[ninjaphone]

A lot of the posts here have explained the graphs pretty well 

 but just to define the terms:  frequency refers to how many sound waves pass through a given point (say, your ears for example) in a single second.  So if you are listening to a 400 Hz sound wave, that means 400 waves hit your eardrum in one second of time.  The more waves that hit your eardrum per second (Hz means per second) the louder you perceive the sound.  And vice versa.  
 
The deciBel (dB) is a scale measuring how loud we perceive sound.   If you know what a logarithm scale is in math, thats the jist of it-- if not, don't worry about.  Basically, it is loudness relative to how much power the headphones put out.  Lets say I have speakers that are running at 200 watts of power, and the sound is coming out at 60 dB.  If I turn up the power 10 times, that is,
 
10 times 200 W = 2000 W
 
then the sound increases 10 dB, that is,
 
10 dB + 60 dB = 70 dB.   
 
I hope that helps, and wasn't over mathy for you.  (credibility: I am a mechanical engineering major and spent the past two weeks studying sound in one of my physics courses).

 

[CyberSyringe]

  A lot of the posts here have explained the graphs pretty well 

 but just to define the terms:  frequency refers to how many sound waves pass through a given point (say, your ears for example) in a single second.  So if you are listening to a 400 Hz sound wave, that means 400 waves hit your eardrum in one second of time.  The more waves that hit your eardrum per second (Hz means per second) the louder you perceive the sound.  And vice versa.  
 
The deciBel (dB) is a scale measuring how loud we perceive sound.   If you know what a logarithm scale is in math, thats the jist of it-- if not, don't worry about.  Basically, it is loudness relative to how much power the headphones put out.  Lets say I have speakers that are running at 200 watts of power, and the sound is coming out at 60 dB.  If I turn up the power 10 times, that is,
 
10 times 200 W = 2000 W
 
then the sound increases 10 dB, that is,
 
10 dB + 60 dB = 70 dB.   
 
I hope that helps, and wasn't over mathy for you.  (credibility: I am a mechanical engineering major and spent the past two weeks studying sound in one of my physics courses).

 
Wait, what? It's not the frequency of vibrations that your eardrum experiences that makes something sound louder. It's the sound pressure level, or amplitude of the waves. You are seriously misguided in thinking that frequency has anything to do with volume in that sense.
 
The faster your eardrum vibrates, the higher pitched the sound will be. How hard it vibrates, as in how much force it vibrates with, is how loud it will be.

 

[bigshot]

  So if you are listening to a 400 Hz sound wave, that means 400 waves hit your eardrum in one second of time.  The more waves that hit your eardrum per second (Hz means per second) the louder you perceive the sound.

 
No, the more waves per second the higher the sound. Bass drums are around 100Hz cymbals are around 6,000Hz. 

 

[MindsMirror]

  frequency refers to how many sound waves pass through a given point (say, your ears for example) in a single second.  So if you are listening to a 400 Hz sound wave, that means 400 waves hit your eardrum in one second of time.  The more waves that hit your eardrum per second (Hz means per second) the louder you perceive the sound.

 
Frequency is related to the loudness of a sound. At the same pressure level, a higher frequency sound has more energy and is therefor louder. What you said is misleading though. Loudness is most directly related to the pressure level.

 

[bigshot]

You just repeated the misleading part of it!

 

[MindsMirror]

  You just repeated the misleading part of it!

It's misleading if you don't say anything about the pressure level.

 

[bigshot]

If you state everything with the same emphasis, even exceptions and details, it is totally misleading.*
 
 
 
 
 
 
 
 
 
*Footnotes are a good way to let people know that you're just crossing t's and dotting i's and the main point is what counts.

 

[davidsh]

Are you saying there's more energy in higher frequencies if the sound pressure is constant?

 

[MindsMirror]

  Are you saying there's more energy in higher frequencies if the sound pressure is constant?

Yes. Look at pink noise. I'm actually not sure if "energy" is the right term, but anyway, pink noise sounds equally loud at all frequencies, and you can see that the spectrum slopes down because the amplitude or pressure of the higher frequencies is lower. In white noise the amplitude/pressure is constant across the spectrum, and the high frequencies sound louder.

