The available Speakerbench modules in the current website include 'Collect Data from Measurements,' allowing users to merge three impedance measurements into a data container; 'Calculate (Fit) Data,' a data container to compute advanced model parameters; and 'Datasheet Creator,' allowing users to create a standard datasheet with advanced parameters. A fourth item in the menu is the Manual, providing the information needed to understand and explore the tools.
A key feature of this set of tools is the ability to create and use an advanced transducer model that is more accurate than the traditional Thiele-Small model. Speakerbench doesn't do the actual measurements, only offers calculations based on the actual data input from users.
Since 2017, the two authors have been researching and publishing work on viscoelastic lumped parameter models for speaker characterization, and more recently exploring the dual-added-mass technique for determining small-signal parameters. That research was first presented at the ALMA AISE event (now ALTI Expo) and published in the 2017 edition of the Loudspeaker Industry Sourcebook (www.loudspeakerindustrysourcebook.com).
That work led to the publication of an Audio Engineering Society (AES) paper, in December 2017, which explained a novel dual-added-mass method to determine small-signal parameters from three impedance measurements and adding different masses to the cone. These are based on the standard measurements for determining loudspeaker Thiele-Small (T-S) parameters and subsequently largely replaced by Klippel measurements, using the hardware and software solutions from Klippel GmbH, at least for industry and professional applications.
As Claus Futtrup noted, the vast majority of DIY and independent professionals could not afford that equipment and continued to rely on added-mass measurements until today. And that is where the idea for the Speakerbench website was born, offering an approach that is perfectly valid for small-signal analysis. The tool allows performing three impedance measurements instead of two, adding much higher precision and improving over the old-fashioned way of manually dialing in fL, fS and fH, and allowing to accurately compute a new model parameter that measures the level of driver viscoelasticity.
"The dual-added-mass method completely separates the electrical part and the mechanical part of the impedance, facilitating determination of a high-quality electrical model (resistance, inductance, etc.). In a relatively simple yet powerful computation, the mechanical and electrical contributions are separated, without any assumption of the underlying models. It’s a model-free extraction entirely based on the measurement data," the authors describe.
"The electrical model that we prefer is the five-parameter one by Thorborg-Futtrup, which includes motor semi-inductance. This model is versatile; it can describe a wide variety of transducer designs accurately over the full audible frequency range. We would say the model is valid within the speaker’s usable range plus one or more octaves beyond. Although the quality of the results from the dual-added-mass method is high, we are well aware of the fact that some people might find the mathematics to be difficult to approach. Therefore, we decided to create a web-application, which serves the underlying routines to anyone who can measure impedance — something not so hard to do. This application is Speakerbench."
"The additional effort of measuring a third impedance curve is well worth it, because you get a lot more information as well as a quality assessment of the measurement data and model fit," they add.
A complete article about Speakerbench, describing the methods and the research, including a comparison with existing measurement tools and industry practices, is included in the latest 2020 edition of Loudspeaker Industry Sourcebook. And the authors already envisage introducing a box calculation module that implements the proposed transducer model in Speakerbench. This will enable users to export the object prepared from the Datasheet Creator directly into the box module, automatically generating SPL, excursions, vent velocities, and other calculations.