In a vacuum

[labraid]

Lightning round!
If I played my instrument in a vacuum....

-----

supplementary and optional: how much longer would the instrument actually want to sustain with no air to pump?

(my point being, if you're curious, let's on with it!)
(and don't be shy, I've got candy)

[sunburst]

At first guess I thought it would come down to; how much resistance to the vibrating top plate is offered by the air inside and outside the box, remove that from the equation, figure out how much additional sustain would result, and you'd be close...but wait...there's resistance to the actual string vibration from the air, so subtract that too, and then there's the back. "Normally" the air in the box moves the back, but without air, that wouldn't happen, so the sustain might increase more than would be calculated from just the removal of the resistance to top vibration because energy from the "vibrating" air wouldn't be getting "grabbed" by the back plate.
I suppose there would be some back movement from being coupled to the top through the rim, but it would be different than what happens in the air.

Interesting question, and a good way to stimulate the mind to thinking about how an instrument affects and is affected by the air around and in it. One thing's for sure, the instrument would behave differently, and probably more or less unpredictably. Hmmmm...

[12 fret]

[QUOTE] Lightning round!
If I played my instrument in a vacuum....

Your head would explode... yea I win

[John Flynn]

If I played my instrument in a vacuum....
According to the "Bioastronautics Data Book," Second edition, NASA SP-3006, you would lose consciousness in about 10 seconds, followed by generalized convulsions. You would then rapidly swell up to about twice your normal size and die in about 90 seconds. The convulsions might improve your tremolo, but you wouldn't get to appreciate it. Hey, you asked!
http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

[mandofiddle]

Just a guess here, but... Would it make no sound at all?

My guess is based on... Doesn't sound come from how the string vibrations displace the air around it? So if there was no air, would there also be no sound?

Dave

[sunburst]

Right, no sound, as Brian said in his topic title, but the strings would still vibrate (in those first 10 seconds before the player lost consciousness), the strings would still drive the bridge and top, and the string vibration would still sustain for some amount of time.

[mandofiddle]

Oh, you mean, how long would the strings visibly vibrate, since they make no sound?

If that's the case, then I'll guess forever since there is no friction of air to cause them to slow down and stop.

I misunderstood/misread what the topic title meant http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[sunburst]

...I'll guess forever since there is no friction of air to cause them to slow down and stop.
Oh, a perpetual motion machine!
I'm afraid the removal of air from the system doesn't negate the laws of physics. There's friction in the string itself and within the top plate. Most of the string's energy is lost to internal friction and damping within the instrument and only a small amount moves the air and makes sound anyway. Removing the air only removes a portion of the resistance to string vibration.

[KNP String Band Mando]

I asked my physics major roomate, he said it wouldnt be a vaccum if a mandolin was in it, but if you got around that fact. He also said that the mandolin would be crushed by the pressure. And since sound waves move air and thus move our ear drum and what not, you could not here it, altohught it would still vibrate if it was still intact. He said no sound. Hes working for the goverment right now designing a EMP chamber so something like that. Ill see if he has a vaccum chamber in the lab and give him my rogue to put it in. Ill keep ya posted.

[sunburst]

...He also said that the mandolin would be crushed by the pressure....
I'm having a little trouble with that one. Isn't pressure more or less the opposite of vacuum? What pressure would there be in a vacuum to crush the instrument?
There is air in the wood that might cause bursting of wood cells if the instrument was "plunged" into a vacuum, but a slowly evacuated vacuum chamber would allow time for the air to escape and it seems to me the structure would be fine.

[KNP String Band Mando]

Ok I asked him again, and i guess I interperted him wrong, and your right sunburst, if it was plunged into it the top might come off due to the pressure of the air escaping. He said that the wood would swell, and depending on the quality of the vaccum it could be be pulled apart. He is now really intrigued with this concept and said it all depends on what theroy you use to explain it, quantum, particle, string etc.. He said he will keep pondering it. Physics is way to crazy for me. Ill stick to Biotech and chop chords

[groveland]

I've played some of my best stuff in a vacuum - Or so it would seem judging from the audience response. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wow.gif

[JeffD]

Most of the string's energy is lost to internal friction and damping within the instrument and only a small amount moves the air and makes sound anyway. Removing the air only removes a portion of the resistance to string vibration.
I quite agree. No sound, perhaps a very slightly longer lasting vibration.

