Analysis of current domestic public broadcasting equipment quality indicators

After investigating the indicators of several types of products of several public broadcasting brands in the domestic market, the status of the quality indicators after the formation of the basic system is analyzed for the reference of the national standards for public broadcasting, so as to reasonably set limits.

At present, there are more than one thousand public broadcasting manufacturers in China, and the technical level of many manufacturers is relatively large. The quality indicators of products are uneven, but the quality level of first-line manufacturers is relatively good, and the performance indicators are also compared. high. In the actual engineering application, because the country does not yet have a specific acceptance criteria, the engineering and customers are likely to have differences in the project, causing unnecessary contradictions and waste. In response to this situation, the Ministry of Information Industry issued the "2006 Electronic Engineering Construction Standards Quota Revision Plan" issued in June 2006, and proposed to start the "Technical Specifications for Public Broadcasting Systems Engineering" in June 2006, and requested 2007. The draft was completed in June. According to the above arrangement, the first draft of the draft (hereinafter referred to as the “Draft”) has recently been completed by the Standards Station of the Ministry of Information Industry, the Audio Engineering Branch of the China Electronics Society, and the Technical Specifications for Public Broadcasting Systems, edited by Guangzhou Disip.

According to the draft regulations, the acoustic characteristics of the public address system mainly include the maximum sound pressure level, signal-to-noise ratio, and transmission frequency characteristics. Practice has shown that the devices that determine these indicators in the public address system are mainly these types of conventional products: audio equipment, preamplifiers, broadcast power amplifiers, broadcast speakers, and so on. Other devices in the system, such as timing control and partition control, have little impact on these indicators. Therefore, in the public address system, the system block diagram can be simplified as shown in Figure 1 only in terms of acoustic characteristics. According to this system block diagram, the author investigated the indicators of these types of products published by a number of representative first-line manufacturers. The results of the survey are shown in Schedule 1 to Schedule 6. Considering the length, only a few key indicators are listed in the table.



According to the data in Schedules 1 to 6, we can conduct a preliminary discussion on the maximum sound pressure level, signal-to-noise ratio, and transmission frequency characteristics of the public broadcasting system using these domestic products.

Maximum sound pressure level

The maximum sound pressure level in a public address system can basically be considered to be determined by the broadcast speaker, because the current power amplifier output power can easily be several kilowatts, and the single power of the broadcast speaker is generally small, usually several watts. To tens of watts, less than one hundred watts. According to the electroacoustic principle, the maximum sound pressure level SPL of the broadcast speaker coverage area in the public address system has the following relationship with the sensitivity level LM of the broadcast speaker, the electric power P fed to the broadcast speaker, and the distance r between the listening point and the broadcast speaker:

SPL = LM +10 lg P – 20 lg r dB (1)

It can be seen from Schedule 4, Schedule 5 and Schedule 6 that the sensitivity level of each class of Class 3 broadcast speakers is between 89 and 94 dB. A simple analysis is now carried out using the DISP DSP 802 as an example. Assume that the speakers are installed in a 3 meter high ceiling venue. The distance between the speakers is 16 meters. The 1.70 meter high person stands in the middle of the two speakers. At this time, the distance between the human ear and the two speakers is about 8.2 meters. Nesting equation (1) can calculate the sound pressure level provided by a single speaker is about 81.5dB, plus the contribution of adjacent speakers and early reflections can also increase the sound pressure level by about 3dB. This sound pressure level is fully satisfactory for general background music broadcasting. The calculation method is the same when the application is outdoors, but there is basically no early reflection sound group outside.

The above is only a rough calculation. In engineering applications, according to the requirements of the public broadcasting level, it can be achieved by adjusting the broadcast speaker type and configuration distance to achieve a sound pressure level of 80-90 dB.

2. Signal to noise ratio

The signal-to-noise ratio of a public address system is the total signal-to-noise ratio of a signal source device, a broadcast preamplifier, and a broadcast power amplifier. The preamplifier and the power amplifier are devices with gain. The noise floor signal of the signal source device is amplified by the preamplifier, and the amplified noise signal is superimposed with the noise signal of the preamplifier and then amplified by the power amplifier. It can be seen from Schedule 1 and Schedule 3 that the signal-to-noise ratio indicators of typical audio equipment CD players and broadcast power amplifiers are relatively high. The preamplifier has a lower signal-to-noise ratio because it generally has multiple microphone inputs and multiple line inputs. In an actual public address system, the signal-to-noise ratio of the public address system is the signal-to-noise ratio at the output of the broadcast power amplifier.

