【 Weak current College 】 note sound system equipment matching and influence---Power By 【 China power house network 】

Sound system equipment matching between is very important, if the IP is not good, will significantly affect the entire system's playback quality, serious damage to the device or when the entire system to fail. Typically, a suite of device manufacturers, such as: the phonograph, because the device matching between demand has been considered, so it is with problems, for combination of different manufacturers of phonograph, in particular on the issue of adapting the system to give sufficient attention.
Matching on audio systems, international IEC268-15 "sound system equipment parts Internet optimization value", there are corresponding standards--home sound system equipment interconnection request (GB9031-88) and acoustic systems, equipment for the interconnection of optimization with values, and so on.
I. common with Plug and connector
Commonly used with plugs, socket-outlets are the following.
(1) two-or three-wire Plug and socket
With diameter φ 2.5 m 3.5 m, f and f m m m m three mill, generally used for microphone input, external speakers or headphones output, etc. Two cores for mono or unbalanced connection, three cores are used for stereo or balance connection.
(2) TX-concentric plugs
Also known as Lotus plugs, or electric roll-up plug, for the first line of output for electric changtou named, is widely used at present, in addition to electric roll-up, also available for the CD, VCD, plane and other audio devices, etc. as input and output. In short, it is mainly used for audio levels in the various sound around 1V device input and output connections.
(3) YC-5-wire Plug and socket
Also known as Germany DIN standard plug socket, generally used for cassette recorders and amplifier with, for the recorder's line input and output.
(4) card you "plug and socket
Most used in mixing consoles and peripherals, the amplifier's input and output connections. Usually you "plug and socket number of the card for balance connection, its feet Addmethod is: 1 ()-shielded grounded, 2 (+) as the signal is end, 3 (-) to signal negative side. If you plug the card into the balance not received connection, 3-and 1-end shorted.
General Plug and socket connection is relatively simple. In a mixer for Insert (INSERT) plugs are special, in order to be more effect devices through plug and socket connector to input channel mixer, use y-branch plug connection modes (i.e., a mixer of INS using Φ mill m m two-floor plugs, effects units of input and output using a mill in Φ m m core one place plug. Effect equipment input received a two-core to the ring and the output received a two-core to head and land).
On line, in addition to matching with amplifier and speaker line loudspeaker available between General no shielding of plastic wire, other various signal wiring should use single-core, dual-core or multi-core shielded cables to avoid ingress hum or other high-frequency interference. Five-wire DIN plug to use shielded cables is a dedicated five core shielded cord, if not there are available two double-core wire instead of a shield.
Horn line (speaker connector) belongs to the large signal power line, at the request of occasions whilst generally available multiple unit (preferably 20 units or more) plastic thread; but in the high-fidelity playback, loudspeaker cable on effect of sound quality can not be ignored, so you should use a dedicated speaker line, in order to get the best sound effects. As a result of modern power amplifier output resistance is generally very small, only 0.05 ~ 2 Ω, the speaker wiring resistance on damping coefficient has obviously, General requirements and short Horn line rough to reduce wiring resistance.
Second, the system with consideration
An audio-visual system can play all kinds of device performance, it still is very important. If the IP is not good, will clearly affect the system of reproducing and image quality, serious damage when parts or the whole system will not work. Inorder to achieve the correct matching, it should be noted that: first, it is necessary to ensure that all devices in the impedance level, power, bandwidth, etc. to match; second, it is necessary to note the signal transmission, is a balanced or unbalanced manner; the third is to correctly choose the transmission lines and connectors.
