Something I've been curious about for a long time. How come things like mp3 player speakers have an on-off switch? As I type this, I'm listening to a podcast played through a set of Aiwa SC-A2 amplified speakers that I bought in Japan more than 20 years ago. Each speaker has 4 D-cells for the amp, but no on-off switch. It detects when sound is coming in and turns itself on, and if there is silence, after awhile it turns itself off. There's an LED to indicate when it is on.

Since my mp3 player will also turn itself off automatically when it is finished playing a podcast, this works very well. Even if I fall asleep or forget, everything turns itself off when it is done.

I measured current through the batteries when the speakers were off and there appears to be none. So I conclude that the sound itself must be rectified and used to turn on the speaker system. Why not?

So why do we need to have on-off switches on speakers at all? How come I haven't seen this elsewhere? And of course, how can we make a circuit ourselves to do this for all those crazy speakers that still have on-off switches?

The technology still exists, of course. It's just that people *like it* when they can turn things on and off.

I used to have some Cambridge Soundworks speakers that shut themselves off if no sound was detected for a while. This was incredibly annoying because as computer speakers, the computer will often go for many minutes without making sound and I'd have to keep turning them back on.

With music center usage, it would be annoying to keep having to power up if you put a song on pause.

Even if someone were to make one that shut off and turned on with noise detection, there would probably be latency and even a mere 3 seconds would be enough to annoy.

But I agree that it would be nice to have the option and be able to choose whether or not to use it as the circumstance required.