewise reductionist. You learn what the strings do, what the plates do, how they do what they do together, what the air does,......, then you put all those pieces together, and only then do you begin to have an understanding of "What is the function of the body?"

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  12. #59
    Registered User fscotte's Avatar
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    Default Re: What is the function of the body?

    Now, how would you build a mandoln differently if it were meant to be played in outer space...

  13. #60

    Default Re: What is the function of the body?

    I think a lot of being able to find an answer (to any question/subject) on one's own, is *already* knowing enough about it to ask the 'right' question. That's hard to do, and is subject to misinterpretation.

    Ever went to Google to look something up, and been bewildered by thousands of search results because the question you posed wasn't specific enough? Or too specific?

    I learned something important from my dad, one of his favorite sayings:

    "An entire book full of answers won't do you any good if you don't know what all the questions are."
    This is where a person might find difficulty simply being referred to a large technical manual to seek an answer, because some of that stuff might not even make sense without someone to explain what it all applies to. This is where I would be, anyway.

    I guess, generally speaking, part of the task of the more-knowledgeable persons in humankind, is to figure out what it is that someone is *really* asking and distill it down enough to get some usable info, without getting side-tracked with technical disagreements. For instance...

    Computer tech support is a prime example. Casual computer users routinely get their facts mixed up due to their lack of familiarity with the exact meaning of some of the modern technical terms, for instance one of the classics is that they constantly confuse RAM with hard-disk space as if it was all one and the same thing ("But isn't it all just memory?") etc. It's hard to answer their questions when you're not entirely sure the nature of the question, this is where experience comes in handy, after a while you can kind of guess what they are *really* wanting to know. And explain it to them in a way that gives them enough practical info to solve whatever problem they're having. (I'm the family's tech-support/IT person, I have to deal with this stuff all the time.)

    I guess my point is, we are all ignorant in different topics. I wonder, did Einstein know how to set valve lash by ear on the internal-combustion engines of his time, or how to maintain a safe optimal boiler pressure in a steam locomotive? Or the correct procedures to shoe a horse? Would he even be bothered with wanting to know? It (presumably) wasn't his area of specialty. He was smart, but I'd be willing to bet that there were topics that he didn't know enough about to even formulate a proper question to ask about it. No one knows *everything*.

    Anyway, all that aside... I patently refuse to discontinue my use of the word "amplified" in its hundreds-years-old tried-and-true meaning of "now it's louder than it was before". As others have pointed out here, and I've already commented on, the word "amplify" existed centuries prior to humans harnessing electricity, whereupon specialists and technicians and physicists etc gave the word a new narrowly-defined technical meaning. The original and commonly-used by the masses version of "amplify" means "make it louder", regardless of how that is accomplished, whether via electricity or just a megaphone. The *method* of amplification is a mere trivial technical detail in that context, generally speaking the average person doesn't want to know how/why it's louder (whether purely mechanical, or electrical), they just know it's louder and that it's a good thing.

    Not sure of the logic in applying an *electronics* word to an *acoustic* instrument anyway, acoustic mandolins existed long before humans were using electricity and devising specialized forms of old words such as "amplify".

    Speaking of megaphones that others have mentioned, weren't the early record-players non-electrical? Here's a human-powered gramophone, you can see the person winding it up from about 0:07 to 0:20, and it looks like the big flared thing serves as a 'megaphone' which, according to our friendly physicists here doesn't "amplify" the sound in the modern scientific sense of the word, but according to the rest of us folk it's "amplified" alright 'cause it's louder than it was before.

    So... This next bit has already been mentioned by others, but not sure everyone has read it, so I'll reinforce the info a little now...

    Note: While I realize that dictionaries aren't authoritative, rather they just report on how real-life people are using words in everyday life, nevertheless (for better or worse) it's real-life that most of us have to deal with, here are some definitions:

    Amplify
    1. to make larger, greater, or stronger; enlarge; extend.
    2. to expand in stating or describing, as by details or illustrations; clarify by expanding.
    3. Electricity. to increase the amplitude of; cause amplification in.
    4. Archaic. to exaggerate.


