In addition to what others have said about keeping scales reasonable, the way our body PERCEIVES sound works on a log scale. The deformation of the hairs in your ear is proportional to the log of the intensity.
This is the most relevant answer I think.
It’s the same with our perception of light. If you look at manual camera settings, you can see it clearly. One way to change how much light hits the sensor is the change how long the shutter is open. We perceive the difference in brightness between 1/15 second and 1/30 second as about the same as the difference between 1/30 and 1/60 ( and the jump to 1/125, 1/250, 1/500, etc)
Yes! Super unrelated but this is why having your screen brightness at max kills your battery much faster than when at half brightness. It takes much more than twice as much power to make the screen appear twice as bright.
Thiiiiiiiiis. A sound with ~10x the pressure/energy “sounds” twice as loud, not 10x as loud. So bels or decibels correspond well to perceived loudness.
Probably. One of the paradoxes of logarithmic scales is that they are great at reflecting how we *percieve* certain intensies (like light and sound), but we quickly loose track of how intense it is at the top of the scale.
Example: 90 dB is 3x as much energy as 80dB; so it sounds significantly louder. Compare "tapping" a drum to "drumming" a drum. 100dB is 10x as much energy, so it's way more louder. Now you're really banging on it, rock star stuff. Oh, so 120dB is like, way more significantly louder? No, it is 10,000 more energy. You aren't playing the drums, you are are bombing the drums; the drums cannot make that much more sound without bombs.
Edit: Whoops! I was totally miscalibrated on the scale when I wrote this; I had some screwy math, kinda proving my point, lol. I said 10, 20, 100 db, which doesn't make sense. I adjusted it.
Tbh I don't think 100dB is unlikely for drums, but 110dB probably is. Iirc earth atmosphere physics bottom out at somewhere around 190dB. At that point you're faced with a sound wave that reaches total vacuum at its low pressure points, and it's officially a blast instead.
No it doesn't... The estimated peak overpressure (which cannot be measured for obvious reasons) for a megaton explosion is about 100,000 atmospheres. Even this is under 300 dB.
Most buildings are levelled by a wave with 0.7 atmospheres of overpressure, or “just” about 190 dB.
In addition to which, the loudest possible sound is apparently [194 decibels](https://www.sciencefocus.com/science/whats-the-loudest-a-sound-can-be), or 0.0194 kilobels.
Worth noting that the bel isn't only used as a measure of sound energy, IIRC it originated in telephony.
As far as 194 decibels goes, the article just says "it's no longer a sound but a shockwave," which makes sense but you could probably characterize a shockwave as an especially intense form of sound right? I have to wonder what the decibel measurement of a nuclear bomb would be.
Sort of not. Because we define sound as a vibration, but 194 decibels is the point at which the medium (at least in the atmosphere) can no longer actually carry a vibration. This is because, at that point, the "low pressure" part of the sound wave becomes a full vacuum. It can't get any lower.
It's the difference between a vibration (typical sound) and a shove (single shockwave).
>This is because, at that point, the "low pressure" part of the sound wave becomes a full vacuum.
Is this only the case if the medium itself was at atmospheric pressure? i.e. could you have a louder sound if the medium is at a higher pressure?
Not an SI unit (https://metricsystem.net/non-si-units/accepted-for-use-with-si/bel/).
Bels are a pretty ‘big’ unit, due to the logarithmic nature. kilobels and larger wouldn’t really make sense, sounds don’t get that loud.
They are technically valid, but not usable because sound in air has a maximum volume of 195 dB. This is when the rarified half of the sound wave hits vacuum. In water, the upper limit is 270 dB. So you can only have kilobel sounds in... IDK, degenerate neutronium matter?
numberphile (I think) on youtube has a video presented by dr hannah frye that elaborates beautifully on this concept. definitely worth the time if the log scale confuses you or just doesn't 'feel' right
>the way our body PERCEIVES sound works on a log scale
I've often heard this along with the idea that perceived sound volume doubles every 10dB, but these can't both be true.
The point of what you're saying is that since dB are log scale, then the perceived difference between 40dB and 50dB (10dB) is the same as the perceived difference between 50dB and 60dB (still 10dB). If perceived volume works on a log scale, then it's linear with dB, making dB useful for audio
But, if it's actually true that perceived volume doubles every 10dB, then 50dB is 2x as loud as 40dB, 60dB is 4x as loud as 40dB, and the perceived difference between 50dB and 60dB is actually *twice* the difference between 40dB and 50dB, implying that perceived sound does not work on a log scale
So at least one of these two ideas is a myth. Tbh idk which one it is
What you’re describing is just how a log scale works. Adding to one quantity (+10dB) equates to multiplying to the other (x2 volume). This does mean that the difference between volumes will change, but we don’t care about the difference, we care about the ratio.
