After more than ten years of contact, I found that consumers often ask: when buying a speaker, what is its efficiency? What is the impedance? But few people ask: What is the highest sound pressure? Even after reading equipment reviews of some magazines, many people believe that low-efficiency speakers represent high-quality speakers.
There are indeed several famous speakers in the history of audio under the name of low efficiency, such as Rogers' LS-3 / 5a and AR-3a. I saw it with my own eyes when I was a small editor of the magazine more than ten years ago. Mr. Lin Yisheng, a well-known domestic audio teacher, when talking about 3 / 5a, there was a flash of light on his face saying: Its efficiency is low! However, at the home of Mr. Chen Zhengxiu (immigrated to San Francisco) in Banqiao, there were three pairs of small speakers. The 3 / 5a was less than two minutes into the battle, and was bombarded by another speaker, Mr. Gao Zhenmin. !
Earlier, when only LP didn't have a CD, I went to Shangyang Records to buy a record. When choosing a record, I think the background music is weird. How did the tenor Domingo catch a cold? The nasal sounds are so heavy! After asking clearly, I realized that everything is a ghost of the "sullen gourd" 3 / 5a ─ At that time, Rogers speakers were imported and sold by Shangyang.
This is how I feel bad about 3 / 5a. I did not expect that the world-famous BBC-3 / 5a turned out to be a "boring" gourd. After waiting for the trial production of DaLine, I realized that the BBC did not maximize the performance of the KEF monomer. The advantage of the LS-3 / 5a was only its small size and low price. No wonder someone would sell 3 / 5a for my DaLine transmission line speaker. The reason is very simple, according to the specification of 3 / 5a bass unit B-110, it can't be installed in such a small speaker!
This point needs to be explained. In fact, the British BBC does not design speakers, but for the convenience of carrying, it has to design the speakers to be very small. This is no way to compromise.
Low-efficiency speakers have indeed been popular, but after CD began to gain popularity, some people were skeptical about low-efficiency speakers. Famous music critic and head of Yingsheng Company Mr. Cao Yongkun once said that the high dynamics of CD will be eliminated Low efficiency speakers.
Transistor machine tile = Vacuum tube machine tile
After 20 years, the CD system has gradually matured, but low-efficiency speakers still exist in the market, and the concept of low efficiency = high sound quality does not seem to be shaken; only a few changes have been made in recent years.
The vacuum tube turned back, and old factories and new plants have come out of the cage one after another, but the output power of the rear stage of the tube machine is generally lower than that of the crystal machine. The sound quality is supreme, non-WE300B is not used, and as long as it is single-ended, do not push or pull. The single-ended output of 300B is only about 7 to 8W. What kind of speakers can 7W push? Of course, some people use less than 10W of the tube to push the ATC horn at the rear stage. It has sound, but it cannot show the dynamics of ATC.
The ancient Altec, JBL, EV large floor-standing speakers are all highly efficient, because their close friends are tube machines. So when the pipe machine pushed the Altec A7 "Voice of the Theater", the momentum was very different. Can anyone say that the latter stage of the pipe machine is not dynamic?
Watt is Watt, and watts are watts, so the 7W of the tube machine is almost completely equal to the 7W of the crystal machine-the difference is that the tube machine has an output transformer, and the output power is less likely to change with the change in load impedance. Therefore, if someone says that the 7W of the tube machine is more powerful than the 7W of the crystal machine, that is nonsense, because the truth is that the 7W of the crystal machine is usually more powerful than the 7W of the tube machine, and it will never lie to you. There are two special cases, one is the post-stage of OTL no output transformer tube machine, and the other is the famous LS-3 / 5a small horn.
The efficiency of the speaker is expressed in dB, but it is related to the impedance, so the efficiency is exactly the same, but the two pairs of speakers with different impedances have different voltage requirements. Because 1W of 8Ω speaker is input 2.83V voltage, and 1W of 4Ω speaker is 2V input voltage. Therefore, two pairs of speakers with the same efficiency and different impedances must have different sound performances when connected to the same crystal.
Amplifier output power ︳ 8Ω ︳ 4Ω
────────────────────
1W ------------------- 2.83V ------- 2V
2W ------------------- 4V ----------- 2.83V
3W ------------------- 4.9V --------- 3.47V
4W -------------------- 5.66V ------- 4V
10W ------------------ 8.95V ------- 6.33V
Although the demand voltage of a 4Ω speaker is lower than 8Ω, the demand current is relatively high. Taking the 4W output as an example, the 8Ω speaker is 0.7A, and the 4Ω speaker takes 1A current, so everyone says that low impedance speakers are more difficult to push.
dB is decibel, and its calculation formula will be different due to the power or the multiple of voltage and current. The efficiency of the speaker is calculated by power. Let's take a horn with a large change in impedance as an example to illustrate that in most cases, the 7W of the crystal machine is more powerful than the 7W of the vacuum tube machine-the focus is on the current at low impedance.
