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David Beard

Transducer versus amplifier

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Sometimes I see mention of the violin acting as an amplifier, but I not sure I've seen mention of the violin as a transducer.

I'm inclined to think that technically the violin is a transducer, but isn't an amplifier. But I'm certainly not a physicist.

Curious how others think of it?

 

Also, you mostly hear discussion of resonances. But the violin is not just a marimba bar that you strike and out comes a pitch based on body resonance. Instead there is continuing vibration energy being input through the bow. And separately pitch control through fingering.

 

Amplifier?

Resonator?

Transducer?

 

Your thoughts....

 

 

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A remarkably elegant and overly complicated nuisance to theorists and investigators alike.  :lol:

Rather than an amplifier (which implies making an existing signal louder by adding power to it), or a transducer (which only addresses power conversion) I'd describe it as a continuously-tuned multi-frequency modulated audio oscillator, impedance transformer, and radiator, which incorporates parts of the resonator (body) involved in impedance transformation into the radiator.  :)

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Resonator.

Violin body resonates string vibrations which comes thru bridges, violin body has very complex resonance charateristics, it has air resonance (body shape) and wood resonance and they are couplings between the two.

KYC

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Certainly the strings, stopped or open, are resonators. And certainly the violin body and air inside have many resonances that couple with what's going on. But is it that simple? It's also a driven system that responds to and radiates fairly evenly to a chromatic glissando across several octaves.

Do we also call speaker diaphragms and soundboards resonators?

Doesn't a violin also have something in common with these?

 

Seems a rather complex system.

:unsure:

 

 

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It is called " forced oscillation " : it resonates more if the incoming vibration is close to the natural resonance frequency of the body, but it will play any notes it is fed, hence forced ocsillation.

It is simple : bc we understand basically

It is not simple : bc we don't fully understand, actually far from it.

 

KYC

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Definitely not amplifier.

Transducer yes, resonator yes too.

It's a transducer that has resonances.  Simple basic concept, like loudspeakers, which also have resonant frequencies.  The violin just has a pile more of them within the operating range, while speakers generally try to keep resonances out of the operating range.  The speaker transduces electrical power to sound, while the violin tranduces mechanical vibrations to sound.  It's all the resonances and non-linearities that make the violin sound like a violin, as opposed to an electric violin.

Simple basic concept, not simple in the details.

 

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The way I see it, the strings are the variable frequency oscillator, with positive feedback to maintain oscillation provided by the bow. The bridge is sort of a SAW  (surface acoustic wave) filter that couples and impedance matches the strings output to the body. The body itself acts as a passive resonator  and radiator with very complex resonances and filtering.

The body can't really be considered an amplifier as it is only powered by the input signal, there is no increase in power level beyond what is supplied by the driven strings.

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28 minutes ago, Don Noon said:

  It's all the resonances and non-linearities that make the violin sound like a violin, as opposed to an electric violin.

 

 

It's actually amazing that an electric violin sounds as violin-like as it does.

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1 hour ago, Bill Yacey said:

The way I see it, the strings are the variable frequency oscillator, with positive feedback to maintain oscillation provided by the bow. The bridge is sort of a SAW  (surface acoustic wave) filter that couples and impedance matches the strings output to the body. The body itself acts as a passive resonator  and radiator with very complex resonances and filtering.

The body can't really be considered an amplifier as it is only powered by the input signal, there is no increase in power level beyond what is supplied by the driven strings.

Very close.  The player also modulates the oscillator input power amplitude and continually varies the frequency.  The beauty of the performance is dependent on the ability to manipulate the inherent instabilities of a rig like that (e.g., harmonics).  Modulated oscillators are legally banned in commercial and amateur radio transmission for very good technical reasons. :lol:

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11 minutes ago, Violadamore said:

  Modulated oscillators are legally banned in commercial and amateur radio transmission for very good technical reasons. :lol:

Years ago one of my electronics instructors commented on one of the students who was building a small transmitter;  he said "Your frequency control and stability is like a fart in a windstorm."  I thought this was an accurate and comical assessment.

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Suppose you string up a base ball bat, then you have a tiny sound, now you replace it with vn body, you have a bigger sound.

Can't we call this amplification? 

