电子管功放电功率和音量对应表及衰减器的选择

kldguitar

衰减器的作用，是对音量减小之后人耳听觉缺失频率进行弥补。当音量关小时，人对高频与低频部分之听觉会变差，即听觉灵敏度会变低，也就是音量低的时候，低频和高频如不加大其强度，就听不到了。所以大家所要求的衰减器对于信号完全没有改变的要求是错误的，如果真的完全不去改变，那么你得到的听觉结果反而是不好的，会缺失掉很多的低频和高频部分。所以如果你想在小音量下获得大音量的听觉感受的话，必须通过人工手段去对信号进行一定的修正和弥补，在使用衰减器时，你必须尝试抛弃这种原始信号就是好的概念，以你自己听觉为标准，去尝试不同的调试设置，特别是注意随着音量的降低，不仅要调整衰减器的参数(如果有的话)，还应该调整音箱以及效果器上的参数，整体结合调整才可以获得最佳的听觉效果，而不是抱着死观念不放，觉得衰减器就应该只降低音量，而不能使得我的听觉效果受到损失。

Passivity

疯狂的和弦

原帖由 kldguitar 于 2012-5-24 07:15 发表
Z Air Brake让我改变了衰减器的看法，也让我开始喜欢上用衰减器，因为它保护了我的耳朵，而且的确对音色的影响是可以接受的。

可能很多朋友和我之前一样，对音量没有什么太明确的衡量办法，就觉得管箱音量大，会扰 ...

Passivity

theMaster

这个好

laoyao_lee

Passivity

kldguitar

Amplifier Myths, Fantasies, and Facts

Last Updated 07/08/2000

The guitarist cannot begin to make intelligent gear decisions without a basic understanding of tone, power, and volume.  Many experienced guitarists still nurse and cherish "facts" that are so incorrect as to be pure fantasy.  Some of these guitarists have achieved great tone – but only after years of very expensive trial and error and without ever really understanding what they did to finally get the killer tone they were looking for.
Knowing the facts about amplification can help guitarists take the fast track to their ideal rig and save them thousands of dollars along the way.
Each of the following paragraphs debunks a popular myth and tells the real story.  Since most readers are probably more interested in playing than becoming technicians and engineers, I've intentionally simplified some of these subjects a great deal.
You'll find a lot less bias against solid-state amps here than in most articles.  So much so that you might think I'm a fan of solid-state amps.  That is not the case at all – I strongly prefer tube amps and suspect I always will (I'm a sucker for glowing lights and shiny things).  However, this article is about facts and it is a fact that solid-state amps have come a long way and are an appropriate choice for some players and some situations.  In fact, even though I still strongly prefer tube amps, if I were doing the weekend warrior thing I would probably use one of the better solid-state amps for gigs!
Power MythsSeveral common myths about amplifier power are debunked below.  The bottom line is that you should select an amplifier for its features and tone, and consider power level as the least important criteria in your selection.
1) My 100-watt amp is twice as loud as your 50-watt amp.  This is one of those really sad myths that just won't go away in spite of volumes of empirically and mathematically proven, unambiguous, clear, undisputed, scientific knowledge to the contrary – knowledge that every tech worthy of a soldering iron learned very early in their training.  Music store sales weenies on commission love this myth because it's sold thousands of 100-watt stacks (not to mention the follow-on sales of expensive replacement tube sets).  Here are the facts:

• All other things being equal, a 100-watt amp will be just perceptibly louder than a 50-watt amp.  It takes about a ten-fold increase in power to double perceived volume.  That's right, you'd need a 500-watt amp to be "twice as loud" as your buddy's 50-watt amp.  Even more thought-provoking is the fact that a 50-watt amp will only be perceived as a little bit louder than a 15-watt amp driving the same cabinet!
• All other things are almost never equal.  There are so many variables controlling sound pressure level (SPL) and perceived volume that it is quite common for a small amp to sound louder than a much more powerful amp.
• Cab design, speaker size and efficiency, signal compression, and several other factors have far greater impact on perceived volume than does power level.
• The initial purchase price of a 100-watt amp will be significantly higher than a 30-watt amp with similar features.
• It will cost you signficantly more to re-tube a 100-watt amp.
• If you are driving a 30- or 50-watt amp hard enough to require frequent re-tubing, chances are very good that you will also drive the 100-watt amp hard enough to require frequent retubing (at significantly higher cost).