    Synonyms:
    1. increase, intensify, heighten.
    2. widen, broaden, develop.


    Origin of amplify
    1375-1425; late Middle English amplifyen < Middle French amplifier < Latin amplificāre to increase, augment. See ample, -ify.

    -Dictionary.com
    Ah - now this is interesting, seems the geneticists and the physicists need to quarrel over who's using the word right since geneticists use the word to mean something entirely different:

    Amplify
    Genetics: Make multiple copies of (a gene or DNA sequence).

    Example sentences:
    • We performed PCR on wild-type mouse genomic DNA to amplify sequences flanking transposon insertion sites for use as probes.
    • Genes were amplified from genomic yeast DNA using specific oligonucleotides and the polymerase chain reaction.
    • Primers were designed to amplify this gene sequence specifically.

      Origin:
      Late Middle English (in the general sense 'increase, augment'): from Old French amplifier, from Latin amplificare, from amplus 'large, abundant'.

      -Oxford Dictionaries
    Should we thus chastise physicists for using the word "amplify" because they don't use it in a technically-correct way from the point of view of the geneticists???

    Any of those 'specialty' fields are going to use common/old words in new ways, to apply to some particular technical angle in their own field of work. That doesn't mean that the rest of us have to follow suit.

    Although, after reading this thread, the next time I'm in a room full of physicists (like, never) I will refrain from using the word "amplify" at all, lest I use it in a way that they're not accustomed to. I could just put it on my list of other words that are too controversial to use anymore... nah...

  14. #61

    Default Re: What is the function of the body?

    Quote Originally Posted by Bruiser View Post
    It should be said that not all vibrations are equal.

    An object can oscillate side to side, like the pendulum of a clock or the tines of tuning fork. Call that a transverse wave or vibration.

    Or an object can oscillate along its length, like repeatedly pulling on the end of a long spring (like a Slinky toy), so the motion of one end is transmitted along the length of of the spring. Call that longitudinal wave, or a compressional wave, because the spring is being compressed and expanded by the motion of your hand.

    Sound travels through air by compressional waves, by repeated compression and rarefaction of the air molecules, with the molecules vibrating back and forth along the direction of sound travel. Sound can travel through any medium that carries vibration, but our ears and brain usually process compressional waves in air, so that is how sound is usually described.

    Plucking a mandolin string causes the string to vibrate from side-to-side, in a direction perpendicular to the length of the string. That is a tranverse motion. It does cause compressional waves in the air, but they don't sound loud to us because a string has a small surface area; it doesn't move much air.

    However, when the string's vibration is coupled to the soundboard via the bridge, the board has a much larger area and can set up more and larger compressional waves in the air, so it sounds lounder to our ears.

    The ear functions by sensing compression waves in air (or water, whatever). "Sound" can come from any vibration source which causes the air around it to move, but we only call it sound when compressional waves impinge on our ear drums and the auditory nerves tell the brain "Hey, we hear something."

    That's not a physicist's explanation; that's the explanation of a guy who took a few quarters of physics 30+ years ago, but I think it's generally correct.
    For me, that explains everything, thank you! I can almost picture or get a 'visual' of the soundwaves being transformed from the strings' side-to-side (transverse) motion, to the soundboard's compressional waves that our ears notice better. (Did I get that right?) I like your explanation because it reduces all the mystery to something I can visualize and thus understand a little bit better. Thanks again!

  15. #62

    Default Re: What is the function of the body?

