Deang Posted June 26, 2004 Share Posted June 26, 2004 djk suggests trying a 15R 25W resistor in parallel with the speaker and use the 4R tap. I ran the RF-7s that way. Works good. I hadn't thought about doing it with the K-horns. The QUADs do good with them on the 8 ohm taps, but then, the impedance curve of the AK-4 isn't near as wild as what the older networks have. Quote Link to comment Share on other sites More sharing options...
MrMcGoo Posted June 26, 2004 Share Posted June 26, 2004 djk, Do you have an impedance curve for the Reference-7 speakers? My information is that the impedances go below 4 ohms and even below 3 ohms in the bass frequencies. (References available on request.) My experience has been that the bass tightened up when I added an amp that has no trouble with low impedances. Bill Quote Link to comment Share on other sites More sharing options...
Soundthought Posted June 26, 2004 Share Posted June 26, 2004 John- Thanks for the reply. Quote Link to comment Share on other sites More sharing options...
djk Posted June 26, 2004 Share Posted June 26, 2004 "djk suggests trying a 15R 25W resistor in parallel with the speaker and use the 4R tap. I ran the RF-7s that way. Works good. I hadn't thought about doing it with the K-horns." I changed the post to read: (vented designs w/big magnets only). Don't think it will do anything for the Klipschorn or Heresy. Won't hurt. "My information is that the impedances go below 4 ohms and even below 3 ohms in the bass frequencies. (References available on request.) My experience has been that the bass tightened up when I added an amp that has no trouble with low impedances." Muddy bass is power supply related, anemic bass is lack of current. Marketing dictates everything must be liked by Joe Average, and Joe Average likes the sound of muddy bass from his 'boom box'. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 26, 2004 Share Posted June 26, 2004 john never ceases to amaze me! thanks for putting in the time to explain, I now understand yet another aspect of audio engineering that I did not before...regards, tony Quote Link to comment Share on other sites More sharing options...
maxg Posted June 27, 2004 Author Share Posted June 27, 2004 Wow... thanks John, I will be printing this thread off at work tomorrow to read your posts properly - there is obviously a lot more to this than met the eye. Glad I made the post... Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted June 27, 2004 Share Posted June 27, 2004 John is completely correct. Te first reference I quoted ignored the series resistance of the voice coil, and was misleading. Here's something I found on the PS Audio website, which reflects John's statements from a slightly more lay person perspective: The Damping Factor Debate. What do numbers really mean and do high amplifier damping factors have a noticeable effect on performance? Some amplifier manufacturers have introduced circuits that have much higher damping factors than conventional units. A high-quality traditional vacuum-tube amplifier can be expected to have damping factor ranging from 10 to 20, but some of the newer transistorized units boast of damping factors greater than 1000. Moreover, advertising and promotional literature for these models explains that the damping factor is a sort of figure of merit indicating the degree of control which the amplifier has over the loudspeaker. The higher the damping factor, the more accurately the speaker is controlled and the better the performances. Is this right? The subject is really pretty simple, but not that quite simple. To get started on the right track, lets go back and look at a few of the more basic things about audio power amplifiers. We can represent an amplifier as a black box with a set of input terminals on one side and a set of output terminals on the other, as in Fig. 1. And we have indicated a loudspeaker in the same way, except that instead of output terminals there are some waves emanating from the far side oh this particular box. The Loudspeaker Load The next step is to connect the speaker to the output terminals of the amplifier. As far as the speaker is concerned, when it looks at the amplifier, it sees a generator of audio signals which acts as though it has certain effective internal impedance. This can be represented as a resistor connected in series with the output terminals. Dont be missed by the fact that the resistor is imaginary the behaviour of the amplifier is exactly the same as if there were a resistor in plain sight of the back of the chassis. (Of course, generator impedance includes reactive characteristics too, but for our purpose here, a simple resistor will do nicely.) By taking the internal impedance of the amplifier (Rs)and bringing it outside the black box, we arrive at Fig. 2. Rs may be relatively large or it may be small. It may even be non-existent (zero internal impedance is not too hard to achieve in practice). We assume that the black box itself produces a constant output voltage regardless of load. Nevertheless, a certain load impedance is required for a certain output power at minimum distortion. This is the impedance that the amplifier must see when it looks at the speaker load and is the rated load impedance usually indicated at the amplifier output terminals. We will assume that the rated load impedance is 8 ohms in this case, no matter what the value of Rs. If we were going to use the amplifier to drive a constant-resistance load, it wouldnt matter whether the internal impedance was one ohm or 10 ohms or 10 000 ohms. But because the amplifier is used to drive a loudspeaker, the value of its internal impedance becomes a most important factor. For one thing, a loudspeaker does not present a constant load to the amplifier. An 8-ohm loudspeaker may measure 6 ohms at some frequencies and 60 ohms at others. If the amplifier has a high internal impedance, the voltage at the loudspeaker terminals will go up as the impedance goes up and go down as impedance goes down. Secondly, a loudspeaker cone has inertia. It has to be stopped and started and moved back and forth in