By Don Maurer
Over a year ago, I started reading DSP (Digital Signal Processing) books with the hope I could eventually develop a program to automate the process of building digital crossover filters for a multi-way speaker system and then use those filters for the digital playback of CD's or analog inputs.
My background is in Math and Computer Science, so this required lots of new discovery in the DSP world. I wanted the program to measure the magnitude and phase of a driver and automatically create a digital crossover filter that would make the driver respond like a given target (e.g. Linkwitz-Riley 4th order).
I have finally created such a program. It is not perfect yet, but is showing great promise. Below, I'll show some of the results so far.
In less than 15 minutes per speaker side, the program automatically builds digital crossover filters with driver correction for up to a 4 way stereo systems. The program then uses those digital filters for playback of CD's or analog inputs. CD .wav files in a directory are upsampled in real-time to 88.2kHz from 44.1kHz and then the digital filters are applied for each driver. Analog input is sampled at 88.2kHz/24 bit, and then the digital filters are applied. The playback program allows you to change the filter size or filter set in real time for listening comparison tests. The woofer and tweeter levels can be adjusted and so can the woofer phase. A time slider allows a portion of a music cut to be replayed for comparison.
The speaker I chose for my prototype experiment was the PHOENIX which was designed by Siegfried Linkwitz. See www.Linkwitzlab.com . This looked like a speaker with lots of potential given its big brother - the Beethoven Elite - had won honors in 1998 from Stereophile Magazine. Hearing the Beethoven Elite's at the Linkwitz house, finalized my decision to build the PHOENIX. It was probably the best speaker system I'd ever heard!
Digital Crossover Filter Building/Playback Process