Can An Accelerometer Be Used As A Microphone?

Microphones are essential pieces of gear that are heavily relied upon in various industries which rely on the transmission, broadcast and production of audio.

This post will discuss whether it is possible to use an accelerometer as a microphone.

But before I walk you through this let’s get a working idea what an accelerometer does.

The job of an accelerometer is to produce an electrical charge when the piezoelectric material (present in the device) squeezes due to vibration…

With that said, Can an accelerometer be used as a microphone?

An Accelerometer can be used as a microphone by building it into an Accelerometer Contact microphone which can then capture high quality audio signals… provided the accelerometer used, has wide operational bandwidth and micro-g resolution. An accelerometer contact microphone works the best in capturing both low and high frequency sounds.

The Uses of Accelerometer Contact Microphones(ACMs) and Accelerometers

Knowing that Accelerometers can be used to make ACMs, it’s important to also know what these microphones can actually be used for.

Monitor cardiopulmonary sounds and body motion

Various physiological acoustic signatures originate from our body, occurring over a wide range of frequencies.

For example, The frequency content and timing of recorded heart sounds can be used for identification of abnormal heart sounds such as murmurs which may occur due to turbulent blood flow.

The performance of the sensors in terms of recording cardiopulmonary sounds is validated with a medical grade electronic stethoscope.

When paired with the sensitivity of an Accelerometer Contact Microphone an improved detection of heart sound occurring in the higher frequencies (~140 Hz) can easily be achieved due to the high signal-to-noise ratio of ACMs.

Acoustic pick ups in instruments

MEMS (micro-electromechanical system’s)   accelerometer technology has potential for acoustic pickup applications in musical instruments, especially in live performances where acoustic feedback is usually a problem.

A very small, low-power MEMS device can be mounted unobtrusively anywhere on the instrument without affecting its natural vibration characteristics.

Alternatively, multiple sensors can be mounted at different points around the instrument to provide the sound engineer added flexibility to reproduce the natural character of the instrument without fear of acoustic feedback in live sound application.

Speaker box Tests

Science and engineering need accelerometers for countless different applications…..In audio however, one of the areas where it’s handy is in the construction of a speaker box.

General Contact Microphones

Contact Microphones use Piezo disks so let’s start by knowing them better.

A contact microphone is a small flat piezo disk/element that translates physical surface vibrations into voltage.

The piezo discs are simply a layer of crystal in the center of a thin brass disk (usually circular).

When there is a vibration on a surface of an object, the disc bends slightly which generates a small electrical signal.

Piezo crystals basically generate a voltage when deformed or bent. It is commonly used as a thin piezoelectric ceramic round glued to a thin brass or alloy metal disc.

This center disc is positively charged and the brass disc is negatively charged.

The voltage can be measured across those parts and then amplified to produce sound.

If you send an amplified signal to a piezoelectric crystal, it will produce tones.

They can also reproduce complex sounds, but have a limited frequency range in general.

Contact microphones are a form of microphone that are able to sense audio vibrations through contact with solid objects.

Unlike normal air microphones, contact microphones are almost completely insensitive to air vibrations but transduce only structure-borne sound.

Uses of Contact Microphones

Instruments

Contact microphones are commonly used to amplify acoustic guitars, pianos, and other acoustic instruments. On their own they’re able to produce an extremely high impedance signal which is greatly boosted by using a high impedance pre-amp.

In addition to amplifying musical instruments, contact microphones are also often used in the creation of foley sounds for film and video. 

Sensors

Contact microphones can also be used as sensors that are able to transmit data to computers or microcontrollers in order to control media or trigger processes.

Recording in challenging environments

Not only are contact microphones only useful for amplifying sound..  but they are also useful in recording sound in challenging environments, such as underwater under high pressure.

Conclusion

As you’ve probably noted in this article, Accelerometers can be used to make what are known as Accelerometer Contact Microphones.

These microphones are basically contact microphones with added sensitivity.

There are used in different fields such as medicine, audio experiments and so on and so forth.

I’ve deliberately gone the extra mile to explain contact microphones in detail in order to provide you with added context.

I hope you enjoyed reading this post.

Useful Terminology

Accelerometer Bandwith: The bandwidth of an accelerometer is basically the frequency range over which the response magnitude remains within a particular maximum allowable deviation relative to the DC (or low-frequency) value of the magnitude response.

ACM: Accelerometer Contact Microphone