Introduces technical terms related to sound and audio technology, essential physics in sound and audio research and development, terms used in mathematics, and terms on technology that are attracting attention as a trend of sound and audio technology.
Keywords: Free sound field, shy room, sound -absorbing rust, acoustic impedance matching
In recent years, with the advances of semiconductor technology, technology for data storage, signal processing and wireless transmission have been dramatically advanced. As a result, more entertainment products for individuals can now be developed. I feel that among these entertainment products, products with images and sounds and products using data storage media have evolved. For example, there are tablets, VR goggles, and small projectors for individuals. Sound products include wireless headphones, earphones, portable speakers, and wireless desktop speakers. And the data storage media includes products such as SSD and Micro SD card.
Currently, various manufacturers have entered the development of acoustic products, and many products are being developed, from entry models to high -end models. In order to appeal to the functions and performance of acoustic products, evaluation and measurement methods are being emphasized.
I think that the most reliable place in measuring the acoustic characteristics of acoustic products is the "響 響 chamber". Subitled rooms are rooms without reflection. In the ideal innocent room, when the sound is produced from the acoustic product, all the sounds hitting the wall are absorbed, and only in the room can only hear the direct sound from the acoustic products. In other words, the ideal iconic room is an environment where the sounds released from the acoustic products can be measured accurately without being affected by the reflective sound. However, in the actual 響 響 room, sound absorbing characteristics are affected by the performance of the interior. For example, an adultery room aimed at measurement of acoustic products is designed to mainly absorb the sound in the audible bandwidth. On the other hand, radio waves for communication devices that emit radio waves are designed to absorb electromagnetic waves.
In Final, we frequently measure and evaluate the audition in an 響 響 room to develop better acoustic products. Previously on Final Lab TwitterPosts related to the 響 室 roomThis time, I would like to focus on the history of the development of the ideological room. Looking back on the history of the 響 室 chamber, you can know important points to be aware of when using an 響 室 chamber. And if you know more about the acoustic room, you will feel closer when you see the acoustic measurement data such as the specifications and performance of the acoustic product. Both us who develop acoustic products and those who use acoustic products understand how important measurements in an 響 rooms will lead to the further development of the technology used in acoustic products. I believe it is something.
Figure 1. View of acoustic measurement by FINAL in an 響 響 room
Among the documents I referred to, the first statement about the iconic chamber is the 1951 literature [1]. The literature introduced the Laboratory of Metropolitan Vickers Electrical Company in 1928. At that time, it was not the name "Sensitive Room" yet, but was called "a laboratory that resembles a free sound field". In addition, it was mainly used as a laboratory to measure machine noise, such as electric motors, not for acoustic equipment development. Unfortunately, there is no photo of this first acoustic laboratory. Figure 2 is the second laboratory where the acoustic laboratory was added in 1933.
Figure 2. Laboratory without reflection in Metropolitan Vickers Electric Company [1 pp. 158 Fig. 11]
In 1936, E.H. Bedell tried to create a free sound at the Bell Institute. A flat sound -absorbing body sample with multiple cloths overlapped on a multi -layer, and the sample was measured by the vertical incident (acoustic jurisdiction), and it was confirmed that there was a high sound absorbing rate. However, when the sound absorbing rate of the completed laboratory was actually measured using this sound absorbing body, it was found that it was lower than the expected sound absorption rate. At that time, it seems that this was the result because it did not consider the diagonal incidence of the sound waves against the sound absorbing body.
In 1940, German scholars Erwin Meyer announced the concept of matching acoustic impedance for the first time. In other words, it announced that if the sound absorbing material and the sound impedance of the incident sound do not match well, the reflection will occur and the sound absorbing effect will decrease. Based on this theory, he proposed a pyramid -shaped sound absorption. In addition, the relationship between the dimensions of the sound absorbing body and the sound absorbing rate has been examined in detail (Parametric Study), and the shape of the sound absorbing body has been optimized. Thus, 32,000 sound absorbing bodies filled with rock wool were placed in the room as shown in Fig. 3. In this laboratory, as a result of the sound measurement at some measurement points of 3 meters from the measured sound source, the measurement result is within 2 dB for the sound pressure decay forecast value of each frequency band. You can understand, and the acoustic laboratory with sufficient performance has been completed.
