Loudspeakers have been used for many years to convert electrical signals into audio sound waves.
Although the basic principles of the loudspeaker are relatively easy to grasp, the actual design of a high quality unit is not simple: designing one and optimising it for the best sound is a difficult process.
Loudspeakers are complex as the performance depends upon that of the loudspeaker units themselves, how they are combined, if more than one is used in a system, and how the speakers interact with the enclosure. They are even affected by their surroundings, the amplifier and a number of other factors.
The purpose of a loudspeaker is to convert an electrical signal into sound waves providing the most faithful reproduction that is feasible for its design.
There is obviously a very wide range in the quality of loudspeakers. Cost size, and many other factors contribute to the overall quality.
Often loudspeakers are taken for granted. They are either contained within a radio or other audio player, or possibly within a loudspeaker system, possibly containing two or more loudspeaker drive units.
There are a number of different loudspeaker drive unit technologies as described below. These can then be contained within different types of enclosures. Each factor needs to be taken into consideration when designing or selecting a loudspeaker system.
Loudspeaker types & technologies
There are several different technologies and approaches used within loudspeakers. As a result there are several different types of loudspeaker that can be used, and mention of these will be often be seen in the literature.
- Moving coil: The moving coil type of loudspeaker is the type that is most commonly seen. It consists of a cone attached to a coil that is held within a magnetic field. The moving coil loudspeaker s the type which everyone thinks about when looking for a loudspeaker unit. It basically consists of a diaphragm, typically attached to a coil though which the audio is passed.
The coil is suspended within a magnetic field and this means that the variations in current flow resulting from the electrical audio signal cause the coil, and hence the cone to move. This results in the loudspeaker converting the electrical audio signal into sound.
Read more about . . . . the moving coil loudspeaker.
- Horn: The horn loudspeaker type is often used for tweeters. Although it uses the same electromagnetic effect as the moving coil loudspeaker, a diaphragm held within a magnetic field that is varied in line with the audio. This causes the diaphragm to vibrate and these vibrations are then magnified by a horn.
Horn loudspeakers are used in many areas of auto technology, and although they are used to good effect in some high quality applications, they tend to be found more widely in public address and outside uses.
The horn loudspeaker consists of a transducer, which is often a moving coil transducer, and this is connected to a horn. This can be thought of a matching element very similar to a waveguide horn antenna, and this enables much higher levels of efficiency to be obtained. This could be noticed on old gramophones that used a horn to enable the sound to reach usable levels. Without the horn, the gramophone sound was almost inaudible.
- Electrostatic: The electrostatic loudspeaker type is uses a totally different principle to that of the moving coil and horn loudspeaker types. Instead the electrostatic loudspeaker is one in which sound is generated by utilising the force exerted on a membrane suspended in an electrostatic field.
These are various other technologies can all be used to create loudspeakers.
Loudspeaker systems vary enormously. Some only have a single drive unit or loudspeaker unit, but often these single speaker systems have limited response at the low and high frequency ends of the frequency spectrum.
As a result many systems consist of two or even three different loudspeaker drive units, each targeted at covering a different frequency range.
It can be seen from the diagram above of a typical hi-fi loudspeaker system, that there are several elements to the overall system.
- Loudspeaker drive units: The loudspeaker units themselves are of paramount importance as they convert the electrical currents into sound waves. Hi-Fi loudspeakers may have one or more loudspeakers of the different types mentioned below. For free standing systems two and sometimes there speakers with different ranges are used.
- Cross-over unit: If multiple speakers are used, then it helps to have the required frequencies routed to the relevant speakers. Traditionally crossover units tended to consist of inductor and capacitors and many still do today. Modern amplifiers sometimes have different outputs for low end and top end speakers, so into is case the crossover unit is effectively contained within the amplifier.
- Cabinet: There are many different types of loudspeaker cabinet. Often an infinite baffle system is used, that consists of a closed box. This needs to be as rigid and airtight as possible to ensure that the only vibrations come from the loudspeakers themselves. Accordingly these boxes are made from very rigid wood or other material.
- Internal sound absorbed material: To prevent resonances being set up inside the loudspeaker cabinet, sound absorbed material is used within the infinite baffle systems.
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 frequency ranges for the different loudspeakers are only approximate, because different loudspeakers have different frequency ranges and different loudspeaker systems are designed in different ways with speakers covering slightly different ranges.
Most loudspeakers are mounted in an enclosure or cabinet. This not only protects the loudspeaker from damage, but it also enhances the performance of the sound.
Some hi-fidelity systems can cost significant amounts. A huge amount of design can be invested in the loudspeaker cabinet.
Several different types of cabinet and mounting system are used: baffle including the infinite baffle, doublet, infinite baffle, reflex, column, transmission line and more.
Each of these different types of loudspeaker enclosure has its own advantages and disadvantages and can be used to its best effect in different situations.
The study of loudspeaker technology is very interesting. Designing loudspeakers can be very complicated, but the results of developing a good loudspeaker can be very rewarding.
Loudspeaker technology both in terms of the transducer and any enclosures or systems that are developed can be very challenging as there are so many interactions between the electrical, mechanical and other systems. However when a good loudspeaker and loudspeaker system is made, the results are very satisfying.