â— What is a coaxial speaker?
In general speakers, the tweeter and woofer are arranged flat on the panel of the speaker, so it is impossible for their vocal centers to coincide as a single point. In this way, the distance between the treble and bass to the listener is different. The phase deviation thus affects the correct reproduction of the sound image. The coaxial speaker uses a coaxial unit. This unit is actually a combination of a tweeter and a bass unit. The tweeter is cleverly placed at the center of the bass diaphragm, so it can ensure that the acoustic center of the high and low bass is the same point. , Thereby solving the problem of phase deviation. The two most famous types of commercial coaxial speakers are British products, one is Tannoy (Tianlang) using "Tulip" coaxial units, and the other is KEF using Uni-Q coaxial units.
â— What is the arrangement of dumbbell-shaped units?
That is, the tweeter is tightly clamped between two identical mid / woofer units, and the form is a bit like two big and small dumbbells. The dumbbell arrangement can obtain a sound effect similar to a point sound source, which is good for stereo image positioning, so this design is more popular recently.
â— What is double line crossover?
Conventional speakers only have a set of input terminals, and the full-band signal from the power amplifier is sent to the speaker with a set of speaker wires, and the high and low frequencies are separated by the crossover inside the speaker. Bi-wiring uses two sets of speaker cables to connect the amplifier and speakers, so that the high and low sounds are separated from each other, and everyone does not involve each other. Two-wire crossover needs to separate the input terminals of the treble channel and bass channel of the crossover, so the speaker must provide two sets of binding posts. Of course, the speaker with two-wire crossover can also use the conventional single-wire connection method, as long as the two sets of terminals are connected in parallel with the metal short-circuit piece supplied with the box.
Similar to two-line crossover, if three groups of speaker lines are used to transmit treble, midrange and bass respectively, such a connection is called tri-wiring. However, three-line crossover is not as common as two-line crossover.
â— Is two-way crossover better than conventional connection?
The main reason for two-line crossover is that some speaker lines are suitable for transmitting low frequencies, and some are suitable for transmitting high frequencies. If they are transmitted separately, the corresponding wires can be selected according to different needs to achieve the most ideal effect. However, this view is only one word. Some people think that two-line crossovers do more harm than good. For example, the well-known speaker manufacturers Dynaudio and Thiel insist on not using two-line crossovers. For the consistency of the bass phase, if the same line is used, why bother?
â— Why is the bass of the larger speakers usually better?
The low frequency limit of the speaker is closely related to two factors, one is the resonance frequency of the speaker unit, and the other is the volume of the cabinet. Without the box, the low-frequency resonance frequency of the woofer is usually regarded as the lower limit of the effective frequency response of the unit. The larger the caliber of the unit, the lower the resonance frequency is, so the large horn is beneficial to restore lower low frequencies. In addition, the larger diaphragm area can push more air under the premise of the same amplitude, and it is easy to obtain more low-frequency volume sense. After the speaker unit is packed, its resonance frequency will rise due to the stiffness of the air in the box. The larger the volume of the box, the smaller the effect of air on the unit, and the smaller the rise in resonance frequency, which is beneficial to obtain Comprehensive low frequency response. On the one hand, a large speaker is convenient for using a large-diameter woofer, and on the other hand, it has a larger cabinet volume, so low frequencies are usually better.
â— What are the main performance indicators of speakers?
There are many technical indicators for objectively measuring the performance of the speaker. We often see in the product catalog or the manual of the speaker: frequency response, impedance, sensitivity, maximum carrying power and maximum output sound pressure level.