Impedance ｜ Crystal power ｜ Tube power
───────────────────
8Ω -------------- 7W --------------- 7W
4Ω -------------- 14W -------------- 7W
2Ω -------------- 28W -------------- 7W
As long as the drive current is sufficient, the output power of the crystal will increase with the reduction of the speaker impedance, so it is not only 7W. But the tube machine has output transformer cross-connected, the power does not change with the impedance of the speaker. So at this time, is the 7W of the crystal machine more powerful than the 7W of the vacuum tube? This is very simple Aum's law.
3 / 5a is a low efficiency and high impedance speaker with constant resistance characteristics. Therefore, when the speaker impedance drops sharply, the tube machine may not be able to exert force, so it is not easy to push the Dynaudio speaker at the rear stage of the tube machine. Good sound, so the horn wants to eat current, but the vacuum tube is a voltage component and cannot provide current; but it is not the same if it is replaced by LS-3 / 5a.
3 / 5a impedance | Crystal power | Tube power
─────────────────────
15Ω -------------- 3.7W --------------- 7W
11Ω -------------- 5W ----------------- 7W
8Ω --------------- 7W ------------------ 7W
When the 7W crystal machine is connected to the first-generation 3 / 5a, there is only 3.7W, and then the second-generation 3 / 5a is only 5W; however, the tube machine has maintained 7W output. Therefore, when meeting the pair of high-impedance speakers 3 / 5a, the 7W of the tube machine is more powerful than the 7W of the crystal machine. So as far as crystals are concerned, high-impedance speakers are harder to push. But why is the impedance of 3 / 5a as high as 11 ~ 15Ω? The KEF T-27A tweeter and B-110A bass unit it uses are both 8Ω. This is the tricky part. Design the crossover and speakers according to the KEF monomer specifications. Don't be surprised. You will find that the LS-3 / 5a is simply the wrong design!
If it is high impedance combined with low efficiency, then this pair of speakers is hard to serve, but 3 / 5a has this characteristic. So someone pushes it with big power, but 3 / 5a can't eat big power. If the power is too high, it is easy to push its bass to the bottom-its KEF bass unit is not dynamic.
Now let's take a look at the relationship between speaker efficiency and amplifier power. The compared speakers are LS-3 / 5a and Klipschorn of Klipsch. From the table below, it can be seen that low-efficiency speakers are more difficult to serve.
Klipschorn │ LS-3 / 5a
────────────────────────
104dB / 1W -------------------------- 81dB / 1W
107dB / 2W --------------------------- 84dB / 2W
110dB / 4W --------------------------- 87dB / 4W
113dB / 8W --------------------------- 90dB / 8W
116dB / 16W -------------------------- 93dB / 16W
119dB / 32W -------------------------- 96dB / 32W
122dB / 64W -------------------------- 99dB / 64W--?
125dB / 128W--? -------------------- 102dB / 128W--?
The first line 104dB and 81dB are the nominal efficiency of the two speakers. The 99dB of 3 / 5a is marked with a number, which means that 3 / 5a can not withstand 64W continuous input at all. Because the bass will bottom out, 50W continuous input is already the maximum . The Klipschorn speakers get 104dB of sound pressure at 1W input, which is something that the LS-3 / 5a cannot do when it breaks its head. As for 125W plus a question mark, it is the original factory announced Klipschorn maximum continuous work of 100W, so when 128W continuous input, Klipschorn will not be able to. Because the efficiency of Klipschorn is as high as 104dB, if the signal-to-noise ratio of the amplifier is not high enough, the speaker will emit annoying hiss and hum without turning the volume knob. For the residual noise and hum of the amplifier, the high-efficiency horn has a clear effect.
What is the efficiency of 3 / 5a? This article assumes that it is 81dB, as it seems in memory. But in the October 1995 Audio Yearbook, the efficiency of KEF 3 / 5a is 85dB, and the impedance remains at 11Ω. What surprised me the most was that the pair of small speakers soared to US $ 1450! God, does KEF 3 / 5a have this value? If it has a sound quality of 1450 US dollars, then I am not blushing, the pair of DaLine transmission line design sells 2400 US dollars! It's a pity that DaLine speakers are sold out now.