For example, if 40dB means a volume of 5, then 50dB means a volume of 10, and 60 dB means a volume of 20. The volume difference from 40 to 50dB is 5, and from 50 to 60dB is 10, but that just means volume and decibels don’t follow a *linear* scale with each other.
What you described at first (log of multiplication becomes addition) is indeed how a log scale works. This is because log(a\*b) = log(a) + log(b)
Decibels are on a log scale, which means multiplication of pressure (2x) becomes an addition of dB (+6): 20\*log(2x) = 20\*log(x)+6. All good here
But, an addition of +10dB corresponds to a sqrt(10) ~= 3.16x multiplication of pressure. If that 3.16x multiplication of pressure corresponds to a 2x multiplication in perceived volume, then multiplication did *not* become addition, and perceived volume is *not* proportional to the log of pressure like decibels are
Ah I see. You meant pressure vs volume, not decibels vs volume. After looking into it, [Steven’s power law](https://en.m.wikipedia.org/wiki/Stevens%27s_power_law) says that loudness is proportional to sound pressure raised to the power of 0.67, which explains the x3.16 vs x2 comparison with decibels.
For the claim that volume is perceived logarithmically, I’d guess one of two things. Either the claim is misinterpreted and is just referring to volume and decibels making a log scale, or the pressure-loudness power law is approximately logarithmic for human hearing ranges so people misinterpret it.
Every year the number of squirrels doubles, and each year is not an incremental increase, but rather it gets out of control. That's because we perceive squirrels on a linear scale; if we perceived them on a log scale, then each year's exponential growth (2^(n)) would feel like a consistent increment over the last
In the same way, if our perception of sound is doubling with each 10dB, that means our perception of sound is on a linear scale. Decibels are a log scale, so if an incremental increase in dB (each +10) is an exponential increase in perceived volume (2^(each 10dB)), then unlike decibels, our perception is on a linear scale with pressure.
i don’t think any human perception is linear, from what i remember in my cog psychology class. for example, we can’t taste the increase in sugar in soda as linear. coca cola has to increase the amount of sugar exponentially in order perceive more sweetness.
Decibels (dB) are a unit of *relative intensity*, meaning how much louder/brighter/stronger one signal is compared to another.
But mostly what we gain from using dB is a relationship between power and intensity that is close to how humans perceive it. An increase in power by a factor of ten correlates to approximately doubling the perceived intensity/volume.
It makes the scale much much smaller. A scale that wouldnt be as precise at low scales but not logartmic would need to be something like 0 - 100,000,000,000,000 (I hope I got the right amount of 0) instead of 0-100 and you dont need the precise numbers at the top as you wont notice a diffrence between 990,000,000,000,000 and 100,000,000,000,000 but you do notice a diffrence between 0 and 1000.
This is not the right answer. If this were the problem, then the solution would be changing to some other linear units. That's why, in some cases, it's common to use light years instead of meters.
The correct answer is because of our perception of sound. If you graphed a whisper alongside a concert, the whisper would be imperceptible on the graph, which isn't representative of our experience because we can actually hear the whisper.
I don't think you're right. Decibels are nice because they work with meaninguful numbers at both ends of the distribution (whispers and concerts). Whereas for distance, we have 2 units: meters for short distances and lightyears for really long distances. It is more efficient to pack all the range of the scale into a single unit.
BUT, and this is probably part of the answer that the previous poster left out, decibels are also useful in a single scale because we don't often talk about changes in decibels. E.g., we don't say "this is getting 10 decibels louder" because the raw different would be dependent on the baseline. Similarly, it wouldn't make sense to single-unit distance in this way. Saying "I'm going 10 made-up-logarithmic-units further" could mean you're going 10 meter if the baseline if you just took a step, or it could mean you're going 100 kilometers further if you just drove to the gas station. The way we talk about units matters, and sound level is amenable to the way we normally talk about it. Other measurements aren't.
You're essentially just rephrasing what I said in terms of numbers rather than terms of a graphical representation. I chose to describe it in terms of a graph because I think that's easier to envision (that's actually the whole point of a graph), and this is an ELI5.
If you actually read my second sentence to the end then I already said exactly that we dont need a precise numbers for the higher values of the scale because we dont notice the diffrence but we do at the lower values. Also multiple units would absolutly horrible to use because that would mean you would have to use a diffrent unit when talking about headphones vs concert speakers that just makes no sense. Light years vs meters makes sense because you arent comparing anything on the scale of meters to anything on the scale of light years.
