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New member Username: Hi_fi_guyPost Number: 4 Registered: Nov-06 | hello all, I have this query on damping factor. Damping factor as I understand is the amp's ability to control the speaker cones' excursions thereby providing a better controlled sound. (Please correct me if I am wrong of course.) While going through the specs of various amplifiers, such as Musical Fidelity A3.5 & A5, NAD 372/272 etc, I find that their damping factor values are less than 500 or 200. However, the Rotel RB-1080 has a damping factor of 1000. Does this mean the Rotel is that much better than these other amps, or is this parameter to be viewed in consideration with other values as well ?? How is the difference in this value so large when Rotel compares to the other amps ? Thanks, hi_fi_guy |
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Gold Member Username: NuckPost Number: 4712 Registered: Dec-04 | It is a calculated value, dependant upon speaker impedence in one calculation, which makes an advertised value a bit moot. http://www.audioholics.com/techtips/audioprinciples/amplifiers/dampingfactor.php |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9388 Registered: May-04 | . My best advice is to ignore damping factor as a meaningful specification of an amplifier's ability to do anything. It is, as are almost all static measurements of an amplfier's performance, taken under conditions that do not replicate how an amplifier actually operates. Reading Nuck's referenced article and plugging "damping factor" into a search engine will give you more insight into how to interpret the spec you see on paper. Damping factor was at one time considered to be more than adequate if the spec was a factor of 50:1. Then Phase Linear promoted a number of 1000 on their 400 and 700 model amplifiers back in the late 1970's. Since that time damping factor has been kicked around as another relevant spec in the many irrelevant numbers which are meant to describe an amplifier's performance. Any number stated for damping factor is an inadequate reference that cannot take into account the effects of a (totally unknown) dynamic speaker being connected to the amplifier and reproducing a signal that constantly fluctuates in level and frequency. The number has even less value when using a non-dymamic type driver such as a planar, ribbon, electrostatic, etc. Designing an amp for these on paper specs is gamesmanship and not much else as the derived number can be shifted by several means and there are no standards for taking most of these secondary specifications. Somewhat like the home theater in a box power spec that states 1200 watts for $199, what you read might not be what you get. This shouldn't be taken to imply Rotel is dishonest in their numbers, but rather generally they are essentially giving you the facts as they want them to be seen. . |
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Gold Member Username: NuckPost Number: 4724 Registered: Dec-04 | This should not be seen as a kick at Rotel(or MF or Nad either). When a reputable manufacturer states a reliable factor of 100(as opposed to a zilion), they MAY have a quantifiable number driving a known fixed load. Known only to them. |
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Bronze Member Username: LeonskiPost Number: 13 Registered: Jan-07 | If I remember right....follow this. Speakers STORE energy, right? When this energy is released it goes BACK to the amp, or sometimes in the case of harmonics (over driven drivers, for example) can get routed thru the crossover to another driver,(burn, baby, burn) the amp presents an impedence to this return signal. Damping factor is the ratio of Amplifier impedence (going backwards thru the speaker terminals) to speaker impedence. Higher is better, in general. Also, in general this is not quite meaningless. Once you have reached a certain level, increasing it doesn't add much. Also, Jan is right in saying that the conditions under which it is measured are a dicey at best. You might think of damping factor as the ability of an amplifier to absorb BACK EMF from a speaker. |
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Bronze Member Username: LeonskiPost Number: 14 Registered: Jan-07 | One other thought>> the above discussion becomes near-meaningless with a pure resistive load. Now, if someone could explain a 'complex impedence curve', that would be something! |
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Gold Member Username: NuckPost Number: 5686 Registered: Dec-04 | Complex impedence curve is based on resistance and load/time. The impedence is dependant on current x time of transfer, for active or currant impedence. Aw shite, I'm gonna hafta get a beer for this. |
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Gold Member Username: NuckPost Number: 5687 Registered: Dec-04 | However, my new/old Pioneer pre/amp has a damping factor selector on the face, in a 3 position hard selector, defined as a position for both 8 and 16 ohm speakers. This may or may not have an affect on the output impedence. |
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Bronze Member Username: LeonskiPost Number: 15 Registered: Jan-07 | Damping factor switch? Never heard of such a thing! I'd love to see the sketchomatic of that circuit. But back to the complex impedence curve, I remember a magazine that would publish them........a spiral graph, like a nautilus shell. The horizontal center line was pure DC resistance while left to right on the base line was the resistence scale. Now, here is where my memory fails....I don't know what above and below the center line was called. Both areas represented 'stored energy' in the speaker. At cross over points there was a little circle. These graphs were useful in seeing just how difficult a load a speaker would be. You could learn to read these. But as for sound quality? Who knows? Maybe my memory is wrong about what this graph was called, (CRS), but you could tell at a glance how many 'ways' a speaker was, resonant frequencies and any major crossover glitches....I'm going to do a web search for this and see if I can find one to link to this thread.............. |
