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Driving LRAs from Audio Signals and Music

We are sometimes asked for advice on how to drive our linear resonant actuators using audio signals, or how to simulate an audio signal with vibrations.

These enquiries correctly understand that LRAs are built like a speaker (but without the cone to produce audible pressure waves) and are driven using AC signals, unlike our ERM vibration motors which can use a DC voltage. However, it is unfortunately not as simple as connecting the audio source to the LRA.

The first thing to consider is what you want the vibration to represent:

  • Vibration-based on audio volume (amplitude)
  • Vibration-based on an audio pitch (frequency)
  •  Some other aspect of the audio signal

Regardless of which property of the audio signal is to be reproduced as vibrations, a linear resonant actuator will only vibrate if driven at (or very close to) its resonant frequency. See the graph below taken from our C10-100:

This means that for each scenario, there must be some audio processing so that the desired property is represented in the amplitude of a sine wave, fixed at the resonant frequency. This, in turn, can be used to drive the LRA via an amplifier.

As this audio processing must take place to vary the signal amplitude, there is no additional advantage to using an LRA over a typical ERM vibrating motor.

It is also important to note that many audio sources, will not produce a large enough current to drive the LRA. For more help on how to drive linear resonant actuators see Application Bulletin 003: Driving Linear Resonance Vibration Actuators.

Unless of course, you’re trying to drive the C10-100 directly with single note F3, which happens to be 174.61 Hz!  (Ed: the resonant frequency of this LRA is 175 Hz)

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