How Audio Systems Function

In any audio setup, the quality of the speakers is paramount. Even the most pristine recording, stored on the latest technology and played through a state-of-the-art deck and amplifier, will sound poor if paired with subpar speakers.

The speaker in a system is the crucial component that transforms the electrical signal stored on media like CDs, tapes, and DVDs into sound waves that we can hear.

In this article, we'll explore the inner workings of speakers. We'll also examine the variations in speaker designs and how these differences impact sound quality. Speakers are incredible feats of engineering that have significantly influenced our culture. Despite their impact, they remain fundamentally simple devices at their core.

Fundamentals of Sound

To grasp how speakers function, it's essential to first understand the mechanics of sound.

Inside your ear lies a delicate layer of skin known as the eardrum. When the eardrum vibrates, your brain decodes these vibrations as sound, which is how you hear. The most common cause of eardrum vibration is rapid fluctuations in air pressure.

Sound is produced when an object vibrates in the air (though it can travel through liquids and solids, air is the medium we experience when listening to speakers). These vibrations cause surrounding air particles to move, and as each particle moves, it in turn displaces the next, creating a wave-like disturbance that carries the vibration through the air.

To illustrate this, let's consider a simple vibrating object — a bell. When a bell rings, the metal rapidly vibrates — flexing in and out. As the bell moves outward, it pushes air particles around it, causing them to collide with others in front of them, and so on. As the bell moves inward, it creates a pressure drop, pulling air particles inward, which generates another pressure drop that continues to propagate outward. This decrease in pressure is known as rarefaction.

In this manner, a vibrating object transmits a wave of pressure changes through the air. When this wave reaches your ear, it causes the eardrum to vibrate. Our brain interprets these movements as sound.

Understanding Sound Variations

We perceive different sounds from various vibrating objects due to differences in:

A microphone functions similarly to our ears. It has a diaphragm that vibrates in response to sound waves in the environment. The microphone’s signal is encoded onto a tape or CD as an electrical signal. When played back through a stereo, the amplifier sends the signal to the speaker, which converts it back into physical vibrations. High-quality speakers are designed to produce incredibly precise air pressure fluctuations, just like those originally captured by the microphone. In the next section, we’ll explore how speakers achieve this.

Creating Sound

In the previous section, we learned that sound moves as waves of fluctuating air pressure, and that we perceive different sounds based on the frequency and intensity of these waves. We also discovered that microphones convert sound waves into electrical signals, which can be recorded onto media like CDs, tapes, or LPs. These recordings are then converted back into electrical currents by players to be used in stereo systems.

A speaker functions as the final step in this translation process, acting as the reverse of a microphone. It takes the electrical signal and converts it back into physical vibrations, generating sound waves. When everything operates correctly, the speaker reproduces vibrations nearly identical to those originally recorded and encoded onto tapes, CDs, LPs, and so on.

Traditional speakers achieve this by utilizing one or more drivers.

Creating Sound: The Diaphragm

A driver generates sound waves by rapidly vibrating a flexible cone or diaphragm.

Some drivers feature a dome instead of a cone. The dome is a diaphragm that extends outward rather than tapering inward.

Creating Sound: Voice Coil

When the electrical current passing through the voice coil changes direction, the polarity of the coil is reversed.

The voice coil functions as a simple electromagnet.

If you're familiar with How Electromagnets Work, you know that an electromagnet is a wire coil, often wound around a piece of magnetic material, like iron. Passing an electric current through the wire generates a magnetic field around the coil, magnetizing the metal it's wound around. This field behaves just like the one around a permanent magnet: it has a defined orientation with a "north" and a "south" pole, attracting iron objects. However, unlike a permanent magnet, the orientation of the poles in an electromagnet can be altered. Reversing the current flow switches the north and south poles.

This is precisely what a stereo signal does -- it constantly reverses the flow of electricity. If you've ever connected a stereo system, you'll notice that each speaker has two output wires -- usually a black one and a red one.

In essence, the amplifier continuously switches the electrical signal, alternating between positive and negative charges on the red wire. Since electrons always flow from positive to negative particles, the current traveling through the speaker shifts direction, moving one way and then reversing. This alternating current causes the electromagnet's polar orientation to flip numerous times per second.

