Electrodynamic loudspeaker heads with flat diaphragms. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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The development of loudspeaker heads with flat honeycomb diaphragms began in the 80s, however, they began to produce speakers using them relatively recently. Last year, our magazine repeatedly introduced radio amateurs to speakers of various classes based on cellular heads, which are manufactured by the St. Petersburg company "Zvuk". This information interested many readers who asked to tell more about the advantages of such heads, to give parameters. Going to meet their wishes, we publish an article by former employees of VNIIRPA them. A. S. Popov, who were engaged in the development of heads with honeycomb diaphragms.

It is known that the sound quality of speakers is influenced by many factors, but, first of all, it depends on the loudspeaker heads used in them. Given these circumstances, experts in electroacoustics pay close attention not only to improving the design of moving head systems, but also to the materials of the radiating elements. As a result, in recent years, along with traditional cone diffusers, heads with flat diaphragms have become widespread.

The main requirements for the physical and mechanical parameters of the materials of the radiating elements are, as is known, high bending rigidity, low density and high internal losses. The higher the first of these parameters, the wider the frequency range of the head and the less amplitude-frequency distortions it introduces into the signal. The density of the material of the radiating element to a large extent determines the sensitivity of the head and, finally, internal losses contribute to the damping of oscillations at resonant frequencies.

For decades, paper pulp has been used to make cones in dynamic drivers. With the development of Hi-Fi technology, leading manufacturers of high-quality speakers, in order to increase the modulus of elasticity and internal losses of cone heads, began to use all kinds of cellulose-based composite materials for their manufacture (for example, cellulose with carbon or metal fibers). However, it was not possible to significantly increase the rigidity of such materials because of the low internal elastic forces that bind the components.

For this reason, polymeric materials such as mylar, polyamide, polypropylene, polyvinyl chloride, olefin films, tergal, supronil, ceramic olefin, polymer graphite, etc. have been used no less widely for these purposes, composite (backstreng, cobex, kapton), as well as layered materials (mylar and polyester with aluminum sputtering, two-layer polypropylene). The development of the technology of chemical vacuum deposition made it possible to obtain a number of layered metals (titanium-boron carbide, aluminum-magnesium, aluminum-sapphire, etc.). For domed diaphragms of midrange and high-frequency heads, simple metals are also used: aluminum, titanium, beryllium alloys, porous nickel.

However, the production of many of the materials listed above requires very complex and expensive technological processes. In addition, they are not universal, i.e., they cannot be used for the manufacture of radiating elements of all sections of the speaker (LF, MF and HF heads).

For this reason, heads with radiating elements from the materials listed above have not been able to replace heads with paper cone diffusers and, until recently, remain just a few successful achievements of leading foreign companies.

The analysis of the properties of the materials of the radiating elements and the design directions of the loudspeaker heads for the Hi-Fi class speakers was also constantly carried out by the specialists of VNIIRPA them. A. S. Popova [1 - 3, 4]. The results of fundamental research conducted by them in 1980 - 1990. [5 - 8] showed that a very interesting and promising direction in the design of dynamic loudspeaker heads is the use of flat honeycomb diaphragms as a radiating element.

One of the main advantages of this direction is the suitability of such diaphragms for designing low-frequency, mid-range, high-frequency and even broadband loudspeaker heads, as well as the possibility of creating acoustic systems for all purposes, from automotive to Hi-Fi and High End speakers.

It is known that a flat honeycomb diaphragm has a three-layer structure: a base in the form of a honeycomb made of aluminum foil, covered on both sides with skins made of sheet materials.

Three-layer materials based on honeycomb have been used in the aviation industry for many years. However, the specifics of the operation of loudspeaker heads required the creation of new technological processes and special equipment for the production of honeycomb diaphragms [9].

Many years of experience in designing heads with flat honeycomb diaphragms have revealed a number of their advantages over traditional heads with paper diffusers.

First of all, heads with honeycomb diaphragms reproduce a wider frequency range with minimal amplitude-frequency distortion of the audio signal, which makes it possible to create speakers based on them with a frequency response unevenness in the operating range of ±1,5 dB. The use of honeycomb diaphragms makes it possible to significantly reduce non-linear distortions. On their basis, more powerful loudspeaker heads can be created, since the heat from the voice coils is dissipated in them through the diaphragm into the surrounding space, while in heads with paper diffusers through the details of the magnetic circuit, it enters the speakers.

The flat surface of honeycomb radiators does not require special measures to align the centers of radiation, which greatly simplifies the design of the speakers. The electroacoustic parameters of honeycomb heads are less affected by temperature and air humidity, and are more stable in mass production.

At present, Zvuk has developed a line of cellular dynamic loudspeaker heads. Their main technical characteristics are given in the table. The appearance of one of the heads (100GDN) is shown in fig. 1, and the frequency response (with one-third octave smoothing) is different (75GDS) - in fig. 2.

Based on the heads presented in the table, a number of speakers are produced ("Lira", "Neva", "Rus"), with which readers are already familiar.

Literature

1. Demidov O. F., Romanova T. P. Analysis of modern materials and trends in the design of foreign loudspeaker heads with domed diaphragms. - "Technology of means of communication", ser. TRPA, 1979, no. 3.
2. Belogorodsky B. A., Korenkova T. P. Forced vibrations of loudspeaker domed diaphragms. - "Technology of means of communication", ser. TRPA, 1976, no. 1.
3. Romanova T. P., Polyakova I. B. Calculation of dome-shaped diaphragms of new loudspeaker heads for reproduction of medium and high frequencies. - "Technology of means of communication", ser. TRPA. 1980, no. 1.
4. Demidov OF, Romanova TP Development of new loudspeaker heads with domed diaphragms for reproduction of medium and high frequencies. - "Technology of means of communication", ser. TRPA, 1980, no. 1.
5. "Experience, results, problems". Digest of articles. - Ed. "Valgus", Tallinn, 1985, pp. 95-163.
6. Korenkov A. N., Romanova T. P. Calculation of the design of flat honeycomb diaphragms with stiffeners. Proceedings of the All-Union Scientific and Technical Conference "Prospects for the Development of Radio Broadcasting Technology, Sound Amplification and Acoustics". Leningrad, 1988.
7. Korenkov A. N. Oscillations of round and square honeycomb diaphragms with stiffening ribs. - "Technology of means of communication", 1990, no. 2.
8. Korenkov AN, Tovstik PE Forced vibrations and sound emission by a flat honeycomb loudspeaker diaphragm. - "Technical acoustics", volume II, issue 1993, XNUMX.
9. Romanova T. P., Tarasov Yu. V. et al. Production of honeycomb diaphragms for dynamic loudspeaker heads. - "Technology of means of communication", ser. TRPA, 1990, no. 2, p. 37 - 55.

Authors: T. Romanova, A. Bozhko, V. Popov, St. Petersburg

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