Am I saying 100-watt stacks are evil?  No.  No one really needs one (see below) but if you want one be my guest.  All I'm saying is that you should be aware that you are spending a lot of money to purchase a miniscule increase in volume.
2) I need a 100-watt amp 'cause my band has started gigging in clubs.  This is a myth that I believe originates with hormonally imbalanced teens who have more experience watching movies about teen bands than they have playing real gigs.  Unfortunately, it's a self-perpetuating myth because the rhythm player is going to get a big amp 'cause he's being drowned out by the lead player, then the bass has to get a 400 watt amp to be heard at all, then they need a 1200 watt PA system so that the vocals have some chance of being heard over the cacophony from the guitars and bass, and finally they end up having to mic the drummer even in a small club because the drummer is breaking sticks and skins and still can't be heard over the racket.  Within a few years their hearing has been permanently damaged and they all decide that they need bigger amps!  Three-quarters deaf, they finally make the big time and the guitar magazines write about the gang of three 100-watt stacks that the guitar hero uses on stage and all the wannabees have just gotta have the same rig. . .  As you can imagine, this is another myth that sales weenies on commission are in no hurry to debunk!  Well, here are the facts.

• There is absolutely no venue that requires a larger amp and cabinet than one suitable for use as a stage monitor – provided that the members of the band don't get into a juvenile competition to outdo each other.  Need more feedback?  Fine, move closer to the amp, for crying out loud!  Typically, a really good 30-watt rig with a suitable cab is ample!  Depending on the composition of your band and the variety of venues you play, an even smaller rig mic'ed to the PA and then pumped to stage monitors may be even better.  Note that while a good 30-watt rig has ample volume you may end up having to buy a more powerful rig to get other desired features.
  • At a small venue, a 15 to 30 watt amp can be placed behind the band in a traditional position and used without a mic.  In this position the rig serves as a monitor for the guitarist and as the primary amplification for the guitar.
  • At a medium venue, the small rig can be placed in front of and facing the guitarist as a monitor, and be mic'ed and run through the band's PA.  The band's PA speakers are placed along the front of the stage and facing out.  This arrangement allows the sound to be balanced at the mixer and allows the band to flood a medium to large venue without damaging their hearing.
  • At a large to giant venue, that same small rig can be arranged much as described above but now the band's mixer feeds the house PA.  This is the only way to reach the back of the room without dangerous SPLs near the stage at a large venue and would be required no matter how powerful a rig the guitarist has.
• Smaller equipment takes up less space on cramped stages.
• The money you save by purchasing a smaller amp can fund a nice power conditioner to protect your equipment and clean up powerline noise – the conditioner will cost less too since now you don't need one that will handle a billion watts.
• If the band members will agree not to compete, all of them can recognize significant savings by not having to purchase unnecessary equipment.
• Your band is far more likely to be called back for a repeat engagement if you provide a well-balanced, easily managed performance than if you are just obnoxiously and uncontrollably loud.
• Many guitarists already have the monster amp – it isn't necessary to get rid of it.  You can use an attenuator (see the attenuator myth) and perhaps a smaller cab.

3) I need a small combo because I live in an apartment.  This is sort of the opposite of myth two, above, and is closely related to myth one, above.  While a small combo will certainly take up less room, it may or may not be easier to get good cranked tone out of it at apartment levels.  First, read myth one again.  If it's true that we have to increase power ten times to double perceived volume, then it is also true that we have to reduce power ten times to cut the perceived volume in half.  Thus, even a tiny 5-watt single ended tube amp is going to sound about half as loud as a fifty-watt stack (actually, it will be a bit quieter than that because it is probably driving an eight or ten inch speaker instead of a 4X12 cab).  Even that five-watt amp will be way to loud to run cranked in an apartment unless your neighbors are very tolerant.  Here are some facts you should consider:

• Even a 5-watt tube amp with an eight inch speaker is very loud by the time you crank it into distortion.
• You can use an attenuator with either a large amp or a small combo.  Keep in mind, however, that attenuating below about 1 watt per speaker starts to adversely affect tone – it seems that a certain amount of speaker drive is required to round out distortion (see recent articles on 3-stage amplification architecture tests atamptone.com).  Even one watt into an 8" or 10" guitar speaker is likely to get you evicted.
• Many small combos do not offer a master volume, thus making it impossible to even get preamp saturation at acceptable volume levels.
• To get true "cranked tube tone" in an apartment at lease-safe levels you are almost certainly going to have to use a combination of attenuation and a sound-proof speaker isolation box with a microphone running to a mixer or stereo.  This is true whether you are running a 5-watt, single-ended, class A combo with an eight-inch speaker or a 100-watt stack with a 4X12 cab.
• It's not a good idea to run an amp inside of a sound-proof box, so even with a small combo you will need an extension speaker.
• It's not much fun to try to enclose a 4X12 cab, so you'll also need an extension speaker with that kind of rig.

The lesson here, once again, is to select amplifiers based on features, not on power level.  A tiny five-watt class-A amp with an eight-inch speaker and no features may not be very satisfying after a while, will be wholly inadequate for gigging, and still isn't quiet enough to run cranked in your apartment!  Add a few features such as footswitchable channels, master volume, and an effects loop and that 5-watt amp starts to become pretty attractive!
4) My tube amp has a master volume control that lets me get power-amp distortion at low volume levels.  Yet another myth that sales weenies love (seems like there are quite a few of these, huh).  The facts are:

• With the possible exception of some very rare and expensive "boutique" amps, a so-called master volume does not reduce power output after the power-amplification stage as the name would seem to imply.
• The master volume controls found on popular amps cut the power between the final preamp stage and the power amp.
• In all popular tube amps, when you turn down the master volume, then turn up the gain controls to achieve overdrive, you are overdriving the preamp stages, not the power stage.

I firmly believe that manufacturers deliberately misnamed the "master volume" control to deceive consumers – but that does not mean that the control is useless.  Quite the contrary, I regard a "master volume" control as an essential part of a good amplifier.  The "master volume" control permits running the preamp at full saturation or beyond at reasonable volume levels and allows one to balance preamp and power amp saturation for a wide variety of sounds.  I love "master volume" controls, I just think they should be named less deceptively!
5) Power attenuators damage amplifiers.  There is some truth to this myth.  But, attenuators can be safely and successfully used – and every guitarist should know how and when they can be safely used.  Here are the facts:

• A properly designed power attenuator does not apply any more stress to the amplifier than does a speaker cab – in fact a good attenuator will usually apply slightly less stress than a cab alone.  However...
• ...when using an attenuator, guitarists typically drive their amplifier much harder than they ever would when driving a cabinet directly.  Driving the amp this hard will significantly reduce tube life regardless of whether the amp is driving an attenuator or a cab.  As a consequence, it seems like the "attenuator wore out the tubes."  In reality, the guitarist was just enjoying much more overdrive than he ever would have without the attenuator and is paying the piper.
• Some amplifiers are simply not built to be driven hard. When the guitarist uses an attenuator and then runs the amp harder than he would have into a cabinet, very bad things happen and then the guitarist says, "that attenuator ruined my amp."  No, driving the amp at "10" ruined it – the attenuator is only incidental in that you never cranked the amp to 10 because it was just too danged loud!  This problem is particularly common with low-power combos.  I have a little 15-watt class A Ampeg Jet J-12T.  It's a great sounding little amp that I never cranked higher than about about "4."  One day I decided to see if it would do "metal."  Using a guitar with hot humbuckers I cranked the little Ampeg to "10" and played for about 2 minutes before the volume just became too painful (I was not using an attenuator, this was directly into the built-in 12" speaker).  When I turned the amp back down to reasonable levels I could hear a crackling sound.  In two minutes or so I'd blown both of the screen resistors and ruined the tubes.  The tech at my local guitar shop called Ampeg (the amp was still under warranty).  They told him, "fix it but tell the guy not to turn the amp up to 10 anymore."
• Attenuators can be used safely if you follow these rules:
  • Make sure that the attenuator contains some inductance.  This will help maintain natural tone and causes the impedance to increase with frequency.
  • The attenuator should either have approximately the same inductance as a speaker or should be of slightly higher resistance than a speaker.  It is better to reflect a slightly higher than normal impedance through the output transformer than too low of an impedance.
  • Have a reputable tech "cool off" your amp.  Explain to the tech that you are going to be driving the amp very hard into an attenuator and you want it biased a bit cold to save the tubes.  This will cost a bit in tone (chances are you won't notice this because you probably never drove the amp so hard anyway) but will make the tubes last a lot longer and reduce the chances of damage to other components such as the expensive output transformer.  A knowledgeable tech can also tell you if the model of amp you are using is known for blowing transformers and what have you (many guitar amps have output transformers that are not rated anywhere near the amp's max output).

