[Home Theater Network HDAV.com.cn] Is there any emphasis on the audio speaker cable? Those who talk about the speaker cable are really understanding or smashing money. Who is the wizard? Who is the Muggle? Still all!
What is the electronic physical component of the speaker cable, is it a wire, a copper block, an impedance matching transmission line, a capacitor, an inductor, or a resistor?
I am studying electronics, and my music literacy is very poor. I pretend to understand music, opera, symphony, piano performance, tenor and soprano. But in fact, I am just playing the sound settings, appreciate the appearance and circuit planning. Since I was young in designing intermediate-level audio, I thought I could participate in high-level audio discussions.
I think it is necessary to know whether the thickness and material of the speaker cable will affect the sound quality. First, we must understand what is a speaker, what is a speaker cable, what is a loudspeaker, and what is the damping coefficient.
The effect of the speaker cable on the sound quality is...
1. There are real measurable methods, there are curves with numbers
2. Real, but the instrument that can be measured has not yet come out
3. It is the experience of the golden ear, only for the belief can not be challenged.
4. Its quality is good and the materials are exquisite and have collection value.
5. Just tricks to swindle money
I really touched the second item. More than 30 years ago, in order to capture the African market, we designed a circuit called soft clip, which enabled the same amplifier to increase power density by 50%, but the distortion is still within specifications. At that time, the Muggle ears and the top distortion analyzer could not detect the extra distortion in the music.
But then there was a golden ear that insisted that he could hear it, and other gold ears were confirmed, so IHD added a new item to the advanced sound test for it, called "transient distortion value."
In the era of no microcomputer, a million-level instrument is required to measure the "transient distortion value". Even in the 21st century, instruments capable of measuring transient distortion are expensive.
What is a speaker?
When I was just learning electronics, I asked the teacher why the 8 ohms of the horns were only 0.1 ohms. The teacher of the Air Force School did not say a word for a long time.
I learned from the information published by the original factory that 8 ohms were measured with a 1000 Hz AC sine wave. As for the speaker unit or the standard speaker, there is no air cushion, sound-absorbing cotton, is to use small signal test, or high-intensity test, how far is the speaker from the wall? How to set the measurement conditions, I rarely send the line The details are mentioned, and no one really wants to test it because they are all industries Know-How.
The general book is casually said? It is the AC inductance of the coil at 1000Hz.
Is it true? Wrong!
In fact, when there are no speakers, large speakers, and small speakers, the impedance measurement value is completely different. If the paper cone is pressed strongly by hand, the impedance is even more chaotic. Therefore, the impedance of the horn must not be simply the inductance of the coil at 1 kHz. If it is not pure inductance, what is it?
Just as a dipole antenna uses a three-meter meter, the resistance is infinite, but the electromagnetic wave expert says that its RF radiation impedance is 72 ohms.
The 8 ohm of the horn can also be regarded as a pure resistance, not a voice coil.
Z=R+XL=8 ohm
XL = ωL = 2πfL
=2x 3.14 x1000 x ? mH=8 ohm
Rather, the resistance of the audio as it radiates into the air is the radiation impedance of the paper as it passes the energy.
But a speaker that handles 1:1000 times the bandwidth of 20Hz to 20KHz is a very difficult task. Is divided into three speakers,
Bass 20-200Hz,
Midrange 200-2000Hz,
Treble 2000-20000Hz
Each speaker also has to handle a 1:10 bandwidth range.
Compared to the usual radio frequency waveguide can handle 1:2, at most 1:3, the operation of the speaker is very difficult.
Since the voice coil is a coil, many electronics experts naturally think that its impedance is 8 ohms from the inductance Z = XL = 2Ï€fL f is the frequency, L is the inductance value.
However, the measured impedance of the horn at different frequencies will reveal that the impedance curve is not exactly like an inductor, and ä¹–ä¹– varies linearly with frequency. At a very low frequency, such as 50Hz, it will suddenly increase to tens of ohms, and it is a capacitive reactance, which simply negates the inductance theory.
Speakers are affected by paper cones, speakers, air pressure, density, and humidity. In other words, 8 ohm is the sound "radiation impedance" at 1KHz instead of a simple inductive anti-XL.
Damping coefficient of the amplifier
The final output mechanism of the amplifier is like a variable voltage battery. The current is controlled by the transistor. The power is output through the speaker line, so that the current flows on the voice coil of the speaker to generate a magnetic field. The magnetic field and the magnet absorb each other and push the horn paper. The basin, vibrating the air produces sound. In addition to this, the final stage crystal should also provide damping to absorb the power generated by the horn voice coil, otherwise the paper cone will vibrate. This control ability is called damping.
Because the paper cone voice coil has mass and elasticity, the air inside the speaker has air pressure. Once the thrust is over, the paper cone will want to bounce back. At this time, the voice coil of the speaker will pass the magnetic field line of the magnet. According to the æ„£ time theorem, the coil It will generate electricity like a generator, and this power must be absorbed and controlled by the output impedance of the amplifier. At this point, the final crystal of the amplifier must be turned on to guide the current and consume it into heat. It's like a car's brakes, which prevents the car from rushing down the slope when going downhill.