very complicated patterns. If the internal impedance of the amplifier is too high, the speaker will move the way it wants to move instead of the way the amplifier tells it to move. The Damping Factor Rather than specify the value of Rs, it has become common to translate this into a figure which is called the damping factor (DF) of the amplifier. As we have seen, it really has more to do with coupling than damping. One definition of damping factor is the ratio of rated load impedance to the amplifiers own internal impedance. For our 8-ohm black-box amplifier, an internal impedance of 8 ohms gives a damping factor of one. An internal impedance of one ohm gives a damping factor of 8. And if Rs is only 1/10 ohm, the damping factor is 80. These factors are shown in Fig. 2. This being the case, common sense leads us to believe what the proponents of high damping factors say in their sales literature, namely, that the damping factor is a numerical indication of coupling between amplifier and loudspeaker and the higher the figure, the better off we are. Unfortunately, we cannot always rely entirely on common sense. For one thing, a particular loudspeaker may not require a high damping factor to accurately follow the signal from the amplifier. Some loudspeaker systems give smoothest performance if the amplifier has a damping factor somewhere between one and three. But there is an other property of dynamic loudspeakers, all dynamic loudspeakers, that has to be appreciated to really understand how the damping factor works. It is this other half of the actual damping factor which so many people seem to ignore. A dynamic loudspeaker has a voice coil, and the voice coil has electrical resistance. In most practical cases, the d.c. resistance of a loudspeaker is about 80% of its rated impedance. This is not always the case because different manufacturers use different impedance-rating methods, but such variations will not affect what we are talking about. Let us suppose, therefore, that our 8-ohm black-box speaker has a d.c. resistance of about 6,4 ohms. The voice coil resistance is effectively in series with the working parameters of the loudspeaker, just as is the internal impedance of the amplifier. And this time it isnt even an imaginary resistor; it is a real coil of wire that measures 6,4 ohms. Instead of the circuit of Fig. 1, what really happens is shown in Fig. 4. the resistance that isolates the loudspeaker from the amplifier is not just Rs, but rather Rs plus Rvc. When the two are connected together, ,either the speaker not the amplifier can distinguish between Rs and Rvc. The actual damping factor depends upon the sum of these two resistances, not upon one or the other. Table 1 shows the specified damping factor of an amplifier against the actual over-all damping factors for a wide range of generator impedance values when the amplifier is connected to an 8-ohm speaker. The actual damping factor values are computed by adding Rs and Rvc, the dividing by the rated load impedance. In this instance we have used an 8-ohm loudspeaker with a d.c. resistance of 6 ohms to prepare the chart. The exact figures are not particularly significant the point is that the resistance of the speaker voice coil is the limiting factor. Amplifier R (ohms) Amplifier DF Actual Over-All DF 8 1 0.57 4 2 0.80 2 4 1 1 8 1.14 0.5 16 1.23 0.25 32 1.28 0.125 64 1.30 0.05 160 1.32 0.025 320 1.33 0.0125 640 1.33 0.0000 Infinity 1.33 Table 1: The actual damping factor (with loudspeaker connected) is limited by the speaker voice-coil resistance. Figures are for 8-ohm output terminals to which speaker having nominal 8-ohm impedance and 6-ohm voice-coil resistance is connected. Note that changing the amplifier damping factor from unity to 8 makes a substantial change in the actual damping factor, though it is not a 1:8 change but a 1:2 change. But changing the damping factor from 8 to 16 makes very little difference in the actual damping factor, and anything more than 16 has very little effect indeed. If we increase the damping factor from 16 to 160, the change is effectively less than 10%, not 10 or one. Conclusions It should be obvious at this point that the quoted damping factor of an amplifier is important only if the figure lies somewhere below 20 or so. Changing the damping factor from 2 to 20 does change the performance of the loudspeaker system (for better or for worse, depending upon the speaker). But trying to prove that a damping factor of 200 or even more is somehow better than one of 20 is pretty unconvincing because the effective difference in the practical case cited is only that between 1,25 and 1.32. But someone is bound to insist that exhaustive tests have been made with such and such amplifier and that a very high damping factor is better than one down around 10 or 15. The bass is just a little cleaner, just a little more natural and open, is the way the argument usually runs. In a given situation, this may very well be true. Rs is a byproduct of negative feedback. The more such feedback that is thrown into a power amplifier circuit, the lower the generator impedance and the higher the damping factor. The point is simply that if a lot of feedback has to be used to lick the distortion in a particular circuit, fine use it. But dont believe that the reason it sounds good because of some astronomically high damping factor. When I get a letter from someone who is worried about buying a certain amplifier because it has a specified damping factor of only 15 to 16, I cant help but remember an old, old joke. It goes like this: A scientist is given a public lecture. During the course of his speech, he predicts that in 100 billion years human life will become extinct. A man in the audience, obviously upset, ask the lecturer to repeat the statement. I said, quotes the professor, that in one hundred billion years, human life will no longer exist. Oh, thank goodness, replies the man, much relieved, I thought you said one-hundred million!. By George L. AUGSPURGER, James B. Lansing Sound Inc., January 1967 Quote Link to comment Share on other sites More sharing options...
