Basic knowledge of audio technology

1. Technical status of foreign speakers and speakers

1.1 Professional speakers

Mainly refers to the speakers and speaker boxes used in movies, stages, halls, stadiums and other occasions. In recent years, with the development of new materials, new technologies, new structures, and new processes, the application of stereo technology, digital technology, the popularity of CDs and VCDs, professional speakers and their systems have also made great progress, and new products have continuously emerged . American JBL, EV, BOSE companies; British KEF, TONNY companies; Japanese Panasonic, Pioneer, Mitsubishi, TOA, YAHAMA companies, in recent years have launched a variety of professional speakers and speaker systems. Their distinctive features are that they bear high power, all above 200W; high efficiency, generally 98-100dB; and wide directivity.

In order to achieve the above-mentioned characteristics, the world-renowned loudspeaker manufacturers have passed through the sea, showing their magical powers. The main methods adopted are as follows. First, adopt new magnetic materials and apply new magnetic circuit design methods. For example, the SFG magnetic circuit design adopted by JBL Company includes a new structure setting of magnetic flux balance, reducing the inductance of the driving source and heat conduction. The magnetic material used has a magnetic energy product above 3.6MGsOe. This increases the capacity of the speaker to withstand power, and the bass reproduction is strong and powerful. Second, the use of new materials, such as the use of aerospace titanium materials for the tweeter diaphragm, because titanium E · P is superior to the aluminum material, it is suitable for manufacturing high-quality tweeter diaphragms. Tweeters using titanium diaphragms have a large extension of high frequencies, and the power capacity has also been greatly improved. The woofer uses laminated high-density composite paper cones. The voice coil uses a flat wire. Due to the high space factor of the flat wire and the high utilization rate of the magnetic circuit gap, a higher sensitivity can be obtained. The technology was invented by JBL, and other major companies have followed suit. Third, the use of new model horns, the exponential horn loudspeaker that has been used for a long time in professional sound reinforcement has been replaced by a new type of directional horn. The key technology of equipotential horns is that the horns use different-shaped side walls. In the past, the simple linear and exponential formulas became complex and discontinuous functional formulas to achieve constant directivity. Fourth, extensive use of computer CAD, CAM and CAT technology, using modern technology to tap the potential of traditional speakers, so that professional speaker products keep improving. Representative products, such as JBL's MR professional speaker speaker series, SR professional speaker speaker series.

1.2AV speaker speaker

Mainly refers to the speakers and speakers used in the home high-fidelity combined audio system, karaoke cabaret, dance hall and home theater sound system. AV speakers have made great progress in recent years, and new products are constantly emerging. The world's major speaker companies have launched various forms of AV speaker speakers. They not only have advanced technical performance, but also from the technical characteristics of practical modeling, improving sensitivity, expanding the dynamic range, widening the playback frequency band and good transient response. Common two-way crossover speaker speakers: use an 8-inch rain or 6.5-inch mid-woofer unit plus dome tweeter. Since the middle and low frequencies share a speaker, the speaker unit is required to have a wide piston vibration range without splitting vibration to ensure ideal directivity and phase characteristics. In accordance with the requirements of audiophiles pursuing bass effects, companies have successively developed dumbbell-type speaker speakers, with a dome tweeter sandwiched between two 8-inch or 6.5-inch mid-woofer units, aiming to strengthen the bass. Three-way crossover speaker: add a midrange unit on the basis of two-way crossover. Its advantage is to make full use of the piston vibration frequency band of each unit, reduce distortion, and improve the power bearing capacity. Another significant feature of AV speakers is that they have good anti-magnetic leakage performance, and the magnetic circuit must have a magnetic shielding design to ensure that it does not affect the video image.

