Zaph|Audio - SB Acoustics 2-Way : Crossover Software
Design Software Alternatives
Many design software products are available, both commercial and free. Some of the emerging free software approaches the results that may be obtained with the even more elaborate commercial software if used appropriately. One prominent example is the Passive Crossover Designer (PCD), an Excel spreadsheet created and made available by Jeff Bagby. Jeff is a long-term denison of the discussion boards at Madisound and Parts Express. He has developed some Excel spreadsheets that can be used to design crossovers and boxes. An example of the PCD is shown for one of the crossover designs listed along with a full set of files that you may download. If you get the urge to alter the design to suit your own tastes, everything that you need is available. It's probably most useful for the fine tailoring such as the top end rolloff or overall level adjustment of the tweeter. The latter is an area where small changes in level make large changes in perceived response since a level change is very broad and easily heard. A simple resistor change can alter the response from the crossover Fc up to the limits of your hearing.
You may even decide that you would prefer a different overall sensitivity. If you add a subwoofer at some point, this could be helpful since you may want to eliminate the peak that was created at the woofer low end due to the limited extension. This would be accomplished by raising the overall sensitivity, but would require a nearly complete re-design of the crossover. The natural sensitivity that would yield the flattest overall response for such use would be around 85db. Keep in mind that this won't take other factors into account such as floor bounce, but that's another topic altogether and won't be adressed in these pages.
Using the Passive Crossover Designer
The curves for the raw drivers, the driver/crossover responses and the summed response are shown below. The scale was expanded to show more of the stop-band area. Keep in mind that the woofer curve above about 15KHz was truncated, then extended for optimization since it's output won't contribute enough to measure with the crossover in place. It makes it much easier to get a reasonable phase response since the model uses minimum-phase data that was calculated using the Hilbert-Bode Transform (HBT) for the files imported.
The individual driver sections are shown below. Each driver can be optimized separately and the sum viewed simultaneously with any indiidual driver crossover changes. It's really a very user-friendly setup. You can download the files to use in the PCD or many other packages for that matter. The individual raw driver files to use with the PCD project files are provided. Two versions are provided.
One version has the excess-phase data so that they can be used directly without a model that has the acoustic offset. No optimization at other points works without some calculation of the relative distance change. This version is useful if the design is made only at the measurement point.
The second version has the minimum-phase data. This also requires the acoustic offset (included in the minimum-phase PCD project file). This allows you to optimize at points other than the measurement point. This will still only be for the crossover issues and will not include diffraction changes at other axes. But even so, it's still useful for working with the crossover axis variations.
 SB Woofer Files |
 SB Tweeter Files |
Another set of files includes the individual raw driver measurements on the baffle in-box plus the manufacturer supplied files for the woofer and the Parts Express passive radiator. The measurement files are the LAUD measurements on which the others were based.
David L. Ralph © 2009