Interview with Joachim Gerhard of Audio Physic

By Lars Mytting
29 Jul 1996

Introduction

Joachim Gerhard Fig. 1. Joachim Gerhard, founder and head engineer of the German loudspeaker company Audio Physic, is one of the most innovative speaker designers today. His range of speakers has been met with great praise, much due to his ability to combine new, exciting ideas with great technical insight and precision in build quality.

Now the promising news for all the frustrated speaker hobbyists out there: In the beginning, Gerhard was as an amateur speaker builder like everyone else. After building several speakers for own use, he started to design kits for the German market. He worked with this from his home until 1983. Then he entered the real business and founded Audio Physic.

- I still enjoy amateur speaker building a lot. It brings people into high-end, and we need it badly, because there is no school where one can completely study speaker building. Myself, I have studied engineering, but both me and many in our company are self-taught when it comes to the really important skills in speaker building. I'd say that the special knowledge we have is a kind of synergy between technology and art.

- How will you characterize today's standard of audio technology?

- The thought of audio having reached perfection is only something for the marketing people. Yes, we get good results now, but we have far from solved all problems. The more you get into it, the more you realize that the nature of sound reproduction is very complex. Siegfried Linkwitz, who is one of my colleagues and also a very good friend, agrees that in the current state of audio, we are just little children playing on the strand. So I am very skeptical to theory. I always want to do my own tests and inventing, and that is something also a amateur speaker builder should do. When I read magazines I don't believe a word. Neither should one be totally satisfied with what an "expert" tells.

-What worries you the most of today's trends?

- What I find dangerous, is that we have an extremely high level of mediocrity in the audio business. Nowadays you can buy a fair tweeter for five dollars. We have a huge amount of products which does not hurt the ear, but they are not exciting.

We also have a lot of people that are brilliant mathematicians and also are 100% aware of the technical requirements in speakers. Lots of papers are publicized on loudspeakers, there is a lot of good measuring equipment available. So this means that nearly anyone is able to make something competent. The trouble is to make speakers that we can call transcendental - something that breaks boundaries. And for building a great speaker, you also need some personality. I have never heard a purely scientific loudspeaker that sounds really great. Also, there is ridiculously much ego in loudspeaker designing. Everyone is the best guy in the world and has the best technology. It is a joke. You hear the results. People that are sensitive to music and aesthetics, they hear. But unfortunately, marketing is ruling today. And not emotion.

- So what has caused the loss of eagerness for pioneering?

- My opinion is that knowledge is sometimes a boundary to invention. In the old times of audio, we had lots of shit, but also a few things that were truly brilliant. And also very innovative, with a lot of personality. Like the Klipschorns, the Quad electrostatics, some JBL designs. There was a huge variety of solutions, and of course the experts did not agree. But on the other hand, that stuff had great emotional and physical impact. Nowadays, it is no problem to design a two-way loudspeaker with a flat frequency response. That has become very easy. So in that sense, the worst things don't happen anymore. But I am afraid that the audio industry is losing this eagerness of breaking boundaries. There is less and less great pioneering activity. I think the important thing is to push the envelope by inventing things. Not only doing things you can read in a book.

-But still, there has been quite a change for the better in the general state of audio?

- Indeed. Sometimes I find a record which I have not played for years. When I put it on the turntable, I suddenly get shocked when I realize how far we have come in just a few years. When I compare the technology from the old times, it is basically the same. We still use paper, we still use copper. We have magnet systems and cabinets of wood. So the improvements has not come from any radical technical change, but from a constant fine-tuning process and a desire of making things better. For the moment, I think this is also the state of my own company, because the last five to ten years we have not learnt so much in terms of theoretical knowledge. The understanding on a theoretical level is very deep. On acoustics and electronics, maybe 95 percent of what is available is known. But though we know the theory fairly well, we still don't know how to solve the problems that we know we have. This is what we learn better and better; how to use the material and the tools. We are working for closer tolerances, tighter specifications, more honest tuning. In the old days we had bad amplifiers and bad records, so what we did was tuning. And maybe we added a lot of mistakes that gave a pleasant result. Nowadays, the signal sources are better, so the better we have to fine-tune, or we will lose the musicality. The cleaner the input, the cleaner the window has to be.

