The Basics Of Loudspeakers By Allan Potenciano

Loudspeakers come in many different shapes, sizes, and configurations, but they all do the same thing: they convert audio signals into sound waves.

Most audio systems include several loudspeaker drivers to reproduce both low frequencies (LF) and high frequencies (HF). From lowest to highest frequency, the most common types of drivers are subwoofers, woofers, mid-range, and high frequency.

Loudspeaker frequency ranges

When looking into speakers and their technology, reference will be seen to a number of different types of loudspeaker for different frequency ranges. Often some hi-fi speaker systems are made up from a number of different speakers to enable them to cover the complete audio frequency range as it is not possible for a single speaker to cover the whole range.

• Sub-woofer: The sub-woofer loudspeaker is intended to reproduce the very low frequencies, especially giving a sense of ‘feel’ to the sound. Typically a sub-woofer loudspeaker would reproduce frequencies in the region of 20Hz or so up to just over 100Hz. Sub-woofers are present in systems where extending the bass response to very low frequencies is needed.


• Woofer: The woofer is the loudspeaker that is used in many loudspeaker systems to provide the reproduction of low frequencies. Often its range will extend down to around 30Hz or so and possibly up to 500 Hz or may be even 1 kHz.


• Mid range - squawker: As the name of this type of loudspeaker implies, it is intended to reproduce the mid range sounds A mid range loudspeaker might typically be used to cover frequencies between about 200 or 300 Hz and 5 kHz to 7 kHz or thereabouts.


• High frequency loudspeaker - tweeter: The high frequency loudspeaker is often called a tweeter in view of the fact that it reproduces the high frequencies, often above 2 to 5 kHz.

The loudspeakers are, by far, the most important component in any stereo system. If you are building a component stereo system from scratch, you should plan to spend about half of your entire budget on the loudspeakers. Speakers, after all, are where the sound comes from.

Loudspeakers are the least accurate of our components. They are the typical stereo system's biggest source of distortion, coloration, un-natural resonances and other problems. Unlike the electronic components, they interact with the listening room in which they are used, as well as the listener's ears. No two people hear sounds, especially music, identically and we play different kinds of music at different listening levels. All of this complicates speaker selection.

Full- or wide-range drivers, which provide good low and high frequency response, are also available, though some people think they have reduced output at both ends of the frequency range. (In other words, they’re not great at either extreme.)

Some loudspeakers, called two-way, three-way, or even four-way systems, include more than one driver in a single speaker cabinet. To keep things simple, we’re going to focus on two basic driver types: direct radiators and compression drivers. Let’s start with a direct radiator.

In order to translate an electrical signal into an audible sound, speakers contain an electromagnet: a metal coil which creates a magnetic field when an electric current flows through it. This coil behaves much like a normal (permanent) magnet, with one particularly handy property: reversing the direction of the current in the coil flips the poles of the magnet.

Inside a speaker, an electromagnet is placed in front of a permanent magnet. The permanent magnet is fixed firmly into position whereas the electromagnet is mobile. As pulses of electricity pass through the coil of the electromagnet, the direction of its magnetic field is rapidly changed. This means that it is in turn attracted to and repelled from the permanent magnet, vibrating back and forth. The electromagnet is attached to a cone made of a flexible material such as paper or plastic which amplifies these vibrations, pumping sound waves into the surrounding air and towards your ears.

The frequency of the vibrations governs the pitch of the sound produced, and their amplitude affects the volume – turn your stereo up high enough and you might even be able to see the diaphragm covering the cone move. To reproduce all the different frequencies of sound in a piece of music faithfully, top quality speakers typically use different sized cones dedicated to high, medium and low frequencies.

A microphone uses the same mechanism as a speaker in reverse to convert sound into an electrical signal. In fact, you can even use a pair of headphones as a microphone!