C J Evans By C J Evans, 30th Apr 2011 | Follow this author | RSS Feed
Posted in Wikinut>Guides>Music>Recording & Production

A look at the function of loudspeakers and how they work in an audio situation.

So How Do Speakers Work?

Low Frequency Drivers

Efficient reproduction of low frequencies requires that a large volume of air to be moved. This in turn, requires one or both of the following:

1. Long diaphragm excursion
2. Large diaphragm area.

In sound reinforcement, low frequency drivers are invariably electromagnetic linear motors with cone diaphragms. When flush mounted on the front of an enclosure ( i.e. without a horn ), this driver is also known as a 'direct radiator'. Dome=Dust cap. Spider=suspension. Frame=also called basket.

Low Frequency Enclosures

Cone type low frequency drivers are always mounted in enclosures. In practical loudspeakers the baffle's function is assumed by the enclosure. The most common low-frequency enclosures used in sound reinforcement are the vented and horn loaded enclosures. These are very popular in audio studio environments.

VENTED ENCLOSURES: Vented enclosures are generally used for a direct radiator. A direct radiator system is one in which the driver diaphragm is coupled directly to the air. The opening is called a port or vent ( Helmholz resonator ). In a vented enclosure the back wave from the driver is used to reinforce the front wave at the resonant Frequency. The resonant system of the enclosure and port shifts the phase of the back wave by 180 degrees, so it is in phase with the front wave.

High Frequency Drivers

In sound re-inforcement practical high frequency loudspeakers are most often 'horn loaded'. The drivers used at high frequency are designed specifically to drive the high acoustical impedance found at the horn throat and are thus called COMPRESSION DRIVERS. High Frequency reproduction requires less excursion than low frequencies.

Supertweeters may also be used in sound reinforcement loudspeakers. They may either be the electromagnetic type or piezo-electric, in either case they are invariably 'horn loaded'.

The Speaker Cone

The speaker cone is mostly made of paper, tough carbon composites, PVC, polypropylene or aluminium. There are two types of manufacture:

- FOLDED CONE, this is the cheapest method but the adhesive join can cause distortion.
- MOLDED CONE, paper pulp is strained into a mold. This is more expensive but gives a more uniformed result.

The Dome

The dome acts as a dust cover for the voice coil. High frequencies tend to radiate from the dome and the shape helps reduce directionality of dispersion.

The Suspension

This centralizes the cone and ensures it can only move in the front/back axis. The suspension determines the compliance of the speaker, how easy it is to move the cone. High compliance- hard to move.

The Voice Coil

This is a very tight wrap of wire wrapped around the 'former'- a card/myler tube. When current travels through the coil a magnetic field is generated ( induced ). This interacts with the field from the magnet causing it to move ( voice coil ).

The Magnet

The magnet can be made from:
- Ferric material
- Alnico
- Samarium coblat
- Neodymium.


Audio, Audio Device, Audio Engineer, Audio Engineering, Speaker Sounds, Speakers, Studio, Studios

Meet the author

author avatar C J Evans
I reside in the South Wales area of the UK. The articles I write are based on my many interests.

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