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Best Practices for Designing Micro Speaker Enclosures

By Bruce Rose, CUI Devices

Micro speaker enclosures serve to both protect the speaker from unwanted damage and to enhance its audio volume. By understanding the basics of proper speaker enclosure design techniques outlined in this article, users can work to improve the audio performance of their intended application.

Basic speaker construction

There are several parts that go into a speaker’s basic construction. At the core of any speaker is a wire coil, which is placed between the poles of a permanent magnet and then attached to a diaphragm. The diaphragm is then suspended in a way that allows it to freely move forward and backward. When an electrical signal is applied to the wire coil, its movement in the magnetic field also causes the diaphragm to move. This movement leads to air pressure waves radiating from both the front and rear of the speaker that are detected as sound. However, because these waves are out of phase they can partially or completely cancel each other out. This is where the proper design of a speaker enclosure can enhance the reduced sound level produced by these out of phase waves.

Diagram of basic speaker constructionFigure 1: Basic speaker construction (Image source: CUI Devices.)

Micro speaker enclosure basics

Providing physical protection for the speaker, but also minimizing the attenuation of its desired sound is the role of the enclosure’s front cavity. The front cavity is commonly constructed with a screen or by forming holes in a solid plate. A hole pattern roughly the size of the speaker will allow for efficient sound propagation and can be achieved by removing as little as 20% of the solid plate area. Attention should also be paid to the spacing between the front of the enclosure and the speaker, where a gap of 1 to 2 mm will prevent the moving speaker diaphragm from contacting the front of the enclosure in most cases.

When it comes to a micro speaker’s rear enclosure, designers should create an air-tight cavity that prevents radiation of the rear sound pressure waves. This can be achieved by placing sound absorbing material inside the cavity or by selecting a rigid material for the housing that will not radiate sound. In some rear enclosure designs it is possible to use the rear pressure wave to improve the frontal sound waves, but that is a practice best left for more complex applications.

Diagram of front and rear speaker enclosureFigure 2: Front and rear speaker enclosure (Image source: CUI Devices)

The next piece to consider for a rear enclosure design is the delicate balance between enclosure size (volume) and pressure changes. A smaller rear cavity volume is often desired for the compact applications where micro speakers are employed but comes at the cost of large air pressure changes caused by the moving speaker diaphragm. These changes in air pressure ultimately limit movement of the diaphragm and consequently the sound produced from the speaker. As a rule of thumb, a speaker’s diameter provides a good baseline for determining the rear cavity depth that will minimize air pressure changes and maintain the compact size desired in micro speaker applications. However, in applications where depth may be a concern, the area of the rear cavity can be increased, while reducing the depth in order to maintain the same volume.

Micro speaker enclosure mounting

Mounting of a micro speaker also plays a vital role in the final sound quality of a product. The front and rear of the enclosure should be tightly fit with the speaker mounted securely in between and serving as a part of the rear enclosure structure. This will not only help to reduce sound propagation from the rear of the enclosure but will also prevent rattling sounds from being generated. High density foam can further assist in the creation of a secure and tight-fitting junction.

Conclusion

It does not take an audio expert to improve the sound quality of a chosen speaker or micro speaker. With an understanding of the basic guidelines outlined above, engineers are well on their way to audio excellence in their design. CUI Devices makes this process even easier with a range of micro speaker options in compact packages as small as 10 mm and depths as low as 2 mm.

Image of CUI’s micro speakers offer a variety of package typesFigure 3: CUI Devices' micro speakers offer a variety of package types (Image source: CUI Devices)

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Bruce Rose, CUI Devices

Article Authored by Bruce Rose, Principal Applications Engineer, CUI Devices.