Common Loudspeaker Format

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CLF2 v2 with optional phase, filters and multipart files was released Sept 8, 2011
The CLF format has been available since April 15, 2005

Latest software updates March 4, 2020

Download the free viewer to view the contents of CLF distribution files and check with software developers to see if/when they will support the CLF.


The CLF (Common Loudspeaker Format) Group was formed for the purpose of defining and maintaining a single, open file format that loudspeaker manufacturers could use to supply data to end users in the professional sound and acoustics community. As more acoustic and sound system design software has developed, the number of formats used for loudspeaker data has increased. The CLF Group have agreed to support a common format, making loudspeaker data easier to supply and use.

Note: a new format, the Common Instrument Format (CIF) based on the same principles as the CLF, has been developed for natural source directivities such as musical instruments, talkers, singers, and noise sources. The CIF format is close to release and potential CIF authors can request a beta version from

Our goal is to make loudspeaker performance and polar data available in an open but secure format.

CLF is defined in two parts, a text-based format used for data input and editing, and a binary format for data distribution. The CLF Group is making a set of tools available for data editing, conversion from text to binary distribution format and viewing binary data.

CLF is an open format. The CLF Group controls the format but the definition is freely available. The tools for creation of binary format files are available on request. The tools will include a unique identifier so that binary data is always tagged with its source. Together with other security features included in the binary format, the end user will know the source of the data and can be confident that it has not been altered. Note that to ensure data integrity it is central to the CLF that only the person or organization that measured the data, or arranged to have it measured via an independent measurement service, can become author.

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