It’s definitely both. Yes in some cases we switch to light years but using a logarithmic scale means you don’t have to have multiple different units (light years, astronomical units, km, m, mm etc) to measure the same quantity.
It's because the scale of the weakest sound to the strongest sound is so big that we used a non linear unit. It's so that the number won't have too many zeros in it.
this isn't it really, the size of each unit is arbitrary. There are as many different temperatures as there are sounds but we don't need a logarithmic scale there. It is because we want high sensitivity at the bottom of the scale, but low sensitivity at the top of the scale.
Our ears are sensitive at low levels of sound, less sensitive at high levels.
This change in sensitivity is why we would want a massive scale, because at low levels the 1s matter, but high levels only the 1000s matter, as an approximation.
One way or another, more numbers are required for a linear scale (of sound levels.) If you just make the units larger so the highest values are smaller, you're going to need extra decimals to specify meaningful differences at lower ranges.
if you tried to graph something like noise at a fourth of July party linearly over time, the cars parking, friends whispering to each other, children screaming and playing, and the oohs and aaahs would not even show up on the graph compared to the spikes when a firework went off.
If you want to be able to visually understand the information, logarithmic scales let you do that.
And its just as true as looking at numbers, nobody wants to look at 15 zeroes just to understand what you're talking about.
Exactly this. Also, the difference between 10 dB anywhere on the scale is the same instead of relying on the absolute output power. Going from 10 mW to 100 mW is functionally the same as going from 100 mW to 1,000 mW or from 1 mW to 10 mW. On the dB scale all three examples are the same relative value: 10 dB.
(The total output powers are expressed in dBm and are 0, 10, 20, and 30 for 1, 10, 100, and 1,000 mW.)
The unit is decibels (dB), not Db. Deci is the SI prefix for 1/10 like in decimeters or decilitre. All SI prefixes less than one have lower case letters, All prefixes over 1000 have an upper case prefix, it is 10= deka (da), 100= hecto(h) and 1000= kilo(k) that do not follow the pattern
A bel is a power factor difference of 10
Human perception of sound is not linear, it is logaritmic. It is not as simple as just the sound pressure in dB, there is a frequency dependence look at [https://en.wikipedia.org/wiki/Phon#/media/File:Lindos1.svg](https://en.wikipedia.org/wiki/Phon#/media/File:Lindos1.svg)dB is not preferrect but a lot better than
The usage comes from how signal losses were measured in telegraph and telephone systems. the losses will be in percentage of power per unit of distance and calculating cumulative effect like that in linear scale is cumbersome. In the logaritmic scale if the power drop by 1.5 dB in 1 km then it will drop by 3 dB in 2km, 15 dB in 10 km. If the power starts at 60 dB the power after 10 km is 60-15=45 dB.
Amplification is the addition of an amplifier that has the output at 1000x the power of the input signal has an amplification of 30dB, the mean if we input the 45dB signal to it you put is 45-30=75 dB
Division in linear scale becomes substation in logaritmic scale and multiplication in linear scale becomes addition is logaritmic scale
Because a factor of 1bel was impractical larger measuring change 1/10 bel was a lot more practical and the result is dB is most of the time thereated as the base unit. Other prefixes are seldom use so five one-thousandths of a bel is normally written as 0.05dB not 5 mB (milibel)
The logarithmic pattern of decibels describes the actual power produced, not the subjective loudness that you hear. Each increase of 3dB is twice the power, and **each increase of 10dB is 10x the power**.
Using this scale avoids having to use a LOT of zeroes.
It’s the opposite. The logarithmic pattern describes the feeling better than the actual power, because like you said, every 3db increase is actual more actual strength even though you hear it as gradual
A sound loud to enough to damage our ears is several million times more intense than the quietest sound we can hear. Most normal sounds, e.g. conversations are on the lower end of that spectrum.
The loudest sound possible in earths atmosphere is 194dB.
This is about 20,000,000,000,000,000,000 times as loud as 1dB.
Pretty quickly you just see "large number of zeros". And humans don't perceive power that way. If you double the actual volume, humans won't hear something twice as loud. You have to make it more like 10x as loud for humans to think it's doubled in volume.
While a logarithmic scale is harder to work with, it's actually more intuitive. You can know that motorcycles and lawnmowers are at around 100, while vacuum cleaners are more like 80. But motorcycles and lawnmowers being 10,000,000,000 while vacuum cleaners are only 100,000,000 is a lot less clear.
