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In 1954, Edgar Villchur changed the home audio world forever by introducing the Acoustic Research AR-1. This speaker was like no commercial loudspeaker before it. Up until this point, to get accurate, low bass you needed a speaker with a stiff suspension, and a refrigerator-sized ported enclosure. The AR-1 was revolutionary, because it took a speaker with a loose suspension and mounted it in a small air tight box. The air inside the box acted as the suspension (hence the term 'acoustic suspension').
This Acoustic Research AR-1 had one drawback--it was nowhere near as efficient as the existing hi-fi speakers (which were driven by diminutive, but musical tube amplifiers). Instead of 10 or 20 Watts, your amplifier now needed to put out 60 to 100 Watts. This encouraged the solid state revolution during the 1960s within home audio, since it was much cheaper to build a 60 Watt / Channel transistorized amplifier, than a 60 Watt / Channel vacuum tube amplifier.
Some people like it loud--they want to feel like they're right there, experiencing the music live. There's a right way and a wrong way to achieve concert level sound. Most people think if they just throw 1000 watts at their speakers, they'll reach nirvana. Instead, they end up overdriving their speakers, and killing them. When woofers are pushed past their limits, the cone overextends, pulling the voice coil out of alignment with the magnet assembly. After a few minutes of voice coil rub, the woofer is dead. Tweeters simply overheat and fry from the excess power.
If planned properly, a home sound system that can reach 104 or 110 decibels and won't break your bank can be acheived. When shopping, be sure to get a speaker that can move enough air in your room and accept a very big amplifier. Then, get the biggest amplifier your budget will allow. You can also give up on deep bass and the highest accuracy and get horn loaded speakers (they are twice as efficient as most cone drivers). It will take less than half the power to drive them to equal SPL's.
During the Golden Age of cinema, the horn loudspeaker was perfected. To this day, horn speakers of this era made by manufacturers such as Western Electric and RCA (to name a few) are prized for their efficiency of sound reproductions and command a small fortune in collector circles.
During the 50's and 60's Horn speaker designs were reduced to the size of a large refrigerator to fit in America's living rooms. Companies like Altec, Electrovoice, and Klipsch successfully marketed horn speakers for the home. Well-designed horn loudspeaker systems are super efficient. Even today, there is a worldwide cult following for horn loudspeakers, and a huge Do-It-Yourself community of Horn Speaker builders. This speaks volumes about their efficiency.
Electrostatic loudspeakers took sound reproduction in new directions. These speakers generally consist of four main parts:
• a power supply that provides electrostatic charge (think rubbing your feet on a carpet and touching a doorknob)
• a rigid plate (or plates) to hold the electric charge
• a flexible plate to act as diaphragm (only a few microns thick) which makes the music
The diaphragm is driven by a step-up transformer to multiply the voltage output from your amplifier to a level high enough to move the flexible plate. Although patented in 1929, the electrostatic loudspeaker did not reach commercial success until the 1956 with the appearance of the British-made Quad ESL-57. Electrostatic speakers (especially the old Quads) are renowned for their beautiful midrange and their frailty. However, if you put more than 20 Watts to them, or try for more than 100 dB of sound, and they are toast. They are the Jaguar XKE of the speaker world--beautiful, but fragile.
Speakers don't like distortion. When a speaker is asked to work outside its designed specifications, audible distortion results and other malfunctions can occur. Voice coils rub, tweeters overheat, and woofers can actually rip themselves from the speaker basket.
Feed speakers a bad signal, ask them to do too much or ask them to work with too little wattage and your tempting fate (and hearing loss). Respect your speakers. Think about how you will be using your speakers before you buy them. How loud you do you want the system to play? Do you want a high power home theater, or a simple system for critical listening? Buy speakers designed for what you want to use them for and they will perform better for you.
Loudspeakers were first used in the telephone industry in the late 1800's. By the early 1900's, however, speakers were being integrated into phonographs, and developed for public address and sound reproduction (these early electromagnetic speakers were not very efficient, and were definitely mono).
In the late 1920's, Bell Labs, General Electric, Western Electric, and Westinghouse made huge advances in loudspeaker design to support the recent advances in motion picture sound. Sound reproduction became a priority, and speakers grew more refined. Horn speakers, moving coil, and electrostatic speakers were developed during this time. Home Audio was primitive and consisted of a console AM radio, with a small paper cone speaker, or perhaps a phonograph player.
There's two easy ways to kill a speaker: using too much power and using too little power. When faced with too little power, a speaker will strain to produce the signal that it's fed. The low-powered amplifier is driven into clipping when the distorted signal reaches the speaker (you can actually hear the clipped-off, 'square' wave). The audible distortion will be noticeably harsh; the highs will sound brassy, the lows will sound muddled. Not only will you blow speakers with this, but you can overload the amplifier and destroy it in the process.
If you're audio system is not producing the sound level, or sound pressure level (SPL for short) you want, it's time to re-evaluate your loudspeaker, and amplifier choices. The easiest way to make a system louder is to get a bigger amplifier. Nowadays, most audio loudspeakers range from 85 to 92 db in efficiency. Some horn-loaded speaker designs can reach efficiency levels of 98 to 105 db. A loudspeaker with this type of efficiency only needs 1 to 10 watts of power to reach maximum SPL's.
Ohm Acoustics developed the first Walsh Driver Speaker in the early seventies with their Ohm A--this speaker took sound reproduction to new heights. Further refinements through the 80's and 90's have produced the current Walsh line of loudspeakers.
The Walsh Series uses a 'Coherent Line Source Driver' (basically an inverted cone driver) with an integral super tweeter. Sound emanates simultaneously from the face of the super tweeter and the top of the inverted cone (this gives the sonic impression of a perfect vertical line source). Once a pair of these speakers is placed correctly in a room they supply unrivaled soundstage and imaging, equaled only by electrostatic speakers, or exotic custom horns.
From the beginning, the motion picture industry drove huge advances in loudspeaker design. Through the 20's, theaters got bigger, and the sound systems evolved to keep up. In 1928, it took a big, efficient speaker to fill a theater with only 2 watts of power. However, the 30's and 40's saw speakers grow more efficient and produce better sound. Amplifiers produced more power, and less distortion. Western Electric, Altec, RCA, JBL and others were responsible for many of the advances in loudspeaker design from this era.
Theater sound was not restricted to the theatres. Companies like H.H. Scott, Magnavox, RCA, and Fisher were pioneers in home audio and hi-fi reproduction. By the fifties most everyone had a hi-fi console stereo in their living room.
|Jennifer Mathes, Ph.D.|