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Gold Member Username: NuckPost Number: 5691 Registered: Dec-04 | Yup, a damping factor selector! Dunno what it does, I plugged in the preamp and it does not light up. D'oh! Gotta go into it today, sober once again. Leo, I think I remember that graph as defining phase angle, the tangents representing crossover points of phase using different orders of XO. The 'stored' energy being the counter EMF generated by the larger motor of the speaker assembly. I hope you stick around, Leo. |
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Gold Member Username: NuckPost Number: 5692 Registered: Dec-04 | VPI, is this useful at all? |
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Gold Member Username: Touche6784USA Post Number: 1166 Registered: Nov-04 | considering the last time VPI logged in was a month ago i am doubting it. but its been useful to me and im sure others. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9705 Registered: May-04 | . ls - "Damping factor is the ratio of Amplifier impedence (going backwards thru the speaker terminals) to speaker impedence." Going backwards? Not sure what that means. Damping factor is calculated from the source impedance (output impedance) of the amplifier in relation to the nominal impedance load it is driving. The most basic problem with the caluclation is neither the source nor the speaker impedance remains constant at varying frequencies or temperatures. So, damping factor is calculated using the static load of an ideal purely resistive circuit at a nominal, usually eight Ohm, value. The output impedance of the amplifier is, to the best of my memory, taken from a 1kHz frequency. If I understand your post correctly, you are incorrect in thinking speakers "store" energy. Yes, they do in some fashion but not for the purposes we would be discussing here. (Though cabinet/driver resonances will affect the load the amplifier plays against.) In the case under inspection, the motor assembly of the driver will produce energy and it is this energy - in the case of an AC driven motor, alternating voltage/current - which the amplifier must "damp" in order to control the motion of the driver. Most amplifiers achieve this damping by way of feedback. By lowering the output impedance (adding more feedback, direct coupled vs. transformer coupled) the effect of the speaker on the amplifier's ability to deliver voltage/curent relative to the rising and falling load impedance of the speaker (its complex impedance curve) is minimized. In simple terms, lowering the output impedance of the amplifier results in fewer frequency response errors as the amplifier is therefore more capable of delivering constant voltage and current to the drivers. In effect the amplfiier "sees" a more ideal purely resistive load. If only it were that simple. BTW, this really has little or nothing to do with harmonics since it is primarily the larger motors of the low frequency system which produce sufficent back EMF to cause problems in most amplifiers. And the back EMF almost always must travel back through the crossover since it typically represents the only path to ground for the driver's motor. I believe you are referring to Audio magazine and its representation of phase angle against impedance relative to frequency. It was all but impossible to decipher the nautilus in a meaningful manner and the measurement usually added significant amounts of text to an otherwise useful article. Stereophile currently produces a far more representative, or at least useful, value which shows impedance as one line and phase angle as another on a simple spreadsheet style table where the baseline is freqquency. I am going to assume "complex impedance curve" is a colloquialism meant to imply the impedance load (a complex mixture of resistance, inductance and capacitance) of a typical speaker system is anything but static. However, the phrase implies the only difficulty in modern speakers is presented by the impedance load itself. In many cases, it is the resulting phase angle derived by the complex LCR crossover components which causes the problems for an amplifier. By careful selection and design which plays inductors against capacitors the overall impedance swing can remain fairly benign while the phase angle takes a severe beating. Since the "phase angle" is obviously tied to the "impedance" of a typical multi-way speaker it is difficult to separate out one from the other under dynamic conditions but it is clear that asking a voltage gain device (such as most contemporary amplifiers) to drive a "complex impedance load" is all but ignoring the nature of either the amplifier or the speaker. Once again I'm left wondering how all this manages to work at all and how in the world it became the norm for audio design. "Damping factor is the ratio of amplifier impedence (going backwards thru the speaker terminals) to speaker impedence. Higher is better, in general. Also, in general this is not quite meaningless." We are treading dangerously close to discussing Negative Feedback here and I try to avoid that topic as much as possible. Unfortunately, the application of NFB is anything but meaningless. It is, however, another topic. . |
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Gold Member Username: NuckPost Number: 5700 Registered: Dec-04 | As is the Global feedback topic. Thanks, Jan. How's that, Leo? Hey I warned ya. |