 

KYC

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23 minutes ago, chungviolins said:

Suppose you string up a base ball bat, then you have a tiny sound, now you replace it with vn body, you have a bigger sound.

Can't we call this amplification? 

 

KYC

No, it's using impedance matching, filtration, and energy storage to get power from the bow (at frequencies produced by the strings) to the air with less loss or blockage.   Amplification requires stages adding more power to an already defined signal to increase its amplitude.  It's the difference between a passive megaphone and a bullhorn/loudhailer.  The first effects an impedance transformation (and increased directionality) between the voice and the air by means of a horn, the second adds electrical power to the voice before focusing it and correcting its impedance. :)

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10 hours ago, chungviolins said:

Suppose you string up a base ball bat, then you have a tiny sound, now you replace it with vn body, you have a bigger sound.

Can't we call this amplification? 

 

KYC

In both cases no power is being added to the original vibrations of the strings.  So neither case is amplification.

But the bat fails to convert much of the string vibration into sound radiating through the air.   The violin body does a much better job converting the energy from the string vibration into radiating sound. But no energy is added, just less is lost.

 

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1 hour ago, David Beard said:

 

But the bat fails to convert much of the string vibration into sound radiating through the air.   The violin body does a much better job converting the energy from the string vibration into radiating sound. But no energy is added, just less is lost.

 

Base ball bat : energy from your arm + bow+ string is reflected back to you, so less sound energy  is propagated to the bat itself and surrounding air, hence tiny sound.

Violin body : energy from your arm + bow + string goes thru the vn much effectively than bat's case and radiates more energy , makes the sound louder.

Actually the player works harder , in the physics sense whether (s)he is aware or not, when (s)he plays vn than bat, that is, more energy flows thru the vn.

Violin body does not add energy ( this is why some ppl don't want to call it amplifier) , but it makes possible that more energy goes thru it.

So if you think, in both cases,  <Same> amount energy is going in and more energy is lost for bat than for vn, that is not what's happening.

Amount of energy going from the player -> bow -> string -> body ( bat or vn body ) are <Different>.

< More > energy is going into the vn than for a bat, so, in that sense, we can call it amplifier.

 

KYC

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The violin is not a perpetual motion machine, nor a free energy offering. No matter how much energy you input, you will always only end up with a fraction of that energy in audio output.

An amplifier using an external source of power will increase the energy output far in excess of what energy the input signal provided.

In the baseball bat example with strings, the majority of the input energy is dissipated as heat, versus the violin which dissipates some of the input energy as acoustic output, and the rest as heat.

There is no amplification taking place here.

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2 hours ago, Bill Yacey said:

 

In the baseball bat example with strings, the majority of the input energy is dissipated as heat, versus the violin which dissipates some of the input energy as acoustic output, and the rest as heat.

 

A bat has a tiny sound not because the majority of it dissipated as heat --- this sounds reasonable but it is a misguided notion ---, but because it is not going it there in the first place.

It comes back to you.

Think of it as an energy flow : bat; small energy going in small energy coming out

Vn : bigger energy going in bigger energy coming out

Please explain what is input & output for bat : bi , bo

And input & output for vn : vi, vo

( we know what bo, vo  are, pls explain  bi & vi .)

They are not as simple as one might think.

 

KYC

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When a base ball player swings a bat and if he didn't hit the ball at the sweet spot, the ball doesn't fly long distance not because the energy dissipated as heat but the energy comes back to the batter.

The player feels pain in his arm or hand because un-transfered energy springs back to him.

 

KYC

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Which is then lost as 'heat' in him. 

To some extent 'heat' is being used loosely as a catchall for any energy that is dissipated as anything other than radiating sound.

As you say, with a batter much of the energy that doesn't go into the ball might well return to the batter to be 'lost' in his arms and body.

Not sure if that applies so well to someone bowing strings, whether on a bat or a fiddle.  But still, some portion of energy from bowing gets transformed into sound, and some portion is 'lost' or dissipated.  The violin is comparatively good at this transforming of energy.

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Thought experiment:

Lift the bridge on the vn so that it doesn't touch the top and play a note.

Let the bridge down on the top and play a note.

The note got bigger.

 

KYC

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