    Quote Originally Posted by JL277z View Post

    Anyway, all that aside... I patently refuse to discontinue my use of the word "amplified" in its hundreds-years-old tried-and-true meaning of "now it's louder than it was before". As others have pointed out here, and I've already commented on, the word "amplify" existed centuries prior to humans harnessing electricity, whereupon specialists and technicians and physicists etc gave the word a new narrowly-defined technical meaning. The original and commonly-used by the masses version of "amplify" means "make it louder", regardless of how that is accomplished, whether via electricity or just a megaphone. The *method* of amplification is a mere trivial technical detail in that context, generally speaking the average person doesn't want to know how/why it's louder (whether purely mechanical, or electrical), they just know it's louder and that it's a good thing.
    Bullseye ...

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    Default Re: What is the function of the body?

    I don't know if anyone has stated this before, but after all the entropy in this thread, this is about all I can offer

    Plucked string instruments are mechano-acoustic devices - systems of coupled oscillators assembled for the purpose of getting vibrations in a fluid (usually air) to a human listener's ears. If you use a definition from genetics, or a dictionary definition from common usage, to claim that the instruments are amplifiers, you are taking the instruments out of their context.

    There is a compelling reason why a string instrument body is not an amplifier; i.e., it is not amplifying anything, and especially not the strings. In particular, it is not making the "sound" from the strings louder. The strings do make some sound, and that sound from the strings is part of what you hear. The total output from a string instrument is the sum of the individual outputs from each of the component oscillators - the strings, air vibrated by the outsides of the plates, and air vibrated by the vibrating air in the region(s) of the soundhole(s). Even if some motion of one of the oscillators is amplified by, say, 10%, it has to be multiplied by a factor of 1.1, but no such multiplications are taking place. Again, the sound output from a plucked string instrument is a sum of component oscillator outputs, and not a multiple of anything. In fact, the 2nd law efficiency of a plucked string instrument is in the neighborhood of 4%. Which means that most of the energy, about 96%, that comes from initially displacing a string (potential energy) and letting it go (kinetic energy) is lost to heat and entropy.

    One might be able to do a semantic dance and claim that an instrument body is an apparent amplifier, but many things that are apparent do not hold up to closer scrutiny. There are apparent exceptions to the 2nd law of thermodynamics too, but none that have held up to closer examination.

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    Default Re: What is the function of the body?

    For the record - and specific to my way of learning - Dave Cohen and John Hamlett are two of the best explainers around. Many many times they have cleared the fog for me.
    A talent for trivializin' the momentous and complicatin' the obvious.

    The entire staff
    funny....

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    Default Re: What is the function of the body?

    What have we achieved? I mean, we could have answered the original question with a terse "remove the body and you'll hear for yourself what its function was", but I bet the OP knew that.
    But we are here for talking, and we have yet again learned a little bit about communication and its pitfalls, probably more than we learned about instruments. The differences in vocabulary are not obstacles for this, they are the fuel.
    the world is better off without bad ideas, good ideas are better off without the world

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    Default Re: What is the function of the body?

    A single string vibrating in air creates a sound wave that is omnidirectional. As a result, the sound dissipates quite quickly over distance (i.e. it's soft unless you're next to it). A hollow body (chamber) with a thin vibrating face (sound board) with a hard back and sides is able to focus the energy from the vibrating string and create a sound wave that is amplified because it's moving more air, and directional since the back and sides of the chamber are relatively stiff... therefore the air movement is limited to coming off the front face (sound board). The result is a more focused sound wave (i.e. louder).

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  24. #67
    two t's and one hyphen fatt-dad's Avatar
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    Default Re: What is the function of the body?

    . . . late to the party!

    My answer? The function of the body is to make a mandolin sound like a mandolin, or a guitar sound like a guitar, or a fiddle sound like a fiddle. They all sound different for physical reasons that I don't quite understand. . .

    f-d
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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: What is the function of the body?

    Dave,
    With all due respect, no one asked you to contribute to this conversation at all. Your choice. If it's burdensome to you, don't chime it. And I know it has gotten burdensome for you. Thus all the comments about the inefficiency of the internet for such discussions.
    Frankly, though, life is entropy. It is not the orderly process you chemists prefer.
    Bill
    IM(NS)HO

  26. #69
    Registered User Hadji36's Avatar
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    Default Re: What is the function of the body?