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Bronze Member Username: LeonskiPost Number: 18 Registered: Jan-07 | yeah, Nuck, I'm good, And while I need to re-read Jan's post several times, I can already see I have a minor disagreement. Jan says: If I understand your post correctly, you are incorrect in thinking speakers "store" energy. Yes, they do in some fashion but not for the purposes we would be discussing here. Speakers DO store energy. When speaker cone is at any excursion from 'at rest', it will generate a small current when going back to rest. A large woofer can generate quite a kick, while tweeters not. If the amplifier can force the woofer into perfect compliance, there will be minimum or no such back emf. A single 'push' will generate DC. However, under dynamic...dare I say complex? load conditions this will be a AC, up to and including hi enough frequencies to get routed to the tweeter....The difference between the desired frequency and what is produced. That is probably why 'faster' drivers are desirable and why Velodyne made that acceleration sensor on some of there Subs.....Do they still do that? In advertising it was said to provide feedback on driver position relative to waveform which the amp used to change ITS signal so the speaker would conform more closely! I need a beer. This is not harmonics in the sense that the amplifier is distorting, but the speaker distorting due to bad tracking to the input (not enough power or pysical limits of the driver) It will be the woofer that is the #1 victim, here. In years past, I saw the then-new Braun Tri-Amps. 10" or 12" 3-ways with a total of 100 watts rms to each enclosure. Divided up as woof=50 / mid=35 / tweet=15 I an considering the section on complex impedence curves. Sounds like Jan has seen these and knows about them.....I haven't seen 1 in a ton of years. I closest I can come, so far, it the Smith Chart, which isn't the same at all. Still can't possibly disagree with your conclusion, however, that Speaker and Amp designers need to sit down for a little chat! ...........thanks........... |
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Bronze Member Username: LeonskiPost Number: 19 Registered: Jan-07 | I just had an idea on how to 'test' this..... take a battery....6 volt lantern would probably do. DO NOT use a car battery, you'll FRY SOMETHING!. You'll need a speaker....a woofer of some sort would work best. Don't use a speaker in a crossover, but a bare driver. Connect an analogue voltmeter to the speaker. An old Simpson VoltOhmist is ideal (260?) use the zero knob to center the meter. Momentarily short the battery with the speaker. The voltage will kick UP when the battery is connected and DOWN when disconnected. Careful measurement with some real stuff will give you the magnitude of the back emf and you can than decide for yourself how much of an issue it really is! thanks again...................... |
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Gold Member Username: NuckPost Number: 5777 Registered: Dec-04 | Leo, I am not sure what your test is going to prove. A simple stroke of a driver will produce a DC enf, but a 'complex' input will produce an AC signal? Even based on frequency, and nothing else, the motor of a driver has no rectifier, only permanent magnets. The outputs of ss amplifiers are de-coupled in several ways depending on the output device used. DC de-coupled devices are common, but a bit messy in the output quality. More sensitive circuits, used in more expensive amps, can introduce feedback in conjunction with sensing feedback. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9733 Registered: May-04 | . Alas, ls, I too have disagreements with your latest posts. I'm thinking you didn't correctly read my post from Saturday, February 03, 2007 - 12:21 PM. Let's address this by looking first at your statement, "Speakers DO store energy. When speaker cone is at any excursion from 'at rest', it will generate a small current when going back to rest." ls, you are mistaking "store energy" with generate energy. The voltage produced by the motion of the driver's voice coil inside the magnetic gap is not "stored" energy. It is produced energy newly "created" ( OK, OK "transduced", please, do not get philosophical on me here) by the motion of the voice coil. Should the driver not move in any direction, practically speaking there would be no energy being sent back to the amplifier. Stored energy is quite another matter all together. Since we are discussing back EMF all this must be addressed with a case by case situational criteria. I believe all this that you said, "When speaker cone is at any excursion from 'at rest', it will generate a small current when going back to rest", simply restates what I posted here, " ... the motor assembly of the driver will produce energy ... " When you say, "If the amplifier can force the woofer into perfect compliance, there will be minimum or no such back emf", you are simply incorrect. It is the mere, or shall I say, very motion of the driver's voice coil in the gap between the magnet and the pole piece which creates a "motor" of sorts. If the driver's voice coil moves within this gap to reproduce a signal, it will generate voltage which must be dissipated somewhere. Hence, back EMF. So, unless the speaker is not moving at all, there will be some back EMF any time the voice coil is in motion. Of course, if the driver is not moving, all of our problems have been solved, save one important item. No sound! "A single 'push' will generate DC", is also wrong. A single "push" will produce essentially nothing as the motor must move forward and backward in order to produce anything. If the voice coil moves forward and stays in that poition, which it will should it be fed DC, it would burn out the motor (voice coil) if the DC were not released. Moving from this extended position to the "at rest" position will once again produce essentially no voltage until it once again moves within the gap. A voice coil represents the armature of an AC motor, to my knowledge, an AC motor cannot produce DC no matter what