How Loudspeakers Work
The fundamentals of speaker technology have not changed significantly in the roughly one hundred years since Chester Rice’s and Edward Kellogg’s dynamic driver hit the market in 1925.
That technology is still the foundation of loudspeakers today, including your phone, home audio system and anywhere speakers are used for public indoor or outdoor events.
How do speakers work?
A speaker driver is the raw electroacoustic component at the heart of every loudspeaker. Functioning as a standard transducer, it transforms energy from one form to another. In this case, the speaker driver converts the amplified electrical waves from your playback device, be that your phone, a CD player, or the cartridge of your turntable, into sound pressure waves in the air for your ears to detect.
Speakers are used in combination with an amplifier that feeds a signal to two terminals on the back of a speaker. These terminals pass the electrical current into a cylindrical coil of wire, which is suspended in the circular gap between the poles of a permanent magnet. This coil moves back and forth inside the magnetic field as the current passing through it alternates in direction with the signal applied, per Faraday’s law. The center of the speaker cone is attached to one end, which gets driven back and forth by the moving coil. This cone is held at its edges by an airtight suspension or surround. As the cone moves, it pushes and pulls the surrounding air. That creates pressure waves in the air which we call sound.
In most loudspeakers larger than a portable boom box, tweeters and woofers also enter the picture. They are usually arranged with a smaller tweeter positioned above a larger woofer. There are several reasons why speakers use multiple drivers in different sizes. One driver may be too small to move enough air to generate bass at an effective level. Larger drivers can move more air, but the problem is that speakers become more directional as the frequencies they are reproducing go up. This is known as beaming.
As frequency increases, the associated wavelength decreases; speaker drivers usually start beaming at a frequency with a wavelength equal to the diameter of the radiating cone. This means the higher frequencies will only be heard by those directly in front of the speaker. That is bad for a public performance where much of the audience is not in line with one of the speakers. The simple solution is to use varied sizes of drivers with each one tailored to reproducing a specific range of frequencies to fully cover every part of the audible spectrum.
Why are speakers mounted in enclosures?
As a speaker driver’s cone moves, it creates a pressure wave from both the front and from the back. As it moves in one direction, pushing the air and creating a positive pressure, it simultaneously pulls the air behind it, creating negative pressure. If the wavelength that corresponds to the frequency of the reproduced signal is large relative to the size of the driver, the pressure generated by the two sides of the driver will effectively cancel each other out and the lower frequencies (bass) are rendered inaudible.
This can be assessed by removing the speaker driver from its enclosure. The result will be sound of an irritating or high-pitched nature due to the removal of the bass and thus domination of higher frequencies or treble.
In a nutshell, the enclosure allows for the speaker to function effectively at all frequencies. It does so by blocking the pressure wave created by the back of the speaker cone from canceling out the wave created by the front of the cone.
How speakers work is relevant every day for Clear Sound and their customers. On a recent project, Clear Sound selected and installed new Community R.5-94Z outdoor speakers for the University of Pennsylvania’s baseball field. The speakers needed to be powerful enough for the sound to carry clearly in the outdoor setting, but small enough to fit in the requested space without being noticeable.
They are compact, weather resistant, full range horn loaded loudspeakers. Clear Sound also had to build custom brackets to hold the speakers off the roof surface of the broadcast building. The pictures tell the tale very well.
Please contact Clear Sound for help with audio visual equipment and installation services at your facility.