The frequency response represents the relationship between the sound pressure level of the speaker output and the frequency. If you draw a graph, it is a function curve with the frequency as the abscissa and the output sound pressure (or the decibel number of the sound pressure) as the ordinate. The overall trend of this curve in the mid-band is horizontal. Of course, there may be many small fluctuations caused by the imperfect system in the middle. At the low-frequency end and high-frequency end, the curve shows a downward trend, and the output of the speaker will decrease. Usually, the two points where the output of the low-frequency end and the high-frequency end fall by 3dB relative to the middle horizontal section become the low-frequency cut-off point and the high-frequency cut-off point The frequency band between these two points is the frequency response range of the speaker. Obviously, the wider the frequency response range, the better, so that the wider range of the music signal can be restored. For the current speakers, the high frequency end is not a problem, and the audio limit has reached 20kHz, and some products are far beyond. The difficulty lies in the low frequency end. The general bookshelf box reaches about 50-60Hz, and the floor box reaches about 30-40Hz. Very good. In addition, the flatter the curve in the frequency response range, the smaller the fluctuation, the better, which means that the speaker can reproduce all frequency signals in the frequency band without discrimination, without distortion of balance.
Generally speaking, the impedance is the resistance to the input current signal in ohms (Ω). The most common impedance values ​​for speakers are 8Ω, 4Ω, and 6Ω. Of course, there are other values ​​such as 3Ω, 5Ω, and 10Ω, but they are not common. Special note: the impedance of the speaker is only a nominal value, and the actual impedance of the speaker changes with frequency. For example, for a speaker with a nominal 8Ω, the impedance is only 8Ω at certain frequency points, and may be 10Ω at other frequencies. , 20Ω, and other frequencies may be as low as 6Ω or 4Ω. The characteristic of impedance changing with frequency can be clearly seen on the impedance curve of the speaker. This change increases the difficulty of driving the amplifier.
Sensitivity is an indicator to measure the speaker's electro-acoustic conversion efficiency. The unit is dB / W / m, which means the sound pressure level that can be obtained at a distance of 1m from the speaker axis when inputting 1W of power, such as sensitivity 90dB / W / m The speaker, which means that the input power is 1W, can get a sound pressure level of 90dB at a distance of 1m in front of the speaker. A loudspeaker with high sensitivity saves the power of the amplifier and should be considered an advantage. However, sometimes the sensitivity and other performance indicators are not easy to balance. Under the balance, it is often better to sacrifice a little sensitivity in exchange for better other performance. This is because the current high-power amplifiers are very common, the price is not too high, and the sensitivity is lower. It's a big problem.
The maximum load power is the safety indicator of the speaker, which means the input power that the speaker can withstand for a long time. Inputs below this value are obviously safe. If the limit is exceeded for a long time, the voice coil will be easily overheated and burned. The maximum load power index provides a reference for us to use the speaker safely, but we should also pay attention to the premise of "long time". It is allowed to exceed the maximum load power in a short time. For example, there are many short-term peaks in the music signal, and its power intensity It is several times or even tens of times higher than the average power, but the duration is very short, that is, fleeting. As long as the average power does not exceed the maximum load value of the speaker, there is no problem.
The maximum output sound pressure level represents the maximum output capacity of the speaker under the condition that the distortion does not exceed a certain standard. The popular saying is that this speaker can put more louds. Generally, the maximum output sound pressure level of home speakers is about 100dB ~ 110dB, and a few high output speakers can reach about 120dB. Obviously, the higher the maximum output sound pressure level, the better. If this index is too low, dynamic compression is likely to occur.
â— What are the criteria for evaluating speakers?
A truly excellent speaker should have both excellent objective performance indicators and good subjective listening evaluation. Excellent performance indicators include wide and flat frequency response, little distortion, fast transient response, high sound pressure output capability, high power carrying capacity, suitable impedance characteristics and reasonable sensitivity. What is a good subjective listening evaluation is an "art", and everyone's standards are different. In theory, since the speaker is a link of the sound-returning system (and the final link that has the most obvious impact on the quality of the sound-returning), then it should be restored with absolute faithfulness. The speaker itself does not carry any personality and cannot carry out any original music signal Distortion or modification and beautification, if it meets or approaches such a standard, is a good speaker. This is the so-called "realist" view. However, some people think that since the speaker is used to reproduce music, the sound quality is the standard for testing the quality of the speaker. This is the so-called "aestheticist" viewpoint. "Aestheticism" allows the speaker to modify the music signal reasonably, and does not care much about whether the technical indicators are perfect, as long as the sound released is "good". "Aestheticism" is more suitable for those of us who listen to music as entertainment, but there is no unified standard for what is "good", and blindly pursuing good taste or personality regardless of performance is easy to fall into misunderstanding. Therefore, objectively speaking, even good speakers recognized by "Aestheticism" should be built on the premise of ensuring basic performance indicators.
