Speaker technology is the cornerstone of the audio world, powering everything from your car infotainment system to your tiny in-ear Bluetooth headphones. Even though most people might not know the ins and outs of speaker design, knowing how speakers actually work can make the difference between buying the right or wrong piece of kit. It’s also exceedingly valuable when repairing a beloved hi-fi setup.
The fundamentals of speaker technology haven’t changed very much in about 100 years—much like the inimitable TRRS headphone connector. Edward Kellogg and Chester Rice’s 1924 dynamic speaker is still the most widely used technology today. Although there have definitely been advancements in technology and quality since then.
But how do speakers work? Let’s start with the basics and go from there.
How speakers work: the basics
The chief principle of speaker technology is the transfer of energy from one state to another. To be more specific, transforming electrical waves from your playback device, be that your phone or a vinyl player, into sound pressure waves in the air for your ears to detect.
The mechanism used to achieve this is simple enough: The speaker cone (the circular bit you can see) vibrates, pushing and pulling the air to create sound waves. The conversion from electrical to mechanical energy occurs through an electromagnetic coil and magnet combination attached to the cone. This coil moves the speaker cone back and forth as its electromagnetic field changes with the electrical current (i.e. your music) passing through it.
However, speakers require much more power to push and pull the air to make sound than it does to move electrons down a wire. So speakers need an amplifier to boost the low power electrical music signal into a higher power state to drive the speakers. Modern solid-state amplifiers boost current to produce enough watts of power, while older valve amplifiers operate at high voltages too.
Portable and lower-powered home speakers always include a built-in amp, ensuring optimal power transfer for the speaker. But more powerful hi-fi speakers often require an external amplifier. This requires careful attention be paid to output power and speaker impedance matching to make sure the setup works correctly.
Tweeters versus woofers
Obviously, not all speakers sound the same. A major contributor to how a speaker sounds is the size of its speaker coils. If you wonder why little portable speakers or your Amazon Echo sounds tinny and lacking in oomph? Chances are, it’s because it has a tiny driver that can’t cover the large wavelengths of low frequencies—or doesn’t have the power to produce them without distortion.
There’s a reason that a speaker’s size affects the frequency of sounds it’s able to produce. Smaller speakers move easily and rapidly without requiring too much power, making them great for high frequencies. Larger cones can move more air and extend to cover the larger wavelengths of lower frequencies for a low-distortion bass sound. However: they’re heavier, take longer to move fully, and require more power.
In most acceptable speaker setups, you’ll find a combination of cone sizes. Combined with crossover EQ circuits to filter the signal to the right speaker. These range from large cones for powerful bass, known as woofers, through to small tweeters for high frequency detail. Home cinema and larger hi-fi setups may also include an even larger low frequency speaker called a sub-woofer.
There isn’t an exact correlation between size and quality at specific frequencies. Instead, you have to break the speaker down even further. For example, tweeters come in a variety of types. Ranging from traditional cones to piezoelectric crystal, ribbon cone, and electrostatic diaphragm types.
The inner workings of a speaker
It’s not just the size of the cone that affects the sound of your speaker. All of the internal components can make a noticeable difference to its sound. Even the materials and shape of the speaker enclosure have an impact, as sound absorbs and reflects off the body. The design of passive radiators and ports also contribute to the frequency response of the enclosure. These are often used like a passive EQ to boost certain frequencies that the speaker otherwise struggles with.
Other key components to sound are found by breaking down the speaker cone and coil itself. Every speaker is built from the following components:
- Diaphragm – just like in our bodies, this is the part responsible for vibrating and moving the air. This term is used interchangeably with cone. Tweeter diaphragms can be made of thin ribbon, for example, although polypropylene plastic is the most common material. Other materials include fiberglass, carbon fiber, aluminum, and PET plastic, which all affect the weight and movement of the cone.
- Surround / Suspension – holds the diaphragm in place while still allowing it to vibrate. Common surround materials include rubber and foam.
- Voice coil – a coil of wire connected to the back of the diaphragm. The voice coil reacts to the magnetic field produced between itself and the magnet when current is driven through the coil. This provides the force that moves the cone and produces sound. Voice coils can either over or under hang the magnetic material, which has pros and cons for coil mass, sensitivity, and movement linearity. Under-hung coils tend to be reserved for high-end speakers.
- Magnet – this permanent magnet sits behind the speaker cone, interacting with the changing magnetic field to move the speaker. Different magnet sizes and materials slightly alter tonal qualities. Common materials include neodymium, heavier ferrite, alnico, or more expensive samarium cobalt.
- Basket / frame – an enclosure, usually metal, that contains all of the aforementioned speaker components.
- Spider – sits between the diaphragm and surround and the basket / metal frame, ensuring that they don’t touch.
While the core concept of speaker design is essentially the same across a huge range of products, there’s a lot of variation across these inner components. Product purpose, cost, and material choices all impact how a speaker sounds.
Why it’s worth knowing
You needn’t stress about the inner materials and workings of most reasonably priced speakers these days. The familiar formulas have been perfected over numerous decades. However, if you’re spending serious cash on a high-end system, researching some of these smaller differences can help ensure that you’re getting your money’s worth.
Knowing how speakers work can also help you diagnose problems. Having a better understanding of why speakers might not sound how you want can help inform better purchasing decisions. You could also save bundle on repairs and part replacements, rather than buying an expensive new setup.