I. Introduction
At present, the noise of domestic household electrical appliances is mainly evaluated by the objective weighting sound power level of the product itself, but there is a certain difference between the subjective auditory feelings of the human ear and the objective test indicators of household electrical appliances noise. Intervention, although the noise sound power test results of some home appliances are qualified, but people's subjective hearing experience is very poor; there are still some hearing experience that can be accepted by the ear, the sound power test results are unqualified In order to be able to evaluate the noise of products in an all-round way, more and more acoustic researchers at home and abroad have begun to study how to quantify the subjective auditory feelings of the human ear. Thus, the concept of noise sound quality has gradually emerged as '1'. .
Second, the research progress and current status of noise sound quality at home and abroad
In 1883, the acoustic sound quality was defined by the acoustician Stumpf, which was used to describe the sound events of physical characteristics and the perception of different sounds. After summarization and a large number of experiments, the factors affecting the sound quality mainly involved three aspects. The first is the environmental factor, which is the sound field currently in existence; the second is about the feeling of hearing, which can also be called psychoacoustics; the third aspect is an autonomous auditory evaluation of the above two points '2'. If you want to quantify the above three factors, you first need to objectively test the relevant acoustic parameters '3'. In the research of noise sound quality, international acoustic workers have outstanding research results, and their research on quality parameters is relatively thorough. However, it is rarely used in actual production, especially the sound quality research of household appliances in China is in its infancy stage '4'.
In 1999, sound quality was prevalent in the automotive industry. Ford and GM first systematically explained the principles and requirements of the auditory group test method. Currently, the Oldenburg Symposium seminar is a sound quality researcher once a year. The grand event, at the University of Oldenburg, they exchanged and shared information platforms. In addition, more and more international acoustic conferences also included sound quality research into a research topic in the conference.
After reviewing a large number of documents, the author found that the research on sound quality is mainly applied in the automotive industry, and there are few related documents in the household appliance industry. However, improving the sound quality has been the goal pursued by more and more home appliance manufacturers, and more and more acoustic papers It also mentions the inadequacies of simply using noise sound power level evaluation products. Some indicators of psychoacoustics have been accepted by ISO (International Organization for Standardization), German Institute for Standardization (Deutsches Institut für Normung) and ANSI (American National Standards Institute) Specifications. For example, ISO 532B steady-state loudness, loudness percentile, loudness level, DIN 45631 time-varying loudness and DIN45692 sharpness, etc. China's standard on the sound quality of refrigerator noise "home appliance noise sound quality ergonomics evaluation Part 1 : Refrigerator has entered the drafting stage. The main technical contents of the standard include refrigerator loudness test method and noise loudness limit '5'.
Third, sound quality analysis test environment
If you want to study the relevant indicators of sound quality mentioned above, you need an ideal acoustic environment and supporting test equipment. Commonly used test equipment mainly includes: Sound quality measurement artificial torso model (generally called artificial head) and corresponding Acquisition and post-data analysis and processing software. Subjective evaluation by recording and playback will also be provided to the evaluator with corresponding sound card and playback-specific high-fidelity headphones. The test equipment will not be described in detail. The test environment will be introduced below.
Because most manufacturers currently have a half anechoic chamber, and the sound quality test is still in the groping stage without the specification of the national standard in this field, most manufacturers choose to directly test the sound quality related parameters in a semi-anechoic room. .
Since the semi-anechoic room has only direct sound and no reflection sound, and when the sound pressure level is too low, the human ear needs to be very hard to listen to, which will affect the performance of the sound. Therefore, some home appliance manufacturers have specially constructed a listening room to perform sound quality. Test and research, which is mainly used for the subjective evaluation of household electrical appliances, or the recording of household electrical appliances is played back in the room, and the evaluators then subjectively evaluate the sound quality. The main design reference is GB/T 50356 "Theatrical and Theatre Design. "Specifications" and JY/T183 "Technical Requirements for Digital Stereoscopic Theater" '6'.
3.1 The noise floor of the listening room
According to the different products in the listening room, the general hearing room will design different background noise according to the needs. This is similar to the anechoic room to ensure that the laboratory can shield the external vibration and noise according to the design needs.
3.2 Reverberation characteristics of the listening room
An important parameter of the reverberation characteristic is the reverberation time. The value of the reverberation is generally directly related to the volume of the room. According to the room size, the best reverberation time of 500Hz is designed according to Fig.1. The design can refer to Figure 2.
