General Question

Dog's avatar

Science of compression: Why does opening a can of beer sound louder than opening a regular soda?

Asked by Dog (25046points) June 3rd, 2008

The sound of opening a can of beer is distinctly different than opening a soda of the same size. Any theories as to why?

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27 Answers

wizard's avatar

The size of the can is different, allowing more air to become compressed inside of the can. When you open it, you are hearing a different sound because a different amount of compressed air is being released from the can. With more pressure built up inside, it gives the can a more powerful release.

Dog's avatar

Great theory- but I opened two cans same volume, one soda the other beer. Beer was audibly louder. Capacity was the same.

wizard's avatar

It may be the shape of the can. But that baffles me as well.

El_Cadejo's avatar

Look at the mouth size though. Beer generally has a much larger mouth then soda thus allowing it to release all at once making it louder. Just a theory though.

ebenezer's avatar

I think the noise difference is mostly due to the exuberance with which one usually opens a beer can.

susanc's avatar

ebenezer is right. according to a massive 2005 study, beer is simply more important
than soda to 92 per cent of adults polled, and the mere approach of a can of it heightens sensory sensitivity. You can
look the study up under Beer vs Pop: The Scoop, in the Journal of Exuberance. Sorry,
not sure of authors.

shrubbery's avatar

Different fizziness?

shrubbery's avatar

And sugar content? And ingredients?

Harp's avatar

Soda has a much higher specific gravity than the beer does, so that for a given volume, the can of pop will weigh more than the can of beer. Opening the can and releasing the pressure sets up vibrations that we hear as sound, but those vibrations have a harder time getting that can of pop moving than the lighter can of beer. It’s like the difference between tapping a thick steel plate and a thin sheet of steel; for the same amount of energy applied, the thin sheet will resonate louder than the plate.

Dog's avatar

Harp- Great Answer!

As much as eagerness to open it appeals to me as a factor I decided to experiment last night again but with my assistant blindfolded. There was a still a distinct difference in sound even when the subject did not know which can she was opening. Specific Gravity- THANKS HARP!

mvgolden's avatar

I think it is due to a phenomena called a Helmholtz Resonance. It is an acoustical resonance that is created by the air in the bottle acting like a spring and the air in the neck acting like a slug of mass. Thus you have a simple spring mass resonator.

In order to calculate the “mass” at the neck you have to know how big the diameter is and what the neck length is. Depending on bottle shape the volume of air can be difficult to compute since you are not really sure where the neck ends and the volume of air begins.

Changes to any of the dimensions can have a profound impact on the frequency of resonance.

The presence of different different gases can also have a strong effect on the frequency of resonance.

Since resonator shape and gases present in beer vs soda is most likely different it is reasonable to assume that they will resonate at different frequencies and thus sound different when opening.

At least that is my best guess. Nothing like a question combining two of favorite topics. Beer and acoustics!

Harp's avatar

But the described effect involved cans, not bottles, so its hard to imagine much of a Helmholtz affect. Also, the gas would be CO2 in both cases.

mvgolden's avatar

@Harp, are you sure the openings are the same size? don’t most beer cans come with “Wide Mouths”?

Harp's avatar

No, I’m not sure about the openings, but my understanding of Helmholtz resonance is that the size of the opening wouldn’t play into it. It would be a function of the mass of the gas below the opening.

mvgolden's avatar

The size of the opening is important. Look at the wikipedia link. The res. freq is proportional to the sq root of the area of the neck and inversely proportional to length of the neck. Further, it is not so much the mass of the gas below as it is the gas’s compliance.

Looking back at your earlier response. I am not sure the specific gravity will have an effect (btw I apologize if I am screwing up affect and effect, I’m an engineer after all). Both beer and soda will damp any vibrations in the metal of the can. For that matter your hand should do a good job of that too.

Harp's avatar

Wouldn’t that mean that the frequency of the beer can would be higher by virtue of its larger opening, and wouldn’t that result in lower amplitude for a given induction? If so, that wouldn’t be consistent with what Dog’s reporting.

I also wonder whether we should even consider the size of the opening given that the noise of the escaping gas occurs even before the mouth is fully open.

Since the Helmholtz effect comes from the oscillation of the gas in the neck space, would that even be possible in a scenario like this where you have a forceful one-way movement of the gas?

mvgolden's avatar

Are you sure that is inconsistent with Dog’s comments. All Dog really said (at least how I read it) is that the two sound different and the beer sounds louder

There is still some effective size as the can is opening.

I think, but I am not sure, that even the forcefull one-way movement will set up vibrations as the flow dissipates. (Any fluid dynamisms out there?)

My question to Dog, do you have a sense of what the pitch of the sound was as it opened. If the beer was louder and higher pitched it still could be a Helmholtz resonance. Since the human ear does not hear all sounds at equal volume

If it is not a helmholtz effect it could be more of a simple pipe resonance, much like a brass instrument. In brass instruments the longer the pipe the lower the note. If we look at the necks effective length that may explain it. I don’t have my acoustics text book at home, but I think the bigger the area the long the effective length. That would give the larger beer can opening the lower note. I think.

Harp's avatar

My suspicion is that the vibration is generated by the rush of the gas past the lip of the opening, which would set the membrane-like top of the can vibrating (like the reed in a woodwind instrument). Then you’d have a system analogous to a crystal glass with liquid in it that you set vibrating by rubbing the rim. The vibrations propagate down the sides of the container and are damped by the liquid. I just tried this with two glasses that have the same resonant frequency (empty). I put water in one, and an identical volume of alcohol (lower specific gravity) in the other. The glass with alcohol resonated at a higher frequency, which indicates that the alcohol had less damping effect than the water.

mvgolden's avatar

OK, I just pulled out two wine glassed and put equal amounts of water in one and OJ in the other and then tapped then with a knife. The OJ did resonate at a lower freq. I have no idea why but I will give it to you that specific gravity does have something to do with it. I will hit the book tomorrow. I will take a look at The Physics of Musical Instruments (Harp since you build your own harps you might like it)

I just don’t buy the rest of your theory yet. If the rush of air, vibrates the tab or the rest of the top I would expect it to be at a MUCH higher frequency then what I typically hear when I open a can. The tab and the top are far to small to support anything but very short wavelengths, and thus high frequency, waves

The other reason I doubt buy it is that if it is behaving like you describe, then it would not take much to damp the vibration on the side of the can. If you take those same glasses you had and even lightly touch the sides of the glass all, or at lease most, sound will stop. Since you usually hold the can in your hand, all vibration would be damped out.

Harp's avatar

Well, I did try the hand on the glass back at my first experiment. I think the difference is that you’re tapping, and I’m rubbing. The touch of the hand kills the “sustain” of the vibration, so that a single tap dies instantly, but as long as you have a constant induction source, like with the rubbing, you can perpetuate the vibration. There is definitely a limit to how much contact the glass system will tolerate, though.

I have actually checked out the Physics of Musical Instruments from my library. Cool stuff.

Well, I’m not quite sure to go with this from here, but I’d love to hear if you figure something out. Thanks for hashing this out with me, it’s been a gas ; )

Response moderated
Harp's avatar

And there you have the sound of a Flutherer decompressing

Response moderated
Cruiser's avatar

The alcohol in beer is a volatile and that will contribute to and exacerbate the CO2 gasses EXPLODING from the opening of the can over just an ordinary can of soda. Kinda of like comparing a firecracker to an M-80 firework.

Dog's avatar

@Cruiser Six LONG years later I have my answer! High-5 and many thanks!

Cruiser's avatar

@Dog I think this deserve a toast!

Dog's avatar

Agreed! This round of beer is on me!

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