The purpose of The Frequency Response Modeler is to allow the user the ability to create and save modeled frequency and impedance files (.frd & .zma) for use in other software, such as crossover design programs. It also allows for the user to import existing frequency response files and modify them in various ways such as splicing box response data, adding in baffle diffraction data, raising or lowering a level, adding or subtracting delay, applying various types of equalization, or applying standard crossover functions to the data. The program can also extract the minimum phase data from a modified frd or zma file as well. The program is broken into four sections, The Response Modeling section, The Impedance Model, The Box Response Model, and The Baffle Diffraction Response Model.
In this main section you will find the "Minimum Phase Equalization Modules". Using these functions it is quite easy to add or remove response peaks from a frequency response. Below this area you will find a Low Pass and High Pass section. You may model the low pass and high pass roll-off characteristics using the Coefficients for a standard Fourth Order polynomial. There are several standardized textbook responses that are available or you may custom shape a roll-off by manually adjusting the coefficients.
The Impedance Modeling and Box Modeling Section are tied together with both using the same data. Almost all of the data is entered into the Impedance Modeler and the Box Modeler simply shows the calculated box response results. Since both frequency response and impedance data are needed for accurate crossover modeling and simulations it was important for this modeler to include a tool that could create a very accurate impedance model that could then be saved out as a zma file.
The Response Modeler's impedance modeling tool is among the most accurate available anywhere. Since voice coil inductance does not behave as a true inductance simply using Le in a model will not generate an impedance curve that is accurate enough for most crossover design modeling. Because of this I have built a complex proprietary expression for a driver's rising impedance with frequency that allows the user to shape the curve to the correct impedance fit. There are three different impedance modeling modes available as well: 1) Modeling using full Thiele/Small parameters, 2) Modeling using only the Voice Coil Parameters and the Minimum Phase EQ modules, and 3) Modifying an imported curve using the Minimum Phase EQ modules only.
Once the driver and box parameters have been entered and the impedance modeling is complete you can move back up to the Main Response Modeling section and prepare to splice this modeled bass response onto the frd file that you are working with. (You can also unsplice the bass response if you don't like the result and adjust some more. This unsplice feature is a useful function at times.)
A very useful feature in modeling frequency response is the accurate model of baffle edge diffraction. Below the Box Modeling Section you will find the Baffle Diffraction Response Modeling Section which will do exactly this. This section offers some features you will not find in many baffle edge diffraction programs. For example, this program will accurately model the diffraction taking into consideration baffle edge radius and driver piston directivity. The program can calculate the baffle response of an open baffle as well, and will calculate the phase response of the diffraction signature. You can model the diffraction as a loss function, a gain function, or you can model it inverted, which is useful if you want to subtract the baffle effect out of a frequency response curve. Once the baffle diffraction is modeled you can save it out as an frd file of its own to use in other software or you can transfer it to the Baffle Diffraction registry and it will be included in the modeled response of the driver. If you already have baffle data saved the program is also capable of importing a BDS file using that instead.
This program also includes a Hilbert-Bode FFT Transform that allows you to extract the minimum phase from an frd or zma file. Once you have made all modifications to a file that you want to do then save the file as an frd file and then click the button for "Auto Extract Phase from FRD File", find that file, let the program extract the phase, and then save as the same file name (or another if you want) and the new file will contain the correct minimum phase data.
The file requires Excel 2000 or higher with Service Pack 1 and 2 installed and must have the Analysis Toolpak and Analysis Toolpak VBA installed in the add-ins, and security must be set to allow running of macros. A small .dll file has been included with this program named "fttdll.dll". This file is needed to quickly perform the inverse Fast Fourier Transform for the minimum phase extraction. The file needs to be placed in your default Excel folder. This is the folder that Excel automatically goes to if you click on "File Open". If the dll file is not present in that folder it will still perform the phase extraction but it will be much slower.
Frequency Response Modeler 2.1 Update Info: Refined the baffle diffraction section with an improved open baffle model. Frequency Response Modeler Version 3.0 Update Info: Completely revised baffle diffraction model to improve accuracy and correct issue with high aspect ratio baffles. Added variable slope high and low pass response extensions. Revised user guide page.