Electromagnetic speakers are the grandparents of electrodynamic ones. The former emerged around 1860. However, it took over 40 years to develop the knowledge of acoustics, materials, math, and frequencies that gave birth to the kind of electrodynamic speakers that we know today. The then recent developments in vacuum tubes were extremely helpful for control of frequencies and power regulation, as well as amplification.
Electrodynamic Speakers: Back to Basics
Nowadays engineers still apply stream and pressure to paper when creating low-cost loudspeakers. The felting process is typical since paper-coned loudspeakers. You make a screen mould in the shape of the desired cone and then press wet pulp into it. By varying the pressure, the heat, and the amount of pulp, engineers can create a variety of cones, ranging from tweeters to subwoofers.
Paper cones can modify their weight when they are in humid environments. For this reason, one can make cones from different materials. The most used one is polypropylene because, with this material, humidity isn’t an issue. Even if these cones tend to have a flatter frequency response, they also have downsides. For instance, the downsides of polypropylene is that it is difficult to fold and has a low melting point, which makes it inappropriate for continuous high power use.
Luckily, this is not the only type of cone one can make. There are also Carbon-fiber and Kevlar cones. They are quite popular because these materials are extremely light and rigid, and they have a fast frequency response.
The Physics Behind the Electrodynamic Speakers
Electrodynamic speakers use electromagnets to provide a strong magnetic field for high wattage speakers. They work by wrapping a large field coil around a core that produces a strong and steady magnetic field. The magnet is pot-type shaped and includes a south pole in the center and a north pole in the periphery. The shape of the core allows the magnetic flux to remain concentrated in the annular gap between the poles. The material of the voice coil is either fiber or aluminum. It is located in the annular gap.
The audio signal from the amp’s output transformer affects the voice coil. In turn, this signal causes a varying magnetic field. As a result, both magnetic fields generate mechanical vibrations in the coil assembly. These vibrations run through the attached cone creating sound waves in the air and radiating energy and sound.
If you’re looking for more…
If electrodynamic speakers are not for you, be sure to consult other options. In Music Production Knowledge we offer explanations on digital ones and rotary woofers, just to name a few.
