sound and noise and stuff

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Oberon
Posts: 229
Joined: Thu Oct 07, 2004 10:25 am
Location: East of the Mississippi

sound and noise and stuff

#1 Post by Oberon »

Wow, three different posts about sound and noise and windows...

I am starting a fourth in the hope that I can answer some questions from all three previous posts in one place. I am thinking that this can get complicated very quickly, so I am going to throw in a quick course on basic sound and terms related to such so that if I use these terms later they may make some sense - please bear with me here.

In order to have sound you need three things, a source, a medium, and a detector.

The source is, well, the source of the sound (kinda self-explanatory).
The medium is whatever is transmitting the sound from point A to point B.
The detector is you.

In order to eliminate the sound, you need to eliminate one of the three elements. Since removing the source is unlikely, and since eliminating the detector is somewhat self-defeating, that leaves the medium as the element that we have to deal with.

Sound frequencies are measured by the number of "cycles-per-second" and are referred to as "Hertz" or Hz. One Hz = one cps (or cycle-per-second)...100 Hz = 100 cps - 1000 Hz = 1000 cps - and so on and so on.

As human beings, we are born with the ability to hear from 20 Hz up to about 20,000 Hz. By the time we are teenagers, we have lost the ability to hear above about 14,000 Hz or so (with exceptions, of course). We also don't hear at the same level at different frequencies. For example, I mentioned that we hear down to about 20 Hz. Well, we don't hear a 20 Hz frequency as well as we hear a 400 Hz frequency. We are tuned to hear specific frequency ranges better than we hear at other frequency ranges. Our best hearing range is from about 1000 Hz to 4000 Hz - and, coincidently, the human voice tends to range from about 400 Hz to 4000 Hz. Go figure - heck of a design feature. Our voice range can go higher and lower than the frequencies noted, but the 400 to 4000 Hz range is generally accepted as "intelligible".

The lower the number the lower the frequency. Traffic noise is low frequency, whereas a child screaming in the aisle next to you at the grocery store tends to be a relatively high frequency - often to the point of pain and distraction.

Sound amplitude, or pressure, or loudness, is measured using decibels or dB. A dB is simply a logarithmic unit used to describe a ratio - or by the dictionary definition:

"A unit used to express the intensity of a sound wave, equal to 20 times the common logarithm of the ratio of the pressure produced by the sound wave to a reference pressure (typically 1 micropascal at 1 meter)."

Forgetting the mathematical definitions for a moment, for our purposes, the higher the dB the louder the sound is. I may reference back to this later because some questions are best answered mathematically (at least partially), but I will try to avoid going there!

A change of 3dB either higher or lower equals a doubling or halving of the sound level. And of course, being a logarithm, the increases and decreases are exponential - meaning that a higher dB can be A LOT louder than a lower dB (and I won't go into that unless someone has a specific question).

There is a little thing used in human acoustics called a "dbA". This is based on our ability to hear one frequency better than another - even at different amplitude levels. Our hearing response may not be the same to an identical dB level at two different frequencies, and because of this, the folks that do such things have come up with a way to measure our response to various frequency stimuli at different dB levels. They call this "dB weighting" or dBA.

dBA is used when designing acoustical systems.

A few definitions:
Amplification increases the sound pressure level (SPL).
Amplitude is the "loudness" of the sound or "power" of the SPL.
Attenuation decreases the sound pressure level.
Sound Transmission Loss (TL) is a measurement of the amount of sound energy that is attenuated, or lost, when sound passes thru a specific medium - actually, not quite that simple, but it works for what we are doing.

Now I have to leave again, but I do anticipate being home later this evening, and at that point I will continue this thing on another post - this one is already long enough!