While a sudden application of a vacuum might not be good for the mandolin, a gradual removal of the air would be fine and the final resulting total vacuum (but for the mandolin and the picker) would probably not have any impact on the structural integrity of the instrument.

The picker on the other hand...

[nelson_luthier]

The instrument should survive just fine if in a bell jar type environment. A vacuum bag would be another story because the outside pressure would then crush the poor thing. I guess any trapped air "bubbles" in the wood fibers themselves would need to be allowed to escape, so you could wind up with some interesting finish complications...

I have to agree with Sunburst. Air resistance is only a small portion of the equation. Now, vibration is movement relative to a fixed point. Is it the string that is vibrating or is the rest of the universe vibrating around the string?

Greg N

[labraid]

Is it the string that is vibrating or is the rest of the universe vibrating around the string?
Hey, I like that.

I was really intrigued wondering how these highly vibrational areas on the plates, depending on the notes, how much they're actually having to work to move the air around, how much of the string energy is going to this end. The same experiment could be thought of with a tuning fork. And if decay of amplitude were graphed, how much would it be extended if done in a vacuum. And if there were very wide forks, that had to displace greater quantities of air, as mando or guitar or bass plates do...
I hadn't originally thought of the back being less moved without the air. I was half in bowlback mode, just having finished tuning down a new semi-bowl. It seems to me the back is less moved by the air in this configuration, because the sides are not so perpendicular, and not so isolated. In fact, with no sides, a back is right connected to the top and so it seemed they'd move more as a unit than a ribbed instrument.
So, interesting point. Would one instrument be more affected, would a Gibson style instrument just decay quickly without the back to help move things along, while a bowlback showing more sustain than normal...

[sunburst]

The tuning fork thing just made me think of something else. Pitches (frequencies) would probably be slightly higher without air resistance. The strings would probably go out of tune and who knows what would happen to the plate modes(?). I assume the ones that move the most air would speed up the most in a vacuum and the relationships between the modes might change.

[saintjohnbarleycorn]

the vibration would die of its own weight, you said vacuum not total loss of gravity.

Assuming you are wearing a pressure suit and your mandolin survived its entry to the vacuum environment the issue of sustain would be related to the external causes for the damping of string's vibrations. Strings have an internal component of friction but that would not change from atmospheric pressure to vacuum.

In an acoustic mandolin the primary amplification of the sound created by the vibration of the strings is accomplished by transferring the mechanical energy from the strings to the mandolin's top. Though there would be no sound in a vacuum, that mechanical energy transfer would still occur. Since there would be no air inside the body of the mandolin the only path for the mechanical energy to reach the mandolin's back would be through the sides. This mechanical transfer of energy would not change in a vacuum.

So, the damping of the string's mechanical vibrations would be primarily due to the absorbtion of that energy by the bridge and top. Even in a vacuum the bridge and top would continue to absorb that mechanical energy.

The other external damping factor of the string's vibrations would be friction from the atmosphere. This atmospheric damping would not occur in a vacuum.

Conclusion: Slightly more sustain in the vacuum.

[sunburst]

In an acoustic mandolin the primary amplification of the sound created by the vibration of the strings is accomplished by transferring the mechanical energy from the strings to the mandolin's top.



OK, here's a little nit picking.
There is no amplification, technically, in an acoustic
instruments. Amplification requires some source of
power. The top and back (mostly) convert string motion
to air motion so that the sound is louder, but they
don't increase the amplitude (amplify) the waves.



Though there would be no sound in a vacuum, that mechanical energy transfer would still occur. Since there would be no air inside the body of the mandolin the only path for the mechanical energy to reach the mandolin's back would be through the sides. This mechanical transfer of energy would not change in a vacuum.



I'm not so sure about that. Normally, a lot of movement
is transfered to the back by the air inside the
instrument. Without that process going on I suspect the
mechanical transfer that occurs through the rim would
not be the same. I don't know how it would be different,
though.
...

[steve V. johnson]

I didn't think so much about the effects of the vacuum, per se, but about isolating and measuring the mechanical energy in the mandolin structure, sans the effects of the vibrations in air, more along the lines of John Hamlett's post (the first response to Brian's original).

It seems that the strictly mechanical energy might be calculable... And thus the sustain factors in the structure.

stv

[markishandsome]

I don't see what gravity has to do with it; "vibration" doesn't weigh anything.