Tinkerbell says. "That is probably why 'faster' drivers are desirable and why Velodyne made that acceleration sensor on some of there Subs." I can't say for certain about Velodyne's marketing skills, but I doubt this is why the sensor was placed there nor why "faster" drivers are desirable. The "speed" of the driver has no effect on the AC voltage created within the voice coil assembly. Given the same size driver and voice coil, one "fast" and the other "slow", they will both have to move the same amount in order to produce similar frequencies. I believe the sensor was used to correct the non-linear or non-pistonic movement of the driver by way of a servo system. The rest of the gobbledegook was there just for the marketing department. "This is not harmonics in the sense that the amplifier is distorting, but the speaker distorting due to bad tracking to the input (not enough power or pysical limits of the driver)" I have to be honest and say I don't have a clue what that means. And, I certainly don't know what is has to do with damping factor. "Don't use a speaker in a crossover, but a bare driver." ? "Momentarily short the battery with the speaker." ?? Short? Don't you mean "create a circuit"? The problem I have with your scenario, ls, is you are asking me to put DC through the voice coil of a driver. The voltage read on the meter cannot be AC voltage, which is what we are discussing by way of back EMF, since supplied only DC voltage, the driver will only move in one direction. We, therefore, cannot be measuring the back EMF of the driver. And should we think we were, we could quickly see the logical conclusion that the amount of back EMF Ac voltage coming from the driver's coil will be relative to the amount of AC voltage going into the driver. That means, first, as Nuck has stated, speakers have no rectifier and cannot convert AC voltage to DC voltage. And, as you put more voltage into the voice coil in order to drive the speaker to a higher SPL or lower frequency (i.e. more motion), you will get more back EMF from the voice coil headed back to the driver. Without sufficient damping, the amplifier will go into oscillation and burn up. Now we are right back at the beginning of this thread. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9734 Registered: May-04 | . "The outputs of ss amplifiers are de-coupled in several ways depending on the output device used." Not sure why that only applies to ss amplifier. But, the sad fact is, most contemporary solid state amplifiers are direct coupled to the speaker. The inputs of the amplifier are "decoupled" to block DC which might enter the amplifier, but most outputs no longer rely on decoupling. Stop looking at that 1970's Pioneer, Nuck. . |
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Bronze Member Username: LeonskiPost Number: 22 Registered: Jan-07 | I'll make this quick....I have to get up early tomorrow. Let me see if I get this. If you put DC to a woofer, it will move one way and stay. When the current is released, the driver will restore to the center position. It is this movement which will produce a little bit of current. You have stored energy in the speaker surround, which is turned back into electricity when the cone moves back to center. This electricity is what I meant by 'back emf'. You get a current flow any time a coil of wire moves in a magnetic field. The whole idea is that it works BOTH ways. Electric makes motion and motion makes electric. What I meant by the harmonic reference was that there are 2 distortions. I don't know if it makes a difference, though. Your amp can have too little juice and distort, or you can put too much to a speaker and IT will distort. The harmonic which I meant was when a speaker, usually a woofer, is unable to follow the waveform. The result is that frying noise a tweeter can make. I have a CD of Wellingtons Victory,(TELARC) a Beethoven work originally written for an automated orchestra. This recording features 12lb black powder canon which will DESTROY speakers. The first few shots sent me running for the volume control. I thought my woofers were going to eject themselves from the box and the tweeters rang/hissed. (Kenwood amp of 60x2) The DC scenario is to test this theory, only. If you can put some energy into a speaker, you can perhaps measure how much comes out. This would be a worst case measure, since real music is AC and would push the cone back, under control. You'd see a little 'kick' on the voltmeter. I suggested an analogue meter, since I don't know how fast a digital meter is, although there are 'capture' meters which are pretty quick. One final note, than I gotta crash. And then re-read everything tomorrow! Driver speed is important. If you are to get out what goes in, the driver cannot lag in its conformance to the signal. Subs are prone to this since they feature huge excursions and move huge amounts of air. Thus the equally huge amps...to try to force compliance with the input signal. I can't say for certain about Velodyne's marketing skills, but I doubt this is why the sensor was placed there nor why "faster" drivers are desirable. The "speed" of the driver has no effect on the AC voltage created within the voice coil assembly. The Velodyne sensor was an accelerometer. Just compare what the woofer is doing to the input signal and apply correction. Also, the VC creates AC only when it fails to follow the input signal exactly. Speakers also store energy in the Capacitors and Inductors. Which Brings me full circle back to one of YOUR original points, of which there can be NO ARGUEMENT. That is, Why the heck can't speaker designers and amplifier designers just talk? All this stored energy talk is making me nutty. You guys are great. Thanks for taking the time to answer. later.............. |
