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Originally Posted by navin Sorry Santosh, there were some wires crossed earlier today. Now I get what you are talking about. I re-read all the posts and even the ones after the one quoted above and not that we are on the same page let me add.... |
First of all no need to say sorry! and thanks for the elaborate response. I don't really see any contradiction now, for most part I can say that I did actually "validate" my understanding with you.
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Yes it is obvious that a woofer mechanical Q is much higher (huge spider/surround) in fact in many cases Qms = 10 Qes;
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That confirms my suspicion, and the fact that woofers usually need good electrical damping.
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and in a tweeter the electrical Q is higher and Qms < Qes or often Qms is 0.5 Qes.
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My suspicion is not exactly true here, but that can not be termed as disagreement or misunderstanding of the theory. With this information it still means that effect of electrical damping will not be as pronounced as in woofer. Firstly, for a good tweeter, it should be safe to assume here that Qms must not be far from the ideal 0.707 (as compared to how far it goes in woofers). Secondly, even in the worst case when Qms=Qes (Q=0.5Qms=0.5Qes), total Q can only be raised from 0.5Qms to Qms max. with a really bad amp having infinite output impedance (open circuit
). In case of woofers too, Q can potentially be raised till Qms, but since its value is much larger than 0.707 it is possible that very bad amp (HU?) can make it quite resonant.
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Also when the speaker is put in a closed box (lets keep it simple and assume a closed box) the Qtc is always the woofer's Q in the box. The tweeter being sealed is not in the mechanical circuit.
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I think so far I was (indirectly!) talking about simpler systems with a speaker (either a woofer or a tweeter) directly connected to an amp. Things have already crossed the 1st level of approximation with inclusion of a crossover! I am not really inclined to go any deeper, but in this case instead of saying speakers Q is that of woofer in the enclosure, wouldn't it be best to treat them as two different speakers? How you divide the crossover between woofer and tweeter, whether you consider it as a part of speaker or amp etc. will add to the complexity. I would prefer to leave it at that
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(just ask any valve amp aficionado).
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I haven't researched valves much, thinking they are outdated technology with a lots of THD/IM and other disadvantages. I know however that certain harmonic distortions can actually make the original sound "sweeter" or more "musical" (have heard samples over net with exaggerated effects!). Many people say that the patterns of harmonic distortion generated by valves can actually appeal to valve lovers, due to this reason. In other words, they have developed and carried over weired tastes since valve days.
Another reason preached in favor of valves is cross-over distortion in transistor amps, dominant in class B and AB at low listening levels. It is supposed to be absent in class A or class D (PWM) amps (and it makes sense to me)
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Santosh, since you have read SL's website You must have also read that of John K. (Zaphaudio). John has tested a bunch of drivers for IM and THD and all sorts of stuff. Fostex's fared rather poorly in these tests.
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I vaguely remember to have visited Zaphaudio too, but I don't think I have read any THD articles there. Will definitely do that.
I have a few follow up questions about distortion, but I think it is better to postpone them for another time or thread.
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Der Alte, Tube amps are so dependant on their "iron" it is their weakest link. Even today finding good iron is hard.
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Just curious, what is iron here? (transformers?)
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LBM, talking about just a maximally flat frequency response does not divluge the full picture. Impluse response, decay etc. are also to be considered.
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Yes, LBM. Maximally flat FR is far from "the" qualifying factor for SQ. It is of course necessary but not at all sufficient. A very flat system can actually have significant non-linear distortion in it which is a different story. First of all, to be technically precise, FR constitutes of both amplitude response and phase response together (Most of the time only amplitude is considered). With a complete FR, it is theoretically possible to get impulse response, decay time etc (and the other way round).