hi people ...

i have a question about speaker signals ... I mean what signal shape that when applied to a speaker causes it to produce recognizable voice (i.e., tone or police sarien)

I tried to apply a 5V DC, but i got continous noise zzzzzzzzzzzz

I tried to apply ramp signal, but I heared the same noise but the sound got louder as the voltage increases ...

can anybody help ..??

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A tone is a single pure frequency- a sinusoid.

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hi,
Look at this link:

http://www.howstuffworks.com/speaker3.htm

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The ZZZ you're hearing is likely just line noise from the power supply. Don't run a speaker this way as it will quickly burn the voice coil out. If you want to properly test the speaker make sure you use a capacitor or transformer to isolate the DC and let the AC signals pass. If you want to test it properly a good test signal is a 1khz tone. You can generate this as a square wave though it's not going to sound very good but it's a standard test frequency.

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thanks dknguyen and I will try this sinusoidal signal accross my speakers ...

thanks ericgibbs for the link but it didn't reply my question about the nature of the signal shape that produces recognizable voice or tone ... dknguyen said sine wave, but what about other songs or other musical instruments tones ...??

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All sounds are a bunch of sinusoids added together with different frequencies, amplitudes, and phase shifts. Read up on Fourier series and fourier analysis.

 

ok the power supply already has a transformer ... or you mean that no DC component should appear on speaker ..??

well, but square wave is DC ...?? thus - according to my understanding - will produce the ZZZ while being HIGH and produce no sound while being LOW ...

anyway I will try all these helps and if a problem occur, I will come back ...

Hot thanks to everybody ...

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No, a square wave is not DC because DC is just a constant voltage that goes on (theoretically) forever without ever changing. However, a square wave that is centered around zero volts has no DC component at all while a square wave that is not centered around zero has some DC component. A square wave is produced by switching on and off a DC *SOURCE*, but this does not necessarily mean it contains DC *FREQUENCIES*.

http://en.wikipedia.org/wiki/Square_wave

Correct, no DC component should appear on the speaker (other than required to bias the speaker which is required by some kinds of speakers, but this is not a part of the audio signal). This means the signal you send to the speaker shoudl be centered around zero volts. So if you use a square wave, it must have an average of zero volts (it must spend half of each cycle at +V and half at -V). If it spends a little bit more time at +V than at -V, it is now centered at a slightly positive voltage and therfore has some DC component.

What Sceadwin is saying is that when your square wave is not perfect (it never is) and so has some rippling noise in it when your square wave is high. THe speaker is ignoring the ON voltage of the square wave (which is DC) and only paying attention to the AC ripple on it, which is what you are hearing. When it is low, there is no noise.

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dknguyen ... really ... perfect reply ...

thank you alot

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