How tall is this sound

A 200 hertz sine wave has a wave length of 6.671metres this I understand. Also sound travels at 340.29 m/s. Again easy I can dig out the formulas for these from notes I took at SAE ten years ago, or even easier just look online. But what I've often wondered about is, and this maybe incredibly easy to explain for someone (or just a dumb question) how do decibels(spl) correspond to a physical measurement in metres ? Obviously in the real world you don't get a sine wave traveling nicely across the room in a 2D manor but is there anyway too calculate how tall it would be peak to peak if it were say, 80dBspl ? On an oscilloscope you can measure the height of a sine wave and it changes in a linear fashion as in relation to the voltage. Could this translate to an SPL in any way? Can someone set me straight on this? :)

Doesn't sound propogate as a pressure wave? :shock:

Yeah thats true Adam. I guess what I am trying to understand is the height of that pressure wave for a given pressure level with as signal that is highly directional. The fact that sound doesn't really propagate in a direct line but radiates outward (I understand that the frequency determines how directional the sound is) is, I guess, why you measure the pressure level to determine loudness.

lows radiate in a 3 dimensional sphere from the source and the mids and highs are more directional .............. i think....... but in a small room things bounce off a boundary almost immediately

Your question hard to understand. You made a mistake in your first post when you wrote:

A 200 hertz sine wave has a wave length of 6.671metres this I understand.

It is around 1.7 m. I think your question is answered by pdf pages 50-58 in the JBL Sound System Design Reference Manual part 1. Andre

Thanks Mike and Andre. Yes my question is hard to understand. Even to me! I'll go away, read that reference manual and try to repose the question if I still don't have the answer.

You mean this? If a speaker pushes at air particles they have a certain velocity. If you increase the sound level the particles are moving over a larger distance as the speaker excursion increases . The particle or volume velocity increases. If particles were attached to strings this would influence the rate of speed they travel with, when one particle hits the one next to it with higher or lower speed. but you have to consider air particles as little balls attached to springs. If you hit the particles harder they will have a higher speed and move further away from equilibrium. But the spring will also get more loaded and pull back the particles at a higer speed. The frequency will be the same, the particles move over a longer distance but they move faster, so the frequency is constant. Or the time it takes for the particles to travel is the same as with lower sound levels, ifyou like it that way. at very high sound levels (>150 or 160 dB, I'm not sure), the spring gets loaded so much they aren't linear anymore and you see in a measurement that the positive part of the sinewave is faster than the negative part, causing distortion. This happens f.e. in the mouth of horns. This is also why the speed of sound is constant when level is increased or when frequency changes. For bending waves in solids this is a different story, like in the coincidence effect. Here you have different speed of sound over frequency. I still have to figure out how to explain this in balls attached to springs terminology. Even though I know the 4-order differential equations. :D

Well, I understand the springs and balls explanation Bert. So you can turn that big brain of yours to other things!