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the lamb 2006-01-26 18:18

wave interference?????
i dont know if this post goes here but it also doesnt seem to fit into any other category (if it does to you ... kindly move it)

i have noticed that when the guitar is perfectly tuned (if such a thing exists) the notes that are supposed to be the same(like B ,B) (and in the same octave) when played one after the other


give out a wave like sound (i mean the volume.. it increases and reduces in a wave pattern)

why is this

due to wave interference (constructive and destructive)???

BTW: this helps me in tuning (the longer the duration of the wave the closer are the two notes)

sqol 2006-01-26 18:25

Its that you can never get the two strings perfectly in tune, especially not with a standard handheld/pedal tuner. The 'wave' effect is due to when the two waves overlap, you get a natural 'boost' where the waves are at the same frequency.

the lamb 2006-01-27 16:53

yeah so wave interference

powersofterror 2006-01-27 17:03

Frequency has NOTHING to do with volume at all.

Two unison notes played together out of tune are logically the hell can it possibly be constructive?

:pIf those notes are perfectly in tune, there there should be NO "wah" sound.

the lamb 2006-01-28 14:23

not meaning to brag or anything but u should read a little about wave nature.

and exactly the tuning thing... when the strings get completely tuned the wave length increases to infinity i.e. no wah sound

powersofterror 2006-01-28 16:17

Wait a minute, let me get this straight....

You're a teenager with less education than me, and you are the one that asked the question. Now you're telling me that I don't know what I'm talking about--besides the fact that you have no idea either--and I need to read up on ...what was it....."wave nature?"

I'm 3/4 done with a Bachelor of Arts degree with a major in Music, and I've taken classes on physics of musical acoustics. Have you? Oh, wait, maybe you took high school physics that had 3 weeks dedicated to a chapter on waves. Is that it? Then wow, you must be smarter than me....

Are you an idiot? I think you are, but I'm wondering if you know it too.
You need to re-read these two posts above this one again as well.

sqol 2006-01-28 16:36

powers: what i meant is that the perceived volume is greater if the two notes are the same... a choir all singing the same note is louder that just one person singing it- if the choir were singing different notes, it wouldn't be as loud?

Dyldo 2006-01-28 17:16

He was talking to Lamb of Satan. I think this would better fit in theory.

the lamb 2006-01-29 14:00

powers, yeah i did ask the question and got it answered (that it was wave interference)

but if you say that you havent come across constructive interference of waves .... maybe you are right......

btw wave nature happens to be my fav. topic in high school
even though i m doing first year in computer science (thts in a university)

and thanks darko (for moving it)

Sam Hudson 2006-01-29 16:27

Dont fuck with powers....jus dont.

johnmansley 2006-01-30 04:26

Volume - or loudness - is subjective and related to three things:

1. The energy of the vibrating source.
2. The condition of the medium through which it propagates.
3. The distance involved.

The energy of a soundwave is related to its amplitude such that soundwaves with large amplitudes possess higher energy than those with smaller amplitudes.

Now, constructive interference occurs when the peaks or troughs of two distinct waves travelling in opposite directions coincide. The net effect of such an occurrence is that the amplitude of the newly combined wave is twice that of the original waves, resulting in greater energy.

powersofterror 2006-01-30 10:13

Originally Posted by sqol
powers: what i meant is that the perceived volume is greater if the two notes are the same... a choir all singing the same note is louder that just one person singing it- if the choir were singing different notes, it wouldn't be as loud?

my bad. But I wasn't thinking of that. I was just commenting on "wave like sound (i mean the volume.. it increases and reduces in a wave pattern)."

What makes volume subjective? It can be measured.

johnmansley 2006-01-30 10:42

Loudness is subjective in such that different people have different perceptions of loudness (my hearing compared to my grandmother's, for example).

Loudness is not easily measured in physics. However, sound intensity is more readily measured and comparable. Even then it is measured (in decibels) relative to a pre-determined level of intensity (usually the human threshold of hearing) on a logarithmic scale (i.e. 10dB is 10^1 times more intense than 0dB, 20dB is 10^2 times more intense than 0dB, 56dB is 10^5.6 times more intense than 0dB, etc).

