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Breaking open a speaker (for science)


Hey, what's up everyone! In today's video, we'll be taking a look inside a loudspeaker, and then we're going to have a short discussion on how a loudspeaker works based on what we have learnt about electromagnetism in topic 21 of O Level Physics This is a very old loudspeaker system as you can probably tell

Now, this is a subwoofer, meaning that it is supposed to take care of the low-frequency sounds It actually has some connections here that are supposed to be connected to some smaller speakers which will take care of the high-frequency sounds If we open up the speaker, on the inside, we see that there is some circuitry and this thing here which is the speaker cone Right If you take a look at the circuitry, some interesting things to take note of

Now basically this cirucitry takes care of the signal which is sent from the signal source to the speakers Mainly what it does is it splits the signal into high frequencies and low frequencies Low frequencies would be then sent via this cable to this speaker cone here, okay? Now, we'll touch on that later Now, one thing I want you to take note of is, I hope you can see here that, there is a fuse on the inside Now, fuse is one of the electrical safety devices that we learnt about in topic 19, Practical Electricity

That's somewhere over here, it looks like a glass tube with a wire inside So, the main component of the speaker that we'll be interested in is the speaker cone So, I'm going to take this out now So as you can see, this speaker is pretty old This is a PC speaker from back when I was in secondary school, and if we open it up, this is what it looks like

Okay So, over here we have some circuitry This circuitry will basically just take the signal that is being sent via the connecting cable here and split it into a voltage signal which would be sent to the respective speaker cones which would be sent to the respective speaker cones Okay

And what I mean by speaker cones is this thing over here Now hang on, let me unscrew this first Alright, yes so now I've taken it out, and this wire actually connects to the circuit board, and the circuit board will be sending a voltage signal to this Now, remember that sound is a series of compressions and rarefactions, right, in a longitudinal wave that's been propagated Now, in order for a sound wave to be produced, you need to have a vibrating object Now this speaker cone is the thing that's in charge of producing the vibrations

And basically what happens is when the signal is being passed through these wires, something happens to make this speaker cone vibrate in exactly the right way to produce the sound waves required Okay Some other parts to note are, note that the over here, at the back of this, you'll see that there's two really quite strong magnets that we have at the back here You can see that they are attracting the screwdriver quite strongly So if you just give me a moment, I'm going to connect this up and show you what this looks like when it is vibrating

So now it's all connected up, all I have to do is turn on the power and once I start the signal, you will see this thing start vibrating Now, it's vibrating I've set the signal to 100 Hertz So right now, you probably just see a blur because the speaker is actually moving in and out at a hundred times per second, that's what a hundred Hertz means right? and that's the sound you're hearing now if I place my mic nearer to it you can hear it

Okay So, in case you can't see the vibration, we can demonstrate that this thing is vibrating very quickly by just pouring some objects on it Over here I have some barley seeds Oops Okay, maybe the vibration is a little bit too strong, they are all bouncing off Maybe I can try to turn it down to a lower frequency

Now at 20 Hertz, probably you can start to see that it is vibrating So, you will remember that 20 Hertz is actually the lowest frequency that you can hear In the next part of this video, I will be showing you on the slides how it is that we can use an electrical signal to specify exactly how this cone is supposed to move So, let's move on to the slide Okay, so now we are looking at the slide

If you take a look at the slide here, on the left side, we have a 3D cut-away of what the inside of the speaker cone looks like So as you can see, like earlier we saw that there's this main cone structure here, okay, and on the inside what we have is actually a structure containing a magnet And, as well, notice here that there's this thing called a voice coil Okay, now from this diagram, it's not very easy to tell how this works, but if we simplify it a little bit and take a look at the simplified side view, this is what we will see So basically there's a magnetic structure, okay, now this provides a permanent magnetic field which this voice coil over here, is placed within

Now this voice coil is attached to the cone section of a speaker, the moving part of a speaker that creates the vibrations And, if you look at an even more simplified front view, what happens is the coil is represented by this circular arrow here, and the magnetic structure basically creates a magnetic field that is radially going from the inside to the outside across the coil So let's say if this was the north pole and this outside of the south pole, then what you would see is that there is a magnetic field pointing outwards like this along the radius of the circle, something that looks like spokes of a bicycle wheel So what happens when the signal is sent to this coil? A current will run So in this case you can see that the current is directed in an anticlockwise manner

Okay So let's say we were to look at this portion here where the magnetic field is pointing downwards, okay, if we look at the current at this point where it crosses the magnetic field, the current should be pointing in the direction that is tangent to the circle at this point, right? So, the current direction at this point of the circle is tangent to the circle which means that it is pointing to the right Now if we use the Flemmings Left Hand Rule at this point, we can arrange it like this and you will see that the force direction is pointing into the page, right? It's pushing the coil backwards away from you Okay Now, in the context of the side view, this means that when the current is flowing in this direction, it's going to push the speaker cone back this way

Okay So you can see that by adjusting the amount of current and the direction of the current, then we can push the cone either backwards this way or forwards in the other direction, right, by reversing the direction of the current What's happening when the speaker is running is that the current that's being sent to the coil is very carefully controlled by the circuitry in the speaker Okay, and it is going to switch back and forth very quickly This will control the exact vibration of the speaker cone back and forth, okay, which will then cause the air molecules around it to vibrate and that basically is what sends the soundwaves outwards Okay, so I hope you found that useful

Please like, subscribe, put a comment and let me know what you think, and I'll see you in the next video Thank you!

Source: Youtube

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