Taking the products of Disip as an example, the author conducted actual tests on three types of machines and the system connected to Figure 1. The test results show that the test results of the single machine are basically the same as those announced by the manufacturer. The signal-to-noise ratio of the signal source device MP9907C is 90 dB, the signal-to-noise ratio of the broadcast preamplifier MP9911P is 70 dB, and the signal-to-noise ratio of the broadcast power amplifier MP2600 is 88. dB. The signal-to-noise ratio measured at the output of the broadcast power amplifier is about 78dB after the three machines are connected, even better than the index of the broadcast preamplifier MP9911P. This result is a bit unexpected. The author also began to doubt this result. To this end, three sets of tests were repeated on the above machines, and the final result was very close. This is probably due to the improved cascading of the device, the improved noise matching conditions, and the contribution of the amplifier with high signal-to-noise ratio and large gain.

After the development of domestic public broadcasting products in recent years, the overall technical level has been significantly improved. The conventional products of the first-line manufacturers, especially those mentioned above, have their quality indicators level close to the level of international counterparts.

3. Transmission frequency characteristics

The frequency response of signal source devices and broadcast preamplifiers in public address systems typically has a relatively wide range. Because of the output transformer, the frequency response range of the broadcast power amplifier is generally narrower than that of the stage-type fixed-resistance professional power amplifier. At the same time, many manufacturers will limit the range of low-frequency response for efficiency and reliability. The high frequency response range is completely dependent on the output transformer. With the improvement of the process, many manufacturers have been able to achieve high-frequency response upper limit of high-power output transformers exceeding 20KHz. Broadcast speakers also typically have an input transformer, which is also an important cause of frequency response, especially in high frequency bands. At the same time, due to the price and size limitation, the horn unit and the cabinet are generally small, even without the cabinet (most of the ceiling speakers have no cabinet - the ceiling is the baffle), so the low frequency response of most broadcast speakers is not well. It has been shown that the frequency response range of the broadcast speaker in the whole broadcast system is narrower than that of the signal source device, the broadcast preamplifier and the broadcast power amplifier. It can basically be considered that the frequency response of the system is determined by the broadcast speaker.

The author passed the test of the three models of each model of Desp's three types of broadcast speakers in Schedule 4 to Schedule 6. Each model test is divided into three combinations: 1 is the broadcast speaker alone test; 2 is the broadcast speaker + broadcast power amplifier MP2600 test; 3 is the broadcast speaker + broadcast power amplifier MP2600 + broadcast preamplifier MP9911P test. The test found that several combinations of frequency characteristics are very close to the broadcast speaker frequency characteristics. Figure 2 is a test curve of the DSP308 combination. It can be seen from Fig. 2 that the frequency characteristics of the speaker connected power amplifier and the pre-position are not obvious. Therefore, it can be considered that the frequency response range in the public address system is determined by the broadcast speaker.



Schedule 1. CD player performance indicators




Schedule 2. Preamplifier performance indicators


Schedule 3. Broadcast Power Amplifier Performance Indicators


Schedule 4. Ceiling speaker performance indicators




Schedule 5. Sound column performance indicators





Schedule 6. Grass speaker performance indicators





references

[1] Public Broadcasting Engineering Handbook
After investigating the indicators of several types of products of several public broadcasting brands in the domestic market, the status of the quality indicators after the formation of the basic system is analyzed for the reference of the national standards for public broadcasting, so as to reasonably set limits.

At present, there are more than one thousand public broadcasting manufacturers in China, and the technical level of many manufacturers is relatively large. The quality indicators of products are uneven, but the quality level of first-line manufacturers is relatively good, and the performance indicators are also compared. high. In the actual engineering application, because the country does not yet have a specific acceptance criteria, the engineering and customers are likely to have differences in the project, causing unnecessary contradictions and waste. In response to this situation, the Ministry of Information Industry issued the "2006 Electronic Engineering Construction Standards Quota Revision Plan" issued in June 2006, and proposed to start the "Technical Specifications for Public Broadcasting Systems Engineering" in June 2006, and requested 2007. The draft was completed in June. According to the above arrangement, the first draft of the draft (hereinafter referred to as the “Draft”) has recently been completed by the Standards Station of the Ministry of Information Industry, the Audio Engineering Branch of the China Electronics Society, and the Technical Specifications for Public Broadcasting Systems, edited by Guangzhou Disip.

