Traffic Louder in Rain: True or False?

[wolram]

I am sure this is true, traffic sounds louder when its raining, do you find it so?

 

[brewnog]

Yes. Splassssshhhhhhhh.

 

[Evo]

Yes, it does. You have the added sound of water and dirt and rocks being churned up and thrown by the tires.

 

[Danger]

Damp air is denser, and thus conducts sound better. Same reason that someone in your neck of the woods hears things from farther out at sea on a foggy day than on a clear one. I can't help thinking that you are a neighbour to, and close friend of, Shrek, so you must know what I'm talking about.

 

[Proton Soup]

Damp air is denser, and thus conducts sound better. Same reason that someone in your neck of the woods hears things from farther out at sea on a foggy day than on a clear one. I can't help thinking that you are a neighbour to, and close friend of, Shrek, so you must know what I'm talking about.

air's also generally colder, which transmits sound better.

 

[Danger]

air's also generally colder, which transmits sound better.

Yes, absolutely. I inadvertently overlooked that in my post, although I was thinking it. Cold equals dense. Thank you for pointing that out.

 

[Andre]

Damp air is denser,

Is it? assuming that by some physical laws the number of molecules is the same for any giving temp and pressure then the density of the air/gas depends solely on the molecule mass. The bulk of the air is N₂, with a weight of 28 and O₂ (32), making the weight of one mole of air around 29 gram. Now a water vapor mole is only 18g

 

[Pianoman14]

Definitely. Puddles make most of the noise in my experience. (I actually enjoy the swoosh swoosh).

 

[Borek]

Cool equals dense, I have to remember that.

 

[Danger]

Cool equals dense, I have to remember that.

Alright, you smartasses and Andres...
What I meant was that damp air is usually colder than dry air, and thus has higher density. No matter what numbers you trot out, I can absolutely guarantee that I can stroll around at 0° C without needing my inhalers, and can barely go 20 steps on a hot day. Same for my vehicles, which always gain something like 10 or 20 hp on a foggy day.
Andre, really... are you going to tell me that an aeroplane performs as well on a hot day as on a cool one?

 

[JaredJames]

damp air is usually colder than dry air

I'd say the tropics have about as damp air as you can get and they certainly ain't cool...

And don't the polar regions have the driest atmospheric conditions on Earth?

Andre, really... are you going to tell me that an aeroplane performs as well on a hot day as on a cool one?

Isn't that down to lift production, not engine efficiency? I also don't see what that has to do with there being moisture in the air and it's effect on temperature.

 

[Danger]

Those are extreme circumstances, Jared. Where I live, it is always colder when damp and I've been led to believe by Brit friends that the same applies to the English countryside where Woolie resides. I might be mistaken about his area, but not mine. I went out for a walk earlier, when it was -8°C, and didn't even take my inhalers with me. It finally got to me after over 5 hours and I had to come home, but I couldn't have lasted even 2 hours in summer.

 

[Borek]

And don't the poles have the driest atmospheric conditions on Earth?

No, it is quite damp here.

Edit: hey, you have edited your post!

 

[JaredJames]

No, it is quite damp here.

Edit: hey, you have edited your post!

I saw the joke coming.

 

[JaredJames]

Those are extreme circumstances, Jared. Where I live, it is always colder when damp and I've been led to believe by Brit friends that the same applies to the English countryside where Woolie resides. I might be mistaken about his area, but not mine. I went out for a walk earlier, when it was -8°C, and didn't even take my inhalers with me. It finally got to me after over 5 hours and I had to come home, but I couldn't have lasted even 2 hours in summer.

I'd say the tropics and polar regions (antarctic in particular) are a fairly large area.

So far as Britain goes, not entirely sure what you're on about. The country itself is wet in the Wales/Scotland areas but fairly dry in England. Temperature wise it's a fairly even spread from winter to summer. Nothing that tells me wet = cold.

 

[JaredJames]

air's also generally colder, which transmits sound better.

Sorry, I thought I remembered a thread on this.

Warm air transmits sound better due to the higher energy of the molecules and the increased likelihood of collision with other molecules. Density has little to do with it.

https://www.physicsforums.com/showthread.php?t=448575

If you think of the time needed for one molecule to travel to the neighbouring molecule and then to transfer its momentum (crude mechanical idea but sufficient for this purpose). This tells you the speed at which the 'influence' of vibrations can pass through the air will increase as the molecules travel faster. If the gas density increases then a molecule will meet another molecule in a shorter time but that molecule will need to travel again before it meets a third molecule. The time for the actual 'influence' to travel over a certain distance will, thus, only depend upon the average speed of molecules and not how close they are together.

Furthermore, for solids, the speed of sound depends upon the stiffness (modulus) and the density. Faster for stiffer, slower for more dense. For two substances with the same stiffness, the more dense one will transmit sound slower. If this is counter-intuitive, it's because our experience is that more dense materials are usually / often more stiff.

 

[Gokul43201]

I know of no good reason to expect that wetter days are colder (the converse, however would seem likely), but even if they are, I think that's probably a smaller effect than what dominates any differences that the average human ear can detect easily, and the average human brain can retrieve and compare from memory.

Also, the discussion about sound velocities is somewhat irrelevant (though it is true that temperature, rather than density, plays the dominant role in determining sound velocity). What matters is sound attenuation.

