How Does Sound Reproduction Work

The recording and reproduction of audio underwent sweeping changes throughout the late 19th and 20th Centuries, offering many different new storage mediums, playback systems and methodologies that enabled humans to control the sound wave like never before.

At first relying upon mechanical inscription and re-creation techniques, before advancing onto electrical methods, the analogue and digital recording of speech, music and environmental noise has brought sounds never before heard to the masses, as well as creating two of the most dominant entertainment business on the planet, music and film.

Indeed, when the phonograph (the earliest form of audio recording and reproduction system, partnered with a horn loudspeaker) was first invented in the latter half of the 20th Century, it advertised a system that could ‘transport you to the realms of music’ and that it could ‘bring the theatre or opera to your home’ after a hard day’s work.

It was a revelation. The sound wave had been captured and harnessed by man. No longer was music and speech trapped in the present. Now it could be recorded, stored and replayed in the future. Higher forms of musical entertainment were no longer the reserve of only the rich and powerful, with the best opera and ballet scores transported to the homes of many.

Since that momentous invention techniques and machines used to record and reproduce audio have progressed rapidly, and with them have the loudspeakers necessary to output their signals. Most early phonographs or gramophones used horn loudspeakers, which acted like modern-day amplifiers, and worked by increasing the coupling efficiency (akin to increasing the surface area of an object) between the system’s driver, which was often a small metal diaphragm, and the surrounding air. This mechanical amplification effectively increased the volume of the outputted vibrations emanating from the diaphragm, and made the sound audible to listeners over a wider area.

Now, of course, amplification is normally achieved through electrically driven amplifiers, and the complex loudspeaker systems in use today rely on more than just spreading the surface area of sound waves. Here we take a closer look at how modern loudspeakers work.

How a speaker works

The modern loudspeaker, as demonstrated by the Monitor Audio Apex series, produces sound by converting electrical signals from an audio amplifier into mechanical motion, from which sound waves emanate. Loudspeakers can consist of an individual transducer (audio driver) or a series of drivers encased within a large chassis, each dealing with a certain frequency band to improve the overall gamut and fidelity of reproduced sounds.

For example, larger subwoofer speakers deal with low frequencies, while smaller speakers called tweeters deal with high frequencies. These various drivers are controlled by a filter network, which organizes the different frequency signals coming from the amplifier and directs them to the driver most suitable to deal with it.

The construction of a single loudspeaker driver is a complex process, the central element of which is a concave plastic or paper conical disc. This is the part that moves backwards and forwards in the generation of sound, fixed in the centre of a concave metal frame. Attached to the cone is a hollow cylinder of aluminium and a pair of wire coils suspended by a flexible fabric disc. These coils are attached to the amplifier and positioned inside a narrow cylindrical groove in the centre of a magnet. By doing this, every time a signal travels through the wires, the coil emits a magnetic field that pushes or pulls the cone backwards or forwards, forming sound waves.

Speaker placement can alter sound quality

Due to the fact that sound bounces off of the objects in your room, where you position your speakers will directly effect the quality of the sound that you hear. For instance, placing speakers too close to the wall will increase the bass sound, making it too loud or boomy. Ingeneraltry to keep the speaker 7cm (3.0m) from the wall, the speakers’ distance from the side wall should be 1.6 times the distance from the front wall. Angle the speakers inwards towards the general listening spot.

Multi-driver loudspeaker enclosures

Floor-standing loudspeakers are now being produced which combine multiple audio drivers with audio-friendly, structurally complex cases.

The enclosure of any loudspeaker plays a highly significant role in the reproduction of sound, as well as providing a unit in which the speaker’s drivers, electronic circuitry, crossover control and amplifier are all mounted.

Current state-of-the-art enclosures are built from composite materials and include numerous struts, baffles air ports and acoustic insulation materials and adhesives. These work together to reduce echo and reverberation caused by rearward sound waves generated by the speaker’s drivers reflecting off the back and sides of the case. This is important for audio fidelity and accuracy of reproduction, as rogue or errant sound waves can interfere with forward-generated waves, distorting them and adding effects not part of the original recording. The enclosure, thanks to its complex construction, is also the key factor in reducing vibrations caused by the back and forth movement of the driver diaphragm, shake of the driver chassis and rumble of any subwoofer.

Historically, in early forms of loudspeaker, drivers were often left exposed completely or partially due to heat-related issues with their electronics, as well as because of the fixed, unsuspended nature of the driver chassis and the difficulty in securing a consistent airflow. Further, the materials used in these early loudspeakers (usually heavy metals) were prone to vibration issues and did little to prevent standing waves, while their chunky and bulky designs caused diffraction of sound waves from their sharp edges.

Today, these flaws are minimized by audio-friendly, lightweight polymer casing materials, which are manufactured with smooth edges to reduce refraction and coated with resonance and vibration damping adhesives. Single component plinths, baffles and struts, as well as lightweight driver chassis also aid the accuracy of sound reproduction and, thanks to the inclusion of transmission lines (an internal structure within the loudspeaker enclosure designed to guide up to 90 per cent of a driver’s rear wave output away from distortion-prone areas) in modern cabinets, has allowed sleeker and more compact driver arrays.