Figure 3. The acoustic laboratory designed by Erwin Meyer [3 pp. 361 Fig. 12]
In 1943, American scholars Leo L. Beranek, during World War II, designed a sound laboratory at Harvard University in response to the government. He paraphrased the word freedom and used the word "echo-free (anechoic)" for the first time. He also examined the shape of the sound absorbing body based on the theory of acoustic impedan smatching. He also pointed out that the pyramid -shaped sound absorbing body proposed by meer is high in manufacturing and installation, and claimed that weddings are more efficient. In order to further enhance the sound absorbing effect, we also proposed to provide an air layer behind the sound absorbing body. Beranek has shown that the completed subposal room has sufficient performance based on the measurement results of the reverse two rules and the measurement of the deviation value of the attenuation prediction value used by meer. Unfortunately, after World War II, the U.S. government made two proposals to Harvard University for the purpose of demolishing what was built during the war. One is that the U.S. government will pay for and demolish immediately. The other is that Harvard University buys an $ one $ one, and the university will bear the future operating costs. Harvard University at that time did not have any research on the use of an 響 響 room, so this 響 響 room was removed. [5]
*You cannot post photos of the 響 響 room due to copyright, but if you are interested, you can see it on Google ([[).link]）。
Due to the results of Beranek's research, the rust -like sound absorbing body became a standard specification of almost an acmic chamber. In 1947, the Bell Research Institute also built the oldest iconic room among the existence as much as possible, using a rust -like sound absorbent.
** You cannot post photos of the iconic room due to copyright, but if you are interested, you can see it in Google ([[).link]）。
Wooden and pyramid -shaped sound absorption are a good design that uses the theory of acoustic impedan smatching, but research on sound absorption has not ended. Here are the recent research trends.
The first is optimization of the shape of the sound absorbing body. Design formula of wedge -like sound ([[)link]) In the lower limit frequency, it is related to the length of the sound absorbing body (length and the distance from the root of the rust to the tip, but in the text, the length is rewritten as thickness). But that's not all. The sound impedance changes depending on the sound absorbing characteristics of the homogeneous material used for the sound absorbing body and the shape of the sound absorbing body. And if the sound impedance does not match with an incident sound and a sound absorbing body, the sound absorbing performance of the sound absorbing body is reduced, and the lower limit frequency that can be actually absorbed does not reach the lower limit frequency calculated from the design formula. At the time of the design study of the 響 響 room, the material technology was not as advanced as it is now, so the useful sound absorbing materials were limited (homogeneous lock wool, glass fiber, cloth, etc.). In addition, the sound characteristics of the sound absorbing material were not fully understood, so the only way to match the sound impedance was to look for the appropriate shape of the sound absorbing body through experimental verification. Since it is the lowest cost to make a sound absorbing body with a homogeneous material, it is still the mainstream of the adeque rooms to use sound absorbing bodies using homogeneous materials. However, unlike the time, the progress of material technology has made it possible to select density, for example, even for frequently used glass wool. Currently 32kg/m3, 64 kg/m3, 96 kg/m3You can choose from. Or you can use highly safe polyester materials. In addition, research on sound -absorbing materials has been advanced, and the sound characteristics of the sound absorbing material can now be parameters. In addition, the calculator and the simulation technology have evolved, and it is possible to examine the combination of many sound absorbing materials and shapes in a short time, making it possible to design a sound -absorbing body that optimizes materials and shapes. I did it.
The second is the thinning of the sound absorbing body. In the subacerable chamber where the mey was completed, the pyramid -shaped sound absorbing body accounted for about 50 % of the total volume of the room. [4] Many studies have been conducted to reduce the thickness of the sound absorption in order to solve the problem of the huge volume of this sound absorbing body. In 1963, the Kobayashi Research Institute's Children's Children showed that the tip of the sound absorbing body was weak and could be damaged if people and equipment came into contact. In addition, the experiment revealed that the sound absorbing characteristics were almost the same even if the tip of the wedge -like sound was cut from the tip to 30%of the total length of the taper. In this way, we were able to further expand the valid range in the 響 響 room. Currently, there is such a study that the sound -absorbing body of an acmic chamber that uses the rust -like sound in Japan is almost trapezoidal. By the way, there are many 響 響 rooms that have not yet cut the tip overseas.
Figure 4. Cut the tip and become a trapezoidal sound absorbing body
In recent years, research on sound -absorbing mechanisms and further evolution of material technology have made it possible to produce sound -absorbing bodies that combine a variety of sound absorption structures and materials. A study that succeeded in developing a flat sound-absorbing body, which is thinner than the rust-shaped sound absorbing body and has inferior sound absorbing performance, has been reported by using this multi-layer material. [7-8]. One example is a sound -absorbing body with a thickness of 350 mm thick and a lower frequency of 50Hz shown in Fig. 5.
