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Thread: Positive and Negative

  1. #46
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    Quote Originally Posted by millionrainbows View Post
    But both conditions, normal or higher pressure, are both "positive" values. There is no negative pressure, as you say. The sound wave is acting upon values of pressure which are all positive.

    Mean atmospheric pressure is a force which is constantly positive, and which is "pushing in" on the eardrum. The natural state of the eardrum, then would be no pressure at all. So all of this "pushing and pulling" and "waves and troughs" are occurring under atmospheric pressure which is, to begin with, a state of positive pressure. Anything less than that is not a "negative" value, only a lesser positive one.
    Look carefully at this picture:



    The ear drum (also called tympanic membrane) separates the outer ear (where sound comes in) from the middle ear (also called tympanic cavity). The middle ear is not vacuum, it is full of air at atmospheric pressure, it is connected to your throat by the auditory tube (also called the eustachian tube). So yes, all pressure is positive. The ear drum is subject to atmospheric pressure from the front (the outer ear) and atmospheric pressure from the back (the tympanic cavity). So the natural state of the eardrum is equilibrium, no net pressure since there is equal pressure pushing in and pushing out on the eardrum. Suppose you hold up a piece of paper. Does atmospheric pressure rip it out of your hands? No. There is atmospheric pressure exerting enormous force on the front of the piece of paper, but there is also atmospheric pressure exerting an equal and opposite enormous force on the back of the paper. They cancel and there is no net force on the paper. The same with your eardrum.

    Now, back to the original claim, that an audio signal should be always positive because sound pressure is always positive. This is not correct. It is true that sound is a fluctuation of the positive pressure of the atmosphere. The audio system does not need to provide the positive pressure. It is always there. The weight of the atmosphere above our heads is producing atmospheric pressure, about 100,000 Pascals, or 15 lb/in^2 whether you have a sound system or not. The sound system only needs to provide the small momentary fluctuations above and below the mean atmospheric pressure. A transducer is designed to produce a pressure perturbation proportional to the voltage input. Positive voltage the transducer element moves forward, making a positive perturbation to the pressure (which propagates away as sound). Negative voltage the transducer moves backward, making a negative perturbation to the pressure (which propagates away as sound). It is the change in the signal that produces sound from the transducer. Whether the signal bipolar (fluctuation around zero) or always positive (fluctuating around some positive offset voltage) makes no difference. The positive pressure of the atmosphere does not depend on the speaker.
    Last edited by Baron Scarpia; Jun-25-2019 at 18:07.

  2. #47
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    Quote Originally Posted by Baron Scarpia View Post
    A transducer is designed to produce a pressure perturbation proportional to the voltage input. Positive voltage the transducer element moves forward, making a positive perturbation to the pressure (which propagates away as sound). Negative voltage the transducer moves backward, making a negative perturbation to the pressure (which propagates away as sound). It is the change in the signal that produces sound from the transducer. Whether the signal bipolar (fluctuation around zero) or always positive (fluctuating around some positive offset voltage) makes no difference. The positive pressure of the atmosphere does not depend on the speaker.
    I think it does. Ideally, a speaker should be "at rest" (zero voltage) and only make positive excursions. Likewise, an amplifier should only produce positive voltages.
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    I'm not positive if this thread sucks or blows.
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  5. #49
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    Quote Originally Posted by millionrainbows View Post
    I think it does. Ideally, a speaker should be "at rest" (zero voltage) and only make positive excursions. Likewise, an amplifier should only produce positive voltages.
    To clarify, "I think it does." applies to my closing sentence, "The positive pressure of the atmosphere does not depend on the speaker"?

    Can you really mean that?

    You are an Aristotelian. You decide how things should be and conclude that they are that way because everything must be as it should be. Learned people took Aristotle's physics as gospel for 2000 years. It was completely wrong. Newton discovered this when he took the radical action of observing how the world really works.

    The inventors of audio reproduction found bipolar systems appropriate. The researchers, designers and manufacturers of audio equipment to this day find bipolar systems appropriate. All of the bipolar equipment in use works just fine. You do not think this is evidence you are wrong?
    Last edited by Baron Scarpia; Jun-26-2019 at 19:58.

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    I just called my local TV weatherman and told him to take all the L's off of his weather charts... only H's are allowed!
    Last edited by bigshot; Jun-26-2019 at 18:12.
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    Quote Originally Posted by bigshot View Post
    I just called my local TV weatherman and told him to take all the L's off of his weather charts... only H's are allowed!
    Maybe Trump will appoint you to the National Weather Service. That would be a sweet gig.

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    I'm going to start overdrawing my bank account. Which giant box set should I get?

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    The National Debt has been erased in one fell swoop!
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    "Negative," or what falls below "zero," is an abstraction. You have to be a "believer," I suppose. That's metaphysics, not reality. The only reality lies above the threshold of "zero."

