The speed of sound in an ideal gas is independent of frequency, but it weakly depends on frequency for all real physical situations.
jarednjames said:Here's a start for you:
http://www.madsci.org/posts/archives/1999-11/943317470.Ph.r.html
If you read through here:
http://en.wikipedia.org/wiki/Stokes'_law_(sound_attenuation)
You will note that as the frequency of the sound increases, the attenuation also increases (by the square of the frequency).
Put simply, the higher the frequency of the sound, the more attenuation there is as it travels through the medium (in this case air) and as such the quicker the intensity drops over distance.
ymalmsteen887 said:Actually the part about the 100hz wave traveling four times as far as the 400hz wave wouldn't a 100hz wave require more energy to travel the same distance as 400hz given any level?
jarednjames said:Energy of a sound wave isn't related to its frequency. So no, it wouldn't require more energy to travel the same distance.
What the article refers to is that for the level of attenuation a 400hz wave encounters over a set distance, a 100hz wave would have to travel four times as far to encounter the same level of attenuation.
Not that a 100hz wave travels four times further than a 400hz wave.
jarednjames said:This is where the equations from the second link I gave you come in.
The 12200hz wave has massively higher attenuation than the 20hz wave. So the intensity of the first wave (and as such the pressure) after a set distance will be less than that of the second wave. (The first wave will have a lower decibel reading than the second after a set distance.)
ymalmsteen887 said:Dont you mean the first wave is the strongest and the second wave will have a lower decibel reading.
jarednjames said:No. Have you not read the links I posted?
The higher the frequency, the more attenuation the wave encounters.
This means that after a set distance, the higher frequency wave will have a lower intensity (and as such lower decibel reading).
A low frequency wave can have a decibel level equal to a high frequency wave.
ymalmsteen887 said:Tell me if this is right, when a bass speaker moves forward the air in front is compressed and the air behind the speaker rarefacts(whatever the opposite of compression is called) so the air in front will travel towards the back to achieve equilibrium, thus not producing a very loud sound not matter how fast its moving is this correct?
jarednjames said:Ah, I see your problem. You're not understanding what a decibel is and what it means in relation to sound pressure. Read up on these first.
Pressure and volume are not the same thing. A bass speaker can send out a wave that is almost inaudible, but the pressure of that wave can be damaging to the ear. This means the wave has a low volume and high pressure.
The opposite of compression is expansion. I'm not sure about your explanation of a bass speaker. All speakers operate on this principle, so the volume hypothesis above cannot be correct.
ymalmsteen887 said:You know that's why they put the woofers in an enclosure to have the back wave work with the front wave.
jarednjames said:Again, you need to understand the difference between the pressure and the perceived volume.
Your description didn't mention the enclosure, hence it wasn't strictly correct and could apply to all speakers.
I'm not going to sit and argue the technicalities. You've received the answer as to why low frequencies travel further than high frequencies. Any further questions on that are welcome.
ymalmsteen887 said:I got on here to learn about sound, it seems youre saying I can only ask one question, if this forum doesn't allow this kind of back and forth could you recommend a place I can go for that kind of exchange. I wasnt going to ask just one question and it would be a waste to start another thread for different questions.
ymalmsteen887 said:Dont you mean the first wave is the strongest and the second wave will have a lower decibel reading.
jarednjames said:Just to come back to this, energy is related to amplitude not frequency. If both waves have the same amplitude they have the same energy.
Decibels are related to the pressure level, which is related to the energy of the wave.
So a 20hz wave can have a higher pressure reading than a 122000hz wave.
Have a look at these two:
Sound Intensity: http://en.wikipedia.org/wiki/Sound_intensity
Sound Energy Density: http://en.wikipedia.org/wiki/Sound_energy_density
They should help you with the energy / pressure of a sound wave and with your above problem.
