Comment on What is negative voltage?
kernelle@lemmy.dbzer0.com 5 days ago
I don’t think anyone referenced audio applications yet, the concept might be easier to grasp if you visualise it with a speaker.
Sound is just a particular way of moving the air, so a speaker at rest is just a cone sitting in the middle of an electromagnet, not protruding, just resting ready to be pushed out or pulled in according to the desired sound, this is the ‘rest’ state, or 0v.
Amplifiers are provided with a positive voltage to be able to pull the speaker cone one way, and a negative to push out the other way, with a reference (or ‘rest’) in the middle. This voltage, often +12v 0v -12v, is provided be a transformer that has been tapped in the middle. But if you use measure accross the tranformer, you will measure +24v, because that’s the total voltage potential of the circuit.
If you switch your measuring probes the other way around you’ll see -24v on your meter, did anything fundamentally change when you measured the other way around? No! It’s just your reference point that changed.
akunohana@piefed.blahaj.zone 5 days ago
Yet another amazingly hands on example, easy to understand! Thanks!
Does this mean that at the resting position, there could be or could not*l be some current in the system, depending on its design, as long as there is enough wiggle room (here, 24 units in total, 12 “up”, 12 “down”, or whatever range the specific cone needs in order to shake/move) for the specific cone to operate?
I have replaced “volts” with “units” and “wiggle room” in order to make it easier for me to visualize.
kernelle@lemmy.dbzer0.com 5 days ago
You’re welcome! As long as the cone is in its rest position there’s no energy so no current which means (according to Ohms law) that the amplifier at this point is acting as an infinite resistor.
Sound is then created by continuously moving between the -12v and +12v, if you connect just +12v to a speaker the cone will just stick out once and remain there, not much of a sound is it. Sound is a complicated alternating waveform.
Sidenote: this is a physicists rabbithole, magnets moving around in coiled windings will create its own electrical signal. So if you talk into any speaker you can make it act as a microphone and record. So be careful with oversimplifications!
akunohana@piefed.blahaj.zone 4 days ago
This makes me realize how mind blowing the technology is: if I assume correctly, we have electromagnets inside the speaker that can alternate between the two potentials at the same frequency/speed as is required for the tone in question? And that’s just only one tone. Holy shit… how many times per second do the electromagnets turn on and off in order to create sounds that we recognize as music?!
bluesheep@sh.itjust.works 4 days ago
If you want to know something else mind blowing, you can actually use a speaker as a (very shitty) microphone! The same principle of moving the cone by applying a voltage works in reverse: if you move the cone you will create a voltage. And since sound is nothing but moving air, talking into a speaker cone will create a voltage in relation to the sound.
kernelle@lemmy.dbzer0.com 4 days ago
Oh for sure, there’s a famous quote that goes along the lines of “Technology at a certain point to the average person is indistinguishable from magic”
Right on the money! For subwoofers they’re huge cones and huge magnets (I LOVE the pressure of an 18" super scooper), those go at 15-150 times a second back and forth. For your phone speakers or earphones they’ve the tiniest membranes that go at 200-18000 times per second. A quality soundsystem will combine these to get a range from 20-22000Hz which is a little more than our ears ability.