Creating Sound: Magnets

When the electrical current flowing through the voice coil reverses direction, the coil's polarity shifts. This change in polarity alters the magnetic forces between the voice coil and the permanent magnet, causing the coil and diaphragm to move back and forth.

So, how does this fluctuation make the speaker coil move? The electromagnet is placed within a steady magnetic field created by a permanent magnet. These two magnets interact as any magnets would: the positive pole of the electromagnet is drawn to the negative pole of the permanent magnet, while the negative pole of the electromagnet is repelled by the permanent magnet's negative pole. When the electromagnet’s polarity reverses, so do the forces of attraction and repulsion. This results in the alternating current constantly shifting the magnetic forces between the voice coil and the permanent magnet, pushing the coil back and forth quickly like a piston.

As the coil moves, it pushes and pulls the speaker cone, causing the air in front of the speaker to vibrate, which in turn creates sound waves. The electrical audio signal is essentially a wave, and its frequency and amplitude determine how fast and far the voice coil moves. These, in turn, control the frequency and amplitude of the sound waves the diaphragm produces.

Different driver sizes are more effective for specific frequency ranges. That's why loudspeakers often divide a broad frequency spectrum among multiple drivers. In the following section, we will explore how speakers allocate the frequency range and discuss the primary types of drivers used in loudspeakers.

Types of Drivers

In the previous section, we learned that traditional speakers generate sound by moving an electromagnet attached to a flexible cone. While all drivers follow the same basic principle, there's a vast range in their size and power. The fundamental types of drivers are:

Woofers are the largest drivers, crafted to produce low-frequency sounds. Tweeters, on the other hand, are much smaller and specialize in high-frequency sounds. Midrange drivers handle the middle frequencies of the sound spectrum.

This makes perfect sense when you think about it. To produce higher frequency waves, where the points of high and low pressure are tightly packed, the diaphragm of the driver must vibrate at a faster rate. A larger cone struggles to achieve this due to its mass. On the flip side, a smaller driver has difficulty vibrating slowly enough to produce very low-frequency sounds, as it's more suited to quick movements.

Chunks of the Frequency Range

To achieve better sound quality across a broad frequency range, it's efficient to divide the full spectrum into smaller segments, each handled by a specialized driver. High-quality speakers often include a woofer, tweeter, and sometimes a midrange driver, all contained within a single enclosure.

To allocate specific frequency ranges to each driver, the speaker system must first divide the audio signal into different segments — low, high, and sometimes mid-range frequencies. This task is managed by the speaker's crossover.

The most common type of crossover is a passive crossover, which doesn't require an external power source as it's powered by the audio signal itself. This type of crossover uses inductors, capacitors, and occasionally other components. Capacitors and inductors are only effective conductors under certain conditions. A capacitor in a crossover will conduct electricity efficiently when the frequency surpasses a certain threshold, but not below it. In contrast, an inductor will conduct well only when the frequency is below a certain point.

When the electrical audio signal flows through the speaker wire, it first passes through the crossover units for each driver. To reach the tweeter, the current must pass through a capacitor, allowing mainly high-frequency signals to flow to the tweeter's voice coil. To reach the woofer, the current passes through an inductor, ensuring the driver primarily responds to low frequencies. A crossover for the mid-range driver uses both a capacitor and an inductor, establishing upper and lower frequency limits.

Active crossovers are another type. These electronic devices isolate different frequency ranges in an audio signal before it reaches the amplifier (which drives each individual speaker). They offer several benefits over passive crossovers, with the primary advantage being the ability to adjust frequency ranges easily. In contrast, passive crossovers have fixed ranges determined by their circuitry components, and changing them requires installing new capacitors and inductors. However, active crossovers are not as widely used because they are more expensive and require multiple amplifier outputs for each speaker.

While crossovers and drivers can be purchased separately, most people opt for speaker units that incorporate the crossover and multiple drivers within a single box. In the next section, we'll explore how speaker enclosures influence the speaker's overall sound quality.

Sealed Speaker Enclosures

In most loudspeaker systems, the drivers and the crossover are housed within a speaker enclosure. These enclosures serve several key purposes. At their core, they simplify the setup process by keeping all components in one unit and ensuring the drivers are positioned correctly to work in harmony for optimal sound. Typically made from dense materials like wood, enclosures absorb the vibrations from the driver. If a driver were placed directly on a table, the vibrations would cause the table to shake, resulting in muddled and diminished sound.