    Since air is a fluid, and sound waves move longitudinally through fluids, I would think that the difference between a good and great mandolin would be how those sound waves are manipulated within the sound chamber, as well as other factors. That would put into play those sound waves reflecting off of and directed by the back board, as well as other factors such as the efficiency of the bridge transferring the vibrations of the strings to the soundboard. We all know that when we add mass to the bridge, we lose volume (lessens the efficient transference of the vibrating strings to the soundboard) and when the back of the mandolin is tight against our bellies, it somewhat dampens the sound. I would think that other factors, such as backboard wood species would come into play as well. We've heard that softer back and side woods give softer tone/sound. I would think that this would be a factor of absorption or less than efficient sound wave reflection.

    Of course I could be way off...but, I did stay at a Holiday Inn Express last night.

    Here is an interesting quick read on sound waves which may play into the discussion:

    http://www.physicsclassroom.com/clas...gitudinal-Wave
    "If you pick it... It will never heal." - Mom

  27. #70
    I may be old but I'm ugly billhay4's Avatar
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    Default Re: What is the function of the body?

    Thanks for the link Hadji36.
    Bill
    IM(NS)HO

  28. #71
    Registered User sblock's Avatar
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    Default Re: What is the function of the body?

    The discussions of the meaning of the word "amplify" are beginning to sound like the parable of the blind men and the elephant! Yes, words can be used in many ways. If you want to use "amplify" to just mean "make it sound louder," then fine. But please realize that when you do so, you seem to miss an important point, stressed by many of the scientists on the forum who've chimed in, which is this:

    An acoustic stringed instrument cannot amplify (that is, increase) the ENERGY associated with a vibrating string. Once a string has been set into motion (say, by flatpicking it), it carries a certain amount of vibrational energy. That energy cannot increase thereafter because there is no further input of energy from any other source. Energy is conserved. The string eventually loses all its vibrational energy, and rings down. The vast majority of that energy goes right into heat (pure damping). A small portion of the energy goes into driving other vibrations, and it is this energy that mostly contributes to the sound that we eventually hear. In most acoustic instruments, that energy is used to vibrate the tonewoods (i.e., the walls of the soundbox) and to vibrate a partially enclosed volume of air (the air cavity of the soundbox). These structures, in turn, radiate their sound into the air surrounding the instrument, which eventually reaches our ears.

    The "purpose of the soundbox" is to couple efficiently the energy of vibration of strings, through the intermediate of the wood and air that comprise the instrument's soundbox, into airborne vibrations in the region outside the instrument. No more, and no less. And generally speaking, the more efficiently the soundbox functions, the louder we hear the sound. This improvement in coupling efficiency (which makes things sound louder) is not, strictly speaking, a form of "amplification" in any sense that a physicist might use the word. That's because the energy is always getting lost, and never increased! But the higher the soundbox efficiency, the less the loss at the level of your ears. So, if you tend to think of "less loss" as being a kind of "gain", then go ahead and call it "amplification." But realize that this is equivalent to saying "I just bought a fuel-efficient car that gets more miles to the gallon, and am now saving fuel. My new car amplifies the fuel!"

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  30. #72
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    Default Re: What is the function of the body?

    Quote Originally Posted by billhay4 View Post
    Dave,
    With all due respect, no one asked you to contribute to this conversation at all. Your choice. If it's burdensome to you, don't chime it. And I know it has gotten burdensome for you. Thus all the comments about the inefficiency of the internet for such discussions.
    Frankly, though, life is entropy. It is not the orderly process you chemists prefer.
    Bill
    That is some strange logic. No one invites anyone to post, nor for that matter, to initiate messy threads. With the comment about "orderly process", you are making an assumption about something with which you are not very familiar. No scientist will tell you that science is completely orderly. We try to bring some order to it after going through the process. We make hypotheses, and perform some experiments. More of those experiments don't work than do. Same goes for the hypotheses. Then we start over, and repeat, and repeat, and,,,,until we have some results that can support some conclusions. Takes a lot of time and effort. Not very orderly, imo.