Regardless of any improvements, the maximum sound pressure of 3 / 5a is still not as good as Klipschorn's basic nominal efficiency. Then calculate the range from "nominal efficiency" to "highest sound pressure", 3 / 5a is about 18dB, and Klipschorn is about 21dB.
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There are two points revealed here. One is to push the Klipschorn speaker with a 300B single-end 7W tube machine per channel. Its performance will definitely be easier and more courageous than pushing a 3 / 5a speaker with a 40W × 2 crystal rear stage. The second point depends on everyone's joint research. Does high efficiency also mean high dynamics?
If this is the case, Mr. Cao Yongkun has a foresight. According to this principle, we should choose high-efficiency speakers, so that the output power of the rear stage does not have to be hundreds of watts. Of course, high-efficiency horns with hundreds of dB are usually huge. If they are close to the wall, they will not be able to hear the sound field and depth. But for the average family to listen to music or watch AV, the efficiency seems to be above 90dB. However, low efficiency speakers represent low dynamics? Unfortunately, 3 / 5a and my DaLine are proof. Of course, ATC may disagree. ATC ’s SCM20 is 8Ω / 83dB-the efficiency is slightly higher than DaLine, but its continuous withstand power is 200Wrms, so the highest sound pressure is calculated to be as high as 106dB. Comparable.
Driving a high-impedance speaker with a crystal machine will reduce power, but there are exceptions. Although McIntosh is a crystal machine, its output power will not change with load impedance changes because it has an output transformer. Fortunately, there are not many special cases in the audio circle. Vacuum tube machines without output transformers are rare, and only crystal machines with output output are McIntosh. Speakers with a nominal impedance higher than 8Ω have also been rare in recent years. Therefore, the output transformer of the modern tube machine should only need to have two winding outputs of 4Ω and 8Ω.
Should choose high efficiency, high dynamic speakers
When connecting low-efficiency and low-dynamic speakers, the output power of the rear stage should not be too low to prevent it from being pushed; but the output power should not be too high to prevent the speakers from tolerating, so it is often a dilemma. If the six words "inefficient and low dynamic" cannot be understood, it is more obvious to change to eight words "inefficient and low maximum sound pressure".
There are so many speakers in the world, but those who clearly indicate the highest sound pressure on the specification table are less than 1%. If there is the highest withstand power-continuous or not instantaneous, it can be calculated from the efficiency. For example, a speaker with an efficiency of 86dB, which continuously withstands 160W of power, we can easily calculate its maximum sound pressure: 108dB. Use the engineering computer to press a few keys, 160 log × 10 = 22, 86 + 22 = 108 (dB); and 22dB is roughly the dynamic of this speaker.
The value of dynamic range is expressed in dB, the higher the value, the better. The audio equipment performance table has a dynamic range, probably only CD players and DVD players; speaker manufacturers will hardly note this specification to avoid self-exposure. The dynamic range can be said to change from the lowest to the highest, from the smallest to the largest, and also from the weakest to the strongest, and from the darkest to the brightest. The greater the dynamics of the audio equipment, the better the performance from the weakest to the strongest. The dynamics of CD turntables are rarely less than 90dB, but the speakers are rarely 25dB higher.
Is this direct and reasonable? Of course it is not correct, because the dynamic range of CD turntable is the change of voltage multiple, and the dynamic range of the speaker is the calculation of power. We often say that the tenfold amplification of the previous stage has a gain of 20dB, but the 10W power is converted to 10dBW instead of 20dBW, please see the description below.
Both are dB values. The calculation of power is: the value of log × 10, and the calculation of voltage and current is: multiple of log × 20, so the voltage amplification of 100 times is 40dB. If a pre-stage has a gain of 14dB, what is its magnification? Use engineering computer to press several keys: 14 (dB) ÷ 20 ÷ invlog = 5 (times). If the highest output sound pressure of a certain efficiency 86dB speaker is 105dB, converted to the highest withstand power is: (105-86) ÷ 10 ÷ invlog = 79.5W. And 105-86 = 19 (dB), it is about its dynamics.
Distinguish the dB of the voltage gain and the dB of the speaker power, you will understand why the Hi-End factory is opposed to labeling the output power of the post-amplifier as dBW. Because 50W is 16.9dBW, and 500W is a large power, but it is only 26.9dBW. It seems that the output power of 50W is similar to that of 500W, so manufacturers may object to the labeling of dBW on the grounds of "not easy for consumers to understand".
