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http://www.monsterca...tor_Article.pdf DAMPING FACTOR By Richard Clark At a recent AUTOSOUND 2000 manufacturer sponsored seminar, we were asked to comment on the subject of amplifier damping factor. I was extremely surprised to find how much importance was attached to this single specification. Since most folks are a little unclear as to the true meaning of damping factor, we're presenting the following article. First of all, let's discuss the items that enter into the damping factor calculation. At the heart of this calculation is the output impedance of the amplifier. Most all-modern feedback type amps are of the variety known as constant voltage. This means that they will deliver a constant voltage regardless of their load - at least in theory. Sooner or later the limits of the amplifier's design will prohibit its constant voltage characteristics. It is this constant voltage output characteristic that permits modern car audio amplifiers to deliver more power into a 2 Ohm load than into a 4 Ohm load. A perfect amplifier should be able to double its power every time its output load is halved. Remember, Power = E x E divided by R. As an example, examine the following chart: 8 Ohms = 25 Watts 4 Ohms = 50 Watts 2 Ohms = 100 Watts 1 Ohm = 200 Watts .5 Ohm = 400 Watts .25 Ohm = 800 Watts .0125 Ohm = 1600 Watts If an amplifier were theoretically perfect, then it would be capable of the type of performance described in the chart. However, there are many factors that influence this capability. First there is the power supply section of the amplifier. Even if an amplifier had an unlimited power supply with output transistors that could handle the current, the design would still not be able to achieve the theoretically perfect output. The reason being that we do not have access to theoretically perfect components. Never lose sight of the fact that real components in real amplifiers are subject to real losses. These losses are a result of junction losses; IR drops in connections and losses in resistances and reactance. Losses in the output stages essentially form a voltage divider on the output of the amplifier. This drop is always in series with the load and can be indicated as in Figure N. In the design of an amplifier, the feedback network is usually wrapped around the section with the most losses. These losses can be greatly minimized due to the fact that the feedback node is constantly being corrected. This can be depicted as in Figure O. Output Impedance Determines Damping Factor If the output impedance of an amplifier is extremely low, the effect of loading on the output of the amplifier will be minimal. This means that it will not experience a voltage loss across its own output impedance. This output impedance does more than determine the effect of loading on the amp. It also determines its damping factor. Whenever a signal is fed into a loudspeaker the cone of the speaker will move. Since the cone has mass, there will be mass in motion. Mass in motion means momentum. When the signal is removed from the loudspeaker, the momentum of the cone causes the energy stored in the cone to be fed back into the amplifier. If our perfect amplifier were connected to this speaker, the loudspeaker would be trying to produce a voltage into 0 Ohms. Remember, a perfect amplifier has an output impedance of 0 Ohms which is essentially a short circuit. A voltage cannot be developed across 0 Ohms because it would require an infinite amount of current. It is this same infinite amount of energy that would now be trying to prevent the speaker cone from moving. If such were the case, we would certainly have a "tight" sounding speaker with absolutely no hangover. The good news is that quality amplifiers have very low output impedances. We are very pleased to report that there are many car audio amplifiers on the market with output impedances on the order of .01 Ohms or less! Calculating Damping Factor Let's clarify a few points before starting our calculations. The frequency of the measurement and the impedance of the load need to be specified. For example, the use of a 1 KHz signal and a load impedance of 4 Ohms would be a typical specification. DEFINITION = A good definition of damping factor would the ratio of the output impedance of the amplifier to the impedance of the load specified at a given frequency. An amplifier with an output impedance of 0.5 Ohm will have a damping factor of 8 when connected to a theoretically perfect 4 Ohm loudspeaker (i.e. purely inductive voice coil.) since 4/.5 = 8. The following chart assumes such a 4 Ohm speaker: Output Impedance Damping Factor 4 Ohms 1 2 Ohms 2 1 Ohm 4 .5 Ohm 8 .25 Ohm 16 .125 Ohm 32 .062 Ohm 64 .031 Ohm 128 .0015 Ohm 256 .0007 Ohm 512 .0003 Ohm 1024 .00015 Ohm 2048 .00007 Ohm 4096 .00003 Ohm 8192 Now, for the bad news; it is easy to see how a race to produce such a high damping factor led to a specification so often quoted by salespeople. The numbers on modern amplifiers (with lots of feedback) can get very large and they are easy to compare. Sometimes we can get caught up in these big numbers and we totally miss the point. Effective Damping Factor (EDF) In the case of damping factor, I believe that it could be compared to the old saying of not being able to see the forest because of all the trees. The only thing that really matters is Effective Damping Factor (EDF). Effective Damping Factor more accurately describes the interaction between a real amplifier and a real speaker. Unfortunately real speakers have a real problem with EDF. This is due primarily to the DC resistance of the voice coil. When we calculate