    It has gotten "burdensome" for me, for some of the reasons outlined by Bertram. New members keep asking the same old questions. We answer those questions over and over, and get a great deal of uninformed pushback every time. Worst yet, more than a little of that pushback is ad hominem and personal. I had to have a heckuva lot of patience during my years in the classroom. What was most trying to the patience of any teacher was the assumption on the part of students that because we didn't present the information in a way that was "just right" for them to get it without any effort on their part, we were somehow deficient and were not putting sufficient effort into our work. In fact, I brought work home with me most evenings, often working very late. I am older and crankier now, with less patience. If I were a better Dave than I am, I might have maintained that patience, but sumus quod sumus, i.e., we are what we are.

  31. #73
    Registered User sblock's Avatar
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    Default Re: What is the function of the body?

    Quote Originally Posted by dschonbrun View Post
    A single string vibrating in air creates a sound wave that is omnidirectional. As a result, the sound dissipates quite quickly over distance (i.e. it's soft unless you're next to it). A hollow body (chamber) with a thin vibrating face (sound board) with a hard back and sides is able to focus the energy from the vibrating string and create a sound wave that is amplified because it's moving more air, and directional since the back and sides of the chamber are relatively stiff... therefore the air movement is limited to coming off the front face (sound board). The result is a more focused sound wave (i.e. louder).
    Actually, no, the problem is not (just) one of directionality, and of focusing the radiated sound field. The problem is that the energy in a vibrating string couples only very weakly to the air around it. A moving string is very thin, and it moves very little air around it as it vibrates. It therefore produces very little sonic output, irrespective of the direction! You can experience this directly by plucking the string of a solid-body electric guitar (one that's not plugged in). Almost no volume. You can focus this if you like, but that won't help much.

    As I have written before, the soundbox of an acoustic instrument not only focuses the sound (akin to acting like a megaphone in that regard), but it also couples the vibrational string energy into acoustic waves, by causing comparatively flat tonewood surfaces and partially enclosed air cavities to be set into vibration. The detailed physics of this coupling is complex, and involves resonances, elastic properties, and a whole bunch of stuff. But the underlying idea is simple: lose less vibrational energy to damping, and put more of it into radiated sound.

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  33. #74
    I may be old but I'm ugly billhay4's Avatar
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    Default Re: What is the function of the body?

    Again, Dave,
    You don't have to participate in such discussions.
    Bill
    IM(NS)HO

  34. #75
    I may be old but I'm ugly billhay4's Avatar
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    Default Re: What is the function of the body?

    I'd like to clarify my original post on this topic a bit now that much helpful information has been related. I, of course, had a general understanding of sound and the function of the soundboard and sound box when I posed the original questions.
    It is my impression (and I may well be wrong here) that much scientific research has been done on the theoretical questions of acoustics and music. Like all scientific research, this has followed a strict protocol as outlined by Dave Cohen above.
    Has anything like this been done vis a vis specific instruments, concerning very practical considerations? For example, have there been any controlled studies of the effect of the shape of the soundbox on the sound of the instrument? How about the use of particular woods? Or the shape of soundholes? These would have to isolate a particular variable and measure the effects of certain changes in that variable from one instrument to another. A valid standard of measurement would have to be used. In short, they would have to follow a scientific protocol.
    Is the issue here the subjectivity of sound? Or is it the time and expense of doing such research? Or something else? Or is it that there are just so many variables in the sound an instrument produces that the effect of one or another is too small to measure or make a difference?
    I am interested in such information regarding the mandolin specifically because that is what I play and build. I suppose this removes the question from the theoretical realm to the practical, but I find the question pertinent anyway.
    What I'd really like to see is a foundation dedicated to such musical research. Is there one?
    Bill
    IM(NS)HO

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