According to the draft regulations, the acoustic characteristics of the public address system mainly include the maximum sound pressure level, signal-to-noise ratio, and transmission frequency characteristics. Practice has shown that the devices that determine these indicators in the public address system are mainly these types of conventional products: audio equipment, preamplifiers, broadcast power amplifiers, broadcast speakers, and so on. Other devices in the system, such as timing control and partition control, have little impact on these indicators. Therefore, in the public address system, the system block diagram can be simplified as shown in Figure 1 only in terms of acoustic characteristics. According to this system block diagram, the author investigated the indicators of these types of products published by a number of representative first-line manufacturers. The results of the survey are shown in Schedule 1 to Schedule 6. Considering the length, only a few key indicators are listed in the table.



According to the data in Schedules 1 to 6, we can conduct a preliminary discussion on the maximum sound pressure level, signal-to-noise ratio, and transmission frequency characteristics of the public broadcasting system using these domestic products.

Maximum sound pressure level

The maximum sound pressure level in a public address system can basically be considered to be determined by the broadcast speaker, because the current power amplifier output power can easily be several kilowatts, and the single power of the broadcast speaker is generally small, usually several watts. To tens of watts, less than one hundred watts. According to the electroacoustic principle, the maximum sound pressure level SPL of the broadcast speaker coverage area in the public address system has the following relationship with the sensitivity level LM of the broadcast speaker, the electric power P fed to the broadcast speaker, and the distance r between the listening point and the broadcast speaker:

SPL = LM +10 lg P – 20 lg r dB (1)

It can be seen from Schedule 4, Schedule 5 and Schedule 6 that the sensitivity level of each class of Class 3 broadcast speakers is between 89 and 94 dB. A simple analysis is now carried out using the DISP DSP 802 as an example. Assume that the speakers are installed in a 3 meter high ceiling venue. The distance between the speakers is 16 meters. The 1.70 meter high person stands in the middle of the two speakers. At this time, the distance between the human ear and the two speakers is about 8.2 meters. Nesting equation (1) can calculate the sound pressure level provided by a single speaker is about 81.5dB, plus the contribution of adjacent speakers and early reflections can also increase the sound pressure level by about 3dB. This sound pressure level is fully satisfactory for general background music broadcasting. The calculation method is the same when the application is outdoors, but there is basically no early reflection sound group outside.

The above is only a rough calculation. In engineering applications, according to the requirements of the public broadcasting level, it can be achieved by adjusting the broadcast speaker type and configuration distance to achieve a sound pressure level of 80-90 dB.

2. Signal to noise ratio

The signal-to-noise ratio of a public address system is the total signal-to-noise ratio of a signal source device, a broadcast preamplifier, and a broadcast power amplifier. The preamplifier and the power amplifier are devices with gain. The noise floor signal of the signal source device is amplified by the preamplifier, and the amplified noise signal is superimposed with the noise signal of the preamplifier and then amplified by the power amplifier. It can be seen from Schedule 1 and Schedule 3 that the signal-to-noise ratio indicators of typical audio equipment CD players and broadcast power amplifiers are relatively high. The preamplifier has a lower signal-to-noise ratio because it generally has multiple microphone inputs and multiple line inputs. In an actual public address system, the signal-to-noise ratio of the public address system is the signal-to-noise ratio at the output of the broadcast power amplifier.

Taking the products of Disip as an example, the author conducted actual tests on three types of machines and the system connected to Figure 1. The test results show that the test results of the single machine are basically the same as those announced by the manufacturer. The signal-to-noise ratio of the signal source device MP9907C is 90 dB, the signal-to-noise ratio of the broadcast preamplifier MP9911P is 70 dB, and the signal-to-noise ratio of the broadcast power amplifier MP2600 is 88. dB. The signal-to-noise ratio measured at the output of the broadcast power amplifier is about 78dB after the three machines are connected, even better than the index of the broadcast preamplifier MP9911P. This result is a bit unexpected. The author also began to doubt this result. To this end, three sets of tests were repeated on the above machines, and the final result was very close. This is probably due to the improved cascading of the device, the improved noise matching conditions, and the contribution of the amplifier with high signal-to-noise ratio and large gain.

After the development of domestic public broadcasting products in recent years, the overall technical level has been significantly improved. The conventional products of the first-line manufacturers, especially those mentioned above, have their quality indicators level close to the level of international counterparts.

3. Transmission frequency characteristics

The frequency response of signal source devices and broadcast preamplifiers in public address systems typically has a relatively wide range. Because of the output transformer, the frequency response range of the broadcast power amplifier is generally narrower than that of the stage-type fixed-resistance professional power amplifier. At the same time, many manufacturers will limit the range of low-frequency response for efficiency and reliability. The high frequency response range is completely dependent on the output transformer. With the improvement of the process, many manufacturers have been able to achieve high-frequency response upper limit of high-power output transformers exceeding 20KHz. Broadcast speakers also typically have an input transformer, which is also an important cause of frequency response, especially in high frequency bands. At the same time, due to the price and size limitation, the horn unit and the cabinet are generally small, even without the cabinet (most of the ceiling speakers have no cabinet - the ceiling is the baffle), so the low frequency response of most broadcast speakers is not well. It has been shown that the frequency response range of the broadcast speaker in the whole broadcast system is narrower than that of the signal source device, the broadcast preamplifier and the broadcast power amplifier. It can basically be considered that the frequency response of the system is determined by the broadcast speaker.

