Re: [閒聊] 阻尼係數

看板Audiophile (電腦喇叭音響系統)作者ESL63 (靜電)時間4年前 (2020/07/27 09:49)推噓7(7推 0噓 19→)

留言26則, 6人參與討論串4/5 (看更多)

阻尼因素的高低跟聽感關聯性沒有這麼絕對真空管機沒有高的但是管機低頻控制就都很差嗎相信市場上反應並非這樣以下轉貼 Sterophile 訪問Tim de Paravicini 的片段（Jun 5, 1984) 談他的EAR 509 這機器的低頻控制力速度感都十分厲害但DF只有20 請看看他如何解釋 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! -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 210.242.76.224 (臺灣) ※ 文章網址: https://www.ptt.cc/bbs/Audiophile/M.1595814550.A.795.html

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