Professional cinema power amplifier parameter knowledge

                          Professional cinema power amplifier parameter knowledge

At present, there has been a huge improvement in home theater equipment. Not only the picture is clearer, but also a more powerful audio equipment system in the audio system, which brings people a more realistic and wonderful audio-visual experience. A professional-level home theater system, which it uses The parameters of the products in all aspects should be the top products in the market at present, so how much do you know about the parameters of the top power amplifiers?

At present, high-definition has become a popular element, and high-definition TV, high-definition movies, high-definition cameras, high-definition camcorders, high-definition DV, etc. have unknowingly integrated into our daily life. The power amplifier, as an important part of the home theater, of course has to be upgraded to high-definition.

If we take this as the boundary, then the current products on the market are mainly divided into two levels, one is the next-generation power amplifier that supports high-definition, and the other is the ordinary power amplifier in the DVD era. Of course, this classification is not very scientific and complete, because there are many types of power amplifiers, and this category is only suitable for AV power amplifiers. According to the purpose, we can generally divide it into three categories: professional power amplifier, civilian power amplifier, and special power amplifier. Professional power amplifiers are generally used for sound reinforcement in conferences and performance halls. The detailed classification of civilian power amplifiers includes HI-FI power amplifiers, AV power amplifiers, KALAOK power amplifiers, and so-called comprehensive power amplifiers that integrate various common functions into one. HI-FI power amplifiers are divided into "split type" and "combined type".

Faced with so many classifications of power amplifiers, even audiophiles have a headache, let alone ordinary consumers. Moreover, there are tens of hundreds of products from more than a dozen well-known brand manufacturers in each field of products, and there are countless unknown ones. Faced with so many mixed products, if you don’t know them, you don’t know if you want to buy them. How to start. What's more, it is really difficult to understand their parameters, characteristics, indicators, etc., because products in each field have their own standards, and each manufacturer also has its own standards.

AV amplifier

AV power amplifier, as the name implies, A means audio and sound, and V means audio and images. Therefore, AV power amplifier is an audio-visual amplifier that integrates audio and video signal processing. It is mainly used to cooperate with image sources to produce audio-visual integration. Create a sound field as the main design purpose, specially for home theater use.

It uses its internal delay and reverberation processing circuits to control the delay time between each channel during playback, and simulates the sound field in various listening environments by adjusting the length of the delay time. The technical indicators of high-fidelity Hi-Fi power amplifiers mainly include output power, harmonic distortion, signal-to-noise ratio, frequency range, rated impedance and damping coefficient, etc., especially emphasizing harmonic distortion and signal-to-noise ratio; while AV power amplifiers also have these Technical indicators, but more emphasis on channel isolation, delay time range, various sound field modes and other index parameters.

(1) Decoding format

At the heart of a home theater system is the surround sound system. With a surround sound system, the effect in the theater can be achieved in the home. Surround sound system is a multi-channel playback system, there are many formats, and different formats have different characteristics. Moreover, the number of various channels of power amplifiers is increasing, not only 5.1, 6.1, but also 7.1, 8.2 and so on.

We all know that 5.1 channels generally refer to two digital multi-channel surround audio formats, Dolby Digital l5.1 and DTS 5.1. The 6.1 channel generally refers to two digital multi-channel surround sound audio formats, Dolby Digital EX and DTSES. This is based on 5.1. In order to make the left and right surround sound better connected, a rear middle surround channel is added, which forms a 6.1 channel format.

As for the 7.1-channel system, it refers to the THX Surround EX system. Dolby also has the Dolby ProLogic IIx technology, which can separate the 2-channel audio tracks into 7.1-channel restoration through complex matrix operations. THX is a certification standard for cinemas from Lucas, not an audio format. When the 6.1-channel Dolby Digital EX and DTSES came out, THX further evolved it into the THX Surround EX system.

In order to be compatible with the original two-way sounding side channel and to enhance the surround sound effect again, two rear channels were added on the basis of the original side channel, which constituted a 7.1 channel.

Finally, there are not many 8.2-channel products currently in use. It is to enhance the effect of the surround sound field. On the basis of the 6.1-channel of DolbyDigitalEX and DTSES, YAMAHA's exclusive front surround channel is added, and a heavy-duty speaker is added. Bass output, rear center surround sound is also expanded from single channel to two channels.

All of the above are various surround decoding format systems in the DVD era. It is obvious that the more channels you select, the more coherent and tight the surround effect will be, and the stronger the sense of envelopment will be. In today's high-definition next generation, new power amplifiers have new features and requirements. With the listing of Blu-ray and HD-DVD, a new generation of multi-channel surround sound formats has also come out, including Dolby Digital plus, Dolby True HD and DTS HD.