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Bronze Member Username: LeonskiPost Number: 23 Registered: Jan-07 | Jan, I have an idea. It is really tough to keep track of everything we are saying. I have a suggestion. Lets see what we agree about. Than we can talk about what we don't agree on. for example: You have said that 'speaker designers and amp designers don't talk'.... I totally agree. What we need to figure out is where we do / don't agree and than we can write to a point without getting so ...global... in reply. Good idea/?........... |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9735 Registered: May-04 | . OK, you start. |
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Bronze Member Username: StryvnPost Number: 18 Registered: Dec-06 | owww. My head hurts. Allright. Back to the top. |
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Bronze Member Username: LeonskiPost Number: 24 Registered: Jan-07 | http://www.crownaudio.com/pdf/amps/damping_factor.pdf Quick article from Crown, on damping factor. Reasonable explanation, easy to follow. |
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Bronze Member Username: LeonskiPost Number: 25 Registered: Jan-07 | Ok, Jan, lets start with stored energy. I have a couple of questions. Do speakers store energy? If so, is the energy mechanical or electrical? Is there interaction of stored energy with driver speed? and last: For the purpose of speakers, is there a difference between stored and generated power? OH, my 'kick' test is just designed to show that a speaker can store energy (mechanical) and release it back to the system as electrical energy. I have a speaker in the garage I will try this with and see. is this an ok start? |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9738 Registered: May-04 | . How about first we set the guidelines that "driver" means a single unit, the item that produces sound whether that be high, mid or low frequencies. It alone contains a motor assembly. "Speaker" on the other hand refers to the complete system of drivers that would make up a multi-driver array and this would include all the components used to make the system including the crossover and the enclosure. "Do speakers store energy?" I would have to say, no, it is impossible for a speaker to "store" energy. When I think of storing energy I have a capacitor/battery in mind. A speaker cannot accomodate that type of energy storage. However, if you rephrase the question, you might get a "yes". The remainder of your questions seem to assume a "yes" answer to the first question. So, I have to stop at this point since I can't answer a question that has no relative meaning regarding how a speaker operates. . |
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Bronze Member Username: LeonskiPost Number: 26 Registered: Jan-07 | Now we're getting somewhere! What can I do or propose to do to prove that drivers and indeed full speaker systems do indeed store energy? Will you accept any proof or is your mind made up? If that were not true, why does anyone concern themselves with back emf? Since full speaker systems are chock full of capacitors (storage device) resistors and inductors (another storage device) I don't see how it isn't the case! As a rephrase of the question, would you accept that speakers store energy for short time periods? What got me onto all this years ago was the Carver Magnetic Field power supply in my 'cube'. There is a choke in there the size of my fist. A choke is basically a transformer winding without a secondary winding. When the field collapses, it puts out quite a surge of electricity. Energy in a speaker is changed back into electricity when the input is removed. As a test (proposed by none other than Nelson Pass, take a bare driver....Woofer preferred and 'thump' the cone. Now, short out the driver with a piece of wire. Re-Thump. The noise will be different, because the current generated will now have somewhere to go. Also, can you help me rephrase the question in a more.....acceptable manner? I will try to find the Nelson Pass article and link it..... |
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Bronze Member Username: LeonskiPost Number: 27 Registered: Jan-07 | http://www.studio-systems.com/audiofeatures/novdec99/dampingFactor/damp01.htm Here is link to article in which the author specifically refers to stored energy.....in the spider and surround.....and he relates it to damping. come to think of it, if speakers perfectly conformed to every input, current return to an amplifier would be very lower than current systems. |
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Gold Member Username: Arande2400dB could probably d..., SouthWest Mi... Too Many DBs... Post Number: 1087 Registered: Dec-06 | As the way I am (Nuck calls me a mad scientist)...I have to try that thump thing!!! |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9740 Registered: May-04 | . "What can I do or propose to do to prove that drivers and indeed full speaker systems do indeed store energy?" I don't know. That is what you will have to decide. My mind is not made up one way or the other, but I will require some sort of proof other than an obscure article which doesn't prove your point that speakers store energy. I'm sorry but the article you linked is very difficult to follow due to the layout of the pages. However, if I understand the flow of the article it merely states, "Now the cone having been pushed forward, due to the spider and suspension, it is free to return ... " This does not indicate the spider and suspension "store" energy. It simply indicates the spider and suspension are the components of a driver which allow pistonic movement of the cone relative to the magnet/center pole. Technically, the spider and suspoension are not "damping" components in a driver but rather, at a base level, the centering devices which must also allow free motion. Both components serve other purposes but centering the driver and determining the Xmax of the driver during motion are their dominant functions. "If