1 Introduction In people's daily activities, the reliability of products is often involved. However, the birth of the reliability discipline is not far away. China has established a reliability test base since the mid-1950s, which has promoted the reliability process of domestic components and laid a good foundation for the widespread entry of domestic components into the world market today. .
China has become a major speaker manufacturing country, but has not yet become a powerful speaker manufacturing country. With the rapid increase in production, quality and reliability still need to be improved. In fact, the reliability of speakers is an important feature of mid-to-high-end products. For this, some speaker manufacturers do not understand enough, and the concept is also very vague. Therefore, it is necessary to reverse the tendency of focusing only on the design of speaker performance indicators, ignoring the reliability design, and fully understand the connotation and significance of reliability.
2 Reliability of speakers
2.1 Definition of reliability and scope of application The definition of speaker reliability is: "The ability of a speaker product to complete a specified function under specified conditions and within a specified time." It is the time quality indicator of a speaker product after it leaves the factory. To describe whether the speaker is easily damaged and reliable during use. With the improvement of user requirements, the structure of speakers is becoming more and more complex (such as car speakers), the output power is becoming larger and larger (such as PA speakers), and the use environment is becoming harsher (such as outdoor speakers), which will lead to the reliability of speaker products Sexual levels have fallen. At the same time, the use of new materials, new processes or new technologies will also increase the unreliable factors of speakers.
The reliability of the loudspeaker can also be defined as: "the number of faults allowed by the loudspeaker product under the specified conditions and within the specified time." The mathematical expression is the mean time between failures (MTBF). It can be considered that random failures are inevitable and acceptable, which also leads to failures due to design reasons or manufacturing processes, as long as they are within the allowable number, no further tracebacks are often made. For this reason, as early as 1995, the traditional definition of reliability and the old concept that random failure is unavoidable began to be questioned internationally. At the same time, the physical method of failure began to be implemented in reliability engineering. In Europe, the maintenance-free service period (MFOP) was also used to replace the original MTBF, and the failure rate of the bathtub curve distribution was broken [21]. Therefore, combining the failure physical method and the failure analysis method _3_, designing a speaker product that does not have random failure may not be a delusion. A considerable number of foreign companies have already carried out effective work in this regard.
The “prescribed conditions†in the definition of reliability determine the wide range of reliability. The reliability of a product has a great relationship with the working status, use conditions, and environmental conditions of storage and transportation of the product. Conditions can be divided into two categories: operating conditions and surrounding environmental conditions. The use conditions refer to the stress conditions that enter the product and function, including various electrical stress, chemical stress and physical stress. The surrounding environmental conditions include various environmental stress conditions such as temperature, humidity, air pressure, harmful gas, mold, salt spray, shock, vibration and radiation. In this sense, environmental tests also fall into the category of reliability tests. These stress conditions can be applied individually or in combination. The effect of comprehensive application on the reliability of speaker products will be more significant.
2.2 Reliability technology
2.2.1 Derating Design The purpose of derating design is to make the key components that have a greater impact on the reliability of the speaker bear the stress lower than the conventional level through design, so as to reduce its basic failure rate. In the design of loudspeaker systems, derating design is widely used. In the design of the speaker unit, the use of larger-area positioning support pieces, larger-diameter voice coils, lead wire and lead wire shape design all reflect the derating design idea.
2.2.2 Redundancy design The idea of ​​redundancy design is not fully reflected in the design of speakers or speaker systems due to cost. The application of multi-strand braided wire or the use of dual positioning support pieces may reflect some of the redundant design ideas.
2.2.3 The failure rate of thermal design speakers will increase with the increase of operating temperature. To reduce the failure rate, the operating temperature must be reduced. Henricksen C. A. The heat conduction mechanism of the speaker is discussed in theory [41. The reason for the heating of the speaker is mainly the heating of the sound hoard, so reducing the working temperature of the speaker can start from reducing the heating of the voice coil and improving the heat dissipation of the voice coil and the magnetic circuit. The heating method of the speaker is as follows: (1) A heat dissipation channel is formed by designing a hole L on the pole core, positioning support piece, basin stand, paper cone root, and voice coil skeleton. At the same time, care must be taken to prevent poor design from generating airflow noise. (2) Use magnetic fluid to improve the heat dissipation capacity of the voice coil. This method sometimes cannot be used with method (1). (3) Use black devices to improve the thermal radiation and thermal conductivity of the device. (4) When the cost permits, add heat sinks to dissipate heat. (5) For speakers with extremely high power and continuous use, oil cooling or water cooling may be required to improve reliability. (6) Improve the heat resistance of materials and adhesives. Many speaker designers will instinctively adopt this method when they encounter problems, but simply improving the heat resistance of materials and adhesives is not a good reliability design idea. Because the stability of adhesives and materials may become an uncertain factor for the reliability of speakers. Of course, when using rubber or plastic parts, special attention should be paid to the resistance of these parts to temperature or temperature shock.