Dolby Digital Plus starts with 7.1 channels, and the sampling rate is expanded from 96-640kbps of Dolby Digital to 32kbps-6Mbps, and it is developed for the digital surround with the largest 13.1 channels. And DolbyTrueHD is based on MLP lossless technology, including higher bit rate, additional channels, enhanced stereo mixing support and extensive metadata functions.

As for DTS HD, it also starts with 7.1 channels, supports a high bit rate of more than 1.5Mbps, and a sampling frequency from 8-192kHz. Compared with the 768kbps compression technology used in ordinary DVD discs, the sound quality of DTS HD will be greatly improved. The data flow of DTSHD can be flexibly converted according to the required sound quality. Through the exclusive lossless compression technology, the DTS compression ratio is smaller and the details are richer, providing higher-quality sound recording and a maximum of 32-channel surround output.

Finally, the analog sound field that everyone often talks about, whether it is the DSP analog sound field advocated by YAMAHA, or Sony's exclusive Digital Cinema Sound, is a surround sound post-processing method that simulates the spatial characteristics of movie theaters and concert halls. If you want to compare the difference between the two in a sensory way, most people think that SONY's DCS pays more attention to the sense of envelopment of the sound, while YAMAHA pays more attention to the sense of open space. The two can be said to have their own strengths.

(2) Power matching

The focus of the AV power amplifier is to create an ideal listening environment with visual effects, creating a realistic sense of orientation, presence and shock. Therefore, the design focus of the AV power amplifier is more on the clarity of the dialogue and the large dynamic "burst" effect of the audio-visual environment, restoring or simulating the sound field positioning of the integration of sound and picture, and creating various sound field atmospheres. In this way, not only the frequency range of the AV power amplifier is required to be as wide as possible, the degree of distortion is small, the signal-to-noise ratio is high, the transient characteristics are good, the sound quality and timbre are beautiful and pleasant, etc., but more attention is paid to the sound pressure level: that is, under the premise of low distortion, to ensure Large enough output power.

The unit of power amplifier output power is watts (W). Since the measurement methods of various manufacturers are different, there are some names with different names. Such as rated output power, maximum output power, music output power, peak music output power, etc. The rated power of the front main channel of the high-end AV power amplifier is generally above 80W to meet the 107dB sound pressure level requirements of the cinema.

However, some imported AV power amplifiers have 5-7 channels, each channel has a total standard of more than 100 W, and the total power is thousands of W, but the power transformer is so large. I really don’t know what power standard is used to calculate it. Japanese AV The most obvious is that 6 ohms is always used to bluff people, and it is actually 100W if calculated at 8 ohms. Anyone who has used an AV power amplifier knows that the feet tend to be soft when there is a large dynamic. Therefore, it is recommended to buy an AV power amplifier, it is best to choose a mid-range or above, otherwise it will be useless.

Generally speaking, the bigger the power amplifier, the better. But the main function of the power amplifier is to drive the speaker, so it depends on the power amplifier must match the speaker. However, the configuration of power amplifiers and speakers involves many aspects, such as the brand of power amplifiers, the selection of power tube types, and which power amplifiers should be configured for low-sensitivity speakers. It is difficult to find a unified standard.

It is worth noting that the general audiophiles believe that the selection of power amplifiers must be determined by the speakers, and there should be no concept of "power reserve" to configure power amplifiers. The specific standard for power amplifier and speaker power configuration should be: under certain impedance conditions, the power of the power amplifier should be greater than the power of the speaker, but not too large. In general applications, the undistortion rate of the power amplifier should be about 1.2-1.5 times the rated power of the speaker; while in large dynamic occasions, it should be about 1.5-2 times.

(3) Interface

The signal transmission of traditional home theater is nothing more than through optical fiber, coaxial and RCA analog interfaces. For example, the previous DTS and Dolby’s various codes all transmit digital compression codes to AV amplifiers through optical fiber and coaxial interfaces. decoding. As the latest generation of digital interface, HDMI has been widely used in various digital products, and with the application of HDMI interface in audio-visual products and the maturity of technology, more and more power amplifiers have also begun to use this theoretically lossless power amplifier. the transmission method.

Moreover, HDMI itself has gone through three versions. The earliest interface specification of HDMI, HDMI1.0, was announced in December 2002. The current highest version is the HDMI1.3 specification released in June this year. Generally pay attention to distinguishing clearly, their differences and applications are very large. For example, technologies such as Dolby Digital plus, Dolby TrueHD and DTS HD can only be transmitted through the HDMI1.3 interface, so you should pay attention when purchasing, only the power amplifier with this interface can enjoy the music of the next generation.