Figure 5. Conceptual diagram of sound absorbing body developed by FAIST in Germany [8]
The history of the adultery chamber, which has eliminated the sound of rust -like sound, has been long, and the theory and design methods are becoming clearer with the accumulation of research so far. However, the drawback of the rust -like sound absorbent is its thickness. In order to lower the lower frequency, a very thick rust -like sound absorbent must be used, and as a result, a large land and space is required to create an 響 響 room. However, as a result of the development of a thin sound absorbing body with multi -layered materials, the decision -making conditions (floor area, indoor space volume) regarding the construction of an innocent chamber have been alleviated, enabling a more compact acoustic room. In addition, there is also an assembled and portable 響 響 box that can be placed indoors such as factories and companies. Of course, the frequency bandwidth that can absorb these assembled 響 響 rooms is still narrower than the conventional iconic room. However, I hope that if such a research and development of such technologies progresses, it will be possible to create an acoustic room in a smaller indoor space (for example, 6 tatami mats). 。
References
[1] A. FLEMING, B. G. Churcher and L. J. Davies, “The Research Laboratories of Assortical Industries LTD.”, Proc. Roy. SoC. A, Vol. 210, iSSUE. 1101, pp. 145-172, 1951.
[2] E. H. Bedell, “SOME DATA on a Room Designed for Field Field Measurements”, J. ACOUST. SOC. Am., Vol. 8, pp. 118-125, 1936.
[3] E. MEYER, G. Buchmann and A.Schoch, “Ein Neue SchallschluckanordNUNG HOHER WIRKSAMKEIT UND DER BAU EINES SCHALLGEDäMPFTEEN RAUMES”, Akust. Z., Vol. 5, pp. 352-364,1940.
[4] L. L. Beranek and H. P. Sleeper, “The Design and Contraction of Anechoic Sound Chambers”,J. ACOUST. SOC. Am., Vol. 18, No. 1, pp. 140-150, 1946.
[5] NO Writer Attributed. (1971 MARCH 30). The Harvard Crimson.
[6] Children Katsu, "Soundproof room, Subitled room, sound insulation chamber -How to achieve the required performance and realization", Audiology, Vol. 6, No. 4, pp. 269-277, 1963.
[7] J. F. XU, J. M. Buchholz and F. R. Fricke, “Flat-Waled Multilaymed Anechoic Linings: Optimization and Application”, J. ACOUST. SOC. Am., Vol. 118, No. 5, pp. 3104-3109, 2005.
[8] Helmut V. FUUCHS, XUEQIN ZHA and GERHARD BABUKE, “Broadband Compact Absorvers for Anechoic Linings”, CFA/DAGA, Strasbourg, 2004.
Explanation of acknowledgment and copyright
Figure 2 is quoted from the reference [1], and the photos are posted in compliance with the copyright policy of Proceeds of the Royal Society A.https://royalsociety.org/journals/permissions/
Figure 3 is quoted from the reference [3], and this literature is open access, here [link] Can be viewed from.
Seki
Currently, various manufacturers have entered the development of acoustic products, and many products are being developed, from entry models to high -end models. In order to appeal to the functions and performance of acoustic products, evaluation and measurement methods are being emphasized.
I think that the most reliable place in measuring the acoustic characteristics of acoustic products is the "響 響 chamber". Subitled rooms are rooms without reflection. In the ideal innocent room, when the sound is produced from the acoustic product, all the sounds hitting the wall are absorbed, and only in the room can only hear the direct sound from the acoustic products. In other words, the ideal iconic room is an environment where the sounds released from the acoustic products can be measured accurately without being affected by the reflective sound. However, in the actual 響 響 room, sound absorbing characteristics are affected by the performance of the interior. For example, an adultery room aimed at measurement of acoustic products is designed to mainly absorb the sound in the audible bandwidth. On the other hand, radio waves for communication devices that emit radio waves are designed to absorb electromagnetic waves.
In Final, we frequently measure and evaluate the audition in an 響 響 room to develop better acoustic products. Previously on Final Lab TwitterPosts related to the 響 室 roomThis time, I would like to focus on the history of the development of the ideological room. Looking back on the history of the 響 室 chamber, you can know important points to be aware of when using an 響 室 chamber. And if you know more about the acoustic room, you will feel closer when you see the acoustic measurement data such as the specifications and performance of the acoustic product. Both us who develop acoustic products and those who use acoustic products understand how important measurements in an 響 rooms will lead to the further development of the technology used in acoustic products. I believe it is something.