The speaker enclosure also influences the sound production itself. While we previously focused on the way the diaphragm vibrates to produce sound waves in front of the cone, it's important to note that as the diaphragm moves, it also generates sound waves behind the cone. Different types of enclosures handle these "backward" sound waves in various ways.

The most prevalent type of enclosure is the sealed enclosure, also known as the acoustic suspension enclosure. These enclosures are fully sealed, meaning no air can escape. As a result, the forward sound wave travels into the room, while the backward wave is contained within the enclosure. Because the air inside cannot escape, internal air pressure fluctuates – increasing when the driver moves inward and decreasing as it moves outward. These changes in pressure create a difference between the air inside and outside the enclosure, and the air naturally moves to balance these pressures, constantly pushing the driver back toward its neutral position where internal and external air pressures are equal.

Sealed enclosures tend to be less efficient than other designs because the amplifier must increase the signal power to compensate for the pressure forces. However, this force plays a crucial role – it functions like a spring, keeping the driver in its proper position. This helps ensure more precise and controlled sound production.

Other Speaker Enclosures

Other speaker enclosures are designed to redirect the inward pressure outward, using it to enhance the forward sound wave. One common method is to incorporate a small port into the speaker. In bass reflex speakers, the backward movement of the diaphragm pushes sound waves out of this port, amplifying the overall sound output. The primary advantage of bass reflex enclosures is their efficiency. The power driving the driver is utilized to produce two sound waves instead of one. The drawback, however, is that there is no air pressure difference to return the driver to its original position, leading to less precise sound production.

Passive radiator enclosures are quite similar to bass reflex units, but with a key difference. Instead of allowing the backward wave to escape through a port, it moves an additional passive driver. This passive driver resembles the main active driver, but lacks an electromagnet voice coil and isn't connected to the amplifier. It moves solely due to the sound waves produced by the active drivers. This design offers better efficiency than sealed enclosures and greater precision than bass reflex models.

Some enclosure designs feature an active driver on one side and a passive driver on the opposite side. This dipole configuration disperses sound in all directions, making it ideal for use in the rear channels of a home theater system.

These are just a few examples of the many enclosure types available. The market offers a wide variety of speaker units with diverse structures and driver setups. Visit this page to explore some of these designs in more detail.

Alternative Speaker Designs

Traditional loudspeakers typically use conventional drivers to produce sound. However, there are alternative technologies available that offer certain advantages over the traditional dynamic speakers, although they have their own limitations. For this reason, they are often paired with other driver units.

One of the most popular alternatives is the electrostatic speaker. These speakers generate sound by vibrating air with a large, thin, conductive diaphragm that is suspended between two fixed conductive panels charged with electrical current from a wall outlet. These panels create an electrical field with both a positive and a negative side. The audio signal passes a current through the diaphragm, alternating between positive and negative charges. When the charge is positive, the diaphragm is pulled toward the negative side, and when the charge is negative, it moves toward the positive side.

Through this method, the diaphragm moves rapidly, vibrating the air in front of it. Due to its light mass, the panel responds quickly and accurately to changes in the audio signal, delivering clear and highly precise sound reproduction. However, because the panel doesn't move far, it is less effective at producing low-frequency sounds. As a result, electrostatic speakers are typically paired with a woofer to handle the low-frequency range. Another drawback is that electrostatic speakers require a power source from the wall, making them harder to place in a room.

Another alternative to traditional speakers is the planar magnetic speaker. These use a long, metal ribbon suspended between two magnetic panels. The operation is similar to electrostatic speakers, but instead of an electric field, the diaphragm moves in a magnetic field as the alternating current changes the charge. Like electrostatic speakers, planar magnetic speakers excel at producing high-frequency sounds with remarkable precision, but they have less defined low-frequency output. Consequently, planar magnetic speakers are typically used as tweeters.

These alternative designs are gaining popularity among audio enthusiasts, yet traditional dynamic drivers remain by far the most commonly used technology. You can find them everywhere, not just in stereo systems but also in alarm clocks, public address systems, televisions, computers, headphones, and countless other devices. It's incredible how such a simple idea has transformed the modern world!

If you're interested in learning more about speakers and related subjects, be sure to check out the following links for additional information.