Nowadays, popular multi-dimensional stereo and home theater systems refer to showing the audio-visual effects of theaters in ordinary homes. Surround sound is a part of it, and it is an important part. The popular surround sounds on the market are roughly divided into two types. One is Dolby directional logic surround sound evolved from the early "four-channel"; the other is DSP surround sound developed by YAHAMA company first. DSP surround sound uses digital processing technology to simulate the sound effects of different spaces (such as a movie theater, concert hall, etc.). This requires that the front, center, and rear indicator speakers have balanced sound and ideal directivity. Engineers in the electro-acoustic industry have made unremitting efforts to improve the performance indicators of AV speakers. Through system design, experiments and simulations, they continue to explore the mysteries of the AV speaker world. Occupy an important and necessary position. Representative products, such as JBL's home theater speaker system, include a total of 7 speakers in the front main channel, center channel, surround channel and subwoofer. The front main channel adopts two 200mm woofer units, two 127mm midrange units, a titanium membrane dome tweeter and a horn type tweeter. Horn-type tweeters are used in movie mode. Use horn-type tweeters in movie mode and titanium diaphragm dome tweeters when listening to music. The playback sound quality design is very comprehensive, using multi-channel sound equalizer and 7-channel sound quality equalizer, using digital technology to create a magnificent cinematic sound effect in a small family space.

1.3 Subwoofer

In the past, in order to achieve a true subwoofer output, designers used as large a cone as possible. Such as KLIPSCH company's 27-inch subwoofer; EV company's 30-inch cone-shaped subwoofer and so on. In recent years, the boom in the home theater audio market has driven the research and development of large-amplitude subwoofers. Representative products are: 18-inch subwoofer of AURA SOUND radial neodymium magnetic system. By controlling the thickness of the top plate and using a 0.5 inch voice coil in a 2 inch long magnetic gap, a larger linear motion range is obtained. PINEER's subwoofer has a unique initiative. From the outside, people may think that it has no overhangs. In fact, it sticks the overhang-like structure behind the diaphragm, allowing the diaphragm to work in a cylindrical frame. Longer piston movement. The cone of this subwoofer can move up and down to 2cm, and the 6-inch caliber woofer can achieve a sound pressure level of 100dB at 50Hz, which is difficult to achieve with traditional woofers. Representative products, such as KEF's AV1 active active subwoofer.

2. Main features and unique new technologies of loudspeaker boxes of famous foreign companies

2.1 JBL Company

The characteristics of the speaker are: high withstand power, 200-300W; high sensitivity, maximum sound pressure level above 110dB; good frequency response, flat frequency response and excellent transient characteristics.

Unique new technology:

(1) The magnetic pole core of the low-frequency loudspeaker used for the sound box is quite thick, the magnetic pole core is hollow, and the inserts formed by wire cutting are inserted on it. This specially designed magnetic pole core can reduce the weight of the speaker, which is conducive to heat dissipation, and aims to improve the power endurance.

(2) As an advanced technology, the flat wire voice coil was invented by JBL. Initially used in woofers, and later tweeters are also commonly used, both aluminum wire and copper wire. The flat wire has a high space factor and a high utilization ratio of magnetic voids, and is designed to improve sensitivity. According to the test, in the same magnetic circuit, the flat wire voice coil can increase the sensitivity by about 1dB than the round wire voice coil.

(3) Titanium diaphragm dome-type unit is also the first JBL company started to succeed. The Young's modulus of titanium material is superior to that of aluminum material. For high-frequency speakers using titanium film, the upper limit of high frequency can be broadened and the power capacity can be greatly improved.

(4) SFG symmetrical magnetic field magnetic circuit titanium diaphragm is JBL's patented technology. This patented technology ensures that the FB value distribution on the magnetic gap is symmetrical and equal to the upper and lower positions of the voice coil, which includes the structural settings of magnetic flux balance, reducing the inductance of the driving source and heat conduction. Effectively suppress low-frequency distortion, improve power endurance and damping characteristics.

2.2BOSE Company

The characteristics of the company's speaker box are: actively use the reflected sound of the listening environment to improve and modify the radiation characteristics of the speaker, and develop a world-renowned sound field type speaker box.

Bose's new technology:

(1) Direct / reflective speaker technology. The bose speaker box uses direct / reflective technology to restore the mixed sound reflected from the walls, ceiling and floor to the listener, and uses direct / reflective theory to express the level and positioning of the sound most vividly. Representative products are 901, 701 and 501 series speakers.

(2) Audio air flow bass technology. This technology uses the airflow generated by the "A-cousTIc Mass" structure to work in three independent sound chambers, which can reduce the resonance of the woofer diaphragm and reduce distortion while providing a great dynamic range.