 

[castleofargh]

now you've probably lost the poor chris on the road. this has not much to do with understanding FR graphs.
 
some measurement tool will deal with a signal of same amplitude at each freq(freq sweep using one freq at a time), and others will need pink noise because we show the result on a log scale for the frequency range. it's a representation problem, not an energy one.
and it's not about what we hear, just listen to one frequency at a time and you get the equal loudness contour that certainly doesn't keep going up in the trebles. so energy shouldn't even come up in here, as long as the guy doing the measurements knows what he's doing, we don't have to care about energy at all, and only need to care for amplitude of the signal as that's what you find on a record.
 
the energy thing can be confusing because a 1khz signal doesn't have less energy than a 10khz signal. the difference in energy comes when you look at the energy of an entire octave of sound. and then indeed one octave in the trebles will have more energy than one in the bass. because octaves are not linear scales, not because trebles are special. you double the frequency range each time you jump to a higher octave. one will be from 440hz to 880hz, the next one from 880hz to 1760hz. so it's not hard to guess that the total energy inside the second will be bigger as it is double the range of the previous octave and contains double the frequencies when you listen to noise.

 

[cjl]

   
Frequency is related to the loudness of a sound. At the same pressure level, a higher frequency sound has more energy and is therefor louder. What you said is misleading though. Loudness is most directly related to the pressure level.

No, at the same pressure level, the volume is the same. This is pretty clear when you realize sound volume is measured in SPL, which stands for sound pressure level.

 

[adamlr]

  The more waves that hit your eardrum per second (Hz means per second) the louder you perceive the sound. 

 
look at a speaker, the round thing that vibrates when you play music is what id call an "element" (it has other names). the material that vibrates is called a membrane.
"how many times the membrane vibrates per second" = frequency.
"how far the membrane goes forward and backward" = amplitude.
the membrane can go backward and forward 50 times per second (50 Hz) gently, with the membrane only moving forward and backward slightly, and then youd hear a soft 50 Hz tone, or it can vibrate 50 times per second with drastic movement, going way forward and then way backward, (but still 50 times per second) and then you hear a very loud 50 Hz tone.

   
Frequency is related to the loudness of a sound. At the same pressure level, a higher frequency sound has more energy and is therefor louder. 

if anything, a high frequency will sound less loud, when played at the same level as a midrange frequency. look up "fletcher monsoon" on google. 
 
our ears are more sensitive to sounds in the middle of the frequency scale than the sounds on the edges...
 
for example (based on a fletcher monsoon graph i randomly looked at on google), if you play a 1KHz tone at 80 dB, youd have to play a 7 KHz tone at 90 dB, i.e 10 dB louder, to make it sound equally loud to a human ear. thats more than twice as loud, in order to be perceived as equally loud.

 

[cjl]

   
look at a speaker, the round thing that vibrates when you play music is what id call an "element" (it has other names). the material that vibrates is called a membrane.
"how many times the membrane vibrates per second" = frequency.
"how far the membrane goes forward and backward" = amplitude.
the membrane can go backward and forward 50 times per second (50 Hz) gently, with the membrane only moving forward and backward slightly, and then youd hear a soft 50 Hz tone, or it can vibrate 50 times per second with drastic movement, going way forward and then way backward, (but still 50 times per second) and then you hear a very loud 50 Hz tone.

Interestingly, the distance traveled by a speaker will decrease as frequency increases for a given sound level. The pressure produced will stay the same, but the distance a speaker needs to travel at 1kHz to make a sound wave at 1mPa pressure level (for example) is much shorter than the distance a speaker cone must travel to make a similar 1mPa sound at 50Hz.

 

[davidsh]

Yeah, and cold air at ~30% relative humidity dampens the sound best.

 

[adamlr]

  Interestingly, the distance traveled by a speaker will decrease as frequency increases for a given sound level. The pressure produced will stay the same, but the distance a speaker needs to travel at 1kHz to make a sound wave at 1mPa pressure level (for example) is much shorter than the distance a speaker cone must travel to make a similar 1mPa sound at 50Hz.

i didnt know that, but none the less, i was explaining amplitude, and my explanation still holds.. frequency = pitch, amplitude = volume.
 

 
ninjaphone was saying that a higher frequency meant a high level, which is not the way it works

Yeah, and cold air at ~30% relative humidity dampens the sound best.

youre right, all this talk is just theoretical, all these numbers and rules where reached in "lab" conditions. when in an actual room or whatever environment, air pressure (i.e hight relative to sea level), temperature, humidity, wind, acoustics and alot more all come into play, changing everything