Loudspeakers are the most variable elements in any audio system, and are responsible for marked audible differences between otherwise identical sound systems. Loudspeaker performance or accuracy in reproducing a signal without adding distortion is significantly poorer than that of other audio equipments.

Some important men who made history
Ernst W. Siemens was the first to describe the dynamic or moving coil transducer, with a circular coil of wire in a magnetic field and supported so that it could move axially. He filed his U. S. patent application for a Magneto electric Apparatus for obtaining the mechanical movement of an electrical coil by electrical currents transmitted through it was granted patent No.149797 on April 14, 1874.

Oliver Lodge filed for British patent No.9712 on Apr. 27, 1898, for an improved loudspeaker with nonmagnetic spacers to keep the air gap between the inner and outer poles of a moving coil transducer. This was the same year he applied for a patent on his famous radio tuner.

Thomas Edison was issued a British patent during 1881, for a system using compressed air as an amplifying mechanism for his early cylinder phonographs, but he ultimately settled for the familiar metal horn driven by a membrane attached to the stylus.

Harold Arnold around 1925 began program at Bell Labs to improve phonographic sound recording. The first priority was the electronic amplifier using the new vacuum tube, second was the microphone, and third was the loudspeaker that would improve the balanced armature units developed for public address.

Bell Laboratories in 1931 developed the two way loudspeakers, called divided range for the demonstration by H. A. Frederick of vertically cut records. The high frequencies were replaced by a small horn with a frequency response of 3000 to 13,000 hz, and the low frequencies by a 12 inch dynamic cone direct radiator unit with a frequency response within 5db from 50 to 10,000 hz.

How the loudspeakers used to work
The first loudspeakers used electromagnets because large, powerful permanent magnets were not available at reasonable cost.

The coil of an electromagnet, called a field coil, was energized by current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a choke coil filtering the power supply of the amplifier to which the loudspeaker was connected.

AC ripple in the current was attenuated by the action of passing through the choke coil. However, AC line frequencies tended to modulate the audio signal being sent to the voice coil and added to the audible hum of a powered up sound reproduction device.

The quality of loudspeaker systems until the 1950s was, by modern standards, poor. Continuous developments in enclosure design and materials have led to the significant audible improvements. The most notable improvements in modern speakers are improvements in cone materials, the introduction of higher temperature adhesives, improved permanent magnet materials, improved measurement techniques, computer aided design and finite element analysis.

Loudspeaker is an electro mechanical transducer that converts an electrical signal into sound. The term loudspeaker can be applied to any of the individual devices or drivers or the complete system consisting of an enclosure incorporating one or more drivers. A Loudspeaker consists of a number of drivers to reproduce a wide range of frequencies for high sound pressure level or high fidelity applications. These drivers comprise of the subwoofers for very low frequencies, woofers for low frequencies, squawkers for middle frequencies, tweeters for high frequencies and super tweeters for very high frequencies.

Most loudspeakers consist of drivers built up in an enclosure or a cabinet with a back opening for connection of the wires and to make any adjustments. They generally use two wiring points to connect to the main source, say, to the audio amplifier or receiver. This is done by using the binding post or the spring clips at the back of the enclosure. If both positive and negative connections and the amplifier of each drivers are not connected in phase with each other, the loudspeaker will produce a destructive sound wave and interference will occur when a common signal is sent to each speaker. This is generally termed as out of phase. These errors in connection will not damage the speakers but can positively tamper the sound waves that partially cancel those from nearby speakers.

The simplest way to check wiring phase problems with your loudspeaker system is to temporarily adjust the bass tone control up and the treble control down, then move the balance control so that sound is alternately heard from both left and right speakers separately. If the music has the bass tones mixed to mono the bass should be loudest with the control centered. If the bass is louder with only one channel playing, you should know that there may be a wiring error or the music signal is not mono in the low bass.

Now let us look at some brief points on the characteristics of loudspeakers which are suitable for live-like sound reproduction. When the sound of any instrument or voice reaches us but the source is blocked from our view, we will be able to determine whether it is coming from the loudspeaker or live. This is due to the power response, the radiation in all directions that is often different between a speaker and a live source. Most loudspeakers have a power response that drops 10dB to 20 dB from low to high frequencies. Or it could be through the slow decay of transients due to energy storage in resonant mechanical and acoustical structures of the speaker which we recognize as typical for a loudspeaker and missing in the corresponding live event.