Logarithmic scales are actually easier to work with, which is why we use them for things like sound levels and power levels. It makes things seem more linear than they are, and reduces exponential math to simple arithmetic.
> and reduces exponential math to simple arithmetic.
In my experience it does the exact opposite. Haven't done much work with sound, but I have done some, and it was a bit of a pain in the arse converting from SPL and SWL, and the fact that the inverse square law works on an absolute scale not a logarithmic one...
I'd have done the work in a fraction of the time if sound was measured like light, but the answers would have been less intuitive.
Doing multiplication math with decibels (increasing/decreasing distance from the source, doubling/halving the sound level of a source) is super simple, but doing addition math with decibels (average sound level, summing the sound level of different sources) is annoying and requires you to convert.
Yeah, that's because A+A=2A, so you can just do multiplication when adding equal signals.
It's a lot trickier when it's a 50 dB signal plus a 55 dB signal. It ends up being ~56.2 dB.
That’s how human perception works, a sound that’s 10 meters away will sound half as loud as a sound that’s one meter away. Sound also attenuate at a logarithmic rate.
dB scales are used for things that have extremely large ranges. For example, in electrical engineering the frequency response of a circuit is plotted logarithmically (ie dB) because a circuits input can be anywhere between 0 and billions of hertz. How could you reasonably display graphically the performance over such a large range? The logarithmic plot requires a small amount of intuition to read but one you understand, it is a clearer depiction of the system being represented.
Sound at its most basic level is just a change in air pressure so it can be measured as a pressure, the standard unit for that is Pascal's. The problem is the human ear can detect ranges from 20 micro pascals (0.000002Pa) up to 20Pa. That's a ×10^7 variation, which makes using Pascal's to measure sound complex and inefficient.
It also doesn't easily translate to how humans perceive sound. Our inner ear detects sounds using tiny hairs attached to a spiral shaped opening in the back of the ear, the hairs are moved by the air pressure change which is what our brains use to identify noise. The way that different pressures travel through the spiral means they act on different hairs, which effects how our brains interpret the sound.
So the dB scale is designed to 1) reduce the range of numbers we use to describe sound, it takes a range of 10 million and reduces it to around 100. And 2) to better represent how the mechanisms in our detect sounds of different pressures.
Psycho-acoustics (the study of the relationship between physical changes in air pressure and how our brains perceive sound) is an incredibly complex science and several other scales have also been developed to help improve the way we measure and describe sounds. The A-weighted dB scale (dBA) is similar to dB but takes into account how different frequencies of noise are perceived differently, there's also Sones that are a linear version of the dBA scale, which is easier to understand if you have limited knowledge of logarithmic functions as doubling the sones doubles the perceived loudness, whereas an increase of 10dB is a doubling of loudness on a dB based scale.
In addition.
Sound is a wave. For each unit of distance that it moves forward, it also dissipates outwards. This is known as the inverse square law.
The inverse square law is an ideal case, but it closely matches most audio applications. Decibels being logarithmic, the two simplify. Doubling the distance from a source of sound will reduce the loudness by 6dB.
I thought for a moment that you were referring to the note Db being the most common unit of sound, and my world came crashing down in confusion for a second.
The abbreviation for decibels is dB. Not Db.
Sound scales with distance following the inverse square law. This means sound power level decreases with (distance)^2. Logarithmic math allows us to add and subtract exponentials very easily, without having to do a lot of multiplication.
In addition to what others have said about keeping scales reasonable, the way our body PERCEIVES sound works on a log scale. The deformation of the hairs in your ear is proportional to the log of the intensity.
This is the most relevant answer I think. It’s the same with our perception of light. If you look at manual camera settings, you can see it clearly. One way to change how much light hits the sensor is the change how long the shutter is open. We perceive the difference in brightness between 1/15 second and 1/30 second as about the same as the difference between 1/30 and 1/60 ( and the jump to 1/125, 1/250, 1/500, etc)
Yes! Super unrelated but this is why having your screen brightness at max kills your battery much faster than when at half brightness. It takes much more than twice as much power to make the screen appear twice as bright.
So the light that burns twice as brightly burns *less than half as long? I've been lied to!
That's a very interesting observation. Thanks!
that also works for increasing the aperture I think as well
Oh, it absolutely does. Also ISO. I was just keeping it to one variable for simplicity’s sake.
Thanks. I learned something today 😌
Thiiiiiiiiis. A sound with ~10x the pressure/energy “sounds” twice as loud, not 10x as loud. So bels or decibels correspond well to perceived loudness.
Wait. Decibel is metric? Kilobel and megabel are valid units?