6) Power attenuators kill tone.  Actually, it seems that well-designed power attenuators with inductive elements have little effect on tone until you attenuate to below about one watt per speaker.  I suspect that the real issue is not so much the power level as the excursion of the speaker coil.  At very low power levels the coil has very slow linear movement for a given frequency and thus has very little momentum accumulated when it reverses direction.  At higher power levels the linear movement rate is much higher and the speaker tends to overshoot much more, rounding out sharp corners in the input signal.  That's just a hypothesis on my part but, whatever the cause, the effect has been tested and measured by cybermonk at amptone.com.
Distortion Myths and Solid-State vs. TubeThere are so many myths, many of them conflicting, that it is hard to know where to begin.  Probably the most important thing to realize is that distortion can be broadly characterized as "hard" and "soft."  "Soft" distortion is the holy grail for most but it's important to realize that both types of distortion are useful.
1) Preamp distortion is bad.  Preamp (even tube preamp) distortion is much harder than tube power-amp distortion but the fact is that most rock-distortion uses both preamp and power amp distortion.
2) You can get great tube tone using tubes only in the preamp.  The fact is that the "creamy" soft distortion most of us desire occurs only in a saturated power tube section.  Tubes in the preamp do warm up the signal by introducing small impurities not typically present in a solid-state circuit, however.
3) Tube and solid-state preamps sound the same.  The facts are:

• Tubes "warm up" the signal by introducing impurities not present in most solid-state circuits.
• Tubes, even preamp tubes, go into clipping more gently than most solid-state circuits resulting in a slightly smoother transition to distortion.  Running preamp tubes just at full saturation gives a very full tone that simply isn't found in solid-state preamp circuits.
• Amp and effects manufacturers have been fairly successful in modeling tube preamp sounds using digital (DSP) and analog solid-state techniques.

4) Solid state amps suck.  This is only half true.  The facts are:

• Many solid-state amps do suck, especially older models and entry-level models.
• Some newer solid state amps actually sound pretty good, especially for clean tones.  None have truly "nailed" power tube distortion but modeling amps are getting close.
• Many guitarists and most non-musicians can't tell the difference between the best of the solid-state amps and a tube amp except in a side-by-side A/B test – and some can't tell even then.
• A good tube circuit anywhere in the amplification chain can "warm up" a sterile clean signal.
• Solid-state amps are much lighter, more rugged, and more reliable than tube amps.
• Solid-state amps typically deliver a much more consistent sound over a wider range of output volumes.
• Many, many, guitarists who absolutely swear by tube amps and won't even test drive a solid-state amp neverpush their tube amps into power-stage distortion – and power stage distortion is about the only thing that a good solid-state amp can't do well!

Solid-state amps have come a long way but are still not quite "there," in my opinion.  Some of them do a pretty good job of modeling preamp distortion but they aren't quite over the top modeling the power amp with it's complex interaction between power tube, output transformer, and speaker.  Even so, nine out of ten people in the audience at a typical live gig aren't going to know or care whether you are using a good solid-state amp or a tube amp.  If you do the weekend warrior thing and either play mostly clean or mostly with very heavy "metal" distortion then your best choice of gear might well be a multi-effects unit with a tube preamp driving a good solid-state amp!
5) The entire signal path must be tube, there mustn't be any solid state circuitry in the signal path.  This is so silly it would be funny if not for the thousands who make inappropriate and expensive gear choices based solely on the presence or absence of an "all tube" decal on the front panel.  The facts are:

• We like what tubes do to tone because of coloring they add to the tone.  This is true both of clean and overdriven signals.
• Clean (non-overdriven) solid-state circuitry of even mediocre quality reproduces a signal extremely faithfully.  It will not "sterilize" a signal that has been "warmed up" in a tube stage.
• At least one tube stage should be present in the preamp chain to warm up clean tones.  This can be a tube preamp in a tube or hybrid amp or it can be a tube pedal or tube preamp in a multi-effects unit such as the GSP-2101 or RP20.
• Until modeling is perfected, tube power amp sections provide the most "liquid" distortion.  But remember, this is only important if you are looking for liquid distortion!  If you're playing mostly traditional country then you want an almost painfully clean signal anyway.  Similarly, if you are playing in a shock-rock band you probably want mostly "hard" distortion anyway.
• For clean tones there is little practical difference between a solid-state power amp and a tube power amp provided that the signal has been suitably "warmed up" in a tube preamp.

I've seen people pass up a good deal on a great-sounding tube amp because it had a solid-state reverb driver or tremelo circuit and then stick a half-dozen cheap solid-state pedals in the effects loop of the less-capable amp that they purchased because it was "all tube."  P.T. Barnum was right!

kldguitar

时间关系，我吧原文的大纲译出来。功率的神话
1 100瓦功放音量是50瓦的两倍吗？
2。 在俱乐部演出，需要一个100瓦的功放吗？
3。我住公寓房（ 相对house, 别墅） ，我就只要一个小功率的combo 吗？
4， 我的功放有Master音量控制，它可以让我在小音量下获得功放管失真吗？
5。 衰减器对功放有损害吗？
6。衰减器影响音质吗？
失真的神话
1。前级失真音质好吗？
2。你可以只通过前级获得管声吗？
3。电子管和晶体管前级声音一样吗？
4。晶体管的音质是不是缩缩的？
5。整个信号通道都必须是电子管吗？
很多东西很实用，希望大家能静下心来看看。

循环血魔

循环血魔

kldguitar

根据英文帖对１００瓦，３０－４０瓦，５瓦　功放的论述，我归纳如下，不对处请指证：１００瓦和３０－４０瓦机器比较，音质已经没有任何区别，音量增加也不是很多，演出时，完全可以通过PA 获得同样效果。但１００瓦的机器要贵很多。
５瓦的功放音量也足以让邻居找你麻烦，但５瓦的机器受后级功放影响，音质可能会不太理想。
所以最理想的功放瓦数是３０－４０瓦，这个区段的功放如果配衰减器就可在家里用，配PA就可在舞台上用，使用效率比较高；价格也远远低于１００瓦。
目前，国际上比较流行小箱配PA 的演出配置。

kldguitar

终于有时间完成了“疯狂和弦” 老弟布置的任务，进一步的探讨，有时间再做。
100 watts is 1.23 as loud as 50 watts.
80 watts is 1.1562 as loud as 50 watts.
60 watts is 1.0578 as loud as 50 watts.
40 watts is 94% as loud as 50 watts.
30 watts is 86% as loud as 50 watts.
25 watts is 81% as loud as 50 watts.
22 watts is 78% as loud as 50 watts.
20 watts is 76% as loud as 50 watts.
18 watts is 74% as loud as 50 watts.
15 watts is 70% as loud as 50 watts.
12 watts is 65% as loud as 50 watts.
10 watts is 62% as loud as 50 watts.
9 watts is 60% as loud as 50 watts.
8 watts is 56% as loud as 50 watts.
7 watts is 55% as loud as 50 watts.
6 watts is 53% as loud as 50 watts.
5 watts is 50% as loud as 50 watts.
4 watts is 47% as loud as 50 watts.
3 watts is 43% as loud as 50 watts.
2 watts is 38% as loud as 50 watts.
1 watt is 31% as loud as 50 watts.
3/4 watt is 28% as loud as 50 watts.
1/2 watt is 25% as loud as 50 watts.
1/4 watt is 20% as loud as 50 watts.
1/10 watt is 15% as loud as 50 watts.
50mW is 13% as loud as 50 watts
20mW is 10% as loud as 50 watts.
10mW is 8% as loud as 50 watts.
5mW is 6% as loud as 50 watts.