Among the documents I referred to, the first statement about the iconic chamber is the 1951 literature [1]. The literature introduced the Laboratory of Metropolitan Vickers Electrical Company in 1928. At that time, it was not the name "Sensitive Room" yet, but was called "a laboratory that resembles a free sound field". In addition, it was mainly used as a laboratory to measure machine noise, such as electric motors, not for acoustic equipment development. Unfortunately, there is no photo of this first acoustic laboratory. Figure 2 is the second laboratory where the acoustic laboratory was added in 1933.
In 1936, E.H. Bedell tried to create a free sound at the Bell Institute. A flat sound -absorbing body sample with multiple cloths overlapped on a multi -layer, and the sample was measured by the vertical incident (acoustic jurisdiction), and it was confirmed that there was a high sound absorbing rate. However, when the sound absorbing rate of the completed laboratory was actually measured using this sound absorbing body, it was found that it was lower than the expected sound absorption rate. At that time, it seems that this was the result because it did not consider the diagonal incidence of the sound waves against the sound absorbing body.
In 1940, German scholars Erwin Meyer announced the concept of matching acoustic impedance for the first time. In other words, it announced that if the sound absorbing material and the sound impedance of the incident sound do not match well, the reflection will occur and the sound absorbing effect will decrease. Based on this theory, he proposed a pyramid -shaped sound absorption. In addition, the relationship between the dimensions of the sound absorbing body and the sound absorbing rate has been examined in detail (Parametric Study), and the shape of the sound absorbing body has been optimized. Thus, 32,000 sound absorbing bodies filled with rock wool were placed in the room as shown in Fig. 3. In this laboratory, as a result of the sound measurement at some measurement points of 3 meters from the measured sound source, the measurement result is within 2 dB for the sound pressure decay forecast value of each frequency band. You can understand, and the acoustic laboratory with sufficient performance has been completed.
In 1943, American scholars Leo L. Beranek, during World War II, designed a sound laboratory at Harvard University in response to the government. He paraphrased the word freedom and used the word "echo-free (anechoic)" for the first time. He also examined the shape of the sound absorbing body based on the theory of acoustic impedan smatching. He also pointed out that the pyramid -shaped sound absorbing body proposed by meer is high in manufacturing and installation, and claimed that weddings are more efficient. In order to further enhance the sound absorbing effect, we also proposed to provide an air layer behind the sound absorbing body. Beranek has shown that the completed subposal room has sufficient performance based on the measurement results of the reverse two rules and the measurement of the deviation value of the attenuation prediction value used by meer. Unfortunately, after World War II, the U.S. government made two proposals to Harvard University for the purpose of demolishing what was built during the war. One is that the U.S. government will pay for and demolish immediately. The other is that Harvard University buys an $ one $ one, and the university will bear the future operating costs. Harvard University at that time did not have any research on the use of an 響 響 room, so this 響 響 room was removed. [5]
*You cannot post photos of the 響 響 room due to copyright, but if you are interested, you can see it on Google ([[).link]）。
Due to the results of Beranek's research, the rust -like sound absorbing body became a standard specification of almost an acmic chamber. In 1947, the Bell Research Institute also built the oldest iconic room among the existence as much as possible, using a rust -like sound absorbent.
** You cannot post photos of the iconic room due to copyright, but if you are interested, you can see it in Google ([[).link]）。
Wooden and pyramid -shaped sound absorption are a good design that uses the theory of acoustic impedan smatching, but research on sound absorption has not ended. Here are the recent research trends.
The first is optimization of the shape of the sound absorbing body. Design formula of wedge -like sound ([[)link]) In the lower limit frequency, it is related to the length of the sound absorbing body (length and the distance from the root of the rust to the tip, but in the text, the length is rewritten as thickness). But that's not all. The sound impedance changes depending on the sound absorbing characteristics of the homogeneous material used for the sound absorbing body and the shape of the sound absorbing body. And if the sound impedance does not match with an incident sound and a sound absorbing body, the sound absorbing performance of the sound absorbing body is reduced, and the lower limit frequency that can be actually absorbed does not reach the lower limit frequency calculated from the design formula. At the time of the design study of the 響 響 room, the material technology was not as advanced as it is now, so the useful sound absorbing materials were limited (homogeneous lock wool, glass fiber, cloth, etc.). In addition, the sound characteristics of the sound absorbing material were not fully understood, so the only way to match the sound impedance was to look for the appropriate shape of the sound absorbing body through experimental verification. Since it is the lowest cost to make a sound absorbing body with a homogeneous material, it is still the mainstream of the adeque rooms to use sound absorbing bodies using homogeneous materials. However, unlike the time, the progress of material technology has made it possible to select density, for example, even for frequently used glass wool. Currently 32kg/m3, 64 kg/m3, 96 kg/m3You can choose from. Or you can use highly safe polyester materials. In addition, research on sound -absorbing materials has been advanced, and the sound characteristics of the sound absorbing material can now be parameters. In addition, the calculator and the simulation technology have evolved, and it is possible to examine the combination of many sound absorbing materials and shapes in a short time, making it possible to design a sound -absorbing body that optimizes materials and shapes. I did it.
