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Thread: Positive and Negative

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    Senior Member millionrainbows's Avatar
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    Default Positive and Negative

    When you think about speakers and amps and sound itself, a speaker has a negative and a positive travel; it goes from a + number to a - number.
    Real sound is not like this; it exerts a positive force on our ears. It does not "suck" our ears, because it is a positive pressure of air, always starting from zero.

    So how can any amp or speaker be accurate, unless it is totally positive?
    Last edited by millionrainbows; Jun-03-2019 at 15:17.
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    Senior Member Larkenfield's Avatar
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    I am only concerned about whether the speakers are accurate enough - no obvious distortion - and do not expect them to be an absolute reflection of reality. Reproducing anything is going to be different from the original, but of course some speakers are going to be more accurate than others without taking the issue down the rabbit hole. I'm quite happy with the JBLs that I have and the accuracy of my GS-1000 Grado headphones. I feel that I'm not missing much in the way of a good illusion of sound, no matter how it's being produced electronically.
    Last edited by Larkenfield; Jun-03-2019 at 17:01.
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    I'm not sure what we are talking about. Is it phase? Relative phase is important, absolute phase isn't important much at all. Speaker excursion pumps in and out with every waveform. Whether it goes in or out first doesn't matter. The difference between the parts of the soundwave is what defines the sound, not whether the cone goes in or out with the first one.

    Real sound is vibrations. The excursion of speakers creates vibrations. Sound is sound no matter if it's produced by a vibrating string, a vocal cord, or a vibrating cone in a speaker. The only thing that is different with speakers is the degree of fidelity- how close does it come to the intended sound. That depends as much on the room as the speaker.

    In the grand scheme of things, nothing is more important than the transducers. There are good speakers and lousy ones. They're the wild card in any system. It's always best to invest in good headphones or speakers before spending a lot of money on players and amps. Speakers and headphones are the mechanical step that actually creates the sound. It's where the rubber hits the road. Nothing will sound good if your transducers don't sound good.

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    I have a system with a pair of passive subwoofers and everyone says that phase is really important for it. The subs have to be in phase with the main speakers, the main speakers have to be in phase with each other. So I set it up, listened for a few days, checked the phase, found it was out of phase, made the required change.

    I’ll be buggered if I could hear a difference.
    Last edited by Mandryka; Jun-03-2019 at 17:18.

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    Yes, that is relative phase. Yes, that's very important. Phase problems affect higher frequencies more than bass, although bass can be muddled up by phase issues. Subs only carry a narrow band of the signal. That's probably why you didn't hear it as much with your subs. If your mains were wired out of phase, you would have heard it for sure.

    The concept is that you have a positive and a negative signal coming through the wire to the speakers. If one speaker is +/- and the other is -/+ you get phase cancellation... essentially one speaker is sucking while the other is blowing, causing the sound to be degraded. If both are in the same phase +/- and +/- they work together well. It doesn't matter which direction it is, it just matters that all the speakers are wired the same.

    Distance can also affect phase. That's why AVRs ask you the distances between the speakers so it can calculate phase offsets to keep everything in sync.
    Last edited by bigshot; Jun-03-2019 at 19:46.

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    Senior Member philoctetes's Avatar
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    What a shaggy dog question. How long did MR stare at the wall to come up with this one?

    See: output transformer
    Last edited by philoctetes; Jun-03-2019 at 19:42.

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    Senior Member KenOC's Avatar
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    Quote Originally Posted by Mandryka View Post
    I have a system with a pair of passive subwoofers and everyone says that phase is really important for it. The subs have to be in phase with the main speakers, the main speakers have to be in phase with each other. So I set it up, listened for a few days, checked the phase, found it was out of phase, made the required change.

    I’ll be buggered if I could hear a difference.
    I set up a subwoofer not long ago, to be used with physically rather large main speakers. The subwoofer had a phase switch. Toggling it back and forth made a very big difference in the amount of bass.


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    Senior Member KenOC's Avatar
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    Quote Originally Posted by millionrainbows View Post
    When you think about speakers and amps and sound itself, a speaker has a negative and a positive travel; it goes from a + number to a - number.
    Real sound is not like this; it exerts a positive force on our ears. It does not "suck" our ears, because it is a positive pressure of air, always starting from zero.
    Incorrect I think. Sound is a wavelike pattern of pressure changes in the air that push our eardrums inward and then pull them back outward. In other words, the air pressure is alternately higher than the undisturbed air and then lower.