我是屁民

原帖由 kldguitar 于 2012-5-18 09:48 发表
人耳理想的听音是88分贝，但是实际上这个音量已经偏大了。
很多大喇叭箱的灵敏度都比较高，我们不去说专业的有些可能达到99-100分贝，普通的按照90分贝来说，喇叭箱的灵敏度应该表示在功放系统在给予音箱1W的1000Hz ...

这段什么意思，莫名奇妙，其他的写的还不错，这段大失水平

kldguitar

原帖由 我是屁民 于 2012-6-9 19:36 发表

这段什么意思，莫名奇妙，其他的写的还不错，这段大失水平

很抱歉，由于时间关系，有些文章是我原创，有些是 copy, 这里有些问题，一时也没有发现，以后我会注明那些是原创，那些是copy。
从这篇文章上看前面没有太大问题，只是后面论述  功率和声压的部分有点问题，功率应该是加在喇叭上的功率，而不是功放上的，实际加在喇叭上的功率远远小于功放的输出功率，这里有一个电声转化效率的问题

疯狂的和弦

揪小辫子，不能善意理解。这不太好

那个帖子上的东西之前有很多文章提到了。没人信，很快就沉了。
也许和没有人愿意相信一个土匪叫张牧之一样。 妨碍买琴的事情人们愿意选择不去相信。

kldguitar

综合上面文章， 前级和后级放大进行一些探讨，有不对处请指正。相对于后级失真来讲，前级失真音色要硬很多，所以要获得“creamy" soft distortion（"creamy" soft distortion most of us desire occurs only in a saturated power tube section） 就必须有后级失真。这也就是很多 ROCK-Distortion要结合前后级失真的原因。
那么，对于有Master旋钮控制后级的功放来说，master 的功能实际没有宣传的那么大。通过master降低音量，首先就失去了后级失真，接着再向下调整功率时，当后级功率不能包络前级放大曲线时，整个信号就发生变形，想象一下，一个人被人捏住了脖子唱歌，有劲使不出来的感觉，也就是这个样子。

疯狂的和弦

我也跟着说一点吧
我是弹金属的。我认为，很多时候后级过载对金属乐的必要性也没那么强。比如拿jcm 800弹金属乐的三个人，zakk wylde /  jeff hanneman / kerry king  ，后级管全部换成了4根大功率管，前两位是4 x 6550 , 后面那位是 4 x kt88 ,这管子一般认为应该是不容易失真，同时100W配上了4根，更难失真了。  可是为什么最需要大失真的金属乐，他们却换了不容易失真的后级管。 根据我自己的经验，金属乐音色的失真度也往往不需要特别高 :只要音色超级的强劲有力，偏小甚至很小的失真度也会让人觉得刚猛异常。  jcm 800 弹金属在我看就是这个道理，前级失真已经有刚刚超过crunch需要的量，再配合高功率管制造强劲的气势，铿锵的金属音色的质感就出来了 。 况且他们还是要串EQ或者booster的 。

这是我的经验，麻烦KLD用更专业的眼光给分析分析，看看有没有一些道理。

kldguitar

原帖由 疯狂的和弦 于 2012-6-15 08:41 发表
我也跟着说一点吧
我是弹金属的。我认为，很多时候后级过载对金属乐的必要性也没那么强。比如拿jcm 800弹金属乐的三个人，zakk wylde /  jeff hanneman / kerry king  ，后级管全部换成了4根大功率管，前两位是4 x  ...

这个是有道理的，后级失真比较柔美，而金属要的就是刚猛，所以后级失真在金属玩家这里是不需要的。 但要保证比较大的放大，后级功率又必须上去，所以。就要用高增益管来保证。一句话，不同要求不同设计。

kldguitar

另一方面，使用高增益后级管，又保证了前级可以有更大的失真。声音更加刚猛。

kldguitar

The Relationshipof

Voltage, Loudness, Power and Decibels

What a boring title! On the contrary, I think you will　find the information contained herein to be both enlightening (maybe even　surprising) and certainly valuable. This paper will help you to better　understand how the major component parts of your stereo system interact. Inparticular, we will explore the elusive relationship between speaker output(volume) and amplifier output (power).