(3) Audio waveguide technology. This technology is the scientific research achievement of Bose Company after 14 years of research and has applied for a patent. It is characterized by the installation of a long and flexed waveguide in a very small chassis structure, thereby increasing the sense of low frequency and creating a huge sense of stage space that breaks through the volume limitation of the small box.

(4) HOROFINE film technology. This thin-film technology is made of bamboo pulp and wood pulp, with perfect, balanced plasticity and rigidity, and can meet the three main indicators of converting electrical signals into high-quality sound waves: low density and high Young's modulus With a large attenuation index, it can reproduce bright, clear and very natural sound in the middle and high range.

2.3AR Company

The company is well-known for creating air-cushion speaker boxes. This kind of speaker adopts sound suspension technology. It supports the woofer through the spring-like air in the enclosed box, and obtains deep and powerful bass. This type of speaker box has been around since the 1950s and is still in use today.

2.4 French FOCAL Group Company

The company is known for creating high-end speaker units, and also produces a variety of speaker boxes, which are sold all over the world. Some group companies have advanced speaker manufacturing technology, and they have four internationally renowned important inventions.

(1) Invented a new design called "MVF" (eliminate mechanical oscillation) system. Using this system can overcome the shortcomings of mechanical oscillation of traditional cone speakers, reduce the vibration intensity of the cone division and ensure high-fidelity playback.

(2) In terms of diaphragm design, the Polkevlar cone with registered patents is light in weight and strong in rigidity, completely solving the problem of sound staining and accurate frequency response.

(3) Invented Polyglass (polyethylene glass) processing vibrating basin, which makes the vibrating basin with high rigidity and excellent internal damping characteristics, so that the sound of the unit is smooth and natural, and the replayed music is detailed and accurate.

(4) The newly developed diamond diaphragm in the 1990s can reproduce the gorgeous sound.

This company's speakers are characterized by high sensitivity, most products are above 90dB. The mid-range and tweeter units are coaxially mounted on the center line of the panel to produce accurate audio and video.

2.5 Danish DALI Company

The company attaches great importance to the audiometry procedures of the speakers, and never only uses the objective test results as the final basis. The company has an audio-visual jury composed of people with rich practical experience and professional music literacy to make a subjective review of the sound quality of each new DALI product to ensure the unique style of DALI products.

The most notable features of DALI's speakers are: the front panel is as narrow as possible to control the sound diffusion angle; the cabinet is very hard, with a surface absorption layer device, which can effectively eliminate resonance, stabilize the sound field, and make the stereo positioning feel very accurate. The units used by the speakers are tested and matched by the computer.

2.6 Characteristics of British speakers

TANNOY's coaxial speakers are well-known worldwide, and successfully solved the problem of phase distortion; KEF invented the "UNI-Q" coaxial technology, realizing the ideal of co-sounding of treble and bass coaxial, making the stereo image accurate; QUAD specializes in Electrostatic speakers have spared no effort to improve and develop it; the small speakers of CelesTIon and Rogers have a 2dB bump in the test curve at 2000Hz. Some people think that this slight difference will definitely affect the sound, but the two companies ’ The product is a representative product of the British small box, which may be the subtlety of the sound of the British sound.

2.7 New flat panel speakers

British company Verity and NCT company announced in 1996 that they have successfully developed a novel ultra-thin flat panel speaker, which is indeed a major breakthrough in speaker production technology.

The thickness of this type of flat panel speaker is 3mm at its thinnest and 25mm at its thickest. The effective radiation area can be determined according to the design, from 25cm2 to 100m2. Verity's NXT speakers use electromagnetic drivers, while NCT uses piezoelectric ceramic drivers. The vibration plate uses carbon fiber and paper materials, and the speaker is very light. The frequency response range of the speaker is very wide, which means that the angle of each angle is large, and the sound quality is good. This flat speaker does not require a cabinet, and can be hung on the wall or installed in the ceiling like a picture. Experts predict that the application prospects of such ultra-thin flat panel speakers are promising and will become a new generation of speakers in the 21st century.