Therefore, the principle of damping is like the person who pushes the cart on the bridge. When the bridge is down, it is necessary to pull the car to prevent the car from bursting down. The physicist calls it the potential energy.
It is also like the car hitting the hole, the spring would have caused the car body to shake up and down more than 10 times before stopping, but if the oil damper is used to absorb the energy, it can be stopped by shaking. This phenomenon is expressed by physicists using differential equations.
Basically, the damping is how much low-resistance path the final crystal can provide, allowing the counter-electromotive force of the horn to be absorbed.
Therefore, the damping coefficient is defined as the ratio of the impedance of the horn to the output impedance of the amplifier.
For example, the horn impedance is 8 ohms, the output impedance of the amplifier is 0.04 ohm, the damping coefficient is 200, (8/0.04=200) that is, 0.04 ohm has a powerful force to absorb the current, and precisely controls the position of the horn cone. .
General amplifier specifications
0.01% distortion value, 200 high damping coefficient, is the basic function of advanced transistor sound. The vacuum tube machine is usually distorted by 5%, the damping coefficient is only 10, the quality is very poor, it is super poor, but the vacuum tube machine is poorly damped and the control force is insufficient, so the even harmonic distortion generated is pleasing to the ear, sounds Very gentle, no sense of violation. So no one dared to say that the damping of the vacuum tube machine is not good, the control is not good, just like no one dares to say that the king did not wear new clothes.
The evolution of billions of years tells the creature that the rich even harmonics will form a sawtooth wave, representing harmony, safety, food, and deliciousness.
The rich odd harmonics form a square wave, representing a fierce collision, a sudden stop, and a sharp turn. It may be a wave flapping a reef that represents a danger or has a predator approaching.
So humans will feel very comfortable when they hear even harmonic distortion. Listening to music is to be comfortable, isn't it?
The advertisement of Harley's motorcycle said that the exhaust pipe was designed by the tuner. The Muggle commentator said it was very mysterious, but there is no real truth. In fact, it is said that it is adjusted to produce a lot of sweetness. 2, 4, 6, 8 and other even harmonic distortion.
Although the beautiful engine sound is achieved by sacrificing horsepower, the Muggle does not feel the horsepower. Although the racing expert knows it, it will be considerate, because the ear is more important. The speed is only known by myself, but the sound of exhausting sounds, neighbors, passersby will hear. More important. It's like buying a million sounds. If you don't find a friend, you will always miss something. Just like playing golf, the long shot is not important, and the green putting is good to win.
Interestingly, when the exhaust pipe produces the largest second harmonic, it is usually just the best point of engine torque. Damping is like the driving force of a car. The law requires that the brakes must be ten times the horsepower of the engine. The same is true for megaphones, with a damping of at least 10, but most people only use it when it is a sacred number, counting money, and wondering why high damping is needed.
People who know "damping" are qualified to talk about the speaker line, otherwise everything is a talk, a slap, and an adjective.
Those golden ears say what is crisp, high, ball, warm and full. I can't listen. What I want is the physical quantity that can be measured.
Speaker Cable
The DC resistance of the speaker cable is preferably zero to avoid damaging the damping coefficient. If the speaker cable has a resistance of 0.1 ohm, and the output impedance of the amplifier is 0.04 ohm, then the output impedance of the amplifier seen from the horn will become 0.14 ohm, and the damping coefficient is only 57. A good advanced amplifier damping coefficient of 200 was reduced to 57.
0.1+0.04=1.04 ohm
8 ohm / 1.04 ohm = 57
Therefore, the concept that the copper wire in the speaker cable is thicker and better is basically correct, but if the crude DC resistance is only 0.0001 ohm, the meaning is not great. Because the serial value at this time is
0.04+0.001=0.0401 OM
Damping 8 ohm / 0.0401 ohm = 199.5
Therefore, the speaker cable below 3 meters thick to AWG 12 or more gradually becomes meaningless. Using a thicker line is just a waste of copper and adds weight.
resistance
What is the DC resistance of the general speaker cable? Check the electrician data to know.
5.5 square wire is about 0.003 ohms per meter
8 square meters of wire about 0.002 ohms per meter
14 square meters of wire about 0.0006 ohms per meter
So three meters long speaker cable back and forth a total of 6 meters
The 5.5 square line resistance is approximately 0.018 ohms.
The 8.0 square line resistance is about 0.012 ohms.
The 14 square line resistance is about 0.0036 ohms.
