hat you think you know about speakers is really just a stereotype. That image of the little black box floating in your mind is merely one of many bright ideas eggheads have devised for making air move in response to an electrical charge. Technically, there are over 10 different categories of driver designs floating around in the world, each distinguished by their own set of advantages and drawbacks.
We’re not smart enough to understand them all. And some — yeah, we’re looking at you, Plasma Arc — don’t exactly seem like they’ll be eligible for Amazon Prime anytime soon. At any rate, we’ve done our best to boil the major highlights in the loudspeaker world down into one digestible guide.
So read on and scrawl what you need on your wrist before wandering into the hi-fi shop. We’re confident you’ll play the role of the informed buyer like the natural you are. And who knows, maybe you’ll even be inspired to start studying on your own.
The oldest form of loudspeaker design dates back to the 17th century with the advent of the megaphone. How horns manage to amplify sounds without any additional power is a miracle of basic physics.
The fact is, most drivers of sound do a poor job of converting the mechanical energy in the surrounding air into acoustical energy. Attaching a horn to the front of a sound-driving element, however, drastically improves this so-called coupling efficiency, by allowing the source sound to better engage all of the air present inside the slowly widening area of “the throat.”
Powered horn loudspeakers leverage this effect much in the same way, to squeeze impressive sonic results from very low levels of amplification. This makes them often an intriguing option for pairing with acoustically superior but comparably underpowered tube-based amp systems. Unfortunately, horn loudspeakers must be very large in order to provide adequate levels of bass response, making many designs highly impractical for anyone who can’t afford a private Walmart to put them in.
The Dynamic Driver
The dynamic driver is by far the most popular design found in the world of audio today. In fact, it’s what most of us imagine when we think of a speaker. Their basic design consists of a suspended lightweight cone attached to an electromagnet (usually a coil of copper wire), which itself is placed permanently in front of another magnet. When an amplifier applies electricity to the coil, it creates a magnetic field that grows and contracts in relation to the frequency of the audio signal. These directional changes in the field cause the coil to alternate between being attracted and repelled by the permanent magnet behind it. The resulting pull-and-push forces make the coil vibrate, which are in turn amplified by the connected cone to create sound.
The popularity of this type of driver stems from several notable advantages, including its relatively simple and rugged construction. It’s also highly sensitive, handles power in stride and is quite capable of outputting a wide dynamic range. The heavy nature of its components, however, does make the dynamic driver somewhat slower in responding to changes in audio frequency compared to other alternatives. Other acoustic downsides stem from the enclosure it’s mounted in.
Crossovers, in an audio context, are a set of filters that split an incoming audio signal into two or three bands of frequency (think high, mid and low) so that different types of drivers — such as tweeters, woofers and subwoofers — can each handle the respective section of the audio spectrum they are optimized for reproducing. So-called active crossovers differ from passive crossovers by splitting an audio signal before it is amplified.
Most dynamic speaker drivers are built into airtight boxes to stop the emanating sound waves they invariably generate from distorting the output of the main cone. Ironically, trapping these undesirable sound waves creates a catch-22 known as resonance. Thicker walls, unique shaping and internal bracing can all help reduce the distorting effects of cabinet vibration. But too much rigidity can also cause these sound waves to simply reflect back — recreating the very problem cabinets are intended to prevent. Plenty of innovative solutions have been designed to minimize these influences, but none are perfect.
That’s not to say all that sonic influences created from a speaker’s cabinet are unquestionably bad. On the contrary, many listeners feel some level of “boxiness” provides a richness to music that’s missing in other speaker designs.