they look simple, but the science may not be
If you visit the Hifi Chicken, there is a good chance you own a speaker or two or maybe twenty. Most audiophiles are at least a little nerdy when it comes to science dealing with audio. Have you ever actually wondered how a speaker works, or why it works the way it does? Hopefully we will be able to answer those questions for you.
What we are going to do is break this into 3 sections to make it a little easier to digest, then we can put it all together.
- How sound works
- Speaker parts
- speaker types
- putting it all together
How Sound Works
The first part to understanding how a speaker works is to understand sound waves.
In physics, sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the reception of such waves and their perception by the brain.[1] Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound waves above 20 kHz are known as ultrasound and are not perceptible by humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.
wikipedia.com
Anytime something vibrates it will create sound. That sound may not be audible, or a frequency we can hear, but a sound is produced. Think of a tree in a forest with no one around, does it make a sound and does a hipster buy it’s album if no one heard it. With instruments such as drum we create the vibrations by hitting the drum skin with an object or our hands. Drums are very similar to how a speaker makes sounds. The bigger the vibration the louder the sound it will make. This is why larger drums when hit harder are much louder than small drums, they move much more air when vibrating.
Two main parts of what makes the sound, well sound the way it does is frequency and amplitude, these translate to pitch and volume respectively.
Let’s take a look at what that looks like:
In the example both the low frequency or bass tone waves have the same amplitude as the high frequency waves or treble waves. The amplitude is measured from the place of rest, or the centerline of the wave to the crest of the wave. Think of the height of a wave crashing on the beach over the height of the normal water level of a calm sea, the top of that wave is the amplitude, and the frequency is how often they crash on the beach.
Parts of the Speaker
- Cone
- This is a plastic, paper, carbon fiber, or other material dish that moves in and out to push air and create the pressure to make sound waves.
- Dust Cover
- this part, made from various materials is a cover for the
- surround
- This a rubber or foam piece that connects the outside of the cone to the basket
- Basket
- The basket is a chassis that all the components mount to and is then mounted to the cabinet
- Spider
- The spider is a support piece to keep the cone centered and moving within the needed tolerances
- Top plate
- Made of iron to secure the magnet to the basket
- magnet
- Typically made from ferrite or powerful neodymium.
- Former
- this part is used to wind the coil around
- voice coil
- Electromagnet that when charged by incoming voltage moves the cone in or out
- pole
- This iron concentrates the magnetism of the coil
- bottom plate
- The bottom plate connected the pole and the magnet together
- wires
- These provide the voltage to the voice coil
How the speaker parts work
Now that we know the parts of a speaker, lets discus how they work together.
First lets talk about the electrical components.
The first step is getting electricity to the speaker, this comes from some type of amplifier. As the current comes into the speaker it goes through the voice coil, depending on the polarity of the current the speaker will move in or out. In most scenarios it is set up to push the cone outward. the surround will keep the speaker from over extending. The voltage of the current and the frequency of the current coming is are what control our loudness and pitch of the speaker. Both of those variables are controlled at the amplifier level. Every Speaker also has an impedance rating, in Ohms, this is the electrical resistance in the voice coil. This is typically 4, 8 or 16 Ohms for home audio speakers, you may see other options as well just less frequently. In practice you want to match this rating to your amplifier’s output rating, using too low of a resistance can burn up internal electronics in your amplifier. The reason being that the closer you get to 0 Ohms, the closer you get to no load or a short circuit. Some devices are built to handle very small loads, please refer to your manufactures specs for this rating. The next electrical measurement you will see on speakers is the watt rating. Wattage is a misleading measurement for speakers, as watts are how many Joules of energy a device uses each second. Generally speaking the more watts a speaker can handle the louder it has the potential to be. Notice we say potential, a third piece of the puzzle is sensitivity. The sensitivity essentially tells you what that speaker does with the watts it’s rated for. Think of the sensitivity the 0-60mph time of a vehicle, 1000 horsepower goes way further in a small car than in a tank in terms of speed. In general you will see a sensitivity rating of between 80 to 90db, with many higher end brands offering 95 or even higher. What is the sensitivity a measurement of? It is the measurement of decibels 1 meter away from a speaker at 1 watt of power.
Now we can connect those dots, two speakers with the same 120 watt rating will have different loudness if one has a sensitivity of 80db and the other 90db. Remember decibel measurements are not linear, they are exponential. To go from 80db to 81db you have to double the actual loudness, so a sensitivity difference of 10db is a massive increase.
Now that we have covered the Electrical side what do the rest of the more static pieces do?
The Basket, top plat, magnet, bottom plate and pole are all stationary parts. Mostly serving as a mounting place for the moving parts, other than the magnet. The stationary magnet is in place to either attract or repel the electromagnet in the voice coil. This is where the push/pull from the cone takes effect. The stronger this magnet, the more current will be needed to move the voice coil, and thus usually making a more powerful over all speaker. Also the lager the cone the larger these components have to be as a lager cone means more surface area to pressurize the air in front of it, which is more resistance, therefor we have to apply a greater force to move the air.
Speaker types
So far we have only really covered standard speakers. There are others as well. Below are a handful of speaker types that you will find in different applications
- Moving-iron loudspeakers
- Piezoelectric speakers
- Magnetostatic loudspeakers
- Magnetostrictive speakers
- Electrostatic loudspeakers
- Ribbon and planar magnetic loudspeakers
- Bending wave loudspeakers
- Flat panel loudspeakers
- Heil air motion transducers
- Transparent ionic conduction speaker
Putting it all together
Now that you have an understanding of how speakers work, lets put it together in the real world. Speakers are rarely if ever listened to outside of a cabinet, why is that you may ask. The cabinet controls where the sound goes. A speaker when just moving in free air will push air in all directions, meaning the sound will travel out into the space uncontrolled. the cabinet design is used to direct the sound to the listeners ears. This way the waves of sound are uninterrupted as much as possible to give you the clearest sound that can be achieved. Cabinet design is just a crucial as speaker design and we will break that down in another how it works article in the future.