- The last five years a lot of splendid speaker simulation software and precise, affordable measuring equipment has entered the market. Do you fear that designers will weight their speakers by the same parameters, making them all sound equal?

- I question a lot of the momentarily knowledge about the mathematical content of the music. Under musical conditions, a speaker behaves different than under Mlssa excitation, for instance. Since measuring equipment like Mlssa and Clio came on the market, people began to look so much on frequency response that they forgot to measure distortion. Some years ago, we invested heavily in distortion measuring equipment, and that paid off tremendously. I was really surprised over how well I could correlate distortion to what I was hearing from the speaker. Currently we are investigating multitone, a signal of maybe 30 tones fed at once. That is a signal which is closer to music. We are also using what we call a differential method, that enables us to extract the difference between the signal that comes into the speaker and the signal which is reproduced. That is also very interesting. When you know what the distortion is, then you can work on it. But that is of course when the big problems show up.

Also, something that especially amateur speaker builders may be aware of, is that the loudspeaker simulation programs and measuring equipment often does not require that the user really understands the input he gives to the program. This may lead to simplified models. For instance, when estimating a system and a cabinet size, you should not look only at the Qts values, but the Qms and the Qes. Qts is just a product of these two, and learning the effect of their values is crucial to the result.

- Do you believe we have to create a completely new technology for speaker drivers to do justice to the latest signal sources?

- Well, yes. But the problem for a new breakthrough lies in marketing and commercial interest. There are no great technology problems, or lack of interest for invention. Believe me, we have tried everything: Plasma tweeters, advanced piezo drivers, electrostatics. I see no boundaries. You can always start a development company that invents new technology, and when there is a commercial interest, you can fly to the moon. Really. We have special machinery and materials available for making exciting speakers, but the global trend in audio is in the other direction, namely perfect mediocrity. There are some companies, mainly European speaker producers, that go a long way to fine-tune their drivers, like ScanSpeak and parts of Vifa and Seas. But for the industry seen as a whole, the trend is in the other direction.

- What would you like to improve with low range drivers?

- We would get several advantages if we could increase the effective area of the driver without losing control over the radiation pattern. And also lowering the mass, make stronger magnet systems and harder, lighter cones.

- Many "old" paper woofers still sound astonishingly good compared to modern drivers?

- Oh, yes. We have not always went to the better. What many driver manufacturers have done the last years, is to increase the damping to make the frequency response more flat. But some old drivers, like the famous 6,5" paper woofer that Jan Paus at Seas made several years ago, (The Seas CA 17 RCY, ed. note) was optimized for low loss. So they made a compromise between frequency response and sensitivity. This driver was very good, and was used by Wilson Audio for many years. Later, in the 80's, manufacturers started to add more mass, they added more damping, and they made surrounds with high loss. That gave an extremely flat frequency response, but also a lot of energy storage. This compared, the old drivers were much quicker. They had some resonances, but you could get rid of that in the crossover. It was this run for flat response that gave a lot of modern drivers this dull, uninteresting sound. And you can also measure higher second and third harmonic distortion in some of them. If you compare the on-axis response between an old and new driver; you will see that the energy in the treble is far higher than in the new drivers. These so-called "modern" drivers often has a Qms of maybe 0.8 or 0.6. The old drivers had Qms values of maybe 5 to 7! We found that drivers with a very high mechanical Q sound more open, more clean and dynamic. And when you look at it, you find it is very simple, because they have less loss. The surround is easier to move, the spider is better constructed, they have better air flow, higher sensitivity. So a high mechanical Q is a very good indicator of energy storage behavior. This is one of our secrets. One of the many!

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