Re: [闲聊] 阻尼系数

楼主: ESL63 (静电)   2020-07-27 09:49:08
阻尼因素的高低跟听感关联性没有这么绝对
真空管机没有高的 但是管机低频控制就都很差吗 相信市场上反应并非这样
以下转贴 Sterophile 访问Tim de Paravicini 的片段(Jun 5, 1984)
谈他的EAR 509
这机器的低频控制力速度感都十分厉害 但DF只有20
请看看他如何解释
Stereophile: We're looking at a damping factor of only 20, right?
De Paravicini: Yes, well, it may only appear to have a damping factor of 20
but that needs to be clarified. People have latched on to the idea that
damping factor is the only important criterion for tight bass.
Now a conventional dynamic speaker is essentially an electric motor in series
with an 8 ohm resistor inside that motor—if you measure the voice-coil
terminal it measures 8 ohms DC [(footnote 1)]. Now if you put a screwdriver
across those two terminals, you have put an infinite damping factor on that
loudspeaker, right?
Stereophile: Right.
De Paravicini: But that electric motor has still got 8 ohms in series with it
to damp its motion. It hasn't really got a short circuit. Now, if instead of
the screwdriver I put an 8 ohm resistor across those terminals, that electric
motor now sees 16 ohms in a series, so in fact it's got half the damping that
it had before, which is expressed as a DF of 2. If we lower that resistor
from 8 ohms to 1, for example, we now have a damping factor of 8. That
electric motor is now seeing 9 ohms, which is only 10% larger than 8 ohms.
We're closing the gap towards that perfect 8 ohm resistor, so if we go
downwards from below 1 ohm to ½ and then ¼ ohm, we're getting ever closer
to that 8 ohm minimum. It just doesn't buy you anything, because you can't
get below 8. So if you increase the amplifier's damping factor beyond 10, the
actual damping on the speaker remains for all intents and purposes unchanged.
Whether you have a damping factor of 1000 or 100,000, the speaker really
doesn't know the difference.
Stereophile: Then why is it that amplifiers with very high damping factor
usually give the tightest bass?
De Paravicini: The reason amplifiers sound apparently tighter or looser is
not their damping factor but the amount and the quality of their feedback and
their low-frequency stability under dynamic conditions. The bandwidth, the
frequency response, the way it clips, the way it recovers from clipping are
all problems that are really of great concern. They are all signatures of the
amp's sound characteristics.
The ideal amplifier should recover from an overload infinitely fast and not
have any subsonic misbehavior. What I am trying to do is to come as close to
that as possible in a transformer-output tube amplifier. That is why my
amplifiers may sound as if the bass is thin—simply because there isn't this
overhang.
Most tube amplifiers cannot deliver current. They have a rated power into one
rated impedance and the minute the impedance deviates significantly on either
side of that, their power output goes to pot. I designed the 509 so it would
still maintain its rated power down to 3 ohms. It has a peak current capacity
—something I don't publish in the specs but that should be mentioned—of 12
amps. That is one of the reasons for the exceptional tightness of the bass.
It can keep the speaker under control, and that's why a cheap 10W receiver
will often bottom its woofers. The amplifier loses control totally, and you
end up with a damping factor of less than 1, momentarily. From a
superficially high figure it disappears, then the speaker lets go and it goes
back, crash!
作者: martinlin77 (mar)   2020-07-27 09:55:00
推....因为ID正确?推好文
作者: yohsiatai (yohsiahsuan)   2020-07-27 11:11:00
id正确XDD随手笔记短心得:1. Benchmark 有特别解释DF的文章,推荐一读。 两篇都主张1000、10000之类的DF意义不大。2. 低频和(负)回授的品质有关,和频宽(~=瞬态)有关,和THD vs. Power的表现有关... (os: 负回授反对派站出来!)3. 我家的扩大机有时候听起来低频比较薄(lol)(os: 所以说DF 20太低啊...)4. 瞬间电流输出能力很重要 (偷嘴小功率后级www)5. 其实这篇主要在说用DF评价机器太简化(这是对的,正确来说要看output impedence/power vs. frequency)
作者: djboy (雞尾酒)   2020-07-27 11:47:00
推本文与楼上
楼主: ESL63 (静电)   2020-07-27 12:16:00
以我听/使用过的后级来说 509的低频表现跟大电流晶体机很像家里以前用的Adcom GFA555跟Bryston 8BST都赢不了他这文前面也有提到feedback跟TIM 有兴趣的可以看看
作者: Dopin (ats.twbbs.org)   2020-07-27 12:49:00
OPT 管机常常跳脱一些状况 Q_Qb
作者: yamatai (回避性人格障碍症)   2020-07-27 13:41:00
我之前听的 EAR 509 倒是控制不好 JBL 4343瞬间电流能力跟线路的反应速度跟电源供应关系很大DF根本只要100就够用了 超过 400 根本没意义wilson audio 甚至在他的喇叭上面直接写着 DF 100~400把 DF 拉高很简单,但会劣化音质。但提升电供很贵,但是几乎没啥副作用
作者: Dopin (ats.twbbs.org)   2020-07-27 13:49:00
所以我讲了 实听最准 厂商会吹牛或会说实话 也是很正常

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