◠Can a 4Ω speaker be connected to an 8Ω amplifier?
This is a very common problem, but also a typical problem with conceptual errors. The term "8-ohm power amplifier" is not correct in itself. The questioner may see some power amplifiers marked with "100W / 8Ω" or the like, and they think that the output impedance of this power amplifier is 8Ω, which is actually a misunderstanding and correct. The explanation is: With 8Ω load as the test condition, the output power of this amplifier is 100W.
Both power amplifiers and tube amplifiers are constant voltage output power amplifiers, and their output impedance is very small. Transistor amplifiers are generally below 0.1Ω, and tube amplifiers are higher, but generally below 1Ω instead of 8Ω. Transistor amplifiers have a strong load capacity. In principle, any speaker with any impedance can be connected. Of course, it should also be noted that the impedance cannot be so low that the amplifier can not overwhelm or even overload. For example, connect a pair of 2Ω speakers (if any), large Most medium and small power amplifiers will not be enough. For the tube power amplifier, there is a problem of "optimal load", that is, the performance of the circuit is the best when the load impedance is a certain value. This optimal load impedance is usually several thousand ohms to tens of thousands of ohms, and the impedance of the speaker is only a few Ohm, the difference is too large, so the output transformer should be used for impedance transformation. The output transformer of the tube machine is generally equipped with different taps. No matter what the impedance of the speaker is, as long as the set of taps with the same value (or close to) on the output transformer is selected, it can be "mapped" to the optimal load required by the power amplifier. In summary, when the power amplifier is matched with speakers, there is no need to worry about the impedance of the speakers. The transistor machine can be connected to any impedance speakers, and the tube machine can adapt to the speakers of various impedances by selecting the tap of the output transformer.
â— Why do some speakers eat too much power, what is the reason?
Two reasons: First, the sensitivity of the speaker may be relatively low. For speakers with a sensitivity difference of only 3dB, to obtain the same volume (or sound pressure level), the input power difference will be doubled, such as a 90dB / W / m box, if you want to get 100dB sound pressure level at 1m away , As long as the input of 10W power is enough, and for 87dB / W / m speakers, you need 20W power. If the sensitivity difference of the speakers is 10dB, then the input power under the same output sound pressure condition will reach a difference of 10 times. For example, if the front speaker of 87dB / W / m is replaced with a speaker of 80dB / W / m sensitivity, the sound pressure of 100dB is still obtained at 1m, and the required input power is as high as 100W, which is higher than the box of 90dB / W / m. 10 times.
Second, perhaps the sensitivity is not low, but the impedance characteristics are abnormal. For example, some speakers have a sensitivity of 87-90dB / W / m or more, but they are not low, but looking at their impedance curve, the impedance at some frequency points may be as low as 2Ω or even 1Ω. Such a low impedance is for ordinary amplifiers It's close to a short circuit, how can I push it? It is certain that severe overload distortion will occur at these frequencies. To tame such a speaker, only super powerful amplifiers that can maintain linear growth in power when the load impedance of Krell and Mark Levinson are reduced to 1 Ω. If you encounter a box with low sensitivity and strange impedance characteristics at the same time, the requirements for the amplifier are even more demanding.
â— Someone pushes a pair of large speakers with a tube amplifier with a power of only a few watts. Does this make sense?
