A loudspeaker diaphragm factory

A loudspeaker system released in Nov. 1976.

Diaphragms manufactured at Kofu factory were assembled.

A loudspeaker diaphragm factory


Just after my super-express train for Matsumoto left Shinjuku Station, the water flow of a paper machine started sounding in my ears, and the steam blowing out through a small gap of a press machine came into my mind. The train arrived at Kofu Station while I was thinking about many items in the manufacturing process, “Should I beat* pulp longer? Should I raise the temperature of a die a little bit? Or should I change the paint for over-coating of a diaphragm?” and so on.


Audio Research Inc., Sony’s newly built loudspeaker factory in 1976, was located in Kokubo Industrial Park that was 10 kilometers south from Kofu Station and close to the Fuefuki River.


I was the president of the company with 300 employees. At headquarters in Tokyo, I was extremely busy engaged in both development and marketing of audio products. But, when I visited that place once a month to make decisions for diaphragm manufacturing process by hard discussions with engineers, I could make myself really relaxed. It was my very special and precious day.


When about a year had passed since the factory started, Mr. Kazuo Iwama, the president of Sony at that time, told me, “You look so happy and cheerful when you go to Kofu. You must have gotten a comfortable hide-out for you. Take me there along with you.” I answered immediately, “How about next week? I was just planning to invite you to Kofu and report our progress to you.”


The factory was a three-story building. I introduced him our facilities along the product manufacturing processes.


“On the third floor, there is the beating process where the pulp material for cone paper diaphragms blended with kozo (paper mulberry), mitsumata (oriental paper-bush) and hemp is put into the beater to be beaten into fine fibers. The temperature of water irrigated from the Fuefuki River and stored in a tank varies seasonally. It also rises in the beating process to fracture fibers of paper. I am taking great pains to control the beating process that varies sensitively in accordance with the temperature.”


“On the second floor, there is the process for paper making and press working to have the cone paper completed. Different paper making techniques are applied to central and outer part of the cone paper respectively. And the pressing process is still under study to find how we can put a proper damping factor to the cone paper. Although air bubbles are prohibited for optical discs, we should put suitable air bubbles intentionally into the cone paper to obtain some quantity of variation losses. Thus, the way of cone pressing is so important that we are focusing our attention on this process.” (President Iwama was so interested in the comparison of discs and cones.)


“On the first floor, there is the final stage including an anti-humidity process, etc. We also assemble loudspeaker drivers here. To assemble a cone and a voice coil, it is a knack to adhere a coil to the outer, not inner, side of a cone. We found the sound to be blur when it is adhered to the inner side.”


“As the result of our study for a year, we can obtain a good cone paper to sell. Our next step is to develop new materials. We began to check up on bacterial cellulose, linear high-molecular polyethylene and mica, etc. Our guideline for the new material development is to focus on the frequency-dependence, especially at higher frequency, of E/ρ(specific modulus) and tanδ(internal loss) of diaphragm materials classified according to usage such as for full range, lower frequency or higher frequency.”


I took him to my office in the closing of the tour and treated him to a tasty wine highly-praised to be one of the best-five in Yamanashi Prefecture, and a whisky made from the fine water of the Fuefuki River that was also supplied to control the temperature of our cone paper beating process.


MR. IWAMA: Now I can understand why you come to Kofu so delightfully. I will come again someday. By the way, can you make a living by such a fun job?

NH: We are manufacturing different diaphragms for electret microphones. I can turn a profit by them to make a living.

MR. IWAMA: Who are our competitors? What is your target for the moment?

NH: A US company named Holey Inc., a specialist of cone papers. They are trueborn OEM factory for cone papers. In the future, we will emphasize our strong point by applying cone paper for system-oriented configuration of loudspeakers.

MR. IWAMA: This kind of factory is too unique even in my company. I’m afraid there may be not a few people who cannot understand the philosophy of this factory.

NH: I will transfer our know-hows to the Cone Project by some technical experts in Sony headquarters, as well as preserve them in this factory.  





In 1982, President Iwama suddenly passed away. Half a year later, I moved out to AIWA. The future of this factory was a big concern to me, because I knew there were many persons who did not comprehend the philosophy of this factory as Mr. Iwama had observed. My worries had become a reality soon. The factory was sold to other company only in half a year just after I moved to AIWA.


Some years later, several engineers from the Cone Project developed the D’Egg loudspeaker system in Bifrostec Inc, focusing on the sound field. The key component of the system was a diaphragm made of mica that had a curved surface same as the egg shaped body. The engineers had developed the mica diaphragm following the study outcome by the loudspeaker diaphragm factory of Audio Research Inc. 




* beating: A process to beat pulpy material of fibers extracted from plants in order to make fibers cut, hydrated, swollen and intertwine.