I don't think a wooden instrument would explode in a slowly evacuated bell jar, but it would get very dry, which could lead to cracking if you left it in there too long.

I say send one of those newfangled carbon fiber mandos up on the next shuttle mission. The pickup would still work and the signal could be beamed down live. Bluegrass in space! Don't tell the banjo players! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/mandosmiley.gif

[rohan]

Or, have your physics buddy attach a mechanical pickup to the back of the mando's top plate and wire it to an external amp. Attach a mechanical striker for the strings. Put said mano in the bell jar and pumper down. If the length, diameter and tension on the strings do not change then the "sound" detected by the mechanical pickup will be uneffected by the vaccuum. Without the resistance of the air, the strings will "vibrate" for a measurabely longer time. Out in the room, the air is only a medium for transmitting the string vibrations to you ear drum. The loudness of the mando might be inversely proportional to the square of the distance. Meaning, double your distance from the mando and the "loudness" deminishes 75%. Air is not a good conductor of sound energy. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/coffee.gif

Sunburst, try it again.

"The top and back (mostly) convert string motion to air motion so that the sound is louder, but they
don't increase the amplitude (amplify) the waves."

The sound is louder, therefore it has been amplified. The sound can only be louder if the amplitude of the waves is increased. The amplification of sound was around long before electricity was tamed by humans.



"Normally, a lot of movement is transfered to the back by the air inside the instrument. Without that process going on I suspect the mechanical transfer that occurs through the rim would not be the same."

Two different transfer mechanisms going on here. The top moves air which moves the back (wouldn't happen in a vacuum) and a small amount of the energy from the top is transferred through the sides to the back (mechanical transfer that does not require air and would be the same in a vacuum). The sides and back would still absorb some of the energy from the strings.

And guys, don't forget about the internal frictions of the string.

[sunburst]

Neptune, I'll have to leave it to the real physicists among us to explain about the amplification thing because, as sometimes happens, "I've already told you more than I know", but at some time in the past it was explained to me that acoustic instruments don't amplify sound and the explanation made sense at the time.

As for energy transfer through the rim, perhaps the top would transfer more energy through the rim in a vacuum because the energy that is normally absorbed by friction with the air is available to the rim. Also, the back would normally transfer energy back to the top through the rim, but there's no air driving the back in a vacuum, so that would be different. I don't think we can say with certainty that the "mechanical transfer that does not require air and would be the same in a vacuum". Anything you change in a system affects everything else in the system at least a little.

[earthsave]

Our vacuum is not very large and extremely loud so I do not see how you'd possibly fit or why'd you want to play inside of it.

But if you did, you most certainly would literally suck.

[Antlurz]

As far as amplification, my thought go back to a wind up record player where no boost is built in save for the megaphone cone. I guess a redefinition of "amplification" would be in order.

Because of the density of woods used in instruments. I think any remaining air in the pores would be of a very minimal influence. Would a total vacuum even be able to pull it out? I have my doubts. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wow.gif

If they were made from model airplane balsa, probably so, but I seriously doubt a total vacuum could suck all remaining air from maple, and maybe not even soundboard material unless it was exposed for a very extended period, like what would be required to dehumidify a similar piece of moisture. Interestingly, I think there would be a sizeable change in the strings action setup, much like expressed with the addition or removal of moisture from an instrument. .

Ron

[sunburst]

I think a vacuum would probably remove virtually all the air from the wood in about the time it would take a vacuum kiln to remove all the moisture, (all the moisture would be gone too, so it seems to me the wood would shrink rather than swell as KNB's roommate suspected) but we can remove that from the equation by assuming we're using a CF instrument.

I prefer not to see this thread as a discussion of whether or not the instrument can survive or what damage it would sustain but instead as a hypothetical mental exercise to stimulate the mind to thinking about how an acoustic stringed instrument interacts with the air by pondering how it would behave without air. It's a thought that hadn't occurred to me, and it's already given me some ideas of things to ponder about mandolin construction. Hopefully I can learn from or gain insight from the hypothetical thinking and the contributions of others to this thread. I don't think it's just a silly game, but instead a fun but informative mental exercise and I thank Brian for making me think!