Figure 1 Optimal reverberation time for different room volumes
Figure 2 Frequency relationship between the best reverberation time and 500Hz
Fourth, sound quality mainly evaluates performance indicators and intentions
4.1 The loudness of sound
The loudness of a voice is usually defined as the degree of soundness the human subjectively perceives as '7'. By definition, loudness is a subjective acoustic parameter, but studies have shown that loudness is not only related to the physical strength of the sound, but also to the sound The included frequency components have a great relationship. The loudness is based on the song (sone). Conventional people claim that a pure tone with a frequency of 1000Hz produces a 40dB sound volume of 1 song. In order to better simulate the human ear's response to sound, The research on the equal response curve in the world has been carried out. This study has accelerated the progress of loudness research. The A-weighted equal-frequency network is a 40-degree curve. Since the equal-frequency curve has the disadvantage of frequency unity, it is in our daily life. The noise frequency components are complex, so the development of related standards for loudness calculation is advanced. ISO 532 regulates the parameters related to sound loudness.
4.2 The sharpness of the sound
The sharpness of the sound is defined by the definition of the sharp character of the sound, that is, the degree of harshness. Sounds with different frequency components, if the proportion of components in the high frequency band is larger, the sharpness of the sound is often higher and it sounds sharper. The smaller the proportion of high-frequency components, the sharper it tends to be lower, and it sounds relatively boring. Sharpness uses acum as the basic unit, usually denoted by the symbol S. In order to unify the sharpness specification, a sharpness is defined as 1acum's narrow-band noise, which is a 60-db sound with a bandwidth of 160Hz and a center frequency of 1000Hz. Unlike loudness, sharpness evaluation has not yet been standardized by relevant standards. According to experience, Zwicker and Aures have defined related computational models. Quoted by everyone.
4.3 Sound roughness
The roughness of the sound is the standard physical quantity for calculating the degree of sound modulation. The roughness is mainly reflected in the high-frequency modulation part. The degree of low-frequency modulation is often described by the jitter degree. Both use 20 Hz as the boundary, and the modulation below 20 Hz is often manifested in The degree of jitter. The roughness is asper as the basic unit. It is specified that the pure tone of 60 dB 1 kHz is fully modulated by 70 Hz, and its roughness is 1 asper'8'.
4.4 The degree of jitter
According to the introduction of roughness just now, the modulation frequency of jitter is less than 20Hz. The subjective feeling brought by the jitter degree is more obvious, and the change of the volume over time can be obviously felt. According to a large number of experiments, the jitter The degree of loudness brought by louder voices is much greater than that of loudness. The degree of jitter is usually expressed in units of vacil, and the degree of jitter is specified as 1 vacil when a pure tone of 60 dB 1 kHz is 100% modulated by 4 Hz.
V. Conclusion
There are no relevant standards for noise sound quality research of home appliances. Many manufacturers are still in the exploration stage. The research on car sound quality started earlier. Home appliance manufacturers can learn more about the noise of home appliances by referring to the research methods of noise quality in the automotive industry. It is believed that with the deepening of research on noise quality of home appliances, the acoustic performance of home appliances will become better and better.
references
'1' Shu Gequn, Liu Ning. Research and Development of Sound Quality of Vehicle and Engine Noise. Automotive Engineering, 2002.
'2' XUE Yifei, XU Hao, FENG Jinping. Sound quality evaluation and analysis experimental research of inverter air conditioner outdoor unit. Proceedings of the 13th National Conference on Refrigerator (Cabinet), Air Conditioner and Compressor Academic Exchange, 13-16.
'3' Jin Yong Leon, Jin You, Ho Yeon Chang. Sound radiation andsound quality characteristics of refrigerator noise in real livingenvironments. Applied Acoustics, 2007 (68): 1118-1134.
'4' Shi Yan, Bi Fengrong, Lin Manqun, Jing Yabing. The basic theory of psychoacoustics and its application in subjective evaluation of sound quality. Small internal combustion engine and motorcycle, 2006.
'5' Electrical Appliances 2016/ 11-Regulatory News.
'6' Li Yanqi, Wei Wei et al. Design of Acoustic Environmental Chamber for Subjective Evaluation of Acoustic Acoustic Performance, Home Appliance Technology, 2014.
'7' Su Lizhen. Research on subjective and objective evaluation and control methods of sound quality in vehicles, PhD thesis of Jilin University, 2012.
'8' Li Can. Research on automobile sound quality test and objective evaluation method, Master's thesis of Hefei University of Technology, 2009.