This is a 2W Exciter/vibrator with 4ohm impedence, perfect for hobby projects requiring a simple speaker output.
Measuring 27mm in diameter, the exciters compact form means it can be easily attached and detached to a range of surfaces and appliances.
These are often used in things such as arcade/pub quiz machines where they can be attached directly onto the frame of the machine.
The exciter (or Tranducer as it is also known) is basically a loudspeaker without a membrane. It works by applying an audio signal to the contact pins, the oscillating mass then starts shaking with the frequency of the applied signal. This oscillation is transmitted to the mounting plate and from there on to the surface the exciter is stuck to. The surface then emits the audio signal just like a speaker!
There are some differences in how the sound is emitted compared to a speaker. The excited surface is very large and heavy (when compared to a lightweight cone membrane in a speaker), and thus unable to oscillate coherently. That means that not every point of the surface moves into the same direction with the same amplitude at the same time.
A bending wave is generated which propagates towards the edge of the excited plate, where it is reflected back towards the exciter. To illustrate this behaviour, imagine a stone thrown into a basin of water. From the point where the stone hits the surface of the water, a circular bending wave propagates towards the seam of the basin, where it is reflected. The original wave and the reflected wave interfere with each other, causing a chaotic wave-pattern on the water surface. The same applies to the excited surface: The original wave from the exciter interferes with the reflected waves from the edges of the plate, resulting in an incoherent emission of sound. This incoherent sound emission is the main reason for the very wide, uniformly distributed sound field of an excited surface.
The quality of the reproduced audio signal is strongly dependent on the characteristics of the excited surface, and the material, shape, and dimensions can affect it.
The larger the excited plate, the better the reproduction of low frequencies, the sound output is more voluminous whilst inversely the smaller the excited plate, the weaker the reproduction of low frequencies and the sound output is less voluminous. The lighter a surface the better, as the efficiency factor (sound pressure level compared to input power) decreases with increasing weight of the excited plate. The structure of the excited surface has a great impact on the sound output. Large surfaces with few reinforcing structures work best. Simply attach the speaker to the surface of the plate by gluing or sticking.
We've had great results using sandwich panels with honeycomb structures (e.g. hexagon-structure), thin particle boards (e.g. HDF / MDF), and acrylic sheets.