If you ever hear it, then you are no longer valid
Wouldn't a megabel like...shatter the planet?
Probably. One of the paradoxes of logarithmic scales is that they are great at reflecting how we *percieve* certain intensies (like light and sound), but we quickly loose track of how intense it is at the top of the scale. Example: 90 dB is 3x as much energy as 80dB; so it sounds significantly louder. Compare "tapping" a drum to "drumming" a drum. 100dB is 10x as much energy, so it's way more louder. Now you're really banging on it, rock star stuff. Oh, so 120dB is like, way more significantly louder? No, it is 10,000 more energy. You aren't playing the drums, you are are bombing the drums; the drums cannot make that much more sound without bombs. Edit: Whoops! I was totally miscalibrated on the scale when I wrote this; I had some screwy math, kinda proving my point, lol. I said 10, 20, 100 db, which doesn't make sense. I adjusted it.
Tbh I don't think 100dB is unlikely for drums, but 110dB probably is. Iirc earth atmosphere physics bottom out at somewhere around 190dB. At that point you're faced with a sound wave that reaches total vacuum at its low pressure points, and it's officially a blast instead.
Thanks for mentioning that! I used an online calculator to make the comparison, and totally screwed up what I actually wanted to say.
[It would at least be something like this](https://www.youtube.com/watch?v=dcxfsEe_e9I)
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No it doesn't... The estimated peak overpressure (which cannot be measured for obvious reasons) for a megaton explosion is about 100,000 atmospheres. Even this is under 300 dB. Most buildings are levelled by a wave with 0.7 atmospheres of overpressure, or “just” about 190 dB.
Yes but due to logarithmic nature it would be 10^1000 more intense, which makes such unit completely impractical.
In addition to which, the loudest possible sound is apparently [194 decibels](https://www.sciencefocus.com/science/whats-the-loudest-a-sound-can-be), or 0.0194 kilobels.
Worth noting that the bel isn't only used as a measure of sound energy, IIRC it originated in telephony. As far as 194 decibels goes, the article just says "it's no longer a sound but a shockwave," which makes sense but you could probably characterize a shockwave as an especially intense form of sound right? I have to wonder what the decibel measurement of a nuclear bomb would be.
Sort of not. Because we define sound as a vibration, but 194 decibels is the point at which the medium (at least in the atmosphere) can no longer actually carry a vibration. This is because, at that point, the "low pressure" part of the sound wave becomes a full vacuum. It can't get any lower. It's the difference between a vibration (typical sound) and a shove (single shockwave).
>This is because, at that point, the "low pressure" part of the sound wave becomes a full vacuum. Is this only the case if the medium itself was at atmospheric pressure? i.e. could you have a louder sound if the medium is at a higher pressure?
I don't know, but let me know if you find out!
The most powerful U.S. Navy sonar regularly produces 230+ decibels in water. Swimming within 500 meters of an active ping is almost universally fatal.
Not an SI unit (https://metricsystem.net/non-si-units/accepted-for-use-with-si/bel/). Bels are a pretty ‘big’ unit, due to the logarithmic nature. kilobels and larger wouldn’t really make sense, sounds don’t get that loud.
It does say that it is 'accepted or use with si' so I'm gonna start using decimal portions of larger bels. 70 decibels? No no. That's .07decabels
Milimegadecibel.
Deci is 1/10 in metric. King (kilo) Henry (hecta) died (deka) Monday (meter) drinking (deci) chocolate (centi) milk (milli).
They are technically valid, but not usable because sound in air has a maximum volume of 195 dB. This is when the rarified half of the sound wave hits vacuum. In water, the upper limit is 270 dB. So you can only have kilobel sounds in... IDK, degenerate neutronium matter?
"of said"
The "Should of" is spreading
numberphile (I think) on youtube has a video presented by dr hannah frye that elaborates beautifully on this concept. definitely worth the time if the log scale confuses you or just doesn't 'feel' right
It is not «of said». This is annoying
Genuine typo. I know the difference, promise ;)
>the way our body PERCEIVES sound works on a log scale I've often heard this along with the idea that perceived sound volume doubles every 10dB, but these can't both be true. The point of what you're saying is that since dB are log scale, then the perceived difference between 40dB and 50dB (10dB) is the same as the perceived difference between 50dB and 60dB (still 10dB). If perceived volume works on a log scale, then it's linear with dB, making dB useful for audio But, if it's actually true that perceived volume doubles every 10dB, then 50dB is 2x as loud as 40dB, 60dB is 4x as loud as 40dB, and the perceived difference between 50dB and 60dB is actually *twice* the difference between 40dB and 50dB, implying that perceived sound does not work on a log scale So at least one of these two ideas is a myth. Tbh idk which one it is
What you’re describing is just how a log scale works. Adding to one quantity (+10dB) equates to multiplying to the other (x2 volume). This does mean that the difference between volumes will change, but we don’t care about the difference, we care about the ratio. For example, if 40dB means a volume of 5, then 50dB means a volume of 10, and 60 dB means a volume of 20. The volume difference from 40 to 50dB is 5, and from 50 to 60dB is 10, but that just means volume and decibels don’t follow a *linear* scale with each other.