Just note that a higher frequency doesn't mean a higher decibel reading.
ymalmsteen887 said:I am trying to understand how sound waves add to together how come if I take a bucket and hum some notes certain notes will sound louder than others same thing with a trash can but if I take a dresser shelf or a coffee mug nothing happens no matter what note I play?Also when I play a subwoofer in my room its not as loud as when I put in my truck but when I put it a two door car its not as loud as is was when it was in the room this doesn't add up if the if the truck is louder than the room the car should be some where in between but its the least in volume?(because my room is twice as big a space as the car.)
Pythagorean said:if dimensions of the container are on the order of the wavelengths of the music, then you will have resonance. Pressure fluctuations are doing real work on their environment. Think of a box with a sound source in it for which:
a) the soundwaves are much bigger than the box
b) the soundwaves are equivalent to the box
c) the soundwaves are much smaller than the box
for a) the waves are really large and tend to pass through the box with little attenuation, so they do little work on the box (they don't try to move the box so quickly) but might move the box very slowly. But the whole box will tend to move as one object, slowly, like a boat on a long ocean wave.
for c) the waves are tiny, on the order of the molecules of the box so they try to do work on the atoms (which are far too strong in normal considerations) so they just get attenuated. (a boat with little choppy waves doesn't feel a thing).
for b), now the boat and the water waves (or the box and the pressure waves) are about the same size. The boat starts getting slammed around by the waves, the box has a measurable pressure flux across it now (the wavelength of the pressure wave across the box assures that).
If the wavelength and the size of the box are exactly equal, the waves will reflect off of the sides perfectly, coming back to their peak exactly where new waves are at their peak (because we're still generating sound from the source). Whereas as we drift from perfect match a bit, the peaks start to mismatch and you begin to have destructive interference.
If we allow the surfaces of the box to flex a bit, like a membrane, we will now see the membrane breathing with the pressure waves (and of course, the membrane will respond similairly to a) and c).
ymalmsteen887 said:I didnt understand all of that and it didnt answer my question.
I used to think that when you had a subwoofer in a room that the bass was strong er in the corners because of all the other waves colliding with each other. So I thought that a kickdrum sound you wouldn't get a boost because it was only one wave and wouldn't get any increase but I know realize that's wrong the bass is stronger in the corner becuase the wavelength is still bouncing off the wall and combining with the remaining part of the wave, is this correct?
Pythagorean said:well yes, but particularly because it's combining constructively. All over your room, pressure fluctuations are combining, both destructively and constructively. A low bass note (say 55 Hz) is producing 55 "waves" per second so your room is flooded with a chaotic landscape of spherical pressure waves interacting in just a second. The waves propagate at 350 m/s too, so they're allowed to fill up your room rather quickly.
And of course, it's not really just a 55 Hz tone. It's a harmonic series, and it's interacting with matter in your home, so there will be nonlinear effects (especially in a garage band setting where the sound sources are unusually loud compared to the size of the room).
ymalmsteen887 said:The first wave of the 55hz frequency should have lost too much energy to effictivly increase with the second wave. This is why I want to know a formula to figure this out cause I am wondering what the second wave does when the first wave is coming back in the opposite direction this is hard to wrap my mind around.
ymalmsteen887 said:I understand what you mean. I mistakenly thought when you said the second wave was stronger that the first wave was the second wave once it proceeded past a certain point. You meant the very next wave coming up from the source, correct?
Born2bwire said:Not really. Unless you have a specially designed room, the reflections off of a wall will be pretty strong. Just imagine how long an echo lasts and compare this to the distance that the sound traveled in all that time. For a one second echo, that's 343 m. Take a room of 3 meters cubed and let's estimate that on a 45 degree diagonal that the average path before reflecting is 4.25 m then that's 80 reflections that have occurred. And believe me, even an average room in a house has a lot of echos. We rarely are placed in an environment that is free from reflections to be able to tell the difference.
As for what happens when two waves meet, they simply add up. If the two waves are both in phase, that is their peaks match and their minimums match, then they will add up constructively and support each other. If they are out of phase, where the peak of one wave occurs where another wave has its trough, then they will add up destructively and cancel each other out to some degree.
ymalmsteen887 said:So youre saying that if a note is sustained then it will progressively get louder
Plus when a bunch of people in a room sing together or clap its not much louder than if there wer just 2 or 3 people doing it because like I said the waves that are reflected are much weaker, how come when I go outside I don't seem to notice a drastic difference in the volume of my voice?
jarednjames said:No, this is only true if there is constructive interference.
