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Driving LRAs from Audio Signals and Music

By: Doug Roberts
11 May 2012

  • Can Audio Waveforms Drive Linear Resonant Actuators?
  • Can Audio Waveforms Drive Linear Resonant Actuators?

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 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 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:

  • Resonator Frequency Response, C10-100 (Linear Resonance Actuator)
  • Resonator Frequency Response, C10-100 (Linear Resonance Actuator)

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 (aside from the normal advantages of LRAs, see here).

It is also important to note that many audio sources, will not produce a large enough currents 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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