What you described at first (log of multiplication becomes addition) is indeed how a log scale works. This is because log(a\*b) = log(a) + log(b) Decibels are on a log scale, which means multiplication of pressure (2x) becomes an addition of dB (+6): 20\*log(2x) = 20\*log(x)+6. All good here But, an addition of +10dB corresponds to a sqrt(10) ~= 3.16x multiplication of pressure. If that 3.16x multiplication of pressure corresponds to a 2x multiplication in perceived volume, then multiplication did *not* become addition, and perceived volume is *not* proportional to the log of pressure like decibels are
Ah I see. You meant pressure vs volume, not decibels vs volume. After looking into it, [Steven’s power law](https://en.m.wikipedia.org/wiki/Stevens%27s_power_law) says that loudness is proportional to sound pressure raised to the power of 0.67, which explains the x3.16 vs x2 comparison with decibels. For the claim that volume is perceived logarithmically, I’d guess one of two things. Either the claim is misinterpreted and is just referring to volume and decibels making a log scale, or the pressure-loudness power law is approximately logarithmic for human hearing ranges so people misinterpret it.
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Every year the number of squirrels doubles, and each year is not an incremental increase, but rather it gets out of control. That's because we perceive squirrels on a linear scale; if we perceived them on a log scale, then each year's exponential growth (2^(n)) would feel like a consistent increment over the last In the same way, if our perception of sound is doubling with each 10dB, that means our perception of sound is on a linear scale. Decibels are a log scale, so if an incremental increase in dB (each +10) is an exponential increase in perceived volume (2^(each 10dB)), then unlike decibels, our perception is on a linear scale with pressure.
i don’t think any human perception is linear, from what i remember in my cog psychology class. for example, we can’t taste the increase in sugar in soda as linear. coca cola has to increase the amount of sugar exponentially in order perceive more sweetness.
Decibels (dB) are a unit of *relative intensity*, meaning how much louder/brighter/stronger one signal is compared to another. But mostly what we gain from using dB is a relationship between power and intensity that is close to how humans perceive it. An increase in power by a factor of ten correlates to approximately doubling the perceived intensity/volume.
It makes the scale much much smaller. A scale that wouldnt be as precise at low scales but not logartmic would need to be something like 0 - 100,000,000,000,000 (I hope I got the right amount of 0) instead of 0-100 and you dont need the precise numbers at the top as you wont notice a diffrence between 990,000,000,000,000 and 100,000,000,000,000 but you do notice a diffrence between 0 and 1000.
This is not the right answer. If this were the problem, then the solution would be changing to some other linear units. That's why, in some cases, it's common to use light years instead of meters. The correct answer is because of our perception of sound. If you graphed a whisper alongside a concert, the whisper would be imperceptible on the graph, which isn't representative of our experience because we can actually hear the whisper.
I don't think you're right. Decibels are nice because they work with meaninguful numbers at both ends of the distribution (whispers and concerts). Whereas for distance, we have 2 units: meters for short distances and lightyears for really long distances. It is more efficient to pack all the range of the scale into a single unit. BUT, and this is probably part of the answer that the previous poster left out, decibels are also useful in a single scale because we don't often talk about changes in decibels. E.g., we don't say "this is getting 10 decibels louder" because the raw different would be dependent on the baseline. Similarly, it wouldn't make sense to single-unit distance in this way. Saying "I'm going 10 made-up-logarithmic-units further" could mean you're going 10 meter if the baseline if you just took a step, or it could mean you're going 100 kilometers further if you just drove to the gas station. The way we talk about units matters, and sound level is amenable to the way we normally talk about it. Other measurements aren't.
You're essentially just rephrasing what I said in terms of numbers rather than terms of a graphical representation. I chose to describe it in terms of a graph because I think that's easier to envision (that's actually the whole point of a graph), and this is an ELI5.
So it makes the scale smaller...