Some people think that the large-diameter speakers used for large speakers are heavy and the amplifiers with small power cannot be pushed. In fact, it is a matter of course. The speaker's power requirements for the amplifier are mainly related to the sensitivity of the speaker, but not the size of the unit. Many large speakers, especially the boxes with large-diameter paper cone woofer, such as the products of JBL, Klipsch and other companies in the United States, have very high sensitivity, usually more than 90dB, and some even reach more than 95dB. For such speakers, use A single-end power amplifier with a few watts of output power can push them to the blast. Some audiophiles may know that in Japan, using 8W single-ended 300B amplifiers to push high-sensitivity JBL speakers is a very popular game.
â— My speaker is 100W, can it be pushed with a 50W amplifier? If I push it with a 200W power amplifier, will it burn the speaker?
The first thing to be clear is that the 100W power marked on the speaker manual or nameplate refers to the carrying power of the speaker, meaning that as long as the power exceeds 100W for a long time, the speaker will not be damaged, not that it requires the use of a 100W amplifier. As for how many watts of power amplifiers can be driven, it mainly depends on the sensitivity of the speakers and the required output sound pressure level, which has nothing to do with the carrying power of the speakers. Generally speaking, there are always a few speakers with particularly low sensitivity, and the sound pressure level required in ordinary home environments will not be very large. The 50W power amplifier can already meet many speakers. Of course, some speakers have special impedance characteristics, which is a severe test for amplifiers. At this time, powerful amplifiers with high power and high current output are needed to tame them.
Let ’s look at the second question: Will the 200W amplifier burn the speakers? It depends on how you use this amplifier. Indeed, 200W has exceeded the speaker's maximum load power. If the volume is turned to the maximum, and the amplifier is always at full power output, then this will definitely burn the speaker. But this kind of situation will almost never happen. No one will use the power amplifier's volume suddenly to the end. In fact, when the volume is close to overload distortion (breaking noise), no one will definitely continue to increase the volume ( It is equivalent to increasing the power input to the speaker) to make the speaker completely make a loud noise, but will reduce the volume to make the speaker emit a normal sound, so that the average power input to the speaker is always controlled within the safe range that it can withstand, even if No matter how large the power of the power amplifier is, it only outputs the part that the speaker can withstand. How can it burn the speaker? On the contrary, using a high-power amplifier to increase the power reserve can avoid overload distortion of the instantaneous large dynamic peak music signal, which is also beneficial to ensure the quality of the playback.
â— What does the "20-200W" on the speaker nameplate mean, and what is its power?
This is not an indicator of the speaker's carrying power, but the recommended amplifier power range, that is, the manufacturer recommends using an amplifier with a power in the range of 20-200W to drive.
â— When the speaker is in use, should the net be taken off or put on?
The surface mesh looks like a thin layer of yarn, which actually has an impact on sound radiation. If you use the instrument to measure the frequency response of the surface mesh and the surface mesh separately, you will find that there is a big difference between the two. . Most speakers are tested and calibrated at the factory without a mesh, so the mesh should also be removed during use. Of course, a few speakers are said to have been tested and tuned under the condition of wearing a net, so it is not appropriate to remove them when listening. This is said to be the case with Avalon speakers in the United States.
â— What special requirements does the home theater system have on the speakers?
Home theater systems generally use surround sound playback systems, so the number of channels is large. The currently popular Dolby Digital and DTS systems use five wide-band speakers to form the front and rear channels, and there is also a subwoofer. The requirements for these speakers are the same as those for a high-fidelity two-channel system. They are still common requirements such as wide frequency response, low distortion, less sound staining, and good transient response. In principle, as long as the speakers perform well in music , It is no problem to use in home theater, but those speakers with weak dynamic output capability (such as LS3 / 5A) are not suitable, otherwise they will be easily overloaded and distorted when encountering large dynamic hot scenes. Since the center speaker is generally used on a TV, it should have anti-magnetic performance. In addition, the sound of the speakers of each channel should be coordinated, and it is best to use the same series of products from the same manufacturer.
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