# eli5: How does the TV volume work?

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How do the volume controls on a TV work? Is it through some kind of amplitude modification?

In: Technology

When you press the volume button to increase volume, the signal sent is to increase the voltage, increasing the speaker output. It’s the voltage that is regulated.
In older televisions with the volume knob it was a rheostat.
Eli5 to your answer is that the buttony thing talks to big tv to talk louder through the speaker thingy by increasing the signal power (voltage).

Edit: Analogies are seldom perfect and often misleading. But here goes. A speaker which emits the sound works on a layer of fabric which vibrates. More it vibrates louder the sound. Think of a big gong and voltage determines the strength which is used to hit it. More the voltage, more strongly the gong is hit and a louder sound is made.

Amplitude modulation is a way of encoding information. It’s the AM in AM radio.

If you send a radio wave out at 720khz, but modulate the amplitude of the wave at 440hz, someone with an AM radio tuned to 720khz will hear an A above middle C.

If they want to hear it louder, they feed more volts to the amplifier and send more power to the speakers that are reproducing that note.

They are unrelated concepts.

A speaker works by vibrating the air in front of it. These vibrations in the air make sound waves. If you vibrate the air at a certain frequency, it’ll make a certain sound. The bigger the vibrations are, the louder the sound will be.

Electric speakers use a permanent magnet and a coil of wire. When you run current through wires, it creates a magnetic field. This magnetic field attracts the permanent magnet. By varying the voltage in the wires, you vary the magnetic field, and that makes the permanent magnet move back and forth – hence, your vibrations.

In a speaker circuit you use a rheostat to control how much voltage goes into the coil. More voltage means a stronger magnetic field, and a stronger magnetic field means bigger vibrations, bigger vibrations means louder sound.

It **is** amplitude modification, although that’s a slightly unusual way to say it. The sound signal coming out of the tuner is rather weak, and can’t easily drive a large speaker. So it goes to an amplifier with variable “gain”. (Or a pre-amplifier with variable gain and an amplifier after that.)

“Gain” is the electrical engineering term for how much the amplitude of a signal is increased by an amplifier. That’s the job of an amplifier…to take a small signal and faithfully increase its amplitude, up to some limit.

The way that the variable control on the amplifier is done can vary. In the old days, it was a part of the circuit containing a variable resistor (a “potentiometer”). The value of the resistance would modify how much gain the amplifier provided.

Nowadays, a lot of this is done digitally instead. Turning the volume knob or using the remote tells a circuit to emit digital pulses to the amplifier controls. These pulses encode either “increase the gain” or “decrease the gain”. How that control is done at the amplifier varies. Typically it changes a reference voltage sent to the amplifier, which in turn controls the gain amount.

Not sure if the question is: how does the remote talk to the tv? Or how does the tv increase volume?

Remote essentially shoots a low power laser beam at the tv and the laser has information that encode specials signals. This signal is typically encoding as on/off keying (OOK) also known as amplitude shift keying (ASK) (Digital Communications is a good introduction)

The speaker on the tv has an amplifier that controls the speaker volume. Turning the volume up of down controls the voltage level of the speaker through something called a feedback loop. The amplifier itself is at a fixed voltage but the signal wire to the speaker varies in voltage. (Op-Amp or Operational Amplifier is a good introduction)