[sdiy] [ProAud] Total acoustic energy of an object

cheater00 cheater00 cheater00 at gmail.com
Wed Mar 8 13:17:40 CET 2017


Hi Dick,
You've actually made some more precise arguments and explained what I had meant.

You say that the instrument only *transmits* energy that the player
puts in. That is a good way to look at things. For example, in a
violin, the force exerted by the arm muscle to linearly move a bow is
transformed into a highly complex movement.

The instrument does some work to perform this conversion. (Work as in
the physics definition of work). Heat is generated, molecular bonds
are broken. I understand most of this breakage happens in the strings
and bow. The bridge and nut and tuners will experience much less wear.
The body will experience much less wear than the bridge and nut and
tuners.

So I guess one way to answer my original question is to look at the
lifetime of strings (or "mileage" as Chris Deckard put it). Then you
may say: keeping everything constant, the instrument will fail as soon
as the strings and bow fail.

The next question becomes: what if you have infinite strings? How
quickly will the bridge wear off? I guess that can be explained by
materials science. Similarly, if you had infinite nuts and bridges,
you could probably quantify how quickly the body would wear off (not
quickly at all, obviously).

But, for example, if you take a pencil eraser, and pull it across a
glass surface, it will similarly transform simple linear motion into
sound. Obviously the pencil eraser will be soon gone - it doesn't have
much mileage in it! So maybe the way the "mileage" is determined has
to do with the chemical compound the object is made of. I wonder if
there is a theoretical model for quantifying that.

To all:

Regarding "old instruments sound better": I thought about this for
several years and the best idea I have come up with is this: if it
sounded crap, you'd have thrown it away. The longer you have it, the
more likely you are to throw it away. So if you only select for very
old instruments, and out of those instruments listen to what they
sound like, they're much more likely to sound good than new
instruments, which simply haven't been thrown away yet, or the
musician still hasn't grown to appreciate that they sound bad. This is
a form of Survival Bias.
https://en.wikipedia.org/wiki/Survivorship_bias

According to this concept, if you listened to all Martin guitars made
49 years ago, and they had all been kept intact - rather than
destroying, when they were destroyed, they were "magically" teleported
for safe keeping - the ones you heard still in use after 49 years
would be above average sounding in that group of instruments. So
you're taking a process (keeping an instrument for 49 years) that
naturally selects for better-sounding instruments, and you're
wondering why those 49 year old instruments sound better. Welp. Kind
of obvious if you think about it in this way.


On Mon, Mar 6, 2017 at 3:04 PM, Dick Pierce <dpierce at cartchunk.org> wrote:
> On 3/4/2017 11:08 AM, cheater00 cheater00 wrote:
>>
>> Hi,
>> When using a bow, a horn, a guitar body, or another acoustic
>> instrument, when the object emits sound waves its integrity is
>> diminished in tiny amounts. Eventually it would get destroyed.
>
>
> This, I assume, is a conjecture.
>
> As such, it seems to completely ignore the energy that the player
> MUST put in to make the instrument sound.
>
> But, underlying your conjecture there is some TRVTH(tm) to the
> statement, in that there are phenomena such as wear and fatigue
> that must be accounted for, and is usually accounted for in the
> maintenance of the instrument. There is also the issue of decay
> (e.g., in the wood), chemical and physical changes (e.g., the
> carrier in a varnish slowly evaporates, materials oxidize, etc.).
>
> But NONE of these phenomena have anything to do with the product
> of sound per se. It might be said that the product of sound by
> the instrument is a byproduct of some of these, rather than the
> other way around (for example, drawing a bow across a string
> causes the string to be excited as a result of the friction
> between the bow and the string, and, almost inevitably, where
> there's friction, there's wear: that's why violin strings get
> replaced on a periodic basis).
>
> Some of these phenomena would occur whether or not the instrument
> is being used, some of them are accelerated by use.
>
>> Similarly to total energy that can be released by burning matter in
>> oxygen, or total energy released when an item drops on the ground, Is
>> there some form of "total acoustic output" that can happen over the
>> lifetime of an object? How would you define it, theoretically?
>
>
> As far as the acoustic output is concerned, the source of the acoustic
> energy IS the energy the performer puts in (drawing the bow, plucking the
> string, blowing on the reed, etc.). In general, the efficiency of most
> acoustical devices (from lutes to loudspeakers) is extremely low:
> efficiency her being defined as the ratio of the power put in to the
> contrivance to the acoustic power out, on the order of a few percent at
> best.
>
> And, to get back to your original conjecture, the total acoustic
> energy (which is the product of power and time) is limited only
> by the total energy of the performers, neglecting wear, most if
> not all of which is controlled through normal requisite maintenance.
>
>> One can imagine that forced vibration has a different effect to free
>> vibration.
>
>
> Well, going back to your original conjecture, no: if the instrument
> is making sound, then it should "deteriorate." But, in reality, it's
> not the making of acoustic power that causes the problems, it's
> the mechanical wear and chemical deterioration at the hands of the
> performer or simply the aging sitting idle that changes the instrument.
>
> One could also suppose that if your conjecture were true, the same
> instrument being played in a vacuum should last longer, since it
> cannot, by definition, produce sound (and since the effective acoustic
> impedance seen by, say, the soundboard, is VERY different in a vgacuum
> than in air, there will be a real difference in what happens to
> the energy) Not an easy experiment to do, to be sure, since there are
> a number of uncontrolled variables, like the vapor pressure of volatile
> solvents, and such.
>
> --
> +--------------------------------+
> |          Dick Pierce           |
> | Professional Audio Development |
> |         cartchunk.org          |
> +--------------------------------+
>
>
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