Hearing frequency?

By the way...

Pay attention to your signature.

:wink:

We don't want to give the wrong impression here. I don't believe that ordinary househould dimmers use electronics to dim the lighting.
They use resistence dimming. The wave peak changes rather than clipping of the 120 volt wave.

The clipped waves heliotrope posted are a result of electronic dimming. It used to require dual SCRs before triacs came into being. Basically its a switch that turns off the power during the middle of the wave.

(I used to do electronic dimmer repair in a former life.)

A high pitched sound that is turned on and off at a rate of 3 times a second.


The light being output is a result of the glowing filament. The filament doesn't stop glowing the instant the electricity is turned off. If you were to graph the light output over a cycle when the electricity is cut off in the middle of the high part of a sine wave you would see an angled decrease in light output. A 1000w light can still glow for another second after the electricity is turned off. The electricity is turning off and on but the light output doesn't exactly match the curve of the electric because it retains heat and therefor continues to produce light. Photons are not the same thing as electrons.

You state I am incorrect yet later you agree with my statement. WTF?

This is wrong.
It does not only reflect the electricity to the lamp.
It does truly reflect the light being output from the lamp.

The reason that normal filament bulbs do not flicker is because of the heating effect of the filament. They cannot cool down at the same rate as the electricity is changing and so they give a far more consistent light output at the expense of heat generation and resistive losses.
Flourescent lights DO flicker at the mains frequency because they are going on and off at 60Hz.


That's what I said the first time.
Go back and read it.
I'm not getting into a p*ssing competition with you dude.
Go educate yourself first and then it'll at least be a level playing field.


I didn't say they were.
I didn't even mention photons.
This is your creation entirely without reference to anything I wrote.


Incorrect.
I'm getting tired of saying this...
Go
Read
It
Again.

Your beliefs are irrelevant.
It's the facts that matter.
Dimmers use SCRs or similar devides to chop up the waveform and thus reduce the power going to the bulb. Hence the light output is variable.


Do you have any idea how much power that resistive dimming would dissipate ?
It would not only be incredibly wasteful but where would all the heat go ?
I don't recall seeing cooling systems attached to dimmer switches.
Perhaps you do things differently in the USA.
Maybe you don't need to dissipate the heat because electronics works differently there.
Maybe you don't need to dissipate the hundreds of watts that would be generated in a resistive dimmer.
I don't know, you tell me.


Then you will now exactly what I'm talking about.

Well Mr Smartypants, perhaps you can tell me when the light being output by an incandescent lamp on an AC circuit goes negative then.

The light being produced is at its brightest in both the positive and negative amplititudes of the electrical cycle. The light being produced does NOT have the same wave as the electricity. The filament doesn't care which way the electricity is flowing. It only cares about how much is flowing. A graph of the light produced would have a positive amplitude height at the both the positive and negative amplitudes of the electricity. It is in no way the same wave form.

But this is all a rather stupid argument that has nothing to do with the original question.

Lets go back to sound.
Sound is heard from 20 to 20,000 htz.

In order to figure htz you have to measure from one wave to the next. Is that correct? or do you want to tell us that is different?

Get back to me when you've educated youself and have grown out of the desire for a nit picking contest.

This is all off the top of my head and an attempt to make it easy to understand. I am sure that heliotrope will be back to correct where I am wrong.


Sound is caused by vibration of an object.

We will start with something simple here like a rubber band or rubber binder or a guitar string. If it is stretched and plucked it vibrates back and forth. With some simple physics we can see how it actually does it. It has a resting position when stretched from that resting position and released it passes back through the resting position because of the energy it has. It will not go as far to the other side before it moves back toward the resting position. It will continue to move back and forth, each time not traveling quite as far until it finally loses all its energy and returns to its resting position again. When the movement of the string is graphed it is a sine curve with the same frequency throughout the time it moves but the amplitude is reduced each half cycle. As the string moves it causes the air to move in a similar fashion. We hear 2 things, volume and pitch. Volume, or how loud the sound is, is caused by the amplitude of the wave. Pitch is caused by the number of times the item vibrates per second.

The same thing happens anytime sound is created. An object vibrates losing energy each vibration until it reaches its resting position. If the vibration is roughly between 20 and 20,000 htz humans are capable of hearing it. Htz is the measument of how many times a second the vibration is occuring.

More simple physics here. If you throw a ball up into the air, gravity will bring it back down. There are two forces exerted on the ball. The speed of the ball will decrease as it goes up until it reaches zero, then gravity will speed it up as it comes down. The same principle is in play in vibration. The speed of the string as it goes through the resting position after being plucked is gradually reduced to zero before it starts back the other direction. The two forces involved mean the string can not stay at zero for any length of time in either extended position.

To try to understand hearing we will now look at it all works together. (Heliotrope talked about some of this earlier.) This time we will use a drum. A drum has a diaphragm stretched over it. As it vibrates it causes the air to move. If we think of it in slow motion we can see as the diaphragm moves down it creates more space for the air to fill so pulls air towards it. As the diaprhagm moves up it pushes air away from it. If you take a tube and put a diaphragm over each end so that no air can leak out you can see as you push in on one end it causes the other end to extend outward. This is the same basic principle in hearing. As something vibrates it causes the air to vibrate which causes your ear drum to vibrate. The thing to remember is everything vibrates. It doesn't matter what it is. When you supply energy to drive it from its resting position, it will move in a direction then come back the other direction past its resting position. The object could be so hard that the vibration only occurs on the molecular level but it does occur. This is basically how sound travels through solid objects.