    Quote Originally Posted by apricissimus View Post
    I'm going to start overdrawing my bank account. Which giant box set should I get?
    My advice: Don't spend money that you don't have.
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    Quote Originally Posted by bigshot View Post
    I just called my local TV weatherman and told him to take all the L's off of his weather charts... only H's are allowed!
    Low & high are perfectly logical; "negative" values work only in relation to actual values, and those must be "real" values which actually exist. "Negative" is only a "model" which is used in circuit design.
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    Quote Originally Posted by millionrainbows View Post
    "Negative," or what falls below "zero," is an abstraction. You have to be a "believer," I suppose. That's metaphysics, not reality. The only reality lies above the threshold of "zero."
    To fathom negative numbers you only have to be a "believer" in subtraction.

    Quote Originally Posted by millionrainbows View Post
    Low & high are perfectly logical; "negative" values work only in relation to actual values, and those must be "real" values which actually exist. "Negative" is only a "model" which is used in circuit design.
    "Negative is only a "model" which is used in circuit design? Have you ever used actual wires to connect a circuit?

    The existence of negative and positive potential in electronic circuits is not a "model" or "virtual." Electrical phenomena derives from the existence of positive and negative charges, which have opposite effects.

    Beyond this, how can you say "So how can any amp or speaker be accurate, unless it is totally positive?" if you do not even accept the existence of negative values? If, in your mind, negative values don't exist except as a "model," what are you complaining about?
    Last edited by Baron Scarpia; Jun-26-2019 at 23:54.

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    I tried hooking up my speakers by just connecting the red lead and not the black one. Now my blacks are blacker.
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    Red & black are opposites, but they both exist above zero.

    IF you have a receiver with "A & B" speaker outputs, hook up your "A" speakers as normal, then on the "B" outputs, hook a third speaker up to either both reds or both blacks. Position the third speaker behind you, as if you are in a triangle. Viola, instant surround sound.
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    Quote Originally Posted by millionrainbows View Post
    Red & black are opposites, but they both exist above zero.
    What does it mean for something to "exist above zero?" You have a penchant for making statements that are so vague that it is impossible to contradict them.

    There are two obvious ways to characterize the output pins of a power amplifier, current sourced, or electrical potential.

    If a load is attached to the outputs (a speaker, a resistor, etc) one will source positive current and the other will source negative current at any given instant. The sum of the current on the red and black pins is zero, so if one is positive the other must be negative. As the waveform develops the current changes and may flip sign, so that the pin that was sourcing positive current sources negative current, and vice versa.

    If we consider electrical potential, then there is no "absolute" potential. Only potential differences are physically defined, and the amplifier generates a well defined potential difference between the red and black pins. This potential difference will oscillate between positive and negative as the waveform develops. If you want to define the potential of an individual pin you will have to choose a potential reference. Earth ground is the most convenient reference. For most amplifiers one pin will be tied to ground, which may be ultimately be connected to the case and/or to the grounds of the line-level inputs. If one pin is tied to ground the other will oscillation between positive and negative potential with respect to ground.

    So either way, you cannot justify the claim that both the black and red pins are always positive.
    Last edited by Baron Scarpia; Jun-28-2019 at 23:33.

  18. #60
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    Quote Originally Posted by Baron Scarpia View Post
    What does it mean for something to "exist above zero?" You have a penchant for making statements that are so vague that it is impossible to contradict them.

    There are two obvious ways to characterize the output pins of a power amplifier, current sourced, or electrical potential.

    If a load is attached to the outputs (a speaker, a resistor, etc) one will source positive current and the other will source negative current at any given instant. The sum of the current on the red and black pins is zero, so if one is positive the other must be negative. As the waveform develops the current changes and may flip sign, so that the pin that was sourcing positive current sources negative current, and vice versa.

    If we consider electrical potential, then there is no "absolute" potential. Only potential differences are physically defined, and the amplifier generates a well defined potential difference between the red and black pins. This potential difference will oscillate between positive and negative as the waveform develops. If you want to define the potential of an individual pin you will have to choose a potential reference. Earth ground is the most convenient reference. For most amplifiers one pin will be tied to ground, which may be ultimately be connected to the case and/or to the grounds of the line-level inputs. If one pin is tied to ground the other will oscillation between positive and negative potential with respect to ground.

    So either way, you cannot justify the claim that both the black and red pins are always positive.
    Both voltages exist as "real" values; they are only "positive" or "negative" in relation to each other. You're still stuck in "positive and negative" thinking; those concepts are abstractions. It's all voltage, and it's all real.
    "The way out is through the door. Why is it that no one will use this method?"
    -Confucious

    "In Spring! In the creation of art it must be as it is in Spring!" -Arnold Schoenberg

    "We only become what we are by the radical and deep-seated refusal of that which others have made us." -Jean-Paul Sartre

    "I don't mind dying, as long as I can still breathe." ---Me

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