# How loud is a river at 100 foot distance? [closed]

The river is 60 feet across and flowing about 10 feet per second at its fastest point. It has boulders but no real whitewater. It is too deep and strong to cross by foot.

So, it looks pleasant, but you would not be able to cross it.

You are sitting 100 feet away, uphill about 20 foot elevation, and there are only a few trees between you and the river. There is no wind. The only other sound is insects, birds.

How loud is the river? Either in decibels or relative to the other sounds.

Edit:

I am not certain if this is a world building Q or not; happy to delete. I am building a world very similar to earth where the people have additional traits. Thus, their challenges may overlap ours considerably, but their choice of response may be different due to additional physiological resources and the added complexity that brings

In order to think through how this set of variables interacts, in one instance, I am trying to think through the details of experience, of being near a river. Sound is one consideration.

• probably audible but not too loud Commented Aug 28, 2017 at 16:20
• 30 meters? In the absence of sound pollution you can hear it well enough; it's not loud (a person near you won't have any trouble understanding a whispered sentence), but it's clearly heard. Source: personal experience on multiple occasions. Commented Aug 28, 2017 at 16:25
• I'm not sure how this is worldbuilding, really. As far as I can tell, it's not about creation of an element of an imaginary world or setting. Can you edit to elaborate on how this relates to building a world?
– user
Commented Aug 28, 2017 at 17:01
• 10 ft/s is just over 3 m/s, it is fast. Even without whitewater and rapids, this river will be loud. I would think it's more than 40 dB, but less than 60 dB. Commented Aug 28, 2017 at 17:32
• In response to the recent edit: For that type of question, it's very often better to ask about how factors interact so that you can determine the answer yourself, than to ask about the outcome of the very specific scenario that you have in mind. This question might not be salvagable without invalidating Octopus' answer, and invalidating answers is something that should be avoided, but maybe you can post a new question more along the lines of how to determine how loud a river would be at some distance in a specified environment; i.e., which factors contribute, and how? That might work.
– user
Commented Aug 28, 2017 at 17:54

According to information found at Safe Environments, the sound you describe would be measured at around 40dB.

It's a little hard to pin down exactly the environment you describe, but this seems about right relative to the other sounds they list.

The intensity of some other sounds to compare to:

140 dB   Threshold of pain, Jet Engine at take off
110 dB   Angle Grinder
100 dB   Nightclub, Motorcycle
90 dB   Lawnmower
85 dB   Compliance A weighted noise levels for NSW  WHS Regulations
80 dB   Alarm clock
75 dB   Vacuum cleaner
70 dB   Taking a shower
60 dB   Normal conversation
40 dB   Running water of a creek     <-- The river you describe
30 dB   Library
20 dB   Leaves from the wind
10 dB   Pin dropping
0 dB   Threshold of hearing

An increases in 10dB is typically sensed as roughly twice the volume psychoacoustically, although this changes from person to person and is somewhat dependant on frequency, but this is roughly correct.

For reference an increase in decibels can be described as:

+10 dB is the level of twice the perceived volume or twice as loud (loudness) in psychoacoustics − mostly sensed
+6 dB is the level of twice the (RMS) value of voltage respectively sound pressure − mostly measured
+3 dB is the level of twice the energy or power respectively intensity − mostly calculated
• Oh no no no. Loudness increases linearly with decibel value. (Well, at least for sounds not too feeble nor too strong.) An increase of 10 dB corresponds with a ten-fold increase in physical sound pressure. See the Weber–Fechner law: the sensation increase arithmetically when the stimulus increases geometrically. There is a nice picture in the Wiki article on loudness, comparing loudness in phons and sound pressure in decibels. Commented Aug 28, 2017 at 16:55
• Oh @Alex, Alex, Alex. That is covered in detail in the link. As I stated here, 3dB corresponds to a doubling of energy which corresponds to what you said is ten fold at 10dB. This is entirely different to what we perceive though. Did you check out the linked article? In any case, this is all irrelevant to the question asked, it was merely added as an aside to interpreting the data. Commented Aug 28, 2017 at 17:06
• By definition 10 decibels are a factor of 10. The vulgar logarithm of 2 is close to 0.3 to that 3 dB are close to a factor of 2. And even on that page is a graph showing loudness proportional to the decibels -- which directly means that there cannot be a fixed number of dB corresponding to a doubling of the loudness. Commented Aug 28, 2017 at 19:51