It is important not to associate loudness with intensity in all cases as two sounds with the same intensity but different frequencies will not be perceived to have the same loudness. However, it is often the case that the more intense sounds will be perceived to be the loudest sounds so it is understandable that the association does occur.

powersofterror 2006-01-30 13:57

Right, but I can measure things with my digital mulimeter;). Frequencies, poles, intensity, loudness.....and whatever else the hell it can do (I don't use it much)

johnmansley 2006-01-30 15:20

Well, even the measurement of loudness is subjective to a point. The unit of loudness is the Sone and is scaled to our auditory sensitivity at different frequencies. These different frequencies are likely to have been arrived at statistically by testing a group of 'average' people. One man's average is another's top performance so it's easy to see that the calibration of whatever is measuring the perceived loudness is not based on absolutes.

This is all interesting and is bringing back memories of wet Monday mornings being taught A-level physics in a lab that was very rarely heated to above freezing!

When I was offered the mod-ship of the Theory Forum I wasn't really that aware of how mathematically inclined some of the folk here would be in terms of music theory. It's been pleasantly surprising, to be honest, and long may it continue!

the lamb 2006-01-30 15:34

So i guess you basically mean that loudness (or sound) is a kind qualia
qualia = These properties are, by definition, epistemically unknowable in the absence of direct experience of them; as a result, they are also incommunicable. (

johnmansley 2006-01-30 15:55

Well, we know what sound is; we know how it works in the physical world (through vibrations or pressure waves). We know the mechanics of sound and it's properties.

It's just that agreeing on a standard measurement of loudness based on a non-subjective basis is never going to happen. This is why you will very rarely hear people refer to the Sone when discussing sound: matters of sound are nearly exclusively talked about in terms of intensity (the decibel), which is less subjective since it only depends on one aspect that is considered subjective, i.e. the Human threshold of hearing.

Compare the situation to that of light; we understand fully that light comes in different wavelengths and frequencies that will refract into different colours, but one does not have to have sight in order to understand this. Of course, it would be tremendously difficult to imagine the colours if one was blind from birth, but still. Again drawing a parallel with sound, the SI unit of luminosity is the Candela and this is also based on intensity rather brightness.

the lamb 2006-01-30 16:11

Ok but if i told you to explain what colour is to a person who is blind from birth how would you go about (even if that person knows all that there is to know about the physical properties of light...but has never seen colour)

similarly how would you expalin sound (or in this case loudness) to a deaf person
(we know what sound is; we know how it works in the physical world (through vibrations or pressure waves). We know the mechanics of sound and it's properties.)......but knowing these is not enough ....there is that one variable missing that will give us all the knowledge about the qualia being discussed

Untill we find it (which i hope we dont) i guess humans are better off with measurements made dependent on "general" human experience....

powersofterror 2006-01-30 16:51

I hope you're not getting at some idea that they can't understand sound or color because they can't feel or see it. That's rhetorical and will never be answered.

Colors are wavelengths of light. If a blind person knew all there was to the properties of light, then all they need to do is know the wavelengths that corrispond to the different colors.

And how could you possibly know there is an unknown variable?

Yeah, the percieved loudness is just a range of hearing, but I still think it could always be measured. Even if a species can't hear it, it's still there. So I guess it's like one of those equations with real, balanced answers yet won't make sense or be converted into another measurement form--like you can't turn a gallon into a pound. (or sone to db...)

the lamb 2006-01-30 18:00

OK then tell me this......
if tomorrow some scientist discovered a way to let x-rays invoke sensations in the rods and cones of the human retina (one might say that one can see xray films but that is becoz they are colourcoded to fit the human vision) and he were describing the "colour" of the x ray .........would the wavelength of the ray be enough to describe the sensation!!!!!

we know the wavelength of an xray, of an infra red ray, of nearly all the rays existing.
but ironically humans only have a very, very, very (not enough stress), narrow range of vision.

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