[labraid]

Although, water is hard to remove from wood because it is in a weak bond to the cellulose walls. Air has no such bond as none of the "air" molecules have hydrogen bonding sites [ok, I take that back, water vapor is an air molecule, but looking at O2, N2, and the like which are naturally gases at our atmospheric pressure]. There are tremendous gaps in cellulose on a microscopic level, I'm pretty darn sure an air molecule would pass through it like Jello through a 10 year old.
(sorry)

[Chris Baird]

It is an interesting question. A stringed musical instrument is designed to move air. The air in and around a mandolin is typically part of the mechanical transfer of energy. Inside a mandolin it also has its own resonance which is coupled with other body modes and creates some of the strongest sound producing modes. In the absence of air I don't know what would happen to the modes typically coupled with the internal air resonance.

I'm not sure what percentage of a mandolin's energy actually ends up moving air, but, like most systems the majority of energy is lost to internal friction from anything which the sound travels through; strings, wood, finish, human flesh, etc.

There has been some interesting work done with violins tested in a helium environment. The helium changes things.

Some people get kind of anal about the term "amplification". In musical instruments the strings are rather inefficient at "moving air" and thus don't make much sound. The sound becomes more audibal because the energy is transfered to a more effective "air mover" which is the box. However, the amplitude of energy (not sound) is greater at the string than it is coming out of the box (due to losses). In my opinion, this is a type of amplification, however, it is different from electrical amplification in that the energy isn't being increased but rather transfered from a less effective sound radiator to a more effective one.

[Jim MacDaniel]

Lightning round!
If I played my instrument in a vacuum...
No one could hear if you were out of tune. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/mandosmiley.gif

[JeffD]

as a hypothetical mental exercise to stimulate the mind to thinking about how an acoustic stringed instrument interacts with the air by pondering how it would behave without air.
As long as we are picking nits...

Its a real mental exercise, not a hypothetical one.
Its a hypothetical instrument and vacuum.

I'll stop now before you throw something at me. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

By the way, the sound that hypothetical mandolin is not making is sure beautiful.

Then again, all my hypothetical mandolins sound great. You should hear them.

http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

[sunburst]

OK, I guess that's a misplaced modifier(?). I'll re-word that phrase.

...as a mental exercise to stimulate the mind to thinking about how an acoustic stringed instrument interacts with the air by pondering how it would behave, hypothetically, without air.

(That's the only thing I'll throw at ya.)

[Jim MacDaniel]

OK, I guess that's a misplaced modifier(?). I'll re-word that phrase.

...as a mental exercise to stimulate the mind to thinking about how an acoustic stringed instrument interacts with the air by pondering how it would behave, hypothetically, without air.

(That's the only thing I'll throw at ya.)
I'm sure we would all be happy if you threw one of your mandolins at us ;)

[JGWoods]

On the matter of wood in a vacuum I have some experience. My work in optical filter manufacture uses vacuum chambers. We, Barr Associates, have more than 60 in operation now which might make us the biggest optics house in the world.
In the course of doing repairs on vacuum chambers I used to block up parts using 2x4s, and on a few occasions I forgot and left them in the chambers when I was done making repairs and started pumpdown.
Returning in the morning I was disappointed to find the vacuum readings at around 2x10-5 Torr- or low 5th scale vacuum, about what you find in space. We can pump to the -7 scale in these chambers but the wood delayed the pumpdown as it was giving off water and whatever else all night. I vented the chambers and collected my very nicely dried 2x4s for further use. No splits or cracks of any kind occurred.
I wish I had been more attentive and weighed and measured my blocks before and after but I didn't. What I recall was a nice set of musical blocks- good ringing tone from being so dried out.
Overall my guess is that if you put a wooden mandolin under vacuum in a bell jar, or box coater like we use mostly, it would probably do ok, maybe a split or two might happen as it dried out but I don't think much more would happen and it would probably recover just fine after removal, maybe sound a little different until it absorbed moisture and normalized to the environment.

A carbon fiber mandolin would probably benefit from time under vacuum as it is being built, before the resins set up, as it would pull out all of the air bubbles and give a more solid structure. I think that kind of process is common to such manufacture.

[sunburst]

I guess it would kind of expensive to retain the use of one of those vacuum chambers to put a mandolin, mechanical plucker, and measuring equipment in, huh?

[JGWoods]

I guess it would kind of expensive to retain the use of one of those vacuum chambers to put a mandolin, mechanical plucker, and measuring equipment in, huh?
$500 an hour is the going rate for time and materials/R&D work.
Lets see, an hour to load up, 3-4 hour pumpdown, an hour for the experiment, an hour to vent and remove equipment...
$4k- I'm sure there is grant money just lying around waiting for your application.

