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Comment by Tanoc | Hacker News Reader

This is something I noticed as a kid. We had a creek in our backyard, which,depending on the temperature the water would be louder or quieter. This annoyed our dog, which after a number of times caused me to notice. Running water is louder and much more sharp when it's cold out, and quieter and muffled when it's hot out. In the same way sounds are louder in a colder environment because there's already a low level of ambient energy contained in the air and so the energy disperses much more readily but dissipates much more quickly. Essentially a difference between a quick "crack" and a lingering "whump" in terms of auditory impact. This effect also propagates to solid materials, as cold metals and ceramics transmit sound better than warm ceramics or metals. A church bell quite literally is louder on a cold winter's day.

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There is nothing like a small waterfall in a deep snow on a snowy day. All other sound is muffled by the snow cover and further dampened by the falling snow.

But the creek will ring like a bell. You can't hear it until you're almost on top of it. It's higher pitched, and will almost always have a tempo based on the shape of the bed of the falls.

There's a waterfall on our farm. It plays music in January. It's amazing, and no one believes me.

Next January you should get an audio or video recording. I'd love to hear that!

I would presume this is like capturing rainbows or beautiful skies by photo. Harder than it seems. You can’t capture the dampening effect of the environment by (regular?) microphone.

When I used to bake bread commercially early in the morning, the sound of the HVAC, proofing and baking systems would sound like music to me in concert. I can't tell if I was just hallucinating or what, but something about your experience reminded me of it.

My thought on the general "loudness" of cold months was due to reduced noise blocking or absorbing greenery like tree leaves, grass, etc. Which is then altered by a significant snowfall leading to sounds being softened again.

Shouldn't that be an inverse relationship though? Without leaves on the trees you should get less reflection, consequently more of the noise should radiate upwards. Unless you're standing at the other side of a bush/greenery. In that case it definitely absorbs a lot

Lots of small unaligned surfaces, like leaves, scatter the sound and make it interfere with itself. Reflection only makes the sound louder if you have large smooth flatish surfaces.

Ah, I had never considered the interference aspect of sound reflections

I want to make a joke about the "three leaf" problem in acoustics, but I can't find a way to make it funny. Dang.

You made me chuckle. Mission accomplished.

HN is becoming worse and worse everyday :(

Assuming your comment is serious (rather than some quip), I think what we're seeing is differing visions for HN.

One group (me included) enjoys some levity, as long as it's high quality and doesn't get in the way of substantial discussions.

Another group would prefer that HN avoids that entirely.

It mostly seems like a matter of taste / preference, so I'm not sure how we can come to one kind on this, shy of seeing the pro-humour approach clearly hurting the site.

Usually I see high quality humor make it through. The low-effort Reddit quips get cratered.

The volume of water flow should/would also vary at different times of the year, based on how much the water table is loaded.

Not sure how much of this would be complimentary to the acoustic effect of temperature. Either way, it’s not a simple single-solution explanation.

My guess is that frozen terrain is harder, which reflects more sound and makes hitting it noisier.

Cold air is also more dense, less momentous, and can transfer sound energy more efficiently between particles than hot air where the particles are spread out and have their own momentum to maintain rather than the sound's.

No one here has mentioned temperature inversion [0] which is responsible for a lot of the cold-induced amplification perceived in urban areas. It's quite a fascinating effect.

[0] https://wisconsindot.gov/Documents/doing-bus/eng-consultants...

Could the audible difference be related to varying sound propagation through hot/humid vs cold/dry air?

I think it's this. Sounds are very different based on the temperature and humidity of air. I have a piano at home and the difference is huge and very apparent over time.

Does your piano have a wooden body and sound board?

I'm sure piano techs are all over this topic, but (as a layman) I could imagine the wood's water content being quite relevant.

Piano soundboards are almost always wood. There are a handful of companies that offer carbon fiber soundboards but they are very rare and expensive. As the soundboard gains moisture, it swells and buckles as it has nowhere to go, which makes it louder and also raises the pitch a bit as the strings are pushed a bit. When it gets drier, it goes flat (structurally and musically). If it has been too moist, the wood cells will be compacted and crushed. If it is then dried, it will form cracks as the wooden structure rips itself apart when shrinking again.

