FRD Response Blender and
Minimum Phase Extractor version 2.0
Created by Charlie Laub and Jeff Bagby
last update: January 17, 2014
The FRD Response Blender and Minimum Phase Extractor is a tool for combining acoustic measurements and models into a wide band frequency response from which the minimum phase response can be extracted.
The Blender is written in Microsoft Excel but can be used in programs such as OpenOffice Calc that can open Excel files. There are some features that can be run using VBA macros, however, a non-macro alternative is always available. All calculations are done using worksheet formulas, improving cross-platform compatability.
The Blender helps the user to solve real-world problems that arise when measurements are made in finite-sized indoor spaces. In general, a low frequency measurement or a model of the low frequecy response is combined with a model of the baffle step diffraction. This corrected low frequency response can then be combined with a high frequency measurement using the blending technique. The extreme low and high frequency behavior is modeled using "tails" that are defined by the user and which extend the frequency response to all frequencies. The minimum phase response can then be extracted and the data saved as an FRD file for use in other programs. The resulting blended, minimum phase response represents the free-field response of the driver in the loudspeaker at the acoustic center of the driver.
The user must supply high frequency data in the form of a measurement made in the far-field (e.g. 1m distance). A near-field measurement or a built-in Thiele-Small box model are used to supply the low-frequency data. An easy-to-use model of the driver in the loudspeaker enclosure is also built into the tool to create the baffle step diffraction correction. These models were taken from the widely accepted programs "Woofer Box and Circuit Designer" and "Baffle Diffracton and Box Simulator" written by Jeff Bagby, both of which have been thoroughly vetted in the DIY community.
Some screen shots of the program are found below. The download section contains links to the spreadsheet as well as a tutorial explaining how to use the progam. In addition, a white paper written by Jeff Bagby that highlights the use of the Blender for processing loudspeaker measurements is available, and is highly recommended reading.