Practical Test & Measurement: Loudspeaker Measurements at Home - A Guide for Building Your Own Test Chamber

September 9 2020, 09:10
Given the fact that most audio professionals and developers are working from home, audioXpress asked our friend Geoff Hill, the inventor of the original tetrahedral test chamber (TTC), to explore how to do loudspeaker measurements at home. A lot of Geoff Hill’s work is now based at home, and indeed his front room. And like so many acoustics builders, designers, and engineers in these crazy times, he no longer has access to an anechoic chamber, so how is it possible to still make useful loudspeaker measurements? This article explains how to build a basic tetrahedral chamber to use at home, and then put together a measurement system and check the results.

New Normal for Loudspeaker Measurements
As the pandemic forces us to do a lot of things differently, it’s time to take a fresh look at how we can make loudspeaker measurements during the new normal. First, let us take a look at the alternatives that we have used:

• Free-field measurements
• Ground plane measurements
• Anechoic measurements
• Anechoic IEC baffle or JIS test box measurements
• Windowed/Gated measurements

All of these methods have their advantages and disadvantages, are expensive, and rely upon having a large physical space in which to work. This is not possible when working at home or even in most workplaces, but there are modern standards created to overcome these issues. Using them, we can make accurate, repeatable, calibrated, and transferrable loudspeaker measurements, as an alternative to these traditional methods. We can do this by building our own basic tetrahedral chamber — giving us a convenient, low-cost approach during the new normal.

The tetrahedral chamber concept was launched at the AES Loudspeaker and Headphone Conference in Helsinki, Finland, with the theory being published at the Audio Engineering Society (AES) convention in New York. The theory was based upon a tetrahedral structure that can fit into a corner anywhere. Following peer review, this type of chamber has now been incorporated into international standards [(1) IEC 60268-21-2018, (2) draft IEC 60268-22, and (3) AES 73id-2019] and widely accepted as a valid methodology for comparative loudspeaker measurements. These standards give us a compact and convenient, defined structure, which is small and relatively low-cost and meets our requirements for making accurate, repeatable loudspeaker measurements.
This is the completed tetrahedral chamber, which you can use to to test your loudspeakers when you don’t have access to an anechoic chamber.
This article was originally published in audioXpress, September 2020.

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About the Author
Geoff Hill, the inventor of the Tetrahedral Test Chamber (TTC) and CTO at Hill Acoustics, has been working in the loudspeaker and audio industry for more than 40 years. He is the vice-chair of the Audio Engineering Society’s AES SC-04-03 Working Group on loudspeaker modeling and measurement and a member on the International Electrotechnical Commission’s IEC Working Group TC 100/TA 20/PT 60268-22. Hill is also the author of the book Loudspeaker Modelling and Design: A Practical Introduction (Routledge 2018). He welcomes your comments and can be contacted via email.
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