that were not true, why does anyone concern themselves with back emf?" Because the voice coil generates, or more properly 'transduces", voltage when it is in motion within the magnetic gap. Generating energy or transducing energy and storing energy are vastly different functions in a motor. "Since full speaker systems are chock full of capacitors (storage device) resistors and inductors (another storage device) I don't see how it isn't the case!" First, I think you would have a difficult time convincing a speaker designer an inductor is a storage device in the same fashion as a power supply capacitor or a battery. Even relating the capacitors used as crossover components to capacitors used as storage devices is quite a stretch (compare the function of polarized and non-polarized capacitors to begin with) and, more importantly, entirely misses the point of how back EMF is produced or why it is a problem to an amplifier. "As a rephrase of the question, would you accept that speakers store energy for short time periods?" No, not for the purpose of discussing back EMF and damping factor. The caps in the crossover are not storing energy. Their existence in the signal path has all but nothing to do with any discussion of damping factor. A bi-amped speaker system without crossover components within the system proper would still have back EMF transduced by the drivers in the system. The spider and suspension are not responsible for storing energy. You are yapping up the wrong cypress here. "A choke is basically a transformer winding without a secondary winding. When the field collapses, it puts out quite a surge of electricity." A choke is not a storage device. A choke can be used as a filter, or as an isolation or smoothing device. Its "storage capacity" is measured in milli-seconds. To claim it stores energy is stretching too far. http://www.aikenamps.com/Chokes.html "Energy in a speaker is changed back into electricity when the input is removed." Once again I have no idea what that means. It is, I'm afraid, goobledegook. Remove the AC input voltage and the driver ceases to move. No motion, no back EMF. We are right abck to what I posted yesterday, "Of course, if the driver is not moving, all of our problems have been solved, save one important item. No sound!" "As a test (proposed by none other than Nelson Pass, take a bare driver....Woofer preferred and 'thump' the cone. Now, short out the driver with a piece of wire. Re-Thump. The noise will be different, because the current generated will now have somewhere to go." You'll have to show me where N.P. would have said such a ridiculous thing. If you short the driver's + and - connections together, practically speaking there is no where for the energy to go. Where do you propose it travels to? We could argue that the voltage across the shorted terminals forms a sort of negative feedback loop, but that too is stretching for a point. You have shorted the motor. If you throw a dead short across any AC motor, you will have a hel1 of a time making it move. The larger the motor the more it resists movement. Even if this suggestion were absolutely true, I still don't have a clue what this really has to do with damping factor. Shorting the motor of a driver creates a "damping factor", of sorts, of 1. Is that what we are here to discuss? We can agree the electrical voltage trandsuced by the driver's motor is sent back to the amplifier along the ground return path (though it unfortunately doesn't always follow the ground plane, preferrring instead the path of least resistance - a tweeter perhaps?). So what? We can agree the amplifier must then deal with the negative (out of phase) voltage transduced by the driver's motion which shows up on the amplifier's ground terminals. So? We can agree the lower the amplifier's output impedance, the higher the damping factor. So? And, we can agree the higher the amplifier's output impedance the less effect back EMF will have on the amplifier. So?! None of this has anything to do with energy storage. If we are discussing energy "storage", I tend to think we are not discussing damping factor. " ... can you help me rephrase the question in a more.....acceptable manner?" Uh, no. I don't know how to rephrase a question I disagree with in order to get my approval. ("Would you vote for George Bush knowing what you know today?" "I wouldn't vote for Bush no matter what I knew when." "How can I rephrase that to get you to agree to a positive outcome?" "No matter who Bush is running against, would you vote for the Democrat? Yes!") There you go! See how that works? But, I don't see where you are going with this to get you kick started in the correct direction. Might I suggest you begin by not including articles with references to amplifiers with 16 Ohm taps. They still exist - in fact, I own a pair though their output impedance is not 16 Ohms - but this is not how amplifiers are typically constructed today. I think it is easier to describe damping factor by relating it to a low output impedance amplifier, not one with an output impedance of sixteen Ohms. Besides, 16 Ohm speakers are not very common today either. (OK, I own a pair of those too.) Other problems would plague a contemporary amplifier with a 16 Ohm output impedance making damping factor not much more than another annoying issue with which to eventually deal. Mr. Merchant's description of a typical loudspeaker also does not reflect the average design today. This does not make the information incorrect but doesn't move the discussion regarding damping factor forward in a relevant manner. Possibly you can condense the relevant passages in Mr. Merchant's article to clarify what I seem to have missed. Consider for a moment one sentence which I found important in Mr. Merchant's article. "Due to negative voltage feedback and positive current feedback, the damping factor can be made infinite or even negative!" As I previously stated, "We are treading dangerously close to discussing Negative Feedback here and I try to avoid that topic as much as possible. Unfortunately, the application of NFB is anything but meaningless. It is, however, another topic." . |