A piano soundboard that has been built and kept in a desert for instance will not crack. But if you take a piano from a ~55% humid country and put it in a desert (or overly air-conditioned room! or right in front of a heat radiator!) it will die.

Does a swollen soundboard noticeably affect pitch even when the piano has a cast-metal harp?

The one harp I've seen up close was in an upright piano I disassembled, and that harp was solid.

The harp doesn't actually lie flush on the soundboard; there should be some space in between. The harp is just there to bear the tension of all the strings. The strings are connected to the soundboard via a wooden so called bridge, which is a raised wooden element glued onto the soundboard. It has pins in it which the strings are held against in tension. Bridges have a coating of graphite usually, and combined with the fact that most notes have 3 strings, it creates kind of a blocky pattern.

Here you can see a soundboard, bridge, and hitch pins on the harp. The hitch pins on the harp can be seen up top, then in the middle the bridge and bridge pins, and then below that the soundboard. The hitch pins are located on the opposite side of the keys in a grand, or on the bottom of the piano in an upright. You can see on the right of the image that the harp has a structural element which floats over the bridge, with plenty clearance.

https://www.chuppspianos.com/wp-content/uploads/2014/03/Stei...

P.S. In some pianos you can really hear a metallic undertone produced by the harp, I find Yamaha pianos have a distinct sound that has it.

It’s important, and can change the tuning in spring and fall cycles

most of the US is too dry in the home, and humidification is helpful for all wood in your home - to a point of course. Approx 55% is optimal

Of course in the south it’s the exact opposite - but A/C usually solves the problem.

Every homeowner should monitor their indoor humidity, it’s important for, wood floors, door trims, wood furniture, and our own health. Too much causes mold, too dry is hard on your respiratory system

My piano has a Dammp-Chaser automatic humidifier and dehumidifier system that works well. My piano tech uses a moisture meter to check the soundboard at tuning time and the wood’s moisture has been fairly stable for more than two decades.

Absolutely not. I first noticed this when visiting Iceland. The hot streams bubbling out of the ground sounded the same as boiling hot water being poured from a kettle, not the kind of cold-water stream sound you'd normally expect in the north in winter.

You can try it yourself. Take two identical kettles, boil the water in each of them and pour it somewhere. Obvious difference.

I'd imagine there may also be a component of sound bouncing off things? I think stuff contracts and expands when it hot or cold? So maybe something that is cold and contracted bounces the sound sharper too? Noooooo clue if that makes any sense, just a bunch of guessing from high school science class.

I don't think so. If I pour hot water into a mug from the kettle, it sounds different with cold water with all the same equipment, room etc

That's my feeling as well. I can hear when the hot water has reached my shower.

I hear the same with my shower, but I'd wager most of the change in sound would be to do with pressure change between the hot and cold source.

That was what I thought at first too. However if it were pressure change, the sound would change when you move the knob, not when the hot water reaches the shower.

Also it's more-or-less the same pressure. It's the cold supply pressure pushing water out of your tank or through your tankless water heater.

Yes, the thermostatic mixing valve is worth understanding- it’s pretty neat.

In most plumbing (at least in the US), there is no difference in pressure between hot and cold because the hot input is the same cold water source.

That doesn't surprise me at all. I can tell hot water from cold by how it looks when you pour it, (steam aside).

I turn on the tap in the sink in the bathroom, when waiting for the hot water coming from the cistern. The water in the pipes have cooled down over night. I can hear the difference in the sound when it splashes in the sink, when it is hot. So yeah.

That is definitely a thing, but I can tell when the hot water arrives at the bathroom tap by the sound of the water hitting the bowl. So it’s the water too, I’m pretty certain.

Thank you for the great anecdote and explanation, it was fun an very illustrative to visualize the concepts while reading your comment

The video is also excellent.

https://youtu.be/9w3Zl3KBDpI

The intro was hilarious! Thank you :)

You controlled for the volume / depth of water, which for the same mass would be greater when warmer, and the resulting changed interaction with objects ...?

I wonder how well it maps to notions of a “cold reverb” or “warm synth” in music production.

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