When you turn down or up the volume on devices with either a wheel or button, what actually happens that allows it to sound quieter or louder?
In: Technology
(preface: while only a hobbyist, I’m a self-taught electrical engineer focusing on audio amplifiers, and specifically guitar amplifiers, and specifically vacuum tube based audio and guitar amplifiers.)
Someone once told me “an amplifier is just a power supply that is modulated by its input.” So when you think of a power supply, think of the simplest one for a second: a battery. You have a positive voltage on one side, and a negative on the other (usually grounded, so the negative voltage is only relative to the positive voltage).
If you hook up a 9V battery to a speaker, guess what? The speaker moves. You don’t ‘hear’ the sound, but you’re able to visually SEE what a 9V signal ‘looks’ like. It doesn’t look like the sine-wave you think of when you think about ‘soundwaves’, right? Well, that flat-line can be thought of as a wave with a frequency and/or amplitude of 0. It’s useful to note that if you used a 4.5V battery, the speaker would move the same direction, but not with the same force. If you quickly switched the batteries back and forth, say, 60 times per second, you’d be creating an electrical soundwave. 60hz is (in North America anyway), the frequency that you hear humming from electronic devices. (and fluorescent lights? those are 120hz ‘buzz’. the why 60/120 is another topic for another time!)
If, that signal were wiggled (modulated) at a specific frequency (think pitch) and given an amplitude (this is effectively what becomes volume), you’d hear it out of the speaker. When you listen to a song, it’s not just one tone, it’s a whole lot of different tones being produced–but lets just focus on a single, simple, soundwave. I want you to visualize a sine wave for a moment. The closeness of the peaks/troughs is your frequency (the pitch), the HEIGHT of those peaks and troughs is your amplitude.
The specifics of the circuit will dictate how this is all achieved, but the volume control will either expand or restrict the maximum amplitude (the ‘height’ of that electric signal). Some amplifiers actually have fixed amplification (lets say 100x for a nice round number), but will allow you to limit the input signal on them through a simple resistive divider (a potentiometer, a “knob”). (note: the following is for illustrative purpose and intentionally simplified). So it may take up to 1V of signal coming in, and will shoot out 100V of signal on the other end. The potentiometer here divides the input signal, so say that 1v signal is dropped down to .25V, then that is still amplified 100 times, and comes out as a 25V signal. Other, newer, amplifiers work by raising or lowering the whole working voltage (or power) of the amplifier. So it may take a 1v signal, but the overall level of amplification of the amp is not fixed at 100x. (most do this through some type of power regulating circuitry which can be as simple as a very, very big potentiometer (known as a passive component, similarly a rheostat), or very elaborate involving digital and solid state active components (think transistors, IC chips, etc).
Whether done by active or passive components, this restriction, in turns, limits the electrical signal that is sent to your speakers. Speakers are an electro-motive device. They convert electromagnetic energy (your electric sine wave) into mechanical energy (by vibrating the air, they ‘wiggle’ the molecules in the air; the concept for overall volume is called ‘sound pressure level” or SPL and is measured in decibels, or dB. this last bit is unimportant, but thinking of sound waves you hear as literal pressure waves is neat).
the amplifier that drives the speaker(s) is always “cranked to the max”. the volume knob normally stays in front of it and divides the quiet input signal into two parts – a proportion of the signal is sent to the amp to amplify, and the rest is consumed by something passive e.g. a simple resistor, and is never amplified. so the volume knob usually attenuates the signal so not all of it is amplified; that allows you quieter volume.
Turn the knob marked volume to the right (or press the up arrow) to make it Too Damn Loud & turn it to the left to hide yourself from the monsters.
On electronic devices it’s easier to explain. It’s what the top comments say, but it’s a digital control.
Sound is sound waves, similar to waves in the water.
The device creates sound by sending electricity to a speaker. The electricity pushes the speaker inwards or outwards, creating a larger or smaller wave, depending on how much electricity you send through.
To make it quieter, the device simply sends less electricity. This can be done in multiple ways, e.g. changing the amplification in an amplifier circuit, or just taking the sound wave that it is trying to play, and multiplying it by the volume percentage.
A electronically recorded sound wave consists of a series of numbers. Each number says how much power to send to the speaker at a specific time. The is one number for (typically) every 1/44100th of a second. So if you set the volume to 10%, it simply multiplies each number with 10% (= 0.1) to determine how much power to actually send to the speaker.
See suggested for answers on analog devices. I just wanted to add that some devices save space and material by digitizing the input from a knob or wheel and converting the command to the audio section of a device.
On a digital wheel that you can keep spinning even when the volume is at 0 or 100, the input process is a two step assignment loop input, with short polling. Placing a finger on the wheel sets the start value (step 1). Then the direction the finger moves sets the positive or negative value (step 2). That value is sent to the audio “tap”, telling it to open or close a bit more. The value resets back to zero value of step 1, waiting for another directional input. It repeats that for as long as you’re tracing that finger along the track wheel.
An audio amplifier with a mechanical knob for attenuating the sound level accomplishes this with a variable resistance resistor called a potentiometer. Upon changing volume down, the extra sound that was there is sent to a parallel universe according to the laws of string theory. Energy is conserved due to the increase in volume elsewhere in the multiverse. In fact, it doesn’t matter whether you turn it up or down, even turning it to 11, since all possible outcomes exist in the multiverse, and the one you are experiencing now is just one of an infinite number of universes where another version of yourself is listening to the same song at different volumes. It’s all proven here:
Depends.
On purely analog devices audio is just an electric signal. When you adjust the gain you are controlling how much electricity you are letting through, like a water tap.
On digital devices this is more complicated but, generally speaking, when you press the volume buttons you are also controlling how much electricity is being sent to the speakers although not directly. Some code is interpreting your actions on the volume buttons and then this either results in the digital audio signal having less amplitude, or controlling the analog amplifier, or both.
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Sound travels through your electronic device as a very small electrical current. Think of this current as “flowing” like water.
When the volume knob is all the way up, all of the water is allowed to pass through it, but as you turn the knob down, less and less water is allowed through. The amount of “water” coming through = volume.
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