Flat panel foam speakers are making waves on the Internet, with loud and superb audio quality at an astonishing low price. It’s easy to overlook the potential convenience for gigging musicians. How much easier could it be if speakers were light and thin? A few hurdles remain, such as bass response, but we are getting closer.
Flat panel resonators have been in use since the earliest days of audio, but the wires and magnets of the time put limits on how loud a speaker could be. Various designs of horns were tried to amplify the sound, and some worked.
A strong and lightweight vibrating cone was a good start, and when followed with a horn that matched electrical impedance to acoustic impedance, the physics was right. But no one cared about physics – they tried stuff and listened. A century of incremental improvements later, and the designs are very good. Complicated and expensive, but very good.
Not much attention was paid to resonating panels, but the physics is right for them too. Just like a conventional speaker, a magnet and coil of wire combination, called an exciter, starts the vibrations. Unlike a conventional speaker, there is no attached cone, support structure, or cabinet. Instead, the exciter’s vibrations are transferred directly to a resonating surface, such as a table, wall or car panel.
There is new excitement in this century because the old problems have new solutions. Amplifiers are as powerful as needed, new alloys have dramatically improved the performance of magnets, and new materials have gotten closer to the ideal for flat panel designs.
The ideal panel is lightweight so that vibrational energy goes into moving a mass of air rather than the mass of the panel. The ideal panel is also strong, to withstand continuous vibration.
Any panel will vibrate in various inevitable but undesirable patterns of standing waves, depending on frequency, material, shape and dimensions. The result is uneven response and a distorted sound. The ideal panel vibrates as a whole, with no smaller patterns of standing waves. This is impossible, but new light, strong and stiff materials, such as extruded polystyrene (XPS), gets much closer to ideal.
It has long been known that bass instruments need to be bigger to handle lower frequencies and their longer wavelengths. It has also been known that resonators have to be beefier to maintain stiffness over larger surface areas. We are using lessons from centuries of musical instrument design, but speeding things up a bit with physics, software simulations, and modern measurement systems.
Will it work? We are certain it will! How much can we improve the bass? Stay tuned.