Colin Posted June 27, 2004 Share Posted June 27, 2004 Man, what a tag team, John and Ray, thanks guys, more questions coming, hafta finish reading first Quote Link to comment Share on other sites More sharing options...
rigma Posted June 27, 2004 Share Posted June 27, 2004 John How would an 8 ohm woofer compare to a 16 ohm. Would the 16 have higher net damping? Rigma Quote Link to comment Share on other sites More sharing options...
Did not mean to offend SO SOR Posted June 27, 2004 Share Posted June 27, 2004 Did not mean to offend. SO SORRY! Quote Link to comment Share on other sites More sharing options...
djk Posted June 27, 2004 Share Posted June 27, 2004 "How would an 8 ohm woofer compare to a 16 ohm. Would the 16 have higher net damping?" A trick question? Why shouldn't it be the same? The DC resistabce is twice that of the 8 ohm woofer. Quote Link to comment Share on other sites More sharing options...
WMcD Posted June 27, 2004 Share Posted June 27, 2004 I'd like to point out that John W. brought up something which has more influence than the amp. It is the Bl factor which sets the Qes. The mechanism which prevents the diaphragm from moving when it shouldn't is that the magnet and voice coil are acting like an electrical generator. The stronger the generator, the more difficult it is to crank. The voice coil is acting like a hand on the diaphragm. Now this is to say the voice coil (l) and magnet ( act like a motor when the amplifier supplies current, and like a generator (to make EMF) when the diaphram supplies "flopping around" force. Now it is true that the electrial load on the generator is the voice coil resistance (say 8 ohm) plus the output impedance of the amp feeding it (say 0.8 or 0.1 or 0.01 ohms). As pointed out, that means you can't change the total loop resistance very much by changing the totals to 8.8 or 8.1 or 8.01. But, again, the creator of the damping force is the strength of the motor/generator of the Bl product. As can be infered from the equations, big Bl products lead to a low Qes with some little bit added by the Qms. They combine to for the Qts, which is the Q of the total system of the raw drive. We see in the spec sheets a lot of speakers with an actual voice coil resistance of 8 ohms or so. Yet the Qts vary quite a bit. Hence the actual damping differs. The efficency varies for the same reason. Qes and Qts of raw drivers are caluclated assuming a zero impendance load. So damping factor isn't even in there. Or there is an infitely high damping factor assumed. There other thing which keeps the diaphragm from moving is the air load upon it. The air load is higher on the diaphragm (preventing movement) when there is horn in front of it, making it force air into the throat (small end) of the horn. Also, in a bass reflex speaker box, the load is higher when the springy air in the box and the mass of the air in the vent (or the mass of the passive radiator) go into resonance. There the diaphragm is forced to pump the slug of air in the vent back and forth. We hear some of that in bass reinforcement from the vent. This is why woofer movement is always very low in the frequency range where the vent is working. One recent article showed that when the bass reflex system is tuned to 50 Hz, the effect (going down in frequency) starts at 100 Hz, and is increasing as frequency goes down. Below resonance it drops off. The load on the back of the diaphragm is reduced below box-vent resonance and the diaphragm is free to move. This is why PWK suggested a sub sonic filter to keep record warp and the like from bottoming out the woofer. Of course now Telarc puts infrasonic sound effects in its CDs. It replaces record warp as something to worry about. Smile. Gil Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 28, 2004 Share Posted June 28, 2004 John, We have all heard "good" bass vs. "bad" bass from a given source and given speakers but differing amps. You are saying that there is no valid spec to determine the handling of a reactive mechanical load on the amp? Then what is all the fuss about Damping Factors all about?! DM Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 28, 2004 Share Posted June 28, 2004 ---------------- On 6/27/2004 1:53:34 PM rigma wrote: John How would an 8 ohm woofer compare to a 16 ohm. Would the 16 have higher net damping? Rigma---------------- First off, there is not "net" damping. The electrical damping of a driver (Qes) is a linear function of moving mass (Mms), The resonance frequency of the moving mass (Fs), the DC resistance of the voice coil (Rvc) and inveresly proportional to the B*l-product squared. All of these paramters must be considered. No single parameter can be used to determine Qes. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 28, 2004 Share Posted June 28, 2004 ---------------- On 6/28/2004 2:35:26 PM D-MAN wrote: Then what is all the fuss about Damping Factors all about?! DM ---------------- Ever hear the expression "much ado about nothing?" applies here. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 28, 2004 Share Posted June 28, 2004 ---------------- On 6/27/2004 5:56:34 PM William F. Gil McDermott wrote: Now this is to say the voice coil (l) and magnet ( act like a motor when the amplifier supplies current, and like a generator (to make EMF) when the diaphram supplies "flopping around" force. ---------------- I would like to clarify this statement. The force (F) applied to the cone by the voice coil is F= i x (B*l) where i = the current passing thru the coil, B is the flux density in the gap and l is the length of voice coil wire. As is shown the force is directly proportional to the electrotransduction factor, B*l. The speaker impedance is a combination of the three mechanisms, the frequency dependent resistance, the inductance of the coil and the back-EMF (i.e. motional impedance) of the coil moving in the gap. Consider the impedance plot of a typical woofer in free-air. At high frequencies the impedance is driven by the voice coil inductance and losses associated with eddy currents generated in the top plate of the magnet structure. As the frequency is lowered the impedance drops also until the voice coils DC resistance is the dominant fraction of the impedance. As the frequency approaches Fs, the motional impedance (i.e. back-EMF) becomes significant and the impedance rises again until the Fs of the moving mass is reached. At Fs the velocity of the coil in the gap is at a maximum and impedance peak at Fs is observed. The size and width of this peak is governed by the B*l-product. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 28, 2004 Share Posted June 28, 2004 Horns.... There is another contributor to the total impedance, the air-load that acts on the cone directly and relected to the amplifier thru the voice coil immersed in the magnetic gap. For a direct radiator the contribution to the total impedance is very low <1% and usually ignored. In a horn loaded driver this in NOT the case. Look at the graph below. The blue line is the K33E in free air. The red line is the same driver monted into the Klispchorn. Notice how the mounted driver has a higher impedance above the resonace peak. That is the air-load in the throat acting directly on the cone. Quote Link to comment Share on other sites More sharing options...
maxg Posted June 29, 2004 Author Share Posted June 29, 2004 OK - bear with me a little here - we got real technical real quick and this is not my area. In my original question I was wondering why I get more controlled and better bass with one amp Vs. others. From what I read here the effect of the amp on the circuit is relatively minimal in terms of woofer movement. In other words I should not be observing the very thing I am observing. Have I missed something? Bear in mind I am not talking about an SS amp Vs a tube amp. I am talking about a 70 wpc el34 amp Vs. a 45 wpc KT88 amp. The amps I am refering to are: The 70 watt amp : http://www.tsakiridis-devices.com/Powerhouse.htm The 45 watt amp : http://www.tsakiridis-devices.com/Artemis.htm Although the same lack of bass control is also exhibited by this: http://www.tsakiridis-devices.com/new_Achilles.htm Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 29, 2004 Share Posted June 29, 2004 ---------------- On 6/29/2004 2:33:04 AM maxg wrote: Although the same lack of bass control is also exhibited by this: ---------------- We've already established that bass "control" (i.e. electrical damping) is not provided by the amp so the differences in what you are hearing is not associated with the damping factor. I cannot comment on the individual amplifiers you are referring to but the output transformer, and how it is engineered, is certainly critical to low frequency performance and this is what djk was getting at. The low frequncy limit of the power bandwidth is limited by the physical size of the transformer core and the quality of the material used in it's construction. If the core saturates, the show's over. There's a old saying that goes something like... "Not all heavy output transformers are good ones but all good output transformers are heavy" Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 29, 2004 Share Posted June 29, 2004 I took a peek at the amps you are referring too. A specification that is something worth looking for is the frequency range at full rated output with no more than 1/2% distortion permissible. Quote Link to comment Share on other sites More sharing options...
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