Speaker cable plus amplifier impedance
5.5 squared 0.04+0.018=0.058 ohm
8.0 squared 0.04+0.012=0.052 ohm
14 squared 0.04+0.0036=0.0436 ohm
Damping coefficient
5.5 square 8/0.058 = 137
8.0 square 8/0.052=153
14 square 8/0.0436=183
So at first glance, it seems to make sense to use a 14-square speaker cable, or even a thick copper wire. But in fact, modern low-efficiency horns, the damping coefficient of 10 is enough, because the driving force is 10 times larger than the engine horsepower, it is already very sufficient, no matter how much it is, it is just the slogan of the businessman. Otherwise, how to vacuum the tube machine with only 5-10 damping.
Inductance and capacitance
Inductance and capacitance of the speaker cable
The inductor blocks the high-pitched sound and the capacitor short-circuit absorbs the high-pitched sound.
The 3 meter speaker cable will have 100uH inductance and 300PF line capacitance. These reactance values ​​are negligible at frequencies of 20-1000Hz. But at 10KHz -50KHz they will gradually become more important. It is not because the fear of damping is bad, but that the high frequency will be phase shifted, confusing the sense of positioning.
How to reduce inductance
If you want to reduce the interference inductance of the speaker cable, the speaker cable should be as thick as possible. The thickening is not to increase the cross-sectional area of ​​the copper wire. As long as the original copper wire is taken apart, it can be loosened and fatened. There must be insulation support between the copper wires. Open, make multiple strands, multiple strands are not to prevent RF skin current, but to reduce the inductance value. Why do the same number of wires loosen the resistance?
Please ask the teacher who teaches electromagnetics at the university. After the differential equation analysis, the answer is this. As long as Mugga believes that Master can worship Master, don't waste time understanding it.
If you don't want to be cheated to buy a beautiful and expensive original speaker cable, you can make it at a price of 1/100. The method is very simple. But after I learned, I have to pay my tuition. And gambling can not be used to deceive people.
DIY super speaker cable
You only need to go to Guanghua Mall to buy a cheap scam-type speaker cable, that is, the copper wire is actually very thin, and the optical illusion is generated by the transparent outer skin, which makes people think that the copper wire is very thick. Then tie 7 pieces of cotton tape every 20 cm to make it 3 times thicker. The inductance of the speaker cable will drop significantly below 10uH. The resistance value will also be reduced by 7 times, killing two birds with one stone, and this is done. If you are not addicted, you can use 50 bundles to ensure that the high-pitched "clear" and "clear" bandwidth guarantees up to 99KHz. Even the conversations were heard.
But there will be a loss in doing so. The capacitance between the speaker wires will increase significantly several times.
Parasitic capacitance between speaker lines
When two metals are close to each other, there will be capacitors. The thicker the capacity of the thicker wires, the higher the capacitance will be, and the phase shift will occur. The common parallel speaker cable has a capacitance of about 100pF when it is three meters long. To reduce the capacitance is very Simple, just cut the speaker cable and use the chopsticks to open 20 cm, the capacitance will drop below 1pF.
So if you see 10 million yuan of audio in the future, use a very advanced speaker cable, but it seems very thin and not fat, and go back to the two lines close together. You can ask the seller, this speaker cable, the DC resistance, inductance and capacitance per meter. If the boss can't say the number, only tell you that its sound quality is full, solid, clear, transparent... and other adjectives.
You can smile, buy a gold-plated connector, and then slowly move your foot to leave, think about what I said on the road, and think back to what he said. Bring all the children home safely. Don't let any country lose its way.
Transmission line characteristic impedance
In theory, the speaker line is the same as the feeder of the RF antenna, and the characteristic impedance of the transmission line is preferably the same as the impedance of the speaker. There will be no reflected waves.
The problem is that the horn is different from the antenna, it has no fixed impedance, such as
Tweeter at
If it is 8 ohms at 1KHz
Usually 15 ohms at 2 kHz
Often 30 ohms at 4KHz
At 8KHz it is often 60 ohms
At 16KHz it is often 120 ohms
Woofer
If it is 8 ohms at 1KHz
Usually 500 ohms at 4 ohms
At 50Hz, it is often 30 ohms.
At 20KHz it is often 10 ohms
So the speaker cable is designed to be
30 ohms at 50Hz, still
8 ohms at 1000Hz, or
60 ohms at 8 kHz.
Actually it is not right.
It can be seen that the speaker line cannot be discussed with the characteristic impedance as the RF transmission line.
Therefore, the speaker cable is not a "characteristic impedance transmission line", but merely expands the extension of the body. The resistance, inductance, and capacitance of the conductor can only be as small as possible. Impossible impedance matching.
Hearing and financial investigation
Age hearing audio budget
5 23KHz 300 yuan
15 20KHz 1000 yuan
25 18KHz 10,000
35 15KHz 100,000
45 13KHz 300,000
55 10KHz 500,000
65 8KHz 1 million
75 7KHz 5 million
Akai
2016-11-18
2017-11-18 minor revision
2018-01-08 Greatly rewritten, modify the example numbers for reading comprehension
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The essay is not based on chaos
The above texts are convenient for writing, and the numbers are all captured by memory. Maybe the correctness may be very wrong. Please check it yourself when you look at the official.
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