The audio signal of HDMI does not occupy an additional channel, but uses data packets together with other auxiliary information, and uses 3 TMDS channels to transmit in the form of island data during the blanking period of video signal transmission. It can provide up to 8 channels of high-quality audio signals with a sampling frequency of 192kHz. In contrast, the CD audio standard 44.1kHz two-channel signal and the latest DVD-Audio audio format 96kHz 6-channel signal are inferior A lot.

(4) Channel separation

Separation refers to the ability of the surround sound decoder in the AV power amplifier to restore the audio coded signal to each channel signal, and also indicates the degree of mutual "isolation" of the signals between each channel of the amplifier. The value is expressed in decibels, the larger the dB value, the greater the isolation between them, the smaller the mutual "crosstalk" of the sound between each channel restored by the amplifier, and the better the sound effect. When choosing an AV power amplifier, the larger the difference, the better, generally more than 60dB.

Power amplifiers with poor separation will have inaccurate sound image positioning, unsatisfactory sound field, and poor sound image continuity. A high channel separation is one of the prerequisites for accurate panning. High separation can expand the sound field, produce a wider sense of space, and at the same time make the sound positioning more precise and accurate. aspects have been strengthened. In short, the higher the degree of separation, the greater the effect of the sound field and the more precise positioning of the sound.

(5) Signal-to-noise ratio

The signal-to-noise ratio is referred to as the signal-to-noise ratio or the signal-to-noise ratio, and the unit is dB, which refers to the ratio of the useful signal output by the power amplifier to the useless noise. The current signal-to-noise ratio index of the power amplifier can fully cope with general music programs, so we should pay more attention to the background signal-to-noise ratio. You can try to turn the volume of the power amplifier to the maximum and listen to the noise. Of course, the smaller the better. .

If an amplifier has a high signal-to-noise ratio, it means that the background is quiet. Due to the low noise level, many details of weak sounds covered by noise will appear, which will increase floating sound, enhance the sense of air, and increase the dynamic range. There is no strict judgment data to measure whether the signal-to-noise ratio of the amplifier is good or bad. Generally speaking, it is better to be above about 85dB. If the value is lower than this value, it is possible to hear obvious noise in the music gap under certain high-volume listening conditions. noise.

(6) Delay time range

Anyone who has built a home theater knows that when the surround sound speakers are placed in place, it is generally necessary to adjust the surround delay of the AV power amplifier, so that the sound effects of the front and rear speakers are integrated and perfectly integrated, and a satisfactory overall effect is obtained. This delay time range refers to the adjustable speaker "delay" allowing the processor to automatically compensate for room size.

If the rear speakers are closer to the seat than the front speakers, without adding a short sound delay, the rear speakers will be heard before the front speakers, so to set the delay, you need to measure The distance from each speaker to the seat, and enter these values into the "delay" settings section of the amplifier or receiver.

Common receivers and amplifiers today are available in meters or feet for accurate speaker delay calibration. However, some older devices require you to enter a millisecond delay value. To figure out these delays, use the following calculation: First, measure the distance from the left front speaker to the seat.

Then, measure the distance from the rear left speaker to the seat. You will get two numbers. For every 30 cm difference between these two numbers, add 1 millisecond of latency. For example, the front speakers are 300 cm and the rear speakers are 150 cm, which means a difference of 150 cm, so the delay is 5 milliseconds.

(7) Frequency response

The frequency response indicates the consistency and sensitivity of the amplification of each signal of different frequencies when the amplifies signals of different frequencies, also called "frequency range". The wider its range, the better it can "take care" of signals with more frequency components, the better the performance, and it has practical value.

Under normal circumstances, the audio signal that people can hear is about 20Hz-20kHz with different frequencies, different waveforms, and different amplitudes. Therefore, the amplifier must amplify the audio signal well, so the frequency response of the power amplifier should be at least Should reach 20Hz - 20KHz.

However, the overtones contained in the real musical tone may exceed this range. In addition, in order to improve the performance of the transient response, the amplifier is required to have a higher frequency response range. At present, the excellent power amplifiers generally achieve 10Hz-100kHz. range. For high-end imported power amplifiers, the low frequency can start from 0Hz, because it is rare for the power amplifier to work at full rated power. If the amplifier works normally, the frequency response must be very good, almost a straight line, usually far beyond the audible range ( 20-20KHz)