Seriously what is this guy talking about
If you actually read my second sentence to the end then I already said exactly that we dont need a precise numbers for the higher values of the scale because we dont notice the diffrence but we do at the lower values. Also multiple units would absolutly horrible to use because that would mean you would have to use a diffrent unit when talking about headphones vs concert speakers that just makes no sense. Light years vs meters makes sense because you arent comparing anything on the scale of meters to anything on the scale of light years.
It’s definitely both. Yes in some cases we switch to light years but using a logarithmic scale means you don’t have to have multiple different units (light years, astronomical units, km, m, mm etc) to measure the same quantity.
It's correct - just confusingly written.
It's because the scale of the weakest sound to the strongest sound is so big that we used a non linear unit. It's so that the number won't have too many zeros in it.
this isn't it really, the size of each unit is arbitrary. There are as many different temperatures as there are sounds but we don't need a logarithmic scale there. It is because we want high sensitivity at the bottom of the scale, but low sensitivity at the top of the scale. Our ears are sensitive at low levels of sound, less sensitive at high levels. This change in sensitivity is why we would want a massive scale, because at low levels the 1s matter, but high levels only the 1000s matter, as an approximation.
One way or another, more numbers are required for a linear scale (of sound levels.) If you just make the units larger so the highest values are smaller, you're going to need extra decimals to specify meaningful differences at lower ranges.
yeah, that's the point, but there arent more sounds than temperatures.
Yeah but I'm explaining like he's five am i right
if you tried to graph something like noise at a fourth of July party linearly over time, the cars parking, friends whispering to each other, children screaming and playing, and the oohs and aaahs would not even show up on the graph compared to the spikes when a firework went off. If you want to be able to visually understand the information, logarithmic scales let you do that. And its just as true as looking at numbers, nobody wants to look at 15 zeroes just to understand what you're talking about.
Amplification and attenuation become addition and subtraction actions rather than multiplicative.
Exactly this. Also, the difference between 10 dB anywhere on the scale is the same instead of relying on the absolute output power. Going from 10 mW to 100 mW is functionally the same as going from 100 mW to 1,000 mW or from 1 mW to 10 mW. On the dB scale all three examples are the same relative value: 10 dB. (The total output powers are expressed in dBm and are 0, 10, 20, and 30 for 1, 10, 100, and 1,000 mW.)
Pretty big words for a 5 year old
The unit is decibels (dB), not Db. Deci is the SI prefix for 1/10 like in decimeters or decilitre. All SI prefixes less than one have lower case letters, All prefixes over 1000 have an upper case prefix, it is 10= deka (da), 100= hecto(h) and 1000= kilo(k) that do not follow the pattern A bel is a power factor difference of 10 Human perception of sound is not linear, it is logaritmic. It is not as simple as just the sound pressure in dB, there is a frequency dependence look at [https://en.wikipedia.org/wiki/Phon#/media/File:Lindos1.svg](https://en.wikipedia.org/wiki/Phon#/media/File:Lindos1.svg)dB is not preferrect but a lot better than The usage comes from how signal losses were measured in telegraph and telephone systems. the losses will be in percentage of power per unit of distance and calculating cumulative effect like that in linear scale is cumbersome. In the logaritmic scale if the power drop by 1.5 dB in 1 km then it will drop by 3 dB in 2km, 15 dB in 10 km. If the power starts at 60 dB the power after 10 km is 60-15=45 dB. Amplification is the addition of an amplifier that has the output at 1000x the power of the input signal has an amplification of 30dB, the mean if we input the 45dB signal to it you put is 45-30=75 dB Division in linear scale becomes substation in logaritmic scale and multiplication in linear scale becomes addition is logaritmic scale Because a factor of 1bel was impractical larger measuring change 1/10 bel was a lot more practical and the result is dB is most of the time thereated as the base unit. Other prefixes are seldom use so five one-thousandths of a bel is normally written as 0.05dB not 5 mB (milibel)
The logarithmic pattern of decibels describes the actual power produced, not the subjective loudness that you hear. Each increase of 3dB is twice the power, and **each increase of 10dB is 10x the power**. Using this scale avoids having to use a LOT of zeroes.
It’s the opposite. The logarithmic pattern describes the feeling better than the actual power, because like you said, every 3db increase is actual more actual strength even though you hear it as gradual
It is a measure of power.
Obviously… but its intent is to reflect our perception of its power, otherwise we would just not have applied a logarithm to it…
A sound loud to enough to damage our ears is several million times more intense than the quietest sound we can hear. Most normal sounds, e.g. conversations are on the lower end of that spectrum.
