Hi,

I'm new to the forum and to the subject.

I am currently building a small low-tech 60 channel distributed sound systems using atmega microcontrollers.

When I read that audio signals are A/C I'm curious why that is, and also if that includes the actual output to speakers (and if that is the case why are speakers marked with + and -).

I am currently outputting dc signals to small speaker modules and it seems to be working fine. I am outputting ideal sine waves using hardware pwm with 8 bits resolution. The only issue I have with dc is that silence is pulling current (I just output a pwm of 128).

I am very curious to learn more, and I excuse my ignorance. Maybe this subject is covered somewhere else (book/website/etc)?

Hope someone can help.


Best regards,
Åsmund

aasmund wrote:

Hi, I'm new to the forum and to the subject. I am currently building a small low-tech 60 channel distributed sound systems using atmega microcontrollers. When I read that audio signals are A/C I'm curious why that is, and also if that includes the actual output to speakers (and if that is the case why are speakers marked with + and -). I am currently outputting dc signals to small speaker modules and it seems to be working fine. I am outputting ideal sine waves using hardware pwm with 8 bits resolution. The only issue I have with dc is that silence is pulling current (I just output a pwm of 128). I am very curious to learn more, and I excuse my ignorance. Maybe this subject is covered somewhere else (book/website/etc)? Hope someone can help. Best regards, Åsmund

Sound by its nature is a positive and negative waveform, the air is compressed (positive energy) and rarefied (negatvie energy). Obviously this is mirrored in electronics.

DC does not produce a sound, DC will make the speaker move out and stay out (if it's positive DC), and if you continue to provide DC for extended periods the speaker coil will not cool down and eventually melt.

Back to the drawing baord for you I think.
_________________
Recording Studio Suntans

AC wrote:

Sound by its nature is a positive and negative waveform, the air is compressed (positive energy) and rarefied (negatvie energy). Obviously this is mirrored in electronics. DC does not produce a sound, DC will make the speaker move out and stay out (if it's positive DC), and if you continue to provide DC for extended periods the speaker coil will not cool down and eventually melt. Back to the drawing baord for you I think.

Thanks for your reply.

I have sound output though. Maybe i was unclear: I have pwm (analog) output 0-5V but no negative voltage - so i am producing a waveform, just displaced so that the center is 2.5V instead of 0. I understand that a steady current of +5V would not produce sound and result in melting of the coil.

Do you know why the speaker elements have a +, and a - if one is supposed to run AC on them?

I hope you will overbear my lack of knowledge of the electronics of audio, and help me to understand it better.

No offense man, but he already explained it above.

If you are not sure what AC and DC are and the difference between them, perhaps you should go back and read some.


Your ampfifier on the back has a + and - for you to run your cable. This coincides with the + and - of your speaker.

AC means "Alternating Current" and this alternates between positive and - frequencies, where DC positive and negative charge. Think of getting shocked by a cord or some other thing. If this is at 60 hz, you will actually feel the vibration 60 times a second. (I do not suggest trying this however )

Now imagine getting shocked by a fence, this is one charge. (Sometimes pulsing, but sometimes just continious) where you will feel a constant force.

THe + and - is the phase, and how the speaker reacts. If reversed, you will still get sound, but the phase is then reversed.