The second is the thinning of the sound absorbing body. In the subacerable chamber where the mey was completed, the pyramid -shaped sound absorbing body accounted for about 50 % of the total volume of the room. [4] Many studies have been conducted to reduce the thickness of the sound absorption in order to solve the problem of the huge volume of this sound absorbing body. In 1963, the Kobayashi Research Institute's Children's Children showed that the tip of the sound absorbing body was weak and could be damaged if people and equipment came into contact. In addition, the experiment revealed that the sound absorbing characteristics were almost the same even if the tip of the wedge -like sound was cut from the tip to 30%of the total length of the taper. In this way, we were able to further expand the valid range in the 響 響 room. Currently, there is such a study that the sound -absorbing body of an acmic chamber that uses the rust -like sound in Japan is almost trapezoidal. By the way, there are many 響 響 rooms that have not yet cut the tip overseas.
In recent years, research on sound -absorbing mechanisms and further evolution of material technology have made it possible to produce sound -absorbing bodies that combine a variety of sound absorption structures and materials. A study that succeeded in developing a flat sound-absorbing body, which is thinner than the rust-shaped sound absorbing body and has inferior sound absorbing performance, has been reported by using this multi-layer material. [7-8]. One example is a sound -absorbing body with a thickness of 350 mm thick and a lower frequency of 50Hz shown in Fig. 5.
The history of the adultery chamber, which has eliminated the sound of rust -like sound, has been long, and the theory and design methods are becoming clearer with the accumulation of research so far. However, the drawback of the rust -like sound absorbent is its thickness. In order to lower the lower frequency, a very thick rust -like sound absorbent must be used, and as a result, a large land and space is required to create an 響 響 room. However, as a result of the development of a thin sound absorbing body with multi -layered materials, the decision -making conditions (floor area, indoor space volume) regarding the construction of an innocent chamber have been alleviated, enabling a more compact acoustic room. In addition, there is also an assembled and portable 響 響 box that can be placed indoors such as factories and companies. Of course, the frequency bandwidth that can absorb these assembled 響 響 rooms is still narrower than the conventional iconic room. However, I hope that if such a research and development of such technologies progresses, it will be possible to create an acoustic room in a smaller indoor space (for example, 6 tatami mats). 。
References
[1] A. FLEMING, B. G. Churcher and L. J. Davies, “The Research Laboratories of Assortical Industries LTD.”, Proc. Roy. SoC. A, Vol. 210, iSSUE. 1101, pp. 145-172, 1951.
[2] E. H. Bedell, “SOME DATA on a Room Designed for Field Field Measurements”, J. ACOUST. SOC. Am., Vol. 8, pp. 118-125, 1936.
[3] E. MEYER, G. Buchmann and A.Schoch, “Ein Neue SchallschluckanordNUNG HOHER WIRKSAMKEIT UND DER BAU EINES SCHALLGEDäMPFTEEN RAUMES”, Akust. Z., Vol. 5, pp. 352-364,1940.
[4] L. L. Beranek and H. P. Sleeper, “The Design and Contraction of Anechoic Sound Chambers”,J. ACOUST. SOC. Am., Vol. 18, No. 1, pp. 140-150, 1946.
[5] NO Writer Attributed. (1971 MARCH 30). The Harvard Crimson.
[6] Children Katsu, "Soundproof room, Subitled room, sound insulation chamber -How to achieve the required performance and realization", Audiology, Vol. 6, No. 4, pp. 269-277, 1963.
[7] J. F. XU, J. M. Buchholz and F. R. Fricke, “Flat-Waled Multilaymed Anechoic Linings: Optimization and Application”, J. ACOUST. SOC. Am., Vol. 118, No. 5, pp. 3104-3109, 2005.
[8] Helmut V. FUUCHS, XUEQIN ZHA and GERHARD BABUKE, “Broadband Compact Absorvers for Anechoic Linings”, CFA/DAGA, Strasbourg, 2004.
Explanation of acknowledgment and copyright
Figure 2 is quoted from the reference [1], and the photos are posted in compliance with the copyright policy of Proceeds of the Royal Society A.https://royalsociety.org/journals/permissions/
Figure 3 is quoted from the reference [3], and this literature is open access, here [link] Can be viewed from.
Seki