Loudness, to a great degree, is subjective. What is loud　to one person is not to another. Thus we need a measure that allows us quantify　what we hear. The unit of measure most common is thedecibel
(dB). Most audiophiles are familiar with　the term, but just what does it actually mean? Without getting too technical,the dB is a unit of measure for sound intensity or level. It is a logarithmicscale developed to express wide ranging quantities on a simple scale. Becauseit is logarithmic, it can be a little bit confusing. As an example, a doubling　of volume is not equal to twice the number of dB. The chart below will help you　to better understand the dB and how it relates to what you hear, and what is　happening throughout your system as volume levels change. But first, we need tolook at the other end of the equation.

Power,
in this discussion, refers to watts. Power　defined is the rate at which energy is converted or dissipated, as in the caseof an amplifier driving a loudspeaker. It is important in our discussion indefining the general relationship.

A simple chart will help to understand the relationshipof the terms we have introduced:

dB Change	Voltage	Power	Loudness
3	1.4X	2X	1.23X
6	2.0	4.0	1.52
10	3.16	10	2
20	10	100	4
40	100	10,000	16

Looking at the chart, and starting at the left, we cansee than an increase of 3dB results in a
voltage increase 1.4 times the original, adoubling of power, and yields only a subjective increase in loudness only 1.23times the original. To get a doubling of loudness, it is important to note that　an increase of 10dB is necessary. And to reproduce that volume through ourloudspeakers, note that we require　ten times　more power from the amplifier!

The implications of this comparison in a typical hi-fisystem is significant. Let us assume that you are listening to your stereo at acomfortable volume of 8OdB. We will further assume that this level requires 25peak watts from your amplifier. To just barely increase the volume, we mightincrease loudness by 3dB. As we can see from the chart, this will require adoubling of power from the amplifier, which will now be churning out 50 peakwatts to produce a loudness of 83dB. If we want to double the apparent volumefrom our original level we will need to create 9OdB of sound pressure,requiring 250 peak watts.

It is obvious from the example above that adequateamplifier power is necessary to provide an accurate portrayal of music. This is　especially true when attempting to reproduce realistic levels, or when drivinginefficient speakers. However, even small efficient speakers may requirecopious amounts of power to cleanly reproduce transient peaks. In the finalanalysis, it is difficult to have too much power. While a small amplifier ofonly a few watts output can produce surprising average loudness, the dynamicpeaks will usually suffer unless the sensitivity of the speaker is very high.

Many individuals I have spoken with are concerned withhaving "too much" power. The perception is that an amplifier with anoutput greater than that recommended by the speaker manufacturer would be likelyto damage the speaker. This is not necessarily so. Interestingly, an underpowered amplifier is more likely to cause speaker damage! During my training atthe JBL factory for transducer servicing, I saw more speakers(tweeters/midranges) damaged from use with under powered amplifiers than onesthat succumbed to being overdriven. Sound strange? Not really, once youunderstand what is happening.

When an amplifier is over-driven, it "clips"the wave-form. What was a clean sine wave becomes a distorted, almost square,wave. A square wave is extremely difficult for a speaker to reproduce, as itrequires virtually instantaneous starting and stopping of the diaphragm. Atsufficient power levels, the tweeter will simply die trying to reproduce thiswave-form. A given tweeter rated to handle 50 watts of clean undistortedsine-wave power, will be capable of handling only a fraction of that amount insquare-wave input.

As you can see, clean, undistorted power is the key. A 25watt amplifier, constantly driven to clipping, is more dangerous than a 250watt amplifier that is never taxed. Of course, let reason prevail. I am notsaying that speakers can handle endless input, they cannot. However, extrapower does not mean that speaker damage is bound to occur. If common sense isused, any size amplifier can be employed.

Many factors influence amplifier choice. Some of the moreimportant considerations are: speaker type (efficiency or sensitivity), roomsize, the type of music you listen to and, most importantly, how loud you liketo listen and even how far one sits from the speakers. In an extreme example,one might own an inefficient loudspeaker, have a very large room, and like tolisten to pipe organ music at realistic levels. This individual is going torequire a tremendous amount of power to satisfy his/her needs. The nextlistener, with the same speaker, may have a much smaller room, and preferschamber music at background levels. Here, power requirements might be only onetenth to one-fourth those required in the previous illustration.