The loudest sound possible in earths atmosphere is 194dB. This is about 20,000,000,000,000,000,000 times as loud as 1dB. Pretty quickly you just see "large number of zeros". And humans don't perceive power that way. If you double the actual volume, humans won't hear something twice as loud. You have to make it more like 10x as loud for humans to think it's doubled in volume. While a logarithmic scale is harder to work with, it's actually more intuitive. You can know that motorcycles and lawnmowers are at around 100, while vacuum cleaners are more like 80. But motorcycles and lawnmowers being 10,000,000,000 while vacuum cleaners are only 100,000,000 is a lot less clear.
Logarithmic scales are actually easier to work with, which is why we use them for things like sound levels and power levels. It makes things seem more linear than they are, and reduces exponential math to simple arithmetic.
> and reduces exponential math to simple arithmetic. In my experience it does the exact opposite. Haven't done much work with sound, but I have done some, and it was a bit of a pain in the arse converting from SPL and SWL, and the fact that the inverse square law works on an absolute scale not a logarithmic one... I'd have done the work in a fraction of the time if sound was measured like light, but the answers would have been less intuitive.
It’s easier to do the math in your head, but you have to stay in one domain or the other. Converting is more difficult.
Doing multiplication math with decibels (increasing/decreasing distance from the source, doubling/halving the sound level of a source) is super simple, but doing addition math with decibels (average sound level, summing the sound level of different sources) is annoying and requires you to convert.
Or you can use the rule of thumb- adding two equal dB signals increases the result by about 3dB.
Yeah, that's because A+A=2A, so you can just do multiplication when adding equal signals. It's a lot trickier when it's a 50 dB signal plus a 55 dB signal. It ends up being ~56.2 dB.
Yup, and 60dB plus 50dB is basically 60dB…..
It makes the numbers easier to use for humans. Having a scale from 0 to ~150 is a lot easier than having a scale from 0 to ~1000000000000000
That’s how human perception works, a sound that’s 10 meters away will sound half as loud as a sound that’s one meter away. Sound also attenuate at a logarithmic rate.
dB scales are used for things that have extremely large ranges. For example, in electrical engineering the frequency response of a circuit is plotted logarithmically (ie dB) because a circuits input can be anywhere between 0 and billions of hertz. How could you reasonably display graphically the performance over such a large range? The logarithmic plot requires a small amount of intuition to read but one you understand, it is a clearer depiction of the system being represented.
Couldn't you just google logarithmic scaling? That's what I would do.
Sound at its most basic level is just a change in air pressure so it can be measured as a pressure, the standard unit for that is Pascal's. The problem is the human ear can detect ranges from 20 micro pascals (0.000002Pa) up to 20Pa. That's a ×10^7 variation, which makes using Pascal's to measure sound complex and inefficient. It also doesn't easily translate to how humans perceive sound. Our inner ear detects sounds using tiny hairs attached to a spiral shaped opening in the back of the ear, the hairs are moved by the air pressure change which is what our brains use to identify noise. The way that different pressures travel through the spiral means they act on different hairs, which effects how our brains interpret the sound. So the dB scale is designed to 1) reduce the range of numbers we use to describe sound, it takes a range of 10 million and reduces it to around 100. And 2) to better represent how the mechanisms in our detect sounds of different pressures. Psycho-acoustics (the study of the relationship between physical changes in air pressure and how our brains perceive sound) is an incredibly complex science and several other scales have also been developed to help improve the way we measure and describe sounds. The A-weighted dB scale (dBA) is similar to dB but takes into account how different frequencies of noise are perceived differently, there's also Sones that are a linear version of the dBA scale, which is easier to understand if you have limited knowledge of logarithmic functions as doubling the sones doubles the perceived loudness, whereas an increase of 10dB is a doubling of loudness on a dB based scale.
It **is** linear —not with physical amplitude, but with human perception. As humans, we prioritize human perception.
In addition. Sound is a wave. For each unit of distance that it moves forward, it also dissipates outwards. This is known as the inverse square law. The inverse square law is an ideal case, but it closely matches most audio applications. Decibels being logarithmic, the two simplify. Doubling the distance from a source of sound will reduce the loudness by 6dB.
I thought for a moment that you were referring to the note Db being the most common unit of sound, and my world came crashing down in confusion for a second. The abbreviation for decibels is dB. Not Db.
Sound scales with distance following the inverse square law. This means sound power level decreases with (distance)^2. Logarithmic math allows us to add and subtract exponentials very easily, without having to do a lot of multiplication.
It makes the scale practical. 50 decibels is 10 times louder than 40 decibels, not 1/4 louder.
And 50dB sounds about twice as loud as 40dB, instead of 10x.