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Gold Member Username: Arande2400dB could probably d..., SouthWest Mi... Too Many DBs... Post Number: 1091 Registered: Dec-06 | Aren't you basically talking about potential energy stored up from the speaker being off of it's natural/neutral position? I guess it's the fact that the v-coil is moving through a magnet acting sort of like a generator giving a signal back against the amplifier. I don't what really know what you're talking about, not sure if it's damping factor though. I've still got a load of stuff to learn though. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9742 Registered: May-04 | . "Aren't you basically talking about potential energy stored up from the speaker being off of it's natural/neutral position?" Am I? No. I am not talking about "potential" energy nor am I discussing "stored" energy. Back EMF is about neither. "I guess it's the fact that the v-coil is moving through a magnet acting sort of like a generator giving a signal back against the amplifier." Yes, a coil of wire moving through a magnetic field is a basic description of a motor. And while I have used the term "generate" for convenience, the more correct term is "tranduce". As the coil moves back and forth, it is transducing mechanical energy into electrical energy, which is the inverse of what happens when the driver's coil is set in motion by the amplifier. . |
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Bronze Member Username: LeonskiPost Number: 28 Registered: Jan-07 | Yes, the cone and everything attached has potential energy when pushed to a position other than 'at rest'/ centered. Such a push can be from music or from simply (gently) pushing the woofer cone in. Connect a voltmeter to a bare woofer driver and push it in and let is spring back. That twitch of the meter is...call it what you will, transduced or generated current. But stored it is until released. We may have a semantics problem. I call this energy 'stored', even though a physics guy may say 'potential' If back EMF is not about the release of stored energy, than what produces it? It's gotta come from somewhere! What's left of my poor brain cell says it has to come from energy stored (or transduced, if you prefer) in the speaker by whatever means. Jan Said: We can agree the electrical voltage trandsuced by the driver's motor is sent back to the amplifier along the ground return path (though it unfortunately doesn't always follow the ground plane, preferrring instead the path of least resistance - a tweeter perhaps?). So what? So what, indeed! I rather suspect this can be a source of fried tweeters. Not to mention audible distortion. Good article on Chokes. NOW, how did Bob Carver use them in his 'magnetic field' design? Some posts mention Triacs (glorified SCR's?) as a way to use the power stored in the chokes magnetic field. Jan Said: Yes, a coil of wire moving through a magnetic field is a basic description of a motor. And while I have used the term "generate" for convenience, the more correct term is "tranduce". As the coil moves back and forth, it is transducing mechanical energy into electrical energy, which is the inverse of what happens when the driver's coil is set in motion by the amplifier. I would add that the 'inverse' of of turning electricy into motion, is the source of back EMF! If the speaker were to perfectly follow the input signal and be controlled in All its motion, there would be no back emf. I have some research to do! And contrary to what you may think, I am learning lots here. I have some 'homework'. 1. Find the source of the Nelson Pass statement about the thump test. 2. Read about NFB and how it relates to the issue of Damping factor. 3. Find a woofer and play. I will need a decent DVM, too. 4. Cut out the relavent section of the Merchant article. |
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Platinum Member Username: Project6Post Number: 12863 Registered: Dec-03 | Whatever happned to VPI...the original poster? |
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Bronze Member Username: LeonskiPost Number: 29 Registered: Jan-07 | Jan, Please check out this link from Nelson Pass. Paragraph #2 of the Power Transconductance Amplifiers section, where he refers to the 'back electromotive force (EMF) produced by the cone motion.' http://www.blackdahlia.com/html/tip_46.html |
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Bronze Member Username: LeonskiPost Number: 30 Registered: Jan-07 | Here is the article where the 'thump test' is proposed. http://www.crownaudio.com/pdf/amps/damping_factor.pdf Jan, give this a read and lets talk more. thanks again................ |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9745 Registered: May-04 | . ls - This, http://www.crownaudio.com/pdf/amps/damping_factor.pdf, is the same article you linked to here, Posted on Thursday, February 08, 2007 - 03:18 pm. Been there, read that, got the T-shirt. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9746 Registered: May-04 | . Paragraph two of the Power Transconductance Amplifiers section reads; "The most precise way to develop that specific current is with a current-source amplifier. Such an amplifier ignores the impedances in series with the circuit, the resistance and inductance of the wire and voice coil and the back electromotive force (EMF) produced by the cone motion. As I said, most speakers are designed around voltage sources but there are few instances where a current source can be used to advantage. One of the best ones is the category of full-range high-efficiency drivers." OK. What am I supposed to take from that paragraph? I'm going to have to object once again to using a vastly different amplifier such as the First Watt as a reference for anything we have been discussing. As you can read, the First Watt has a damping factor of 1. The First Watt is a current source amplifier and therefore unlike virtually every other amplifier on the consumer market. With that said, I don't know how or why you chose that paragraph to cite. ls, I am not at all certain what we are trying to accomplish here. Could you possibly help me out. What is it you are trying to prove? "Yes, the cone and everything attached has potential energy when pushed to a position other than 'at rest'/ centered. Such a push can be from music or from simply (gently) pushing the woofer cone in. Connect a voltmeter to a bare woofer driver and push it in and let is spring back. That twitch of the meter is...call it what you will, transduced or generated current. But stored it is until released." I can agree the suspension of the driver has "potential" energy when in any position other than center. This would be similar to the potential mechanical energy from a stretched rubber band. But stored electrical energy it is not. You are trying to mix mechanical forces with electrical forces and thinking potential mechanical energy (a stretched rubber band) is the same as stored electrical energy (a capacitor). It is not. "If back EMF is not about the release of stored energy, than what produces it?" What produces EMF? The motion of the coil within the magnetic gap. I thought we had agreed to that already. You state that a driver out of center has "stored" energy and "stored" energy is what produces EMF. But, because a moving coil within a magnetic field are the basic components of an AC motor, a driver at rest will produce EMF whenever its coil moves forward or backward within the magnetic field. If the driver is at rest there is, according to you, no "stored" energy. Therefore, "stored" energy is not what produces EMF. Only motion/action produces EMF. I don't understand why this concept of "stored" energy is so important to you. The fact the coil produces EMF when it is set in motion should be all you need to worry about when discussing damping factor. All the rest is simply muddying the waters. "What's left of my poor brain cell says it has to come from energy stored (or transduced, if you prefer) in the speaker by whatever means." Stored energy and transduced energy are not the same thing. Can we agree on that? One (stored) denotes the capacity for work. The other (transduced) defines one form of energy being converted to another form of energy (electrical to mechanical or vice versa). "So what, indeed! I rather suspect this can be a source of fried tweeters." Then you would be wrong. "I would add that the 'inverse' of of turning electricy into motion, is the source of back EMF!" Yes, I thought we had agreed to that. What are we trying to establish here? "If the speaker were to perfectly follow the input signal and be controlled in All its motion, there would be no back emf." You are once again incorrect. Your statement immediately preceding this sentence should tell you this statement is misguided. Only one of these two statements can possibly be true. I have already agreed to the first statement. I think you are seriously missing the point of damping factor. It is a simple equation which has been explained in at least two articles in this thread. What more needs to be said? Please, help me out here. I have no idea where this is going or what will end the discussion. . |
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Platinum Member Username: Project6Post Number: 12868 Registered: Dec-03 | I believe it will end when you believe it HIS way. |
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Bronze Member Username: LeonskiPost Number: 32 Registered: Jan-07 | Jan, Sorry if I've pissed you off. The good news is that I've been reading a lot about this subject, and boy is it complex! Much opinion, conjecture and good hard physics all mixed in. However, what got me started was your original statement, backed up by yourself in another line about Speaker guys and Amp guys simply not talking. (carver amps posting). With this there can be NO disagreement. I can only think of 2 examples.......Nelson Pass and Bob Carver. I'm sure there are others. I haven't seen the 'Amazing Loudspeaker' in.......20 years, so I don't know how that turned out, but if this leads anywhere, it is in the direction of better communication between these 2 groups. Funny load? Constant current? Constant voltage? So while I never (I don't think you did, either), advocated hi or lo damping, it is still worth some time to investigate. I work in a highly technical industry. We talk about measurements in angstroms and the smallest detail can eventually matter. I will run this whole thing by a couple of EE's, one of whom is also degreed in physics and the other a Phd in EE. They will set me straight and be able to explain what is going on in a speaker. The one guy also drives a homebrew electric car, so he is also quite practical in his knowledge. I also re-read the article Nuck ref'd at the very beginning of this post. It makes more sense, after having read other articles on the same subject and reading some Nelson Pass aritcles. back to work............. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9812 Registered: May-04 | . "Jan, Sorry if I've pissed you off." You didn't, but neither did we seem to be getting anywhere. Beware EE's when you discuss hifi. |
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Gold Member Username: NuckPost Number: 5956 Registered: Dec-04 | leo, you would know pissed off! |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 9813 Registered: May-04 | . Thank you, Nuck. |
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Bronze Member Username: LeonskiPost Number: 35 Registered: Jan-07 | Yeah, they tend to wander? no wonder? |