Based on the enclosure (cabinet) construction, speaker designs include the following:

Acoustic suspension enclosures (closed-box) are air-tight, since they use the enclosed air to dampen the behavior of the woofer. When the woofer moves forward a vacuum is created behind the woofer that sucks the woofer back to its resting position. When the woofer moves backward there is an internal air pressure increase, which pushes the woofer to its resting place. A properly designed acoustic suspension loudspeaker has tight and deep bass with a gradual roll off below its cut-off frequency.

However, acoustic suspension loudspeakers tend to be inefficient since the acoustic energy generated by the back of the woofer is not used. A ported enclosure is another way to use the energy that is wasted by an acoustic suspension loudspeaker. By opening an appropriately sized hole (bass reflex) in the enclosure and attaching a pipe of specific length to it, the low frequencies generated in the enclosure come out in phase with the bass generated by the front of the woofer. Varying the size of the hole and the length of the pipe varies the low frequency extension. Ported enclosures are much more efficient than closed-box designs, resulting in much smaller enclosures for the same cut-off frequency. As for the bass response below the cut-off frequency, this rolls off more steeply than in the closed-box configuration.

A loudspeaker (or ‘speaker’) is an electro-acoustic device that converts electrical signals into sound. Speakers pulse in accordance with the variations of an electrical signal and sound waves propagate through air.

We will give a brief description of how electrodynamic speakers (the most commonly used type of speaker) work to reproduce as faithfully as possible the various sounds that nature and musical instruments produce.

Electrodynamic speakers are the most popular speakers. They come in various shapes, sizes and price brackets. Our familiar cones and domes characterize electrodynamic speakers. They are the diaphragms that generate the sound and usually the only visible parts of a loudspeaker. The electrodynamic speakers’ operation is based on the principles of electromagnetic induction. That is, when a conductor moves in a magnetic field it experiences forces that result in the generation of an internal electric field and potential differences at its ends.

At the heart of the electrodynamic speakers there is a strong permanent magnet, cylindrical in shape, with a cylindrical shaft (the pole) at its centre. Between the pole and the magnet there is a space of a few millimeters, in which a very strong and homogeneous magnetic field exists. The space between the magnet and the pole holds the voice coil. The voice coil is free to move in the magnetic field and supported by an elastic suspension, which makes sure that the coil does not touch the pole, and behaves as if it is floating. When the audio signal in the form of alternating current is conducted through the coil, forces are generated that cause it to move back and forth. On the outside of the coil a diaphragm is attached, the size of which determines the lowest frequency that can be reproduced. The diaphragm moves and sound is generated.

Larger diameter cones require larger voice coils and magnets. This creates speaker drives with large mass and inertia, which require more power to drive. In an effort to minimize the mass of the diaphragm while keeping the required rigidity, synthetic and sometimes exotic materials are used, such as polypropylene, Kevlar, titanium etc.

When the cone of a loudspeaker moves forward to impart pressure on the air layers in front of it, then an equal and opposite-directed decompression is created behind it. The low frequencies generated in front of the cone are non-directional and move to cover the area in front and behind the cone. This causes their cancellation, since they interfere destructively with the equal, yet out of phase, low frequencies generated behind the cone.

The ideal way to avoid this phenomenon is to place the speaker in the middle of a large surface. This is known as an ‘infinite baffle’. Of course, this solution is totally impractical so manufacturers resort to surrounding the speaker with a cabinet. Cabinets are therefore used to support the speaker drives and nullify unwanted cancellations.

The cabinet design contributes greatly to the response of the loudspeaker and either mimics the free loudspeaker behavior (infinite diaphragm design) or uses the enclosed air to improve performance (bass reflex and acoustic suspension design). The ideal speaker cabinet is rigid so that it does not vibrate from the internal air pressure variations. In addition the cabinet must have significant damping behavior to minimize unwanted sound radiation.

Speaker manufacturers face many challenges in designing speakers. High-frequency reproduction requires fast and accurate diaphragm movements. These diaphragms must have low weight to minimize heat generation and increase speed and control.

Tweeters, reproducing high frequencies, have low-weight diaphragms and powerful magnets, such as those manufactured from high-density neodymium. Many other materials are used for tweeter diaphragm manufacturing, with aluminum being particularly well suited for this task. They are rigid and low mass, and reproduce fast transients with high speed, accuracy and distortion-free sound. Nomex and silk also make excellent diaphragms.

Yet low frequencies require large diaphragms that are capable of moving the required volume of air to generate low-frequency sound waves. Large diaphragms weigh more, have greater inertia and decreased sensitivity, while also requiring more power to be set in motion.

Woofers, reproducing mid and low frequencies, require drivers with larger diaphragms. Kevlar cones are an industry favorite due to their natural mid-range response. Another excellent choice for middle frequency speakers are Alucone® speakers, which have a rigid low-mass aluminum sandwich alloy cone for fast transients, accuracy and distortion-free sound.

As for the dedicated low-frequency subwoofers, excellent choices for the diaphragm materials are carbon fiber, polypropylene and light but rigid specially-treated paper cones.

When the cone of a loudspeaker moves forward to impart pressure on the air layers in front of it, then an equal and opposite directed decompression is created behind it. The low frequencies generated in front of the cone are non-directional and move to cover the area in front and behind the cone. This causes their cancellation, since they interfere destructively with the equal yet out-of-phase low frequencies generated behind the cone.

The ideal way to avoid this phenomenon is to place the speaker in the middle of a large surface – known as an ‘infinite baffle’. Of course, this solution is totally impractical so manufacturers surround the speaker with a cabinet. Cabinets are therefore used to support the speaker drives and nullify unwanted cancellations

The cabinet design contributes greatly to the response of the loudspeaker. It either mimics the free loudspeaker behavior or uses the enclosed air to improve performance (bass reflex and acoustic suspension design). The ideal speaker cabinet is rigid so that it does not vibrate from the internal air pressure variations. In addition the cabinet must have a significant damping effect to minimize unwanted sound radiation.

High-frequency reproduction requires fast and accurate diaphragm movements. To increase speed and control, and minimise heat generation, diaphragms must be low weight. Likewise, low frequencies require larger diaphragms, which are capable of moving the required volume of air to generate low-frequency sound waves.

However, large diaphragms weigh more, have greater inertia and decreased sensitivity, while also requiring more power to be set in motion.

To overcome the conflicting drive requirements for low and high frequencies, speaker manufacturers resort to two or more designs where dedicated drivers reproduce specific frequencies. This technique requires the use of a crossover circuit, which separates the frequencies and routes them to the appropriate drivers.