2.2.4 Reliability prediction Reliability prediction has always been controversial. It has been suggested that the term reliability estimation should be used because it is found in practice that the reliability prediction has little correlation with the actual reliability of the product, lack of experience or improper application. Can produce poor design. In the GJB / Z299B-98 "Electronic Equipment Reliability Prediction Manual" circle, the mathematical model of speaker failure rate is not given like other components, but the working failure rate of the speaker is directly given as p = O. 13xl0 ~ / h.
3 Reliability test of the speaker Because the user range of the speaker is extremely wide, the test method of the speaker reliability is similar, but there are certain differences in test stress and failure criterion, so the author mainly makes the test from the test purpose, test stress and failure criterion discuss.
3.1 Classification of reliability tests Reliability tests are generally divided into environmental tests, life tests, screening tests, field tests, and qualification tests. Loudspeaker reliability tests are often exposed to environmental tests, life tests, and field tests. The maximum noise power test of the loudspeaker can reflect the reliability of the loudspeaker to a certain extent, but it is not a strict reliability test. However, because of its test method, test stress and failure criterion, etc., it has great relevance to other reliability test items. Some controversy also stems from the understanding of the test, and some discussion is needed. The program source filters commonly used in this test project are GB, IEC, DIN, JIS, EIA, and IHF, etc. The first 4 items are equivalent, and some users may not understand them well and need to explain them well. A considerable number of foreign users, especially large users, require testing in the range of 20 Hz to 20 kHz, which is different from the provisions of the GB standard, and the test results show an increase in failure rate. , GB Factory r9397-1996 "General Specification for Direct Radiation Power Loudspeakers" Yan described the failure criterion as "There should be no thermal or mechanical damage after the test and meet the requirements of 4.2". The requirement of 4.2 in the general specification is to judge the abnormal sound, and the abnormal sound means silent, bump, obvious garbage sound, serious abnormal sound and mechanical sound. Therefore, the test failure criteria should be divided into two categories, the first category is thermal damage and mechanical damage, and the second category is abnormal sound. The actual situation is that when the second type of failure (abnormal sounding) occurs, the first type of failure (thermal damage and mechanical damage) must occur. When the first type of failure (thermal damage and mechanical damage) occurs, the second type of failure (abnormal sound generation) may not be clearly noticeable. For example, the multi-strand braid of the speaker has broken several strands, and there has been a fire phenomenon. It is dangerous to use in the environment, but pure tone listening can still meet the requirements of 4.2 in the general specification. Another example is a speaker with plastic parts. The plastic knee parts are deformed or hot-melted. Under the laboratory conditions, pure sound listening can also meet the requirements of 4.2 in the general specification. However, due to the difference in actual use conditions or installation conditions, it may be This kind of deformation or hot-melt phenomenon of the speaker plastic parts tends to be serious and cause failure. Therefore, only the second type of failure as the failure criterion of this test is one-sided, which is the main reason for the dispute of the test results. Some users will put forward requirements on the change range of the loudspeaker index before and after the test, such as resonance frequency, impedance and sensitivity. If the change range is small, it is quite difficult for low-end speakers. After testing the pure tone listening power, quite a number of users require listening at rated power.
3.2 Life test The life test of the loudspeaker is an important part of the reliability test of the loudspeaker. Through this test, you can understand the reliability characteristics of the product such as the failure rule, failure rate and average life. In order to solve the contradiction between the number of test samples and the test period, an accelerated life test can be used. Accelerated life test is divided into constant stress accelerated life test, stepped stress accelerated life test and progressive stress accelerated life test. SJ / T10601-94t71 ((Reliability Requirements and Test Methods for Household Speakers) and EIA-426B-1998f8 (Loudspeakers, OpTImum Amplifier Power) provide methods for the life test and constant stress accelerated life test of speakers. AES2-1984 (r2003) t91 (AES Recommended PracTIce SpecificaTIon. of Loudspeaker Components Used in Professional Audio and Sound Reinforcement) can be used as a reference for loudspeaker stepped stress accelerated life test. The stepped stress accelerated life test can be used to determine the limit level of the loudspeaker subjected to safe electrical stress, When comparing speakers of different batches or different manufacturers, it is easy to find out the impact of process changes or design changes on product performance. It should be noted that the stepped stress accelerated life test of the speaker should only be used as the constant stress accelerated life test of the speaker The preliminary test or the supplementary test of the speaker constant stress accelerated life test. During the speaker life test, the monitoring of the test samples ensures the accuracy of the test results. Due to the particularity of speakers, especially high-power speakers, monitoring is usually more difficult Using test equipment PC platform can solve this problem. China has started production of this instrument.