the EDF of an amplifier and speaker, it is absolutely necessary that we include this DC resistance into the formula. Figure P illustrates the inclusion of the speaker's impedance into the EDF. The actual impedance of the speaker may be 4 Ohms. If we measure the voice coil of this speaker, we will probably find that it has a DC resistance of about 3 Ohms. When calculating the EDF effect on this speaker, we must add the 3 Ohms of DC resistance as if it were a resistor between the output of the amp and the voice coil of the speaker. Remember the resistive part of the speaker is the part where the signal is turned into heat. No work is actually done in this resistance. The inductive element of the voice coil is the only part that does work to create sound. This is one reason speakers are so inefficient. Most of the voice coil is a resistive element that can do no work. Someday if we develop room temperature superconductors and can afford to use them for voice coils, we are going to see some really efficient speakers. From the damping factor chart it is obvious that the most damping we can expect from our amp/speaker combination is only about two. An amplifier with a damping factor exceeding 10 times this amount is no longer going to play a significant role in this overall calculation. This would yield a practical limit on amplifier damping requirements to about twenty. There are times when the actual damping factor can exceed this number; one such case would be that of a dynamic loudspeaker in resonance. As we have learned, at resonance a loudspeaker's impedance is at a maximum level. At resonance, the DC element stays the same and only the reactance increases. This means that the ratio gets larger and the DC element becomes a smaller percentage of the total. For example, if the speaker impedance at resonance increased to 40 Ohms and the DC resistance was still 3 Ohms and the amplifier were .1 Ohms, and then the actual damping could be 40/3.1, or 13. This is certainly much better than 2, but quite a bit short of the 100, 200, or 500 claimed by salesmen who unknowingly think this factor so important. Fortunately for most loudspeakers this extra damping happens where they need it the most. This is because at resonance, speakers typically are very uncontrolled and have the least mechanical damping. It is also this factor that enables us to be able to connect speakers in series and not have to worry about losing damping. The actual impedance of the loudspeakers in series is doubled, but the ratio to the amplifier must also be increased by a factor of 2 to 1. The result is no change in performance. It is quite possible that this information may be in stark contrast to current marketing trends. However this does not change the fact that this information is accurate. The best way to achieve total control over speaker movement is with a servo system. Only armed with a quality servo system can effective damping characteristics be achieved. A servo essentially puts the loudspeaker in the corrective feedback loop of the amplifier. This topic will be the subject of a future article.

Another great read that I felt was worth having here also: Anatomy of the Power Amplifier Dissecting the Modern Audio Power Amplifier and Power Supply By Robert Zeff With the Proliferation of Different Amp Types, Which is the One for You? In the past we had essentially two types of amplifiers to choose from: Class "AB" and class "A". Today we have AB, A, D, G, H, & T, in addition to some that do not have a class name. New technology brought down the size and price while improving performance and efficiency. We'll review the various topologies of the modern amplifier, spending extra time on the aspect of efficiency (as the quest for smaller, more efficient designs have spawned the class D, G, H, & T designs). We'll also try to dispel some of the misconceptions and folklore that seem to surround amp design. Amplifiers require circuitry for short and thermal protection, fan control, turn on delay, and over voltage protection. In the past we littered the designs with dozens of components to handle these events. Today we can use a single microprocessor to handle all of this in addition to having many more features without additional cost. The microprocessor can monitor the battery voltage, internal voltages, temperature, control volume and crossovers, and drive external displays. These embedded computer chips also allow features like compression and power limiting with little added cost. Of course, what is an amplifier without a power supply? First we'll visit the power supply designs, as every amplifier needs one. The Power Supply The purpose of the supply is to convert the auto's battery voltage to a higher voltage. For example, if an amplifier is to produce 100 watts into a 4 ohm speaker, we need 20 volts RMS. This implies that we need about +/-28 volts. (20 volts R.M.S. = 28.28 volts peak). We call that the "rail" voltage. Since the amplifier's output transistors cannot pull all the way up to this rail, we actually need a slightly higher voltage. The process is to convert the 12 volts DC into AC, feed it to a transformer and convert it back to DC again. Converting the 12 volt battery voltage to AC is simple, a PWM (pulse width modulator) IC feeds a bank of MOSFETS (MOSFETs are switching transistors perfectly suited for this task). The 12 volt power is switched at a very high frequency, somewhere between 40 and 150 kHz. Slower switching speeds require a larger transformer, but high speeds have more switching loss. Advanced transformer core materials, faster rectifiers, and clever winding methods have enabled us to utilize very high