How Speakers Make Sound: A Beginner's Guide to Audio Engineering

We ask the impossible of our modern portable electronics. From a device that fits in a backpack, like the CHOYONG LC90, we demand the deep, resonant bass of a floor-standing speaker and the sparkling, clear highs of a dedicated hi-fi system. We want a sound that is both powerful and detailed, loud and nuanced, all from a small, battery-powered box. On the surface, this is an unreasonable demand, a flagrant violation of the laws of physics. And yet, engineers deliver. They perform a kind of modern magic, a form of alchemy that transforms the lead of a simple electrical signal into the gold of rich, immersive sound.

This isn’t magic, of course. It’s a masterful application of science, a delicate dance of electronics, acoustics, and clever compromises. To truly appreciate the sound coming from any modern speaker, we must venture inside, past the grille, and follow the journey of an audio signal from a stream of data to a physical wave in the air. Let’s step into this audio laboratory and witness the alchemy, step by step.

The Source Code of Sound: The Digital Signal Processor (DSP)

Before a single physical component moves, the audio signal begins its life as a stream of numbers. This is where the first, and perhaps most crucial, alchemical process takes place, inside a tiny chip called the Digital Signal Processor (DSP). The DSP is the brain of the operation, the grand conductor of the sonic orchestra. Its job is to take the raw digital audio and intelligently shape it before it ever becomes an analog signal.

Think of the DSP as a master sound sculptor. One of its primary tools is Equalization (EQ). It can look at the incoming signal’s frequency content and make thousands of adjustments per second, boosting frequencies the speaker struggles with and taming those it tends to over-exaggerate. This corrects the inherent physical flaws of the drivers and enclosure, much like a photo editor adjusts colors to make an image look more natural.

The DSP also acts as a traffic cop, managing the dynamic range. It can subtly compress the signal, raising the volume of quiet passages and lowering the peaks of loud ones, to prevent distortion and damage to the speakers at high volumes. Furthermore, it can apply sophisticated psychoacoustic tricks. Based on the Fletcher-Munson curves, which describe how human hearing sensitivity changes with volume, the DSP can apply “loudness compensation.” It automatically boosts bass and treble at low volumes, ensuring the sound remains rich and balanced even when you’re listening quietly. This digital wizardry, based on complex mathematical algorithms, is the secret foundation upon which all modern high-performance portable audio is built.

Once our digital alchemist, the DSP, has purified and shaped the signal, it faces a critical choice. The signal contains the entire spectrum of sound, from the deepest bass to the highest treble, but no single speaker can handle this entire range gracefully. It’s time to divide and conquer.

The Fork in the Road: The Crossover

The signal is now sent to an electronic circuit called a crossover. Its job is simple in concept but incredibly complex in execution: it acts as a traffic director, splitting the single audio signal into two or more paths based on frequency. The low frequencies (bass and midrange) are sent down one path, and the high frequencies (treble) are sent down another.

Why is this necessary? Physics. To reproduce high-frequency sounds, you need a speaker cone (or diaphragm) that is small, light, and stiff, allowing it to vibrate thousands of times per second with precision. This is a “tweeter.” To reproduce low-frequency sounds, you need to move a large volume of air, which requires a much larger, heavier cone with greater excursion. This is a “woofer.” Asking a large woofer to vibrate at 10,000 Hz is like asking a sumo wrestler to perform ballet; asking a tiny tweeter to produce a deep 50 Hz bass note is equally futile.

A two-way system, like that found in many quality portables, allows each driver to do what it does best. But the crossover’s job is more than just splitting frequencies. A great crossover design ensures that the signals, once split, remain in “phase.” Imagine two runners in a relay race; the baton pass must be seamless. If the woofer and tweeter are out of phase at the crossover point, the sound will be muddled and unfocused, even if both drivers are technically producing the correct frequencies. It’s this attention to detail that separates mediocre sound from truly coherent, engaging audio.

From Electricity to Motion: The Drivers

With the signal now properly divided, it’s sent to the drivers—the components that perform the most literal act of alchemy: turning electricity into physical motion. A speaker driver is a simple and elegant electromagnetic engine. The signal flows into a coil of wire (the voice coil) attached to the back of the speaker cone. This coil is suspended in a magnetic field created by a permanent magnet. As the alternating current of the audio signal flows through the coil, it creates a fluctuating magnetic field, which interacts with the permanent magnet’s field, pushing and pulling the coil back and forth with incredible speed. Since the cone is attached to the coil, it moves too, pushing and pulling the air in front of it, creating the sound waves that eventually reach our ears. This fundamental principle is at the heart of the vast majority of speakers in the world.

The Secret Weapon: The Passive Radiator

But even a dedicated woofer has its limits, especially when trapped in a small, portable box. Physics dictates that to produce deep bass, you need to move a lot of air. When you can’t make the woofer bigger, engineers have to get creative. They employ a form of acoustic magic, a secret weapon that appears to break the rules: the passive radiator.

A passive radiator looks just like a regular speaker, but it’s missing the entire engine—the voice coil and magnet. It’s just a diaphragm with a specific weight and suspension. So what does it do? It’s a clever, physics-based cheat. As the active woofer moves back and forth, it doesn’t just create sound waves outside the box; it also creates intense pressure changes inside the sealed enclosure. The passive radiator is mounted in this enclosure and is moved not by electricity, but by this internal air pressure.

By carefully tuning the weight and compliance of the passive radiator to the characteristics of the woofer and the volume of the enclosure (using a set of calculations known as Thiele/Small parameters), engineers can make it resonate at a very low frequency. It effectively acts as a second, much lower-frequency woofer, using the otherwise wasted energy inside the box to produce deep bass that the small active driver could never achieve on its own. It is the single most important innovation for getting impressive bass out of a small speaker.

The Body of the Sound: The Enclosure

Finally, we must consider the box itself. The enclosure is not just a protective case; it is an integral part of the acoustic system. Its primary job is to prevent a phenomenon called “acoustic short-circuiting.” As the woofer cone moves forward to create a pressure wave, it simultaneously creates a negative pressure wave behind it. Without an enclosure, these two waves would simply meet and cancel each other out, especially at low frequencies. The enclosure isolates the back wave, allowing the front wave to propagate freely. Its rigidity is also critical; a flimsy, vibrating cabinet will color the sound in unpleasant ways, smearing the details. The sealed, rigid enclosure, working in concert with the passive radiator, becomes the resonant body of the instrument, shaping and amplifying the sound in precisely controlled ways.

Conclusion: The Art of Compromise

From the intelligent algorithms of the DSP to the precisely tuned resonance of a passive radiator, creating great sound in a small package is a symphony of engineering. It is the art of the possible, a series of brilliant solutions to a set of unforgiving physical constraints. The final product is always a compromise—between size, cost, battery life, and acoustic performance.

The alchemy of audio, then, is not about turning lead into gold. It is about taking the common elements of magnets, wire, plastic, and silicon, and through a deep understanding of the laws of physics and human perception, arranging them in such a way that they create something that can move us emotionally. The next time you listen to a surprisingly full-bodied sound from a small device, you’ll know it’s not magic. It’s something far more impressive: it’s great engineering.