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I connected my speakers to my sound system switching the +ve and -ve one of the speakers I can notice them beating out of phase but how come I don't hear any difference and at what position will it undergo destructive interference and the sound will be of 0 intensity ( I've never experienced it in real life so I'm guessing its not correct but why doesnt my theory happen in real life?).

QuestionEverything
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  • Here's one related question. – 299792458 Jul 19 '14 at 19:00
  • How do you means you can notice them beating out of phase, does this depend on your position relative to the speakers? – fibonatic Jul 19 '14 at 19:01
  • @fibonatic, I can see the base beats out of phase(the diaphragm of the speaker beating out phase). But when i connect it properly the base on both speakers beat the same. My question if they have a phase difference then why do the not cancel each other? – QuestionEverything Jul 19 '14 at 19:04
  • I suppose your ''beat'' doesn't refer to the beats phenomenon, or does it? – 299792458 Jul 19 '14 at 19:07
  • Is there a detectable change in volume if you try to place your head equidistant from the two speakers? – alemi Jul 19 '14 at 19:12
  • @alemi , not that i can notice. Can this be because of a single wavefront Splitting into many so even if one is destructive the other can compensate? Or can it be because the walls and other objects reflect the waves fallen on them? – QuestionEverything Jul 19 '14 at 19:19
  • @MasterAwesome to have destructive interference, the waves have to be exactly out of phase. If you wire the one speaker backwards, it should act like a source that is directly out of phase with the other source, but the phase changes as it propagates. You would have to be equidistant from the sources. The effect should be better for lower frequencies (longer wavelengths). Can you try to listen to this bass test as you move around the room? – alemi Jul 19 '14 at 19:32

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The pattern of destructive and constructive interference depends on frequency. A single tone will show exact cancellations and amplitude doubling, a narrow band signal will show slight damping and gain, and a wide band signal will show a position dependent filtering.

The positions of gain and dampening also depends on reflections from the surroundings but if you arrange the room to be symmetric about the midplane between the speakers then you should be able to create wide band cancellation in that plane.

You are using a mono signal, right?

Richard RP
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In an ideal experiment (say, a large room with sound-absorbing walls) you should be able to readily identify the null points. In practice, however (e.g., in your house) the sound from your speakers will impinge on and reflect from the objects in the room.

The reflected wave may hinder the ability for you to readily detect null points. This will depend on the damping characteristics of the room and objects in the room.

user3814483
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