-september.org> 5f8ab6dd   
   From: zekor@comcast.net   
      
    wrote:   
   > On Monday, July 2, 2018 at 1:41:13 PM UTC-4, G wrote:   
   >> I understand effects of electrical damping of woofers. I'm wondering how It   
   >> may affect midranges and tweeters. Is it the same, or does it dimish at   
   >> higher frequencies. Remove any crossover components for direct feed to amp.   
   >> Tone bursts should Show any difference in DF. Without testing, I'm   
   >> guessing.   
   >   
   > To cut to the chase: forget about "damping factor." It's essentially   
   > a made-up "spec" that indicates very little about the performance of   
   > loudspeaker drivers. Really. The important number, if you're worried about   
   > how well a driver is controlled at its resonance, is it's total Q   
   > factor: in the case of the driver itself, it's the Qts of the driver.   
   >   
   > The Q of any resonant system is a measure, essentially, of the   
   > ratio of the amount of energy stored in the resonance to the amount   
   > of energy dissipated. In the case of a driver, you have essentially   
   > three ways by which that energy is dissipated, or lost or, if you prefer,   
   > how it is removed from the system. These are:   
   >   
   > 1. Electrical losses, which, for most drivers, is the largest   
   >    loss mechanism (and is usually specific Qes),   
   >   
   > 2. Mechanical losses, which, for most drivers, is secondary   
   >    to the electrical losses (designated as Qms),   
   >   
   > 3. Acoustical losses, i.e., the sound that is actually radiated   
   >    into the room which, for almost all drivers, is an insignificant   
   >    loss mechanism (this is why speakers are so inefficient).   
   >   
   > Now, #1 might seem contradictory to me declaration that damping   
   > factor is essentially useless, since we are (I assume) talking   
   > about electrical damping, but it becomes clearer once you realize   
   > the fact that it's the total resistance in the circuit that's   
   > responsible for the electrical Q. That not only includes the output   
   > resistance of the amplifier (which is where the "damping factor"   
   > spec comes from), it not only includes the electrical resistance   
   > in the crossover (not impedance, not inductance, but resistance),   
   > it also includes the DC resistance of the voice coil.   
   >   
   > The problem is, far and away, the single largest resistance in that   
   > collection is the DC resistance of the voice coil. That resistance   
   > dominates all others, and attempting to reduce the other resistances   
   > (crossover, speaker wire, amplifier) won't make a hill of beans   
   > difference in the damping of the system.   
   >   
   > Le's take a typical 8-ohm woofer, with an equally typical DC   
   > resistance of about 6.5 ohms. Let's assume the mechanical Q   
   > of the driver is 4, the electrical Q is 0.85, and the resulting   
   > total Qts is about 0.701 (Qts = Qes*Qms/(Qes+Qts). How is this   
   > going to perform with an amplifier whose damping fact is, say,   
   > 1000 vs one whose damping factor is 50. One might be inclined   
   > to say that there will be a factor of 20 difference in the   
   > damping of in each case (1000/50=20), but it turns out not to   
   > be so.   
   >   
   > Whatever with a damping factor of 1000, our "highly-damped"   
   > amplifier has an output resistance of 0.008 ohms, while our   
   > "not-so-well-damped" amplifier has an output resistance of `0.16   
   > ohms.   
   >   
   > The amplifier output resistance will increase the electrical   
   > Qes: in the case of the first amplifier, it will increase it from   
   > 0.85 to 0.851 (Qes' = Qes * (Re+Rg)/Re. In the second case, it   
   > will increase it from 0.85 to 0.87. NOt much.   
   >   
   > But it's the TOTAL Qts that we're interested in. In the first case,   
   > it will change from 0.701 to 0.702. In the second case, it will change   
   > from 0.701 to 0.714. In both cases, the actual damping of the system   
   > changes by less than 2%. This is less than the typical variation in   
   > these kinds of parameters one finds from one sample of a driver   
   > to another.   
   >   
   > The situation with midranges and, especially, tweeters is even   
   > more the case where these external resistances have little   
   > effect, because in these cases, the total Qts is more heavily   
   > dominated by the mechanical losses, and thus changes in the   
   > electrical Q have even less of an effect. Further, in many systems,   
   > the principle resonance is designed outside of the operating   
   > bandwidth of the driver by the crossover, so it has even LESS   
   > of an effect.   
   >   
   >> Tone bursts should Show any difference in DF.   
   >   
   > Tone bursts are very likely to tell you nothing useful at all.   
   > They're not a terribly useful test in and off themselves and,   
   > given the very small changes you're likely to encounter in   
   > the changes you're proposing, a tone burst is not going to   
   > reveal anything. Further, tone bursts are very hard to measure.   
   > Bump your microphone a little bit, change its position, and   
   > you'll measure a different tone burst   
      
   That tells me a lot about what I asked. Thanks.   
      
   Greg   
      
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