frequencies. Some of today's better amplifiers have very small power supplies that produce enormous amounts of power. Regulated Power Supplies Most early audio amplifiers contained unregulated power supplies. Regulated supplies require very high quality filter capacitors (called "low ESR" capacitors), output chokes, and an optically isolated voltage feedback circuit. Regulation occurs by controlling the switching pulse width from 0 - 100% to compensate for changes in the battery and rail voltage. The same action occurs when the audio level increases. As the amplifier draws more power from the supply, the rail voltage drops. Again, the regulator circuitry senses this drop and responds with an increased pulse width. The high frequency PWM waveform is rectified (converted to DC) and applied to the output filter choke and capacitors. This output of this circuit is the + and - DC rails that feed the power amplifier. Unregulated Power Supplies Unregulated power supplies are less expensive than regulated supplies. They do not require an output choke, voltage sense or isolation circuitry. Because the duty cycle is nearly 100%, capacitor ripple current is much lower in unregulated supplies. Lower ripple current requires less expensive capacitors throughout. Often we hear that unregulated designs have more "headroom". That means that the amplifier will produce extra power during transients. Most home audio amplifiers employ unregulated power supplies. The power supplies in these amplifiers run at 60 Hz, thus the filter capacitors must be 200-500 times larger than those used in high frequency switchers. The extra capacitance in home audio amplifiers results in extra headroom. Headroom for anything other than very short transients simply doesn't exist in the unregulated designs. The following is an example of specifications for an unregulated vs. regulated amplifiers. Unregulated designs have a higher supply voltage at low power, causing higher voltage on the output transistors. This reduces the amplifier's efficiency. Small amplifiers (less than 100 watts) cannot justify the extra cost of the regulation circuitry, so we often see unregulated supplies in these amplifiers. Pros and Cons of Regulated / Unregulated SuppliesSome designers try to keep their supplies regulated down to battery voltages as low as 9.5 volts. The supply compensates by increasing the current. The following table shows voltage and currents for a 500 watt over-regulated amplifier operating at full power. The current increases dramatically at the lower voltages. Because of higher currents at the lower voltages, the supply efficiency drops further, requiring even more current. At higher voltages, the pulse width reduces, causing increased ripple current. This high current creates heat in the filter capacitors and can destroy the capacitor's electrolyte. Some manufacturers do not use capacitors of sufficient quality for this range of regulation. These amplifiers may not perform up to specification just one year after installation. Also, the extra current at low voltages is extra hard on a battery that is already suffering! So, we recommend that amplifiers stay in regulation down to about 11 - 11.5 volts. Any properly working charging system can easily keep the battery voltage well above this. The Amplifier Section, Class AB and AClass AB and A amplifiers are similar, so we'll discuss both here. Class AB amplifiers have transistors that pull up to the positive rail and transistors that pull down to the negative rail. This corresponds to the action of pushing the speaker cone out and in. Class AB means that the output transistors do not always have current on them. For example, when the upper transistors are pulling up towards the positive rail (pushing the speaker out), there is no current in the lower transistors. When the output signal swings through zero, towards the negative rail, the output transistor must go through a transition from zero current to a non-zero current. The best analogy that I can think of is driving an old car with too much slop in the steering. As you go from one side of the road's crown to the other, the steering crosses a "dead" zone, and you tend to over-steer. Special temperature compensated bias circuitry reduces this dead zone, known as notch distortion. The figure below shows the output of a class AB amplifier with too little bias and the resulting distortion. Notch distortion increases at higher frequencies and low volume levels. Some modern designs have reduced this type of distortion to very low levels. Class A means that every transistor is always conducting current. They are very similar to class AB amplifiers, but the bias circuitry is set so that there are very high currents in the output transistors. Because these amplifiers do not have this "dead zone', less feedback is required to achieve low distortion. A 100 watt amplifier may dissipate nearly 100 watts internally even when there is no audio output. This type of design is impractical in the harsh auto environment. Many class A amplifiers pedaled for the automotive market are not really class A. They are huge power wasters in the home as well. Input and Driver Stages The amplifier works this way: A small audio signal is presented to the amplifier's input. Transistors are not linear, which means that the input signal will distort somewhat as it passes through the various amplifier stages. To correct this distortion, a portion of the output is compared with the input. The difference creates a correction signal reducing this distortion. The input stage is a special type, called "differential". It has a + and a - input because it must accept both