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Comment by CarVac | Hacker News Reader

I don't think it's entirely wrong, at least for violin-family instruments.

If I put my hand near the f-holes on my cello while I play, I can feel a shocking amount of airflow in and out of the body.

The sound emitted by the holes is indeed unbalanced because that's dominated by the resonant frequency of the instrument, but that's a large part of what gives the instrument such acoustic power.

...

Additionally, it does make sense that the sound is more efficiently emitted by narrow holes with lots of edge area: it's like the skin effect in electrical conductors at high frequencies, where most of the current flows near the surface of wires, rather than in the bulk.

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The air is flowing because it's a tuned resonator, not because it's making sound. That's how the tuning port works. Sound does come out of the hole, but only incidentally. Its value is tuning the chamber, not releasing the sound. The sound would be radiated regardless, conservation of energy and all that.

I think the F shape has a lot more to do with limiting mechanical stress points for cracking. A round hole with the same area as the f-holes would weaken the top and create changes in how the soundboard vibrates. It's different on a flat-top acoustic guitar, where bracing rather than carving governs the strength of the top, and bracing also limits the valid locations for soundholes.

Energy conservation doesn't come into play, because unlike on a plucked instrument, the bow is there continually supplying vibration. If more of it gets emitted, then more of the bow's energy goes into vibration instead of friction.

On the other hand, with a guitar, the more efficient a radiator it is, the louder it is but the less it sustains, because each pluck imparts a fixed amount of energy to the instrument.

Energy is conserved, but you may end up with heat instead of sound. Also, sound near an object behaves differently. As you stand further back you get constructive and destructive interference between different parts.

Beyond that we operate on a logarithmic scale when it comes to sound, what sounds slightly louder to us can be heard over much larger areas.

My unscientific opinion as a guitarist is that thermal loss isn't a dominant factor. Most of the energy put into the instrument is converted to sound.

Admittedly, guitars are different from violins here, but... with a guitar, there's a pretty fixed amount of energy transmitted when a string is plucked. This energy may radiate quickly or slowly. In other words, there's a tradeoff of attack and sustain. An exaggerated case it the banjo. A banjo is loud, but has little sustain. An unplugged Les Paul electric makes little acoustic sound, but sustains for many seconds. Within the narrower world of acoustic guitars, small-bodied guitars tend to be apparently louder, but not as rich as large-bodied guitars, due to this attack/sustain tradeoff.

Sound contains far less energy than you might expect.

80 decibels, ~= 0.001 watts of energy. https://en.wikipedia.org/wiki/Sound_energy_density_level

PS: And yes most home speakers ~1% efficient. https://en.wikipedia.org/wiki/Loudspeaker#Efficiency_vs._sen... At scale they can get into the 20% range, but even that suggests guitars are probably not that efficient overall.

From experience, an acoustic guitar is about as powerful volume-wise as 1/2 to 1 watt electric guitar amp with a moderately efficient speaker. And there just isn't a whole lot of energy transmitted from a guitar pick to a string. Whatever the efficiency is, there aren't wide variations in acoustic guitar volume that can't be explained by the attack/sustain tradeoff.

Bowed instruments get around the attack/sustain tradeoff by having continuous energy input, so the attack strength can be sustained for the duration of a note.

My cello is particularly resonant, and in hindsight (is this confirmation bias talking?) has very little sustain on pizzicato (plucking) compared to my cheap, less-resonant student cello.

When I was learning violin, I used to mess around with my violin to understand how it worked (it was a very cheap one). One of the things I noticed was the covering the holes with paper changed a lot the tone of the instrument but very little the power of it.

Also, my violin teacher had a couple of superb (and very expensive) old violin. And there was a lot of variation in the shape of the f from instrument to instrument. Different f-holes give different "character" to the sound but the impact on the power was really limited.

One of the things I noticed was the covering the holes with paper changed a lot the tone of that instrument but very little the power of it.

That's why violin mutes, which allow a violinist to practice quietly, attach to the bridge...to reduce the transfer of vibration to the chamber via the sound post and bass bar...

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