Then if you want the fancy phd guys to write up results...$$$


Barr (http://barrassociates.com/)

[Dave Cohen]

There is already enough known about damping to point you in the right direction. There are three major damping mechanisms; (1) air or viscous damping, (2) internal damping, and (3) losses to other (coupled) vibrating components. For strings, (1) dominates for steel strings, (2) dominates for gut and nylon stings. All strings suffer losses in a complex way to (3). In the absence of air, strings will sustain longer. So will the body motions, which will in turn take away from string gains due to the loss of viscous damping. At least, it will take away at some frequencies. Of course, sound radiation is the propagation of vibrations in a fluid, so in a vacuum, none of the vibrations would result in audible sound.

Since there would be no air, either inside or outside the soundbox, for the body motions to couple with, the modal frequencies would not be the same. The main body resonance in the presence of air is normally a doublet, occasionally a triplet. It occurs at ca 250-320 Hz, and again at 350-460 Hz. Take away the air, and you would usually have a single main body mode somewhere above 300 Hz (at least in f-hole mandolins). Maybe occasionally a doublet due to the weaker interaction of the top and back plates. And so it would go for the higher body modes.

I don't think that the bandwidths of the modes would be affected very much, as they depend significantly on internal losses in the wood.

I will have two specific characteristic time vs frequency examples for mandolins in the chapter I am writing for the Springer-Verlag book. In the meantime, the Fletcher & Rossing text has a good section on damping, pp 53-56.

[labraid]

I love applicable math and equations with no unhidden fervor, but the thing I like about Dave's responses is the use of words and ideas instead of seemingly endless equations in Fletcher & Rossing.
So this just brought up another interesting (to me) question. If one were to perfectly tune an instrument (the body, holes, etc, not the strings necessarily) in Virginia Beach, and send said mandolin off to a virtuoso hermit living on Rocky Top.. Would it just not sound right? Atmospheric pressure differences... This would also raise the body modes, etc it seems, until everything didn't work _as well_ together anymore... Correct?

[Geoff B]

Amplification- from what i've learned, it is the boost of an original signal by an outside source. #As someone mentioned, the energy from the strings is actually less at the soundboard from various damping encounters. #What makes the *sound louder* is that the energy from the strings (though less) is interacting with *more air*. #In this case, louder does not mean amplified. #Amplified only means louder in the varnacular, not in "physics talk."

[Dave Cohen]

Brian, in my case, the words and ideas go hand-in-hand with the math/physics. Some people have a real aversion to the physics/math, so I try to make it "accessible", as I did in lower-division courses. But the math is a much more compact and efficient way of expressing the ideas. You are at the most general level of understanding when you have a PDE (or its' vector/tensor/matrix equivalent) and the boundary conditions to your problem.

Regarding your question about transporting a mandolin to a different location, I don't think that the differences are enough to make a great sounding mandolin sound less great. From the modal analysis I have done on several vintages mandolins and several of my own, the air resonances are pretty consistent, but the body mode frequencies vary quite a lot. Studies of Golden age violin family instruments also found that body mode frequencies varied a lot, but there were certain relationships between radiation output in certain frequency ranges that characterized the "great" instruments.

[mrmando]

Hm. Well, would a vacuum chamber be any good for drying out freshly cut tonewood, then? Better results than a kiln? As good as air-dry seasoning?

Sorry to get so practical in the midst of a hypothetical discussion.

[mandroid]

another $0.02 the act of the string vibrating is a flexing of the music wire,
and as you can feel when you flex a metal coat hanger it warms up.

so part of the vibrating string decay is lost in heat , and that would be independent of air resistance.

[Dave Cohen]

Mnadroid, what you are referring to is part of the internal damping; it is not a separate damping mechanism.

[Steve Ostrander]

Where can I get a research grant for this? I think a couple million would get the job done. Or I could ride along on the shuttle and play my mando--I would need a new Weber, of course, courtesy of the NSA-- and conduct the experiment. This is vital to our nation's security, so maybe Homeland Security will pay for it.

[Rick Turner]

I'm with John. There's no amplification because that involves controlling an outside power source. Acoustic instruments are mechanical impedance transformers. They transform the mechanical vibration of the strings into plate vibrations which are better suited to moving air. This is analogous to the role of a transformer in electrical circuits which can step voltage up while stepping current down, and vice versa.