the audio input and the input from the feedback circuitry. Excess feedback can lower distortion dramatically, but cause instability. Careful design rules must be followed to avoid this instability. The output of the input stage feeds into the driver stage. The driver stage may use one, two, or three devices. Often this circuitry is referred to "Darlington", or "Triple Darlington". The driver circuit feeds the output stage, which may have two, four, six, or more transistors. The more output transistors, the better. Multiple output devices reduce distortion (requiring less negative feedback) and improve reliability. Bipolar or MOSFET? We have seen both MOSFET (Metal Oxide Silicon Field Effect Transistor) and Bipolar transistors used in audio amplifiers. Claims have been made that each is superior. I have seen claims that MOSFETs have a tube ("Valve" for the Brits) sound. This is more folklore. The musicians and their instruments are supposed to have "the sound", not audio equipment! MOSFETs are tougher than Bipolars, and can pull closer to the supply rail. It takes more Bipolar transistors to achieve the same power as a MOSFET, therefore Bipolar amps tend to be more expensive. But, MOSFETs are very non-linear, compared to Bipolars and require much more feedback to achieve reasonable distortion numbers. They are a great choice for bass amps, as low frequency audio is not difficult for a MOSFET. The most expensive car and home amplifiers almost always use Bipolar transistors. Efficiency What makes an amplifier get hot? Both the power supply and the power amplifier generate heat. The maximum efficiency of the power supply is nearly 100%. Good power supply designs, with the highest quality components approach 85%. The class AB amplifier efficiency at full power can approach 75%. The total efficiency, including the power supply, can be about 65%. But, efficiency drops at lower power and can typically be under 20%. A class AB amplifier actually runs cooler at full power than it does at half power. Run this amplifier into clipping and it might run even cooler! Where is all this power going? The output transistor is basically a large variable resistor. If the instantaneous output voltage should be 40 volts and the power supply is 100 volts, then 60 volts must be "wasted" in the output transistors. Driving a reactive load (like a speaker) causes the efficiency to drop ever further. This brings us to the other audio classes designed to improve efficiency. Class D First, let's dispel another myth: Class D does not stand for digital. The input is converted to a two-state (binary) representation of the audio waveform. That's where the similarity ends. This distinction is important because class D doesn't provide the benefits normally associated with digital components. That being said, class D designs dramatically improve efficiency. Instead of wasting power in the output transistor, the output is switched at a very high frequency between the positive and negative supply rails. If the output is to be zero, then the waveform is at a 50% duty cycle. If the output is to be a positive voltage, then the duty cycle would be greater than 50%. Because the output devices are either completely turned on (no wasted voltage) or completely turned off, theoretically efficiency is 100%. So the audio input must be converted to a pulse width modulated waveform (PWM). The yellow trace below is the output of the amplifier; the blue trace is the PWM waveform. The blue waveform is fed to an output filter, which results in the yellow output waveform. Notice that the output looks somewhat distorted. All of the switching noise and distortion cannot be removed and the result can be seen here. Because of this process of converting the input signal to PWM and converting back to analog, a good deal of distortion is introduced. Conventional feedback like that used in class AB designs is used in these amplifiers to reduce distortion. MOSFETs are the only choice for class D designs. Most class D designs are useful only for bass amps as they can not switch fast enough to reproduce high frequencies. Some high quality, full range class D designs exist for pro audio, but they are complex with multi-phased outputs. Class T Class T (Tripath) is similar to class D with these exceptions: This class does not use analog feed back like its class D cousin. The feedback is digital and is taken ahead of the output filter, avoiding the phase shift of this filter. Because class D or T amplifier distortion arises from timing errors, the class T amplifier feeds back timing information. The other distinction is that this amplifier uses a digital signal processor to convert the analog input to a PWM signal and process the feedback information. The processor looks at the feedback information and makes timing adjustments. Because the feedback loop does not include the output filter, the class T amplifier is inherently more stable and can operate over the full audio band. Most listeners can not hear the difference between class T and good class AB designs. Both class D and T designs share one problem: they consume extra power at idle. Because the high frequency waveform is present at all times, even when there is no audio present, the amplifiers generate some residual heat. Some of these amplifiers actually turn off in the absence of music, and can be annoying if there is too much delay turning back on. Class G Class G improves efficiency in another way: an ordinary class AB amplifier is driven by a multi-rail power supply. A 500 watt amplifier might have three positive rails and three negative rails. The rail voltages might be 70 volts, 50 volts, and 25 volts. As