Requirements do vary widely. It is wise to take allfactors into account before making a decision regarding the amount of powernecessary for your situation.

[ 本帖最后由 kldguitar 于 2012-6-19 10:20 编辑 ]

疯狂的和弦

老潘师傅点击这里就可以看到以前发过的帖子了

kldguitar

谢谢，不过时间一长就没有了

疯狂的和弦

那可以这样

draculazhou

kldguitar

这里的几篇原著文章很好，我是写不出来的，建议大家好好看看。

kldguitar

[em02]

面条

此贴需要让更多的人看到

draculazhou

kldguitar

原帖由 面条 于 2012-6-28 16:44 发表
此贴需要让更多的人看到

特别推荐，那篇英文文章，写的非常通俗，同时又很适用。

kldguitar

[em29] [em29] [em29]

kldguitar

这篇文章怎么变成我一个人顶了，大家宁可问满世界问我有xxx钱，买什么箱子好，不愿意坐下来静静自己看看文章，思考一下吗？

kldguitar

[em13]

kldguitar

目前常用的几种变功率方法： VVR, Power  scaling, power soak , Class various ,attenuator,( pure resistor net, impedance net)

疯狂的和弦

有直代关系的两对管子可以同时用么？？？
比如一对6550,一对kt88 ,放在一颗原来是4 x kt88的音箱里头用

kldguitar

参考http://bbs.guitarschina.com/view ... ;page=1#pid20068517
这样是不行的。

jumping_pro

这篇文章很好，但是开篇的一大堆数据估计吓倒了不少人

尤其楼主对那篇英文进行的大纲式翻译，更是吊足了我的胃口。。。。因为我是学电子出身，所以对音箱的这些特性很感兴趣

想请问高手们：
1，所谓功率衰减器，是不是可以理解成串在后级管和喇叭之间的“电阻”（当然只是比喻）？
也就是说尽管衰减了输出，但依然获得了前级和后级失真，只是少了纸盆失真？

2，比如vox ac4tv，它的控制旋钮为tone、volume、衰减档（有4w、1w、1/4w三档衰减），这个三档衰减究竟是对master的段位化（后级管之前，实际就是master），还是处于后级管之后的功率衰减？

kldguitar

所谓功率衰减器，是不是可以理解成串在后级管和喇叭之间的“电阻”
这个理解基本正确，更广泛一点的理解， 应该是”抗性元件“， 因为有人使用”感性元件， 如变压器，不过有报道说这种衰减器比较容易烧。原因也好理解，感性元件是储能元件，这么大能量储存在那里，搞得不好是要出问题。
另外，还有使用模拟扬声器线圈的电感线圈式衰减器。
这两种衰减器，衰减后，物理信号已经改变。所谓物理信号，对应讲的是心理信号。常用的阻性网络是不改变物理信号的，但衰减量大了以后，由于听力曲线的关系，人们会觉得一部分声音没了。这时关键要进行听力扑偿。
第二个问题也很好，今天没时间回答，改天。

jumping_pro

看来楼主对功率衰减真是有研究
期待楼主的继续解答

kldguitar

vox ac4tv，它的控制旋钮为tone、volume、衰减档（有4w、1w、1/4w三档衰减），这个三档衰减究竟是对master的段位化（后级管之前，实际就是master），还是处于后级管之后的功率衰减？这个问题也是一个很好的问题，提现了提问者技术背景。
首先回答 AC4TV 的问题。 他不是使用master 技术，而是使用了基于Power Soak 的功率衰减技术， 它不仅是在后级管之后，而且是在变压器之后，完全是一个内置的分档衰减器，为什么不采用master 而是用衰减回路？留给大家思考，这体现出设计者对功放认识独到的地方，这不是噱头。在我接触过的所有大牌设计师中，我非常佩服VOX设计师。
另一个问题实际牵扯到内置功率调节技术，夜已深，明天再聊。反正，看帖子的也就那几个，晚点也没什么。哈哈