1. impedance matching
In theory, when a load impedance and signal source internal impedance equal load obtained from the signal power a great value, this time called the impedance matching. However, in audio system impedance matching has a broader meaning, if the signal source device output impedance and as load device input impedance value, will enable the device, as well as the whole system work with satisfaction, we think that reached the impedance matching. Here, between the signal source and the load is not the highest power conversion. In audio system, usually signal levels are low, to high-quality transport, load impedance should be much larger than the signal source internal impedance, this is because the internal impedance of signal generator, the signal source is in the power consumption is low, the output value is the same level requires signal source open circuit output voltage is lower. More important is the impedance low signal sources, you can increase the effective transmission distance of signals, to improve the transmission frequency response. In accordance with international and national provisions, the speed of the device's signal source internal impedance (output impedance) and load impedance ratio should be 1: 5, or signal source impedance smaller. For a video image system, as the signal source device output impedance value and as a load device input impedance value ratio is 1: 1 for impedance matching. Therefore, karaoke and dance halls in TV 0K, VCR, laser disc player, radio and video input and output impedance-75 Ω.
2. level match
Equipment interconnection, the level of IP is just as important. If the IP is not good, will make the incentive or an insufficient; resulting in severe overload distortion. According to the IEC and our standards, audio-visual systems usually have rated output level or rated input voltage, maximum output level or maximum input level, minimum output level or minimum input level, according to valid values. To achieve the level of match, just make the signal level rated State match, but when the signal peaks will not occur overload. If level is not directly match, you should take the appropriate transform methods, such as transformers or resistor divider networkThe level reached match, you transform needs taking into account the impedance matching.
3. power matching and damping factor matches
Power amplifier and speaker adaptors, consider their power matching, impedance matching, damping coefficient match, and phase issues, if not match will seriously affect playback quality and efficiency. Here focuses on how power matching and damping coefficients match.
(1) power matching
In principle, the power amplifier rated output power and the speaker of the nominal power. For power amplifier, its output size only and speaker impedance, and speaker of the nominal power. Regardless of the nominal power and speaker amplifier power rating is the same, the work of the amplifier little impact, just on the speakers themselves are security related.
General high-fidelity amplifiers have sufficient output power to spare. If the speaker impedance match requirements, power amplifier rated power ratio speaker's nominal power, promoting adequate; this power amplifier power surplus capacity is large, the smaller the distortion, especially full-frequency components of music performance. Speakers can with Mu power realities than its nominal power 2 to 3 times the instantaneous safety power up to 4 times. Therefore power amplifier rated output power can be compared to the speaker of the nominal power 2 to 3 times, this is a good match. But if too much, a foot, you might burn speakers. If the amplifier's rated power ratio of the nominal power speaker is small, although both are safe for work, but when the amplifier driving power is not enough, will feel sound loudness, often find amplifier has been open to saturation, distortion, and sound loudness is still interested, this is a poor match.
Speaker of the nominal power and cannot be considered as the speaker for the sum of the nominal power, because for most music signals, bass and bass power energy ratio significantly greater than the tenor and treble the proportion of energy. Therefore, if the speaker is a single large aperture wide band loudspeaker, the speaker of the nominal power is the speaker of the nominal power; if it is a mix of speakers, their nominal power can simply think that is the woofer nominal power plus Alto, treble speakers for half of the nominal power.
(2) damping coefficient match
Amplifier output resistance is actually on the speaker's voice played electric damp, damping coefficient is the amplifier rated output impedance (i.e. speakers of nominal impedance Zo, and power amplifier output impedance in the Ro (including wiring resistance) ratio, i.e. the damping factor DF = Zo/Ro. More generally, the hope that some good damping coefficient. When damping coefficient hours, the speaker output sound pressure frequency characteristics (particularly low-frequency characteristics) and harmonic distortion characteristics are worse, DF = 3, high-fidelity amplifiers should be ≥ 10, professional audio requirements DF, sometimes even up to 200 or more, in order to improve the DF values, should reduce the speaker wiring resistance and contact resistance, the amplifier output and don't have to switch between the speakers and the introduction of the cross-sectional area of large, low number of DC resistance of conductor connection.
