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Reception of audio signal, through AC plug; bypasses a volume switch that works.

  1. Oct 17, 2012 #1
    I post to this forum, because I want to analyze this phenomenon with the aid of those who may understand the various nuances of scientific theory, by which such a thing could occur. I do not feel that posting to a forum dedicated to audio/video would yield quality results.

    This matter relies on several details, without which, your understanding may well suffer a deficit; such is not my intention. Please read this post in full before replying, despite any verbosity which you think may detract from your enjoyment.

    The phenomenon:
    A set of speakers play back a discernible audio signal (I’m not talking about any sort of static; see video below), regardless as to whether or not the input plug is inserted into an output jack. The volume control included with the speakers is irrelevant, as actuating it has absolutely no effect on the signal. It can be shown that the volume control works, external to this phenomenon.

    The only method by which this play back can be terminated, is to unplug the speakers from a power source. This phenomenon occurs without regard to any certain power outlet; as three outlets have been tested that are affected. Those are a grounded outlet in the kitchen, a grounded outlet in my bedroom, and an ungrounded outlet in my bedroom.

    I have lived in three apartment complexes within a one third of a mile stretch on the same road. These speakers have never manifested this phenomenon prior to being plugged in at the most recent complex.

    This phenomenon could not be reproduced using a much less powerful, and much less expensive, average pair of speakers.

    I can show that the volume switch works, using the fourth movement of Beethoven’s Fifth Symphony:

    I can show that play back occurs even with the volume all the way down, and the input unplugged.

    Here is a faithful example of the audio; unhindered by narration. The volume is all the way down, and input unplugged.

    I have a higher quality version of each video; if that may be relevant to anyone. I also have videos showing that the speakers exhibited this phenomenon while they were plugged into different outlets. I may be coaxed to gather the speakers together, with all the cords, to show that they are truly not plugged into anything. I have not had time to undertake such.


  2. jcsd
  3. Oct 18, 2012 #2
    It looks to me as though you are picking up radio frequencies at some point in the circuit. Possibly in the amplification or possibly in the input and being amplified. Being as it only is happening in your current apartment I am going to guess that you either have a ground problem in the apt. power or your in closer proximity to the source of the signal. If you ground the input does it go away?
  4. Oct 18, 2012 #3
    As Dustysnakes said, some radio signal is getting coupled into your speaker circuit. Since the volume knob doesn't effect it, I would assume it is getting coupled in somewhere between wherever that potentiometer is in the circuit and the speaker itself. When you plug the speaker in, there is enough of a load that it kills the reception of that signal so you don't hear it.

    When I was in college my guitar amp use to pick up radio signals in a similar fashion.
  5. Oct 18, 2012 #4

    jim hardy

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    it's not uncommon for a high frequency radio signal to get picked up in wiring and "detected" by an electronic device.

    Is your new apartment complex near a radio or TV tower of some sort?
    What happens is the radio signal gets into a wire and at the first semiconductor junction it encounters, it gets partially rectified by that junction's nonlinearity. Rectification in AM radio is called "Detection" and it's how the audio signal is retrieved off the radio waves themselves. If that first junction is in an audio device , the device will propagate the "detected" signal.

    That's one possibility. Other is that something in the apartment complex is getting into your set - with all the modern stuff my kids have: bluetooth , wifi, who knows? My first CD player ca 1975 intervered with my TV set if it was nearby.
  6. Nov 1, 2012 #5
    Thank you for the replies. I'm sorry it's taken me so long to get back onto this thread. I have some new discoveries about this radio signal.

    To quickly clarify this, this happens whether or not the speakers are plugged into the output jack of a playback device. This morning I was trying to watch the news report about the aftermath of Hurricane Sandy, with constant interruption of, "hey, wave back!" The audio for the news was playing simultaneously with, "hey, wave back!"

    A quick reminder before I continue:
    I have lived in three apartment complexes within a one third of a mile stretch on the same road. These speakers have never manifested this phenomenon prior to being plugged in at the most recent complex.

    What Dustysnakes and Mr. Hardy say here is relevant to my next paragraph:
    The person transmitting the signal that I've been receiving on my speakers was speaking to someone, and he said..."your CB radio". A frequent phrase that I hear is, "hey, wave back!". Or, "I'm going to slow this driver down another gear." Much of what I hear makes me think that the source is a vehicle mounted CB. The distance of the other apartment complexes from the new one are 1/5 of a mile to the south, and 1/3 of a mile to the north. The disposition of the signal would have to be such that moving that small distance allows for reception. I can do nothing but offer conjecture as to this.

    What Dustysnakes, Floid and Mr. Hardy say here is relevant to my next paragraph:
    I moved the speakers to the kitchen, to see if the location in the apartment made any difference. It did not. However, while the speakers were receiving one of the transmissions, I touched the input plug to an unpainted screw head attached to the refrigerator. Playback of the transmission ceased. Note that the receptacle the refrigerator is plugged into has not been tested to see if the speakers exhibit the same issue when plugged into it.

    Video here.

    As Dustysnakes suggested, it would seem that the ground for the receptacles I've tested is either inadequate to quell the reception of the signal, or the ground for the receptacles I've tested is the cause of the reception. Or, as Mr. Hardy and Floid suggested, the signal is coming into play somewhere else in the circuit. What is it that occurs when I touch the input plug to the unpainted screw that does not occur when the input is plugged into an audio output jack? It is my understanding that a device receives only as much ground as is provided by the receptacle which it is plugged into. Would that not suggest then, that the receptacle the refrigerator is plugged into would be providing some grounding effect that the other receptacles are not providing? Given the fact that this issue never occurred at the other apartments in the immediate vicinity, could it be the case that the signal is somehow being received by some attachment of the building, and being transmitted through the wiring; only to be stopped when the audio input plug is touched to that screw?

    Everyone I've spoken to about this looks at me like "a deer in the headlights". I need something I can take to the landlord to help me plead that she check the grounding.
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