Intro to Speaker-Speak

Loudspeaker engineering has its own vocabulary. Unfortunately, perfectly simple ideas can sound intimidating when described with unfamiliar technical terms. Here are some of the terms you will encounter throughout the Altisonus Library, translated into reasonably normal English.

Alignment

The overall way a woofer, cabinet, and any vent or other acoustic loading are designed to work together. Sealed, vented, and aperiodic systems are different alignments. Think of alignment as the operating arrangement of the bass system, not simply the shape of the box.

Aperiodic

An enclosure that deliberately allows a carefully controlled amount of air to escape through a resistive vent. It falls somewhere between a completely sealed box and an open one. The resistance helps control the woofer and reduce resonance.

Breakup

A loudspeaker diaphragm is supposed to move as one piece. Eventually, it doesn’t. At sufficiently high frequencies, different portions of the cone or dome begin moving somewhat independently. This is called breakup and can produce resonances, distortion, and changes in radiation.

Crossover

The part of a loudspeaker system that determines which frequencies go to which drivers. The woofer gets the lows. The tweeter gets the highs. In a three-way system, the midrange gets the frequencies between them. The region where responsibility passes from one driver to another is the crossover region.

Damping / Damped

Damping is the control or removal of unwanted motion or resonance. Imagine striking a bell. It rings. Now put your hand against it. The ringing stops quickly. You have damped it. In a loudspeaker, damping can be mechanical, electrical, or acoustic. Good damping helps the speaker stop producing sound when the signal tells it to stop.

Directivity

A description of how strongly a loudspeaker sends sound in different directions. A driver may radiate broadly at one frequency and much more narrowly at another. Directivity matters because you hear not only the sound traveling directly from the loudspeaker to your ears, but also sound reflected from the room.

Dispersion

Closely related to directivity, dispersion describes how sound spreads from a loudspeaker. Wide dispersion spreads useful sound over a broad angle. Narrow dispersion concentrates it into a smaller area. Neither is automatically good or bad. What matters is whether the dispersion is appropriate and changes smoothly with frequency.

Driver

The component that actually converts electrical energy into sound. Woofers, midranges, and tweeters are all drivers. The complete box containing them is a loudspeaker or loudspeaker system. Calling the entire loudspeaker a "driver" is rather like calling an automobile an engine.

Efficiency

How effectively a loudspeaker converts electrical power into acoustic power. An efficient loudspeaker produces more acoustic output from a given amount of electrical input. Efficiency and sensitivity are related, but they are not technically the same thing.

F3

A useful indication of how far a loudspeaker's frequency range extends. F3 is the frequency at which output has fallen by 3 decibels from its reference level. When someone says a speaker has an F3 of 40 Hz, he is giving you considerably more useful information than simply claiming that it "goes down to 20 Hz."

Frequency

How rapidly something vibrates, measured in Hertz (Hz), or cycles per second. Low frequencies are perceived as bass. High frequencies are perceived as treble. Humans with excellent hearing can roughly hear frequencies between 20 Hz and 20,000 Hz, although the upper limit normally decreases with age.

Frequency Response

A measurement showing how a device responds to different frequencies. For a loudspeaker, it tells us whether some frequencies are reproduced more strongly or weakly than others. Frequency response is important. It is not, however, a complete description of sound quality.

Impedance

The opposition a loudspeaker presents to the electrical signal from the amplifier, measured in ohms (Ω). Impedance is somewhat like resistance, except that a loudspeaker's impedance changes with frequency because a loudspeaker is an electromechanical device rather than a simple resistor. This is why an "8-ohm loudspeaker" is not necessarily 8 ohms at every frequency.

Lobing

When two sound sources reproduce some of the same frequencies, their sound waves can reinforce each other in some directions and partially cancel in others. The resulting radiation pattern develops areas of stronger and weaker output called lobes. Poorly controlled lobing can make a loudspeaker sound different when you move your head or change listening height.

Off-Axis

Any listening or measurement position that is not directly in front of the loudspeaker. Zero degrees is usually considered on-axis. Move sideways or vertically and you are off-axis. Off-axis performance matters because most of the sound radiated into a normal room does not travel directly toward the listener.

Phase

The timing relationship between repeating waves. Two waves arriving together may reinforce each other. Change their relative phase and they may partially or completely cancel. Phase becomes particularly important where two loudspeaker drivers operate simultaneously, such as through a crossover region.

Q

A number describing how strongly a resonant system tends to resonate. A high-Q resonance is strong and relatively narrow. A low-Q resonance is more heavily damped and spread over a wider range. An easy mental picture is a bell. A bell that rings strongly for a long time behaves somewhat like a high-Q system. Touch it with your hand, and the ringing dies quickly. You have lowered its effective Q by adding damping. In loudspeaker design, you may encounter several different Q values, such as Qts, Qes, Qms, and Qtc. They describe different aspects of the driver's or completed system's behavior.

Radiation

The act of sending acoustic energy into the surrounding air. A loudspeaker diaphragm moves. That movement disturbs the air. The disturbance travels away as sound. That is acoustic radiation. The directions in which that energy travels form the loudspeaker's radiation pattern.

Resonance

The tendency of a physical system to respond particularly strongly at a certain frequency. A wineglass has resonance. So does a guitar string. So does a loudspeaker cone, cabinet panel, column of air, and listening room. Some resonances are useful. Others add sound that wasn't present in the original signal. Much of good loudspeaker engineering involves knowing the difference.

Sensitivity

How loudly a loudspeaker plays for a specified electrical input, usually measured at a specified distance. A more sensitive loudspeaker requires less amplifier power to produce a given sound level. Sensitivity should not be confused with sound quality. A speaker can be extremely sensitive and terrible, or relatively insensitive and excellent.

Stored Energy

Energy that remains in a loudspeaker after the original signal that excited it has changed or stopped. Think again of the ringing bell. If a musical event stops but some part of the loudspeaker wants to continue vibrating, the speaker is adding its own little contribution to the performance. Generally, we don't want it to.

Transient

A rapid change in a signal. The initial strike of a drum, pluck of a string, or attack of a piano note contains transient information. Transients are important because they help the ear identify instruments and perceive timing, position, and musical relationships.

Tweeter

A driver designed primarily to reproduce high frequencies. Because high-frequency wavelengths are short, tweeters are usually much smaller than woofers.

Woofer

A driver designed primarily to reproduce lower frequencies. Contrary to popular usage, not every driver producing bass is a subwoofer. A woofer normally reproduces bass as part of the main loudspeaker's operating range.

The Important Part

You do not need to memorize any of this. When you encounter one of these terms elsewhere in the Library, come back here and look it up. Before long, Q, impedance, directivity, damping, and lobing will stop sounding like mysterious engineering language and start describing things you can actually visualize. And once you can visualize what a loudspeaker is doing, understanding why it sounds the way it does becomes much easier.