4. balanced and unbalanced connections
Balance and unbalance, and also the sound system equipment interconnection issues when. Balance connection refers to a pair of signal transmission of two core wire-to-ground impedance equal and not balanced connection refers to both signal transmission line, one grounded. When there is a common mode interference exists, the balance of the two terminals on the interference signal numerical phase, almost polar opposite, interference signal in balance transfer of load can cancel each other out, so the balance circuit has better anti-interference ability. In professional audio systems (in particular use professional mixer system), generally in addition to the speakers, most of the feeder balanced input and output. In home audio systems, in order to reduce costs, often using non-equilibrium State, output. Balance the use of the circuit are transferred transformers (with Center-tapped grounded and without the Center tap), but also useful differential amplifier. When not balance circuit and balance circuit connection damaged the transfer balance, but this sometimes reluctantly, because some equipment uses unbalanced transmission or output mode. But the differential circuit output device does not work with devices connected to the unbalanced input, since this difference circuit output terminal of a short circuit, circuit does not work properly. When the device is not balanced output and device differential input are connected, as long as they do not undermine the differential circuit DC operating point, double-circuit transmission and human difference becomes a single-ended input differential circuit, can work properly.
Third, sound adjustment
In the speaker and sound system right layout, also note the sound system of adjustment or calibration. For stereo sound system, apart from the General volume, loudness, pitch and other regulation, the focus here is to channel calibration, calibration phase correction, balancing, and frequency response correction.
1. channel calibration is to check whether the left and right speakers to add inthe left-right power amplifier output and channel crosstalk between there exists. With the help of the "channel balance knob can perform simple tests. For example the balance knob to the left to the end, left speaker volume should increase significantly, right speaker to be silent; otherwise leave this knob to the right-bottom, right speakers should be audible, left speaker should be silent. To check the results on the contrary, you should set the left and right speaker wiring swap. For there is no balance knob and equipped with left and right channel volume potentiometers of the machine, you can adjust two potentiometers, respectively.
String sound check is best used only to record has left channel signal and right channel signal audition record or tape. Left in the broadcasting system, the birth canal signal should only the left speaker and right speaker sound should be silent, no crosstalk and crosstalk attenuation. System requirements for normal stereo crosstalk attenuation greater than 20dB.
2. phase correction
Stereo playback system requirements for the left and right channels from the sound source (head, changtou, tuner) to speaker phase. Phase correction can use the same single-channel signal (such as replay Mono record or tape) input to the left and right channel, and press the following three methods of testing and calibration:
① station on left and right speakers to listen in on a plumb line, to be sound and image is the midpoint of the two speakers, the description on the left and right channel phase; if feel sound like skip to speaker surround orGo to the back side, the phase contrast. This will be a speaker wiring polarity reversed.
② the listener in the two speakers from left to right on a slow walk, if you feel the sound is smooth change, both in phase; if you feel that the sound from a speaker suddenly jump to another speaker, both RP.
③ the two speakers move closer together, and if left and right channel invert the listener heardthe music of bass considerably weakened, the overall loudness is also much lower.
3. balance correction
Balance correction is correction of the left and right out of balance, it includes amplifier gain differential sensitivity disparity, speakers and room symmetry of differences, etc. Correction method is to: replay a mono music, from the two speakers in a vertical line on the listener should be sound and image in the midpoint of the two speakers. If deviation from the side, two-channel imbalances should adjust the balance knob, will sound like a move to the point.
4. frequency response correction
Here the frequency response is including the room acoustic properties, on the left and right channel of the overall frequency response. Frequency response correction via the left and right channel graphic equalizer in (also known as the multiple frequency compensator). Correction, the available audio signal generator to the left and right channel input 33Hz, 100Hz, 330Hz, 1kHz, 3.3kHz, 10kHz, single audio signal, adjust the graphic equalizer in the potentiometer to make each single audio to sound like in the midpoint of the two speakers, you can view on the left and right channels of frequency response to essentially the same.