Previously in the hi-fi 101 series, we introduced you to a few key terms, and discussed 2 categories of hi-fi component – the amplifier and the source component. In part 4, we’re going to cover the function and types of loudspeakers.
As you’ve undoubtedly deduced, the function of the Loudspeakers, (more commonly abbreviated to the ‘Speakers’) is to convert the electrical signals coming from the power amplifier into a sound pressure wave which you can hear. A typical loudspeaker consists of several components, including:
A speaker driver is a term used to describe a single transducer, sometimes referred too as the speaker itself. It’s worth noting that from this point onwards we’ll be focusing on the traditional speaker driver – electro-static, single-point source, and Magneplanar drivers are beyond the scope of this article.
A driver typically consists of a cone, usually fashioned from paper, attached to a voice coil positioned in front of a permanent magnet. When an electrical signal flows through the coil, it becomes a temporary, or ‘electro’ magnet. This magnet then attracts or repels the permanent magnet, causing the cone to move back and forth, creating a sound pressure wave and pumping sound into the air.
There are several types of speaker driver, characterised by their frequency response (the audible frequencies that they are able to reproduce). These can include:
A sub woofer is a driver designed to handle very low frequency information, usually below 100HZ. It is rare for a typical loudspeaker to contain a subwoofer – in fact, a subwoofer is typically a separate unit, with an enclosure optimised to accurately reproduce such low frequencies.
Woofers are again designed to handle low-frequency information – however, a typical woofer (depending on the size and configuration of the speaker enclosure) can only reach frequencies as low as 30HZ. While the limits of a woofer very much depend on its physical size as well as the enclosure and the crossover, the frequency range of a woofer usually extends from around 40HZ to around the 300HZ mark.
A mid/bass driver is a driver designed to handle both mid and bass frequencies – I.E from 50HZ to 3000HZ (or 3KHZ).
Mid Range Drivers
A mid range driver is similar to a mid/bass driver, but it lacks the ability to reproduce low-frequency information. The frequency response of a mid-range driver typically extends from around 300HZ to 5000HZ. A mid range driver is sometimes also known as a ’squawker’.
A tweeter is a high frequency driver designed to produce frequencies ranging from around 2000HZ to 20,000HZ, considered to be the upper limit of human hearing. Of course, there are some exceptions to the rule – some tweeters can produce frequencies up to 100HZ, far beyond the hearing range of the human ear. Tweeters are found in various forms, including domes and horns, and employ various materials in their construction.
A crossover is a circuit designed to separate the incoming audio frequencies and send the appropriate frequency to each driver. For example, as a tweeter is incapable of producing low frequencies (and attempting to do so would likely damage the tweeter), such frequencies are better handled by the woofer.
Let’s put this into context. A typical 2-way loudspeaker contains 2 drivers – a mid/bass driver and a tweeter. For the purposes of demonstration, let’s say that the tweeter has a frequency response of between 2000 and 20,000 HZ, and the mid/bass driver has a frequency response of 40-3000 HZ. Our crossover would be designed so that all frequencies below the 2.4KHZ (or 2400 HZ) mark would be passed to the tweeter, and all frequencies below the 2.4KHZ (or 2400HZ) mark would be passed to the mid/bass driver. This ensures that both drivers are not handling frequencies at the limits of their frequency extremes, which would typically result in a smoother, more coherent sound with the handoff between the 2 drivers becoming less obvious.
The speaker terminals, typically located on the rear of the enclosure, are the connectors that provide a means to connect the speaker to your amplifier. Common terminals include standards screws (in which a bare wire is wrapped around a screw which is tightened to keep the wire in place) Spring clips (allowing a bare wire to be inserted into a hole and held in place by pressure applied by a sprung retainer) and screw terminals (in which a bare wire is inserted through a hole in a threaded metal post, at which point a nut is tightened against the wire to hold it in place). Many terminals in use today allow for the connection of banana plugs or spade connectors, which make for a neater connection than strands of bare wire and also provide better electrical contact.
The enclosure, typically referred to as the ‘Cabinet’, can simply be thought of as the ‘box’ containing all of the speakers’ components. The enclosure typically contains some dampening material, and is acoustically tuned to provide the optimal frequency response with a given set of drivers.
There are a few types of enclosure that one should be aware of. Bass Reflex, or ported enclosures feature a slot, usually a circular hole containing a tube known as a Reflex Port or bass port cut into the front or rear of the enclosure. As the electro-magnetic voice coil attracts a drivers permanent magnet, causing the diaphragm, or ‘cone’ to move back into the speaker, the internal air pressure inside the enclosure is altered, and the excess pressure is funnelled out through the port. This increases the efficient of the speaker, and typically results in a more obvious low-frequency extension.
Bass reflex enclosures typically trade extreme low-frequency accuracy for volume. that’s not to say that a bass reflex speaker cannot produce accurate bass (quite the contrary) – however the bass output of a ported enclosure is typically increased by around 3DB meaning that the frequency response of a bass reflex enclosure is rarely even across the entire frequency spectrum.
A sealed, or ‘acoustic suspension’ enclosure is an airtight enclosure, in which the movement of the driver diaphragm causes the air pressure inside the cabinet to constantly change. The extra air pressure presses against the rear of the speaker diaphragm, pushing it forwards. This therefore requires more positive power from your amplifier to drive the diaphragm backwards, going against the air pressure.
Think of it almost as a spring arrangement. Air pressure presses the driver forward, at which point power from the amplifier causes it to snap backwards. This causes the diaphragm to move back and forth faster and with greater precision, giving you a crisper, more accurate sound.
Types of loudspeaker
Speakers come in all shapes and sizes. Bookshelf speakers are, as their names suggests, small enough in design to enable them to be placed within a bookshelf or cabinet. However, in hi-fi terms the term bookshelf is usually used to refer to a speaker requiring some form of stand or bracket to elevate it to an appropriate listening position.
Standmount speakers are, as you’ve undoubtedly deduced, designed to sit upon designated stands. Although they’re commonly confused with bookshelf speakers, the 2 terms often being used interchangeably, standmount speakers tend to be physically larger and in general lack the ability to be wall mounted.
Floor-standing speakers are, as their names suggests, speakers designed to be soot directly on the floor. Such speakers are typically tall enough to allow the high-frequency driver to be appropriately aligned with the listener’s ear at an average listening height (for example, seated on a sofa). Hi-fi floor standards typically sit upon a plinth for stability, with spiked feet allowing them to remain secure on carpet. Floor cups are usually provided for those who have wooden floors that area sensitive to scratches.
To summarise part 4 – in this part, you’ve been introduced to the various types and components of the loudspeaker. In part 5, we’ll discuss hi-fi cables. Until then…
Continue to Part 5