See, for instance: http://www.sengpielaudio.com/calculator-air.htm

At a distance of 30m (100ft), which is not unreasonable for window to road separation, the difference between a day with 10% RH and a day with 90% RH is about 5dB or so, which is nearly a doubling of sound intensity on a damp day (relative to a dry one)! I think that's something a person might notice and remember, though I couldn't say I personally have. Still, this is a little bit removed from the sound of traffic heard during rain. I would imagine the sound of the rainfall to have a more significant effect on one's perception, and would do more to mute the traffic sounds than the humidity does to preserve it.

 

[JaredJames]

Also, the discussion about sound velocities is somewhat irrelevant (though it is true that temperature, rather than density, plays the dominant role in determining sound velocity). What matters is sound attenuation.

The claim regarding sound traveling better in "cold dense air" was made and I simply corrected it. I wasn't implying anything regarding a reason for "traffic being louder in the rain".

Personally I think it comes down to there being more variety in the sounds heard (and ones you're likely to hear) on a damp day. For example, on a dry day you just hear a vehicle going past. On a wet day you may hear various splashes of puddles and spray, so you are more likely to notice it.

 

[Gokul43201]

The claim regarding sound traveling better in "cold dense air" was made and I simply corrected it. I wasn't implying anything regarding a reason for "traffic being louder in the rain".

I guess it comes down to what one means by "traveling better". I would imagine that still refers to sound attenuation rather than speed. In any case, I agree with you about the secondary sounds. We just don't know if wollie is including that in his perception, or if he's just hearing louder vroom-vroom sounds.

 

[JaredJames]

I guess it comes down to what one means by "traveling better". I would imagine that still refers to sound attenuation rather than speed.

I can go with that. But I'd say that the slower sound travels through a material, the less well it travels. I don't know how that affects overall distance traveled though, so I suppose that's where attenuation comes into it.

I've looked at your graph and a number of others and they do vary somewhat. There is one that shows you get about 0.5db of attenuation from 10 to 30 percent humidity, but unlike yours it doesn't show the levels of attenuation to be the same.

Yours: 10% = 1.8db (over 30m)
Other: 10% = 0.8db (over 100m)

Not much I know but would certainly alter the 'end conclusion'. So I'm not sure what to make of the actual numbers, but I do agree regarding there being more attenuation at lower humidity.

 

[Gokul43201]

Do you have a link?

Here's another one I found: http://www.csgnetwork.com/atmossndabsorbcalc.html

Numbers agree pretty well (for the handful I checked) with those in the figure above.

 

[JaredJames]

http://www.sfu.ca/sonic-studio/handbook/Sound_Propagation.html

Under section 2:

From the diagrams it can be seen that for the middle of the speech frequency range (2 kHz), the absorption is typically .25 dB/100 m for 30% relative humidity and 20°C (68°F). It should be noted, however, it can be as high as 5 dB/100 m at 8 kHz when the temperature is 20°C and the humidity is 10%.

(Emphasis mine)

I'm no expert on this, it just happened to be something I noted when I looked it up. This shows 5dB per 100m for 8kHz, not 6.5dB per 30m as per your diagram.

You can note the graphed values are significantly different too.

 

[Gokul43201]

Hmm... I don't know why the numbers are different. The trends seem to agree but the difference between 5dB and 2dB could well be the difference between an easily noticeable change in volume and one that's a lot harder to tell, so I reserve judgment on that for now. Your link also says this (which is useful):

Precipitation, rain, snow, or fog, has an insignificant effect on sound levels although the presence of precipitation will obviously affect the humidity and may also affect wind and temperature gradients​

 

[wolram]

I can not explain it much better, but on a dry day the (wosh) from traffic is quieter than on a wet day. i notice this more as it is the first time i have lived within ear shot of a busy road.

 

[Jonathan Scott]

So far I've not seen any mention in this thread of another important effect, which is that a temperature gradient near the ground can cause sound to refract significantly upwards or downwards.

When sound is refracted downwards (because the ground is cooler than the air), sounds from further away are unusually loud, but when it is refracted upwards (because the ground is warmer than the air), distant sounds become unusually quiet or inaudible.

 

[Andre]

Makes me think of one of our shooting/bombing ranges on an island on the beach. Sometimes the explosions went hardly noticed to the surrounding, sometimes the windows burst out of the sils in the neighborhood. It costs us a fortune to find out the reason but eventualy the range was not used anymore under certain meteorologic conditions, that seemed to amplify the noise.

 

[Danger]

I'm beginning to suspect that all of the dispute here is based upon interpretation rather than actuality. I know what I wanted to express, and stand by it, but it is entirely likely that I used the wrong terminology. My apologies if that is the case.

 

[JaredJames]

Even the fact it fills our resevoirs? Waters our crops?

 

[xxChrisxx]

So far as Britain goes, not entirely sure what you're on about. The country itself is wet in the Wales/Scotland areas but fairly dry in England. Temperature wise it's a fairly even spread from winter to summer. Nothing that tells me wet = cold.

Hmm, something tells me you are from the south with your irritating clement weather. It's always raining in Manchester.

 

[JaredJames]

Hmm, something tells me you are from the south with your irritating clement weather. It's always raining in Manchester.

I'll take Manchester and raise you Wales (Scotland to win).