Siegfried Linkwitz

Siegfried Linkwitz was born in Germany in 1935. He received his electrical engineering degree from Darmstadt Technical University prior to moving to California in 1961 to work for Hewlett-Packard. During his early years in the USA, he did postgraduate work at Stanford University. For over 30 years Mr. Linkwitz has developed electronic test equipment ranging from signal generators, to network and spectrum analyzers, to microwave sweepers and instrumentation for evaluating electromagnetic compatibility.

He has also had a long and distinguished second career as an audio engineering visionary. Along with Russ Riley he developed the famed, and widely used, Linkwitz-Riley crossover filter in the mid-1970s. Since then, he has contributed several important technical papers covering a variety of measurement and speaker issues to such publications as the Journal of the Audio Engineering Society, Electronics (Wireless) World, and Speaker Builder.

Most recently, he has joined forces with fellow HP engineer Marshall Kay, CAD (computer-aided design) specialist Kurt Pasquale, and marketing consultant Tom Hoffman to form Audio Artistry. This three-year-old, North Carolina-based company is dedicated to developing and crafting speakers based on the accumulated insights and wisdom Mr. Linkwitz has gained over three decades of loudspeaker research. I spoke with Siegfried about some of these insights and experiences during the course of evaluating the Audio Artistry Dvorak, the review of which is found elsewhere in this issue. My first question concerned what had motivated Linkwitz to get involved in audio.

Siegfried Linkwitz: I grew up in a family in which music was very much appreciated. My father and brother played the piano, and although circumstances during World War Two prevented me from learning an instrument, I've always had a love for music. After graduating from university and joining Hewlett-Packard to design electronics, it was only natural that I wanted to build audio equipment I could use at home, so I got very involved in building power amplifiers, FM tuners, preamps and you name it—anything electronic I needed to reproduce music. Then I had the fortune of meeting some other engineers at HP who were similarly involved in audio, particularly Lyman Miller and Russ Riley. Lyman was very much into electronic design and making recordings while Russ built amplifiers and had a keen interest in speaker development. They really turned me on to investigating things even deeper, and loudspeakers, to us, were the most interesting and challenging area since so little was really understood about them. The speakers then on the market could certainly be improved so we saw a real chance to make a genuine contribution.

Shannon Dickson: Could you share with us some of the fundamental problems you and your colleagues encountered during the early attempts to improve speaker performance?

Linkwitz: One of the problems at the time was that good test equipment wasn't available to us. Russ Riley developed his real-time 1/3-octave analyzer and a pink noise source which we used to make in-room measurements. I bought an early Advent speaker, measured it using the real-time analyzer, and consequently developed an equalizer to flatten-out its frequency response. That was a first attempt on my part. I then experienced a real surprise after we went to some local stores and heard the Electrostatic Sound System's ESS-7. It just sounded great, much better than the Advent. Naturally, I bought the speaker and took it home, but after measuring it, I was astonished—it measured very poorly! That led to a whole investigation into why it sounded so good but tested so badly.

We found out rather quickly how important driver quality was, as well as the distortion contributions of cabinet resonances. We began experimenting with wool stuffing in the box and with various bracing and panel damping techniques. We found that wool could be a very effective loading material. A number of commercial designs sounded much better when we replaced whatever they had inside with natural wool fiber.

In my early designs, we tried two basic concepts built around rather small enclosures, both of which worked quite well. For instance, we made some very rigid, heavily braced small monitors; then we went the other way, using very limp, thin panels for the box construction. These were very easy to damp by applying roofing tar with sand mixed in. As you can imagine, this was a real messy operation—it smelled pretty bad too, particularly if you placed the speaker in the sun. It would out-gas for several weeks before you could tolerate the smell!

While it damped box resonances quite effectively, this approach was not really practical from a commercial point of view, nor would it have been a very welcome addition to most people's living rooms. But it did demonstrate how important minimizing box resonances is and just how difficult it is to really control this form of resonant behavior.

Dickson: You've worked with some of the most respected engineers in audio over the years. Who had the greatest impact on your thinking regarding speaker development?

Linkwitz: I mentioned Lyman and Russ already. Lyman was really into the recording side of things so he did a lot of recordings on a semiprofessional basis and was particularly interested in capturing sounds as close to their natural origin as possible. So we had some great reference material to guide our evaluation. I learned a lot about recording from Lyman and continue to make many of my own reference recordings, which I used extensively during the development of these new speakers.