So you think me and you in the Royal Albert Hall clapping is equivalent into a full crowd doing so?
You are stating the "reflected waves are much weaker", are you sure about this? This is all down to acoustics.
A simple test (if you get the chance) is to whistle in a room when the furniture is in it and then whistle when there's no furniture in it (it's empty). You will notice that in the empty room you get a slight echo, or that the sound of the whistle is slightly different.
ymalmsteen887 said:Im not saying its it exactly the same but a small high school gym full of people clapping won't sound any louder or quiter than a basketball stadium because its all relative to your position. Basically if that logic was true than all the sounds happening anywhere would add together , after a certain distance the waves don't seem to matter anymore actually just one person clapping is preety much how loud it gets the combination of people clapping just gives a more lively sound. The same reason why there are mulitple violins in an orchestra to give that unison sound because the notes arent tuned perfectly the same.
ymalmsteen887 said:So youre saying that if a note is sustained then it will progressively get louder that would mean that sustained bass as opposed to like a kickdrum would be louder yet I've never experienced this. Plus when a bunch of people in a room sing together or clap its not much louder than if there wer just 2 or 3 people doing it because like I said the waves that are reflected are much weaker, how come when I go outside I don't seem to notice a drastic difference in the volume of my voice?
Born2bwire said:Actually, the notes in an orchestra have to be tuned pretty well. If they are off then the orchestra produces beats when it plays a sustained note. Case in point:
http://upload.wikimedia.org/wikipedia/commons/6/6f/Terzosuono.ogg
As the two frequencies just start to diverge we can hear the rumble from the beating that occurs. This starts to happen in the first two seconds of the clip.
Yes, and it does. But the transient time here is too minimal for you to notice. Like I said, 343 m/s is very fast and so the first set of reflections comes in milliseconds. This is too fast for us to really consciously appreciate it though our body does make use of this slight delay for things like positional information.
As for going outside, you most definitely should notice a difference. Try talking in a closed room and then go out to an open field. The difference in terms of echos should be night and day.
ymalmsteen887 said:Im not saying its it exactly the same but a small high school gym full of people clapping won't sound any louder or quiter than a basketball stadium because its all relative to your position.
Basically if that logic was true than all the sounds happening anywhere would add together , after a certain distance the waves don't seem to matter anymore
actually just one person clapping is preety much how loud it gets the combination of people clapping just gives a more lively sound.
The same reason why there are mulitple violins in an orchestra to give that unison sound because the notes arent tuned perfectly the same.
jarednjames said:Not true. It's all about acoustics. One person clapping in a gym sounds different to one person clapping in a stadium.
Read here: http://en.wikipedia.org/wiki/Acoustics
I gave you the links to intensity and energy. You need to read them and ensure you understand them. They explain why waves only travel so far before they "don't matter".
More people clapping gives the perception of more loudness. Again, acoustics.
This is like saying 5 speakers give the same volume as 1 speaker. Although the sound system may show them giving the same output, the actual perceived volume will be louder. (Think of the difference between 2.1 and 5.1 surround sound systems.)
As above, more violins will give you more volume - but it's not a case of doubling the volume as you double the number of violins.
ymalmsteen887 said:Theres definitley a difference in the way it sounds but no real difference in volume.
I still don't get the whole waves adding up wouldn't my body feel the first wave of pressure and then get more intense as the waves build up this would make the sound really bad.
ymalmsteen887 said:Wait a minute you just said that waves travel so far before they don't matter so you understand what I mean by the extra people want make it louder, the people 500 feet away in the stadium arent going to contribute to the overall volume of the people near you.
If the violins are louder because there is more than one what about when they have a violin soloists and you can hear the violin independent of the others which are playing in unison?