3.3 Mechanical test
GB / T9397-1996 "General Specification for Direct Radiation Power Loudspeakers" stipulates the basic mechanical test content of loudspeakers, which can be implemented by reference. However, some users, especially large automobile manufacturers, have higher requirements than the standard. For example, in the drop test, a drop item without packaging is added, and the drop direction when packaged is one corner, three sides, and six sides; the drop impact test, angle A is from 60. Increased to 75. , The linear distance of the fall from 600 mm to 1000 mm; collision test, door impact test (field test) is added, the waveform is an approximate half sine wave, the acceleration is 300 m / s, the duration is 6 ms, the number of impacts is 100 000 times, The speakers are installed vertically.
3.4 Climate environment test Climate environment test mainly refers to temperature and humidity test. The test temperature range of automotive or outdoor speakers may be expanded by 31J-4o-85. C.
3.5 Temperature cycle impact test The temperature cycle impact test of the speaker is one of the ultimate stress tests of the speaker. The purpose of this test is to evaluate the ability of the loudspeaker to withstand extreme high temperature and extreme low temperature, as well as the effect of the alternating change of extreme high temperature and extreme low temperature on the loudspeaker. Due to the speaker design or process, many speakers will fail on this project. For example, the cloth folding ring will be deformed. For different customers, the stress and stress application period of this test will be different. Different stresses and stress application cycles will give different results, and they are not comparable with each other.
3.6 The salt spray test and the alternating salt spray test The speaker salt spray test (iv) has a misunderstanding of the purpose of the test. Contrary to widely held views, the test is not to simulate the effects of the marine atmosphere, but is mainly used to evaluate protection The quality and uniformity of the coating. The experiment to simulate the influence of the ocean's atmosphere is the alternating salt spray experiment [11]. The severity level of the alternating salt spray test is divided into 6 levels. Levels 3-6 are suitable for products that are frequently used alternately in salty and dry atmospheres, such as cars and auto parts. At present, there is no unified understanding of the failure criteria of such tests for speakers, which is quite disturbing.
3.7 Solar radiation test The solar radiation test port of the speaker is to evaluate the thermal effect or photochemical effect of solar radiation on outdoor or car speakers. The test temperature is low temperature 25. C, high temperature 40. c or 55. C. The main failure is the appearance and mechanical failure, especially the plastic parts of the speaker and the coated plastic parts. The premise of this test is that the speaker product is exposed to solar radiation when in use. Therefore, not many customers require speakers to do solar radiation tests.
3.8 Rain test Mainly used to observe the water permeability and sealing of car or outdoor speakers. Usually the loudspeaker plant does not have the main test equipment for the rain test rain room, so the test is generally completed by the OEM. According to the test results, the OEM divides the speakers into several levels that cannot be exposed to water, water seepage, non-water seepage and waterproof, and then selects different levels of speakers according to the different parts of the speakers used in the car.
3.9 Other tests Air pressure, harmful gas, mold and dust tests are basically not carried out on the speakers. Due to space limitations, I will not repeat them here.
4 Reliability test design of the loudspeaker In order to evaluate the reliability of the product, a reasonable test plan must be adopted. Different test plans will produce different results, and they are not comparable when asked. Sometimes in order to find the problem as soon as possible, you need to carry out accelerated test or ultimate stress test. When doing these tests, you should pay attention to the increase of stress and not destroy the original failure distribution law, otherwise the results of the accelerated test or ultimate stress test are suspicious. The reliability test design should include the provisions of the test sample, the determination of the test conditions, the determination of the test cut-off time, the determination of the measurement period and the determination of the failure criterion.
5 Conclusion Reliability discipline and reliability physics are mature and late disciplines, and there is still a lot of research space for speakers in terms of reliability. Loudspeaker reliability technology should run through the entire lifetime of the loudspeaker. It is important to improve the inherent reliability of the product to perform reliability work during the product design and manufacturing stages. Before conducting the reliability test, the speaker manufacturer may need to fully communicate with the user to facilitate the smooth development of the reliability work.
A new experience of true wireless
Automatic seconds connection, can be used with headphones
Professional sound engineering technology
Case Cube/acoustic clear sound reproduction
customized stainless steel acoustic structure, high quality grahene hoop system and obvious environmental noise attenuation will open up a pleasant journmey journey for you to enjoy the sound.
Built-in microphone/ Effective noise reduction/ Clear call/ Easy to carry
Sports can't be abandoned more freely
Close ergonomic design, close to the ear, even wearing for a long time can also enjoy comfortable experience.
And can form a triangular stable support with the ear, even if running and riding, vigorous fitness is still close to the ears, wildly shake off.
Bluetooth Earbuds,True Wireless Earbuds,Wireless In Ear Gaming Headset,Wireless Bluetooth Headphones
Guangzhou HangDeng Tech Co. Ltd , https://www.hangdengtech.com