The author passed the test of the three models of each model of Desp's three types of broadcast speakers in Schedule 4 to Schedule 6. Each model test is divided into three combinations: 1 is the broadcast speaker alone test; 2 is the broadcast speaker + broadcast power amplifier MP2600 test; 3 is the broadcast speaker + broadcast power amplifier MP2600 + broadcast preamplifier MP9911P test. The test found that several combinations of frequency characteristics are very close to the broadcast speaker frequency characteristics. Figure 2 is a test curve of the DSP308 combination. It can be seen from Fig. 2 that the frequency characteristics of the speaker connected power amplifier and the pre-position are not obvious. Therefore, it can be considered that the frequency response range in the public address system is determined by the broadcast speaker.



Schedule 1. CD player performance indicators




Schedule 2. Preamplifier performance indicators


Schedule 3. Broadcast Power Amplifier Performance Indicators


Schedule 4. Ceiling speaker performance indicators




Schedule 5. Sound column performance indicators





Schedule 6. Grass speaker performance indicators





references

[1] Public Broadcasting Engineering Handbook
After investigating the indicators of several types of products of several public broadcasting brands in the domestic market, the status of the quality indicators after the formation of the basic system is analyzed for the reference of the national standards for public broadcasting, so as to reasonably set limits.

At present, there are more than one thousand public broadcasting manufacturers in China, and the technical level of many manufacturers is relatively large. The quality indicators of products are uneven, but the quality level of first-line manufacturers is relatively good, and the performance indicators are also compared. high. In the actual engineering application, because the country does not yet have a specific acceptance criteria, the engineering and customers are likely to have differences in the project, causing unnecessary contradictions and waste. In response to this situation, the Ministry of Information Industry issued the "2006 Electronic Engineering Construction Standards Quota Revision Plan" issued in June 2006, and proposed to start the "Technical Specifications for Public Broadcasting Systems Engineering" in June 2006, and requested 2007. The draft was completed in June. According to the above arrangement, the first draft of the draft (hereinafter referred to as the “Draft”) has recently been completed by the Standards Station of the Ministry of Information Industry, the Audio Engineering Branch of the China Electronics Society, and the Technical Specifications for Public Broadcasting Systems, edited by Guangzhou Disip.

According to the draft regulations, the acoustic characteristics of the public address system mainly include the maximum sound pressure level, signal-to-noise ratio, and transmission frequency characteristics. Practice has shown that the devices that determine these indicators in the public address system are mainly these types of conventional products: audio equipment, preamplifiers, broadcast power amplifiers, broadcast speakers, and so on. Other devices in the system, such as timing control and partition control, have little impact on these indicators. Therefore, in the public address system, the system block diagram can be simplified as shown in Figure 1 only in terms of acoustic characteristics. According to this system block diagram, the author investigated the indicators of these types of products published by a number of representative first-line manufacturers. The results of the survey are shown in Schedule 1 to Schedule 6. Considering the length, only a few key indicators are listed in the table.



According to the data in Schedules 1 to 6, we can conduct a preliminary discussion on the maximum sound pressure level, signal-to-noise ratio, and transmission frequency characteristics of the public broadcasting system using these domestic products.

Maximum sound pressure level

The maximum sound pressure level in a public address system can basically be considered to be determined by the broadcast speaker, because the current power amplifier output power can easily be several kilowatts, and the single power of the broadcast speaker is generally small, usually several watts. To tens of watts, less than one hundred watts. According to the electroacoustic principle, the maximum sound pressure level SPL of the broadcast speaker coverage area in the public address system has the following relationship with the sensitivity level LM of the broadcast speaker, the electric power P fed to the broadcast speaker, and the distance r between the listening point and the broadcast speaker:

SPL = LM +10 lg P – 20 lg r dB (1)

It can be seen from Schedule 4, Schedule 5 and Schedule 6 that the sensitivity level of each class of Class 3 broadcast speakers is between 89 and 94 dB. A simple analysis is now carried out using the DISP DSP 802 as an example. Assume that the speakers are installed in a 3 meter high ceiling venue. The distance between the speakers is 16 meters. The 1.70 meter high person stands in the middle of the two speakers. At this time, the distance between the human ear and the two speakers is about 8.2 meters. Nesting equation (1) can calculate the sound pressure level provided by a single speaker is about 81.5dB, plus the contribution of adjacent speakers and early reflections can also increase the sound pressure level by about 3dB. This sound pressure level is fully satisfactory for general background music broadcasting. The calculation method is the same when the application is outdoors, but there is basically no early reflection sound group outside.

