This measurement will almost always be less than the driver's nominal impedance. This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This is not always the case though, because other parameters affect the ultimate performance as well. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. This parameter is the free-air resonant frequency of a speaker. However, they can be invaluable in making choices because they tell you far more about the transducer's real performance than the basic benchmarks of size, maximum power rating or average sensitivity. Thiele and Small devoted considerable effort to show how the following parameters define the relationship between a speaker and a particular enclosure. Small was, at the time, a Commonwealth Post-graduate Research Student in the School of Electrical Engineering at the University of Sydney.

Thiele was the senior engineer of design and development for the Australian Broadcasting Commission and was responsible at the time for the Federal Engineering Laboratory, as well as for analyzing the design of equipment and systems for sound and vision broadcasting.

These papers were authored by A.N.Thiele and Richard H. In the early seventies, several technical papers were presented to the AES (Audio Engineering Society) that resulted in the development of what we know today as 'Thiele-Small Parameters'. The recognized methods were expensive and often unrealistic for the thousands of individuals needing loudspeaker performance information. Prior to 1970, there were no easy or affordable methods accepted as standard in the industry for obtaining this data. The ability to choose the most appropriate loudspeaker for a particular enclosure is directly related to your understanding of the performance data that manufacturers provide with their products.

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