Have a great day all! And PLEASE, if you have questions about this stuff - ASK! I know that this stuff becomes complex very quickly and I also know that I don't always explain things in the clearest way possible when writing these things... :?

researcher
Posts: 129
Joined: Tue Nov 30, 2004 11:39 am

#2 Post by researcher »

Oberon, are you also an audiophile? Just curious because many audiophiles know this also.

eberry
Posts: 42
Joined: Fri Jan 13, 2006 1:25 am
Location: Central US

Re: sound and noise and stuff

#3 Post by eberry »

Oberon wrote:In order to have sound you need three things, a source, a medium, and a detector.
You are bordering on philosophical ground with the last item here. :)

researcher
Posts: 129
Joined: Tue Nov 30, 2004 11:39 am

Re: sound and noise and stuff

#4 Post by researcher »

every wrote:
Oberon wrote:In order to have sound you need three things, a source, a medium, and a detector.
You are bordering on philosophical ground with the last item here. :)
I don't think so. I see a stapler in front of me and you do not, now I see the stapler because of three things, stapler/source, light/medium, and a detector/brain. Without all three, the stapler is not a fact. If I leave the room, the stapler is no longer a fact,; I may have memory of the stapler, but that memory of the stapler is not the stapler; the stapler is no longer a fact to the brain, it is just a memory of the fact of the stapler. It would be the same if became dark, the stapler is no longer a fact. And if stapler is no longer there, the stapler is no longer a fact. I don't think that this is philosophical.

Now if someone says that the observer is the observer; that would be philosophical untel it is seen as a fact, than it is no longer philosophical.

researcher
Posts: 129
Joined: Tue Nov 30, 2004 11:39 am

#5 Post by researcher »

Memory is a fact because there is awareness of it, memory arises as thought, now the question is, am I 'thought', is this a fact? Or is this philosophical ground ?

Oberon
Posts: 229
Joined: Thu Oct 07, 2004 10:25 am
Location: East of the Mississippi

A tree falls in the woods----

#6 Post by Oberon »

Actually Researcher, I am nothing of an audiophile...heck, I never even figured out how to program the VCR.

But, I do have a background in acoustics - ocean acoustics to be precise.
My understanding of sound performance combines that background with my current position...kind of a professional interest rather than a hobby. In general I would expect the true audiophile could run rings around me in this area, but I have enough knowledge of the subject matter to (hopefully) help folks thru the weirder parts and to occasionally embarrass myself...


Thinking of the tree in the woods eberry? Actually, I even considered using that particular analogy to further confuse the whole idea, but I decided to avoid it.

Nope, my comment on the three things needed to have sound was based on the strict physical definition...of course one can argue that physics is simply a contraction "physical philosopher" and that all physics is ultimately philosophy...but, I digress.

Obviously, the part of the argument relating to the philosophical question has to be the need for a receiver to have sound. Just as obvious, without a source for a sound, then that sound cannot exist. Without a medium, then the physical sound waves produced by the action of the source of the sound cannot exist. Despite Star Trek and Star Wars and the miriad of other deep space extravaganzas, there ain't no noise in space - there is no medium to transmit the sound waves. One of the things (of many) that I really liked about "Firefly" - no sound in the dark.

The stapler was a great analogy. In the same sense as in sound, there is a source, and a medium, but if no one "observes" the stapler - if there is no detector - does that mean that the stapler does not exisit? Despite memory of the stapler....

If one were to carry Shrodinger's thesis to the extreme, then one could say that in that circumstance the stapler exists and does not exist at the same time - depending on an observer...to measure is to affect existance.

Of course like the idea :D of the "cat in the box", the translation of mathematical concepts to simple words does leave something to be desired. One could then argue that that is, afterall, the basis of quantum mechanics - which we "know" works, but we are not always certain exactly how it does so.

And anyone who doesn't think that parts of quantum mechanics borders on the philospohical...!

To paraphrase and totally misquote Albert Einstein...God does indeed play dice with the Universe.

Thanks eberry and researcher, that was fun! Of course now I have to leave and I haven't written a single word about windows! lol :D

And a few additional quotes attributed to Einstein:

"Science is a wonderful thing if one does not have to earn one's living at it."

"The secret to creativity is knowing how to hide your sources."

"The only thing that interferes with my learning is my education."

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