The above is only a rough calculation. In engineering applications, according to the requirements of the public broadcasting level, it can be achieved by adjusting the broadcast speaker type and configuration distance to achieve a sound pressure level of 80-90 dB.

2. Signal to noise ratio

The signal-to-noise ratio of a public address system is the total signal-to-noise ratio of a signal source device, a broadcast preamplifier, and a broadcast power amplifier. The preamplifier and the power amplifier are devices with gain. The noise floor signal of the signal source device is amplified by the preamplifier, and the amplified noise signal is superimposed with the noise signal of the preamplifier and then amplified by the power amplifier. It can be seen from Schedule 1 and Schedule 3 that the signal-to-noise ratio indicators of typical audio equipment CD players and broadcast power amplifiers are relatively high. The preamplifier has a lower signal-to-noise ratio because it generally has multiple microphone inputs and multiple line inputs. In an actual public address system, the signal-to-noise ratio of the public address system is the signal-to-noise ratio at the output of the broadcast power amplifier.

Taking the products of Disip as an example, the author conducted actual tests on three types of machines and the system connected to Figure 1. The test results show that the test results of the single machine are basically the same as those announced by the manufacturer. The signal-to-noise ratio of the signal source device MP9907C is 90 dB, the signal-to-noise ratio of the broadcast preamplifier MP9911P is 70 dB, and the signal-to-noise ratio of the broadcast power amplifier MP2600 is 88. dB. The signal-to-noise ratio measured at the output of the broadcast power amplifier is about 78dB after the three machines are connected, even better than the index of the broadcast preamplifier MP9911P. This result is a bit unexpected. The author also began to doubt this result. To this end, three sets of tests were repeated on the above machines, and the final result was very close. This is probably due to the improved cascading of the device, the improved noise matching conditions, and the contribution of the amplifier with high signal-to-noise ratio and large gain.

After the development of domestic public broadcasting products in recent years, the overall technical level has been significantly improved. The conventional products of the first-line manufacturers, especially those mentioned above, have their quality indicators level close to the level of international counterparts.

3. Transmission frequency characteristics

The frequency response of signal source devices and broadcast preamplifiers in public address systems typically has a relatively wide range. Because of the output transformer, the frequency response range of the broadcast power amplifier is generally narrower than that of the stage-type fixed-resistance professional power amplifier. At the same time, many manufacturers will limit the range of low-frequency response for efficiency and reliability. The high frequency response range is completely dependent on the output transformer. With the improvement of the process, many manufacturers have been able to achieve high-frequency response upper limit of high-power output transformers exceeding 20KHz. Broadcast speakers also typically have an input transformer, which is also an important cause of frequency response, especially in high frequency bands. At the same time, due to the price and size limitation, the horn unit and the cabinet are generally small, even without the cabinet (most of the ceiling speakers have no cabinet - the ceiling is the baffle), so the low frequency response of most broadcast speakers is not well. It has been shown that the frequency response range of the broadcast speaker in the whole broadcast system is narrower than that of the signal source device, the broadcast preamplifier and the broadcast power amplifier. It can basically be considered that the frequency response of the system is determined by the broadcast speaker.

The author passed the test of the three models of each model of Desp's three types of broadcast speakers in Schedule 4 to Schedule 6. Each model test is divided into three combinations: 1 is the broadcast speaker alone test; 2 is the broadcast speaker + broadcast power amplifier MP2600 test; 3 is the broadcast speaker + broadcast power amplifier MP2600 + broadcast preamplifier MP9911P test. The test found that several combinations of frequency characteristics are very close to the broadcast speaker frequency characteristics. Figure 2 is a test curve of the DSP308 combination. It can be seen from Fig. 2 that the frequency characteristics of the speaker connected power amplifier and the pre-position are not obvious. Therefore, it can be considered that the frequency response range in the public address system is determined by the broadcast speaker.



Schedule 1. CD player performance indicators




Schedule 2. Preamplifier performance indicators


Schedule 3. Broadcast Power Amplifier Performance Indicators


Schedule 4. Ceiling speaker performance indicators




Schedule 5. Sound column performance indicators





Schedule 6. Grass speaker performance indicators





references

[1] Public Broadcasting Engineering Handbook

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