    Just like at the beach – when the water bunches up into waves, the troughs between the wave crests get lower since there is only so my water to go around.


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    Senior Member philoctetes's Avatar
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    Quote Originally Posted by KenOC View Post
    I set up a subwoofer not long ago, to be used with physically rather large main speakers. The subwoofer had a phase switch. Toggling it back and forth made a very big difference in the amount of bass.
    Depending on the crossover frequencies, if the subwoofer is out of phase with other woofers this is what you might expect due to destructive interference.

    In Mandryka's case, the phase difference between stereo woofers would have more of an imaging effect, but because of the long wavelength, imaging angles (phase differences) increase with wavelength, so as bigshot said, there is no difference at long wavelengths.

    Imaging angles are related to diffraction effects. d sin (t) = m*l
    Last edited by philoctetes; Jun-03-2019 at 22:15.

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    Senior Member philoctetes's Avatar
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    Quote Originally Posted by KenOC View Post
    Incorrect I think. Sound is a wavelike pattern of pressure changes in the air that push our eardrums inward and then pull them back outward. In other words, the air pressure is alternately higher than the undisturbed air and then lower.

    Just like at the beach – when the water bunches up into waves, the troughs between the wave crests get lower since there is only so my water to go around.
    The actual motion of air or water is to move away from the trough into the nearby peaks, and back again, this is what we call current, I = dV/dt, where V is water in a volume, an AC current which goes positive and negative, so yes there is a sucking and pulsing effect at any point in space at the frequency of wavespeed/wavelength.

    The mean sea level is analogous to mean or DC voltage and the waves are the AC signal. Tides are the same way but their frequencies are daily. At the peak tides the current is minimized, and at mean tide the current is maximum. The pi/2 phase relationship between peak levels and peak current is mainly due to the fact that the derivative of a sine is a cosine, but pools that catch water can act like capacitors and induce small phase shifts...

    In a sound system, DC voltage carries no information or signal and is typically removed in the pre-amp stage by coupling caps in highpass filters. But it may return at the power output stage, where the power amp can be connected to the transformer with no DC removal since transformers don't "see" DC at all.

    "Nature abhors a change in flux" D.J Griffiths on Lenz's Law
    Last edited by philoctetes; Jun-03-2019 at 21:47.

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    Quote Originally Posted by philoctetes View Post
    Imaging angles are related to diffraction effects. d sin (t) = m*l
    I salute you, but this is the last outpost for me. Beyond here it starts flying over my head! I'm not a Doctor. I just play one on TV!
    Last edited by bigshot; Jun-03-2019 at 22:59.

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    Senior Member millionrainbows's Avatar
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    "Zero" is zero. Negative is negative. Reality doesn't "suck," it goes to zero, nothing. Absence of movement. Real sound is like this.
    "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

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    Senior Member millionrainbows's Avatar
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    Quote Originally Posted by KenOC View Post
    Incorrect I think. Sound is a wavelike pattern of pressure changes in the air that push our eardrums inward and then pull them back outward. In other words, the air pressure is alternately higher than the undisturbed air and then lower.

    Just like at the beach – when the water bunches up into waves, the troughs between the wave crests get lower since there is only so my water to go around.
    I disagree; sound in nature is always a positive pressure; it has no negative properties, only "zero" properties. Sound in nature does not "suck" our eardrums.
    "The way out is through the door. Why is it that no one will use this method?"
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    "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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    A sound waveform does have two poles. You don't have any sound without both. You can feel free to disagree, but KenOC is correct about the physics of sound.

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    I'm probably jumping into something I will regret, but aren't you speaking about two different things? The very nature of a wave requires two poles. The volume of the sound is determined on the wave's amplitude (difference between the two poles). On the other hand, waves move outward from the source, in one or more directions, but always outward.* Think of what happens when you throw a rock into a pool of water.

    In other words, the amplitude (height) and frequency (width) of the wave define the sound, but the sound moves away from the source (e.g. from the speaker to your armchair).

    *I suppose echoes (or any type of reflection) are exceptions that prove the rule.
    Last edited by jegreenwood; Jun-13-2019 at 14:11.

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