Now we get to the difference that heliotrope and I are having about whether sound can be a square wave or not. A square wave is a sine wave with the top cut off. What that means is that something has to get to a certain point in its vibration, stay there for an extended period then start back the other direction. There is one problem with that in vibration that creates sound. It means that another energy must be applied to hold that vibration in a stationary position before it starts again. In physics when a ball is set on a table the table exerts an upward pressure equal the the downward pressure gravity is exerting on the ball. Back to throwing a ball up in the air again. The ball goes up in an arc, reaches zero for a brief moment before it comes back down. If we want to create a square toss we need something to hold the ball up there for a while. Now imagine we toss the ball up in the air, just as it reaches the speed of zero it goes on a table, it then rolls across the table and falls off the other end. We would have created basically a square toss instead of an arced one. The question is can we do that with a guitar string. Lets try.

Remember we can only hear certain sounds. That means we need to hit the guitar string fast enough to achieve a speed we can hear then we have to stop it at its height before we release it. I believe there is a certain type of guitar playing that does that. I don't remember what it is called. It involves hitting the string hard with a finger and driving it against the neck and holding it there. But what happens when we do that? Instead of being a real brief sound we get a completely different sound that continues when the finger is no longer moving. Rather than stopping the string from vibrating we have only changed how the string vibrates. By holding the center of the string we have now created 2 shorter strings and instead of holding the energy in the middle it is transferred to each of the 2 shorter strings that are now vibrating. Those are vibrating with sine wave just like the longer string did when plucked. The sound is different because the length of the wave has changed but the type of wave hasn't. It is still a sine wave.

Now lets go back to the experiment that heliotrope suggested I try with a speaker by just applying a constant DC current to it. When we do that it drives the cone out and holds it there. We hear a small sound while that happens. But what is that sound really? Are we hearing just the sound of the cone moving out one time or are we hearing something else? A speaker is made up of several parts. If we move something and stop it suddenly without it moving what happens to the energy? It moves to other areas that aren't held. A speaker is basically a paper diaghram with a way to move the center in and out. The speaker is able to move the center at a rate faster than humans can move. We can do a simple experiment to show how it works though. We will take a drum. Bounce the drum stick off the center of the drum and gives a certain sound. Now we will hit the center with the drum stick and hold it there against the drum not letting it bounce. The sound is different. It acts just like the guitar string. When the center of the drum can't move it caused the other parts of the drum diaphragm to vibrate and give off a different sound.
If we tried this experiment with different sized drums, each one would give off a different sound. Now if we tried the experiment with different sized speakers, each speaker would give off a different pitch "thunk" when we applied the same current to it. The speakers are acting just like the drums. We aren't hearing the one outward movement of the cone but the vibrations of the parts that were still free to vibrate and use the energy.

In electricity we have a way to contain the electricity so it is possible to do square waves. When the sound is actually created it is impossible to contain that energy since the energy will always travel to the path of least resistence. The energy could be converted to a vibration that can't be heard but the vibration will always occur and it will always be a sine curve.

That doesn't mean sine curves can't be interrupted for instance if you hit the drum again in the middle of a curve. It will just create a new curve. But that means you are adding new energy to the system. With the addition of energy you can create all kinds of waves that are chopped up. By doing opposing sounds you can actually create silence.

The original question was how long can a silence be between sounds to still be heard as a sound.

In order to address that we have to know the difference between silence and sound. Sound is the presence of waves on a wavelength audible to humans. Silence is the absence of audible waves.

Silence can not be the distance between 2 square waves because a single square wave can not be sound.

My original speculation concerning the shortest distance of silence is probably just below the audible wave length seems to be wrong as I think about it more. I will expound more later.

I have to say that I disagree with heliotrope. We will not always be able to percieve pulses of constant-pitch sound. As with our eyes, there will come a point when the pulse rate exceeds the rate at which our auditory nerves can reset.

no.
sorry.

At approx. 20 Hz the tone becomes audible. Before that it's too low for the human ear to pick up. And it stays audible all the way up to approx 20 kHz in a healthy ear.

And there really is no difference between the frequency of the pitch and the vibration of the wave. A wave vibrating at the frequency of 440 Hz is the tone we know as A. So is 220 Hz, 110, 880, and so on. In music that's called octaves.


Btw, I didn't have time right now to read the whole thread. If I'm repeating something that's already been said I am sorry.. :wink:

No Cyracuz not the range of audible hearing. A pulsed tone. It is a Bernouli probability trial.

Oh yes, and I like your new look!

I thought pulsed tones were nothing but interruptions of the waves?

In old organs and keyboards they used large fans to interrupt airflow, manipulating not the tone itself but the medium that carries it, creating a tremolo effect, which is essentially a pulsing tone.

It is kind of apples and oranges (but in this case they have common ground). Think about a tone, A at 440 cycles per second (Hertz). Then think about turning it on and off, say at about 3 times per second (3 Hertz). The brain interprets it as two separable and independent auditory phenomena.

They are independant events until the interruptions begin to approach audio frequency. It is really a function of brain chemistry as to when the interruptions, along with the tone, are interpreted as a singular auditory phenomenon. And it is uniquely different for each person listening to the event.

Lucky for us apples and oranges go well together.

How to create a pulsed tone:

Have a mate sit on a chair that can torate. Place a microphone in front of his mouth and have him sing a steady note for as long as he can hold it.

Hit the record button and spin the chair your mate is sitting on as fast as you can.

And don't forget the dramamine.

If you spin the chair fast enough that is a given.

Yes, but what really happens if your angular velocity approaches the speed of light? Does the sound turn into color?

I think you get a temporal echo. A sort of low pitched moan that can be heard in the sky amidst booms of thunder in all ages of time.