If the loudspeaker's highest sound pressure-efficiency is its dynamic range, what is the dynamic of a general household loudspeaker? Whether it is Avalon Asent, Thiel CS5i, B & W 801, it never exceeds 25dB! Looking for the professional field, Rey Audio's RM-8V efficiency is 100dB, the maximum sound pressure is 130dB, there is 30dB dynamic, 30dB is exactly 1000W, that is, RM-8V can withstand 1000W.
Japan's Rey Audio also has a higher sound pressure RM-1800, and its model has two meanings. One is to use two 18-inch bass units, and the other is the speaker height is 1800mm. One year, "Qia Ke and Asuka" held a concert in Osaka and used 4 pairs of RM-1800.
Think about another question, ask Rui Rui to drink éž æž æ±© å¤ c, c efficiency is the same, driven by the same amplifier, will it get the same sound pressure? ─Numbers are usually not deceptive.
It will not be the same. After many years of practical operation experience, it is very different. The efficiency measured in a quiet room may not necessarily cover low, medium and high frequencies, so they are also two pairs of speakers of 95dB / 8Ω, and their minimum driving power (amplifier output power) may be 20W. One is 50W.
But the high-efficiency speaker does have its advantages, in terms of 102dB, it means 1W input; if it is 0.5W input, it also has 99dB! Even with a 0.25W input, it is as high as 97dB. It is difficult to have a chance to emit a sound pressure of 97dB when listening to music in an ordinary home, so the 7W output is definitely enough.
Generally, high-efficiency speakers are relatively large in size, and their common feature is the lack of low frequencies, or that they cannot emit real bass. It ’s easy to test it, just try it with a soundtrack CD. The main reason is that the Fs of the monomers are not low enough. At that time, what they needed was: high efficiency, clean mid-low frequency, and no electronic synthesizer, so the extremely low frequency can be sacrificed. If it is an early large high-efficiency speaker, let's say the low frequency is scattered, the speaker is placed against the wall, and it is only one meter apart from the left and right. Transparency.
Low background noise in the listening environment
The ideal speaker is high efficiency and high sound pressure, because it can show the change from the lowest to the highest music. But to talk about dynamic range, it must not miss the important factor of environmental noise.
The quieter the listening environment, the better. However, unless it is a professional recording studio, the background noise of a slightly renovated audio room is generally more than 35dB-this refers to the measurement when people are quiet at night, and the situation during the day is even worse. The level of background noise is also directly related to the dynamic range. The louder the noise, the higher the loudspeaker pressure is required to present the weakest notes of the music. Therefore, the background noise of the listening environment and the residual noise of the equipment are definitely as low as possible. Even if you appreciate 5.1-channel AV, the requirements are the same.
Due to the high background noise, the "sound" must be louder to hear all the details of the music. But even if the performance of the equipment is not questioned, what's the difference? First, the neighbor will protest to you, and second, it may cause damage to the ears. In the popular discotheque, in order to create an atmosphere and suppress consumers' sound waves, their PA audio is often full horsepower, and the sound pressure is more than 120dB. Long-term exposure to that environment is likely to cause human ears. hurt.
Of course, there are different dance halls at home, and home audio is back in popularity due to the pipe machine. Not only the famous WE-300B is re-produced, but the old JBL and Altec speakers are gradually returning to the market. However, although these horn speakers are quite efficient, they are also very large in size, which is extremely unsuitable for general families. There is also a doubt: are the sound quality of these speakers proportional to their efficiency? Recently, several readers mentioned to me a medium-sized imported high-efficiency speaker from the United States. The sound quality is very rough. Although it is very good, it can't bear listening to it and can only be used for AV.
Low power matching and high efficiency
In order to avoid wasting energy and get the right combination, I personally have two great suggestions, but they need to be recognized by the global audio industry: First, speakers with an efficiency of less than 90dB are not allowed to be manufactured, sold, imported / exported, and the impedance should be as much as possible. Maintain 8Ω; Second, the post-stage / comprehensive amplifier with an output higher than 90W─8Ω / ch─, regardless of transistors and vacuum tubes, is also not allowed to be manufactured, sold, imported and exported (of course, professional equipment is not subject to the above restrictions).
If this is the case, well-known horn manufacturers such as Dynaudio, VIFA, ETON ... will develop high-efficiency horns that are not horn-shaped and have a small size. And because the output power of the amplifier is reduced, the power transformer, filter capacitor ... can be reduced, so the material cost, weight, size and price can be reduced, which is definitely a blessing for consumers and lovers. Are you right?
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