the output of the amplifier moves close to 25 volts, the supply is switched the 50 volt rail. As the output moves close to the 50 volt rail, the supply is switched to the 70 volt rail. These designs are sometimes called "Rail Switchers". This design improves efficiency by reducing the "wasted" voltage on the output transistors. This voltage is the difference between the positive (red) supply and the audio output (blue). Class G can be as efficient as class D or T. While a class G design is more complex, it is based on a class AB amplifier and can have the same clean characteristics as well. Class H Class H is similar to class G, except the rail voltage is modulated by the input signal. The power supply rail is always just a bit higher than the output signal, keeping the voltage across the transistors small and the output transistors cool. The modulating power supply rail voltage is created by similar circuitry that you would find in a class D amplifier. In terms of complexity, this type of amplifier could be thought of as a class D amplifier driving a class AB amplifier and is therefore fairly complex. How to Choose? Regulated or unregulated? Class AB, D, or T?If you're really into a lot of bass, the class D or T may be for you as these amplifiers will produce the highest SPL with the smallest size. If you just want to wake the neighbors, blur your vision, or make a big splash in SPL contests, maybe you just need one of the inexpensive, powerful, & dirty class D designs. Want the cleanest high frequencies? Maybe a good class AB amp would be your selection. Whatever you choose, I hope this information helps you achieve the sound you're looking for! Source: >> Click here for images and diagrams too <<

the amp has 3 more fuses inside making it 240 amps it will do more than rated power i've done research on this amp i was considering buying it before i stumbled across Sundown SAZ3000 at a good price

This definition isn't very accurate either. For "phase cancellation" (destructive interference) to occur between two or more speakers the speakers do not have to be out of phase. For destructive interference to occur, the soundwaves simply need to interact with each other while the soundwaves are not in phase. The speakers may in fact be in phase while this is occurring. This phenomenon is very prevalent in car audio where we sit at different distances from the two speakers or in home theater where the listening positions can vary. There are other ways for destructive interference to occur. In home audio speaker design the center-to-center distance of drivers in speaker may cause destructive interference. The crossover can also cause two drivers in a given speaker to be out of phase since the crossover will shift the phase of the signal (90* phase shift for every 6db/oct increase in slope), in which case you must wire the drivers out of phase in order for the soundwaves to be in phase at the crossover point. You can also have destructive interference with a single speaker due to reflections. The reflected sound may reach the listener out of phase with the original sound. Not nitpicking your definitions.....but also do not want people misunderstanding the information being provided.

The sentences highlighted in red are rubbish and should be excluded from any viable definition of DF. For more information on damping factor see here: Damping Factor

Audioholics article on DF http://www.audioholi...system-response Much ballyhoo surrounds the concept of "damping factor." It's been suggested that it accounts for the alleged "dramatic differences" in sound between tube and solid state amplifiers. The claim is made (and partially cloaked in some physical reality) that a low source resistance aids in controlling the motion of the cone at resonance and elsewhere, for example: "reducing the output impedance of an amplifier and thereby increasing its damping factor will draw more energy from the loudspeaker driver as it is oscillating under its own inertial power." This is certainly true, to a point. But many of the claims made, especially for the need for triple-digit damping factors, are not based in any reality, be it theoretical, engineering, or acoustical. This same person even suggested: "a damping factor of 5, ..., grossly changes the time/amplitude envelope of bass notes, for instance. ... the note will start sluggishly and continue to increase in volume for a considerable amount of time, perhaps a second and a half." Damping Factor: A Summary What is damping factor? Simply stated, it is the ratio between the nominal load impedance (typically 8W ) and the source impedance of the amplifier. Note that all modern amplifiers (with some extremely rare exceptions) are, essentially, voltage sources, whose output impedance is very low. That means their output voltage is independent, over a wide range, of load impedance. Many manufacturers trumpet their high damping factors (some claim figures in the hundreds or thousands) as a figure of some importance, hinting strongly that those amplifiers with lower damping factors are decidedly inferior as a result. Historically, this started in the late '60's and early '70's with the widespread availability of solid state output stages in amplifiers, where the effects of high plate resistance and output transformer windings traditionally found in tube amplifiers could be avoided. Is damping factor important? Maybe. We'll set out to do an analysis of what effect damping factor has on what most proponents claim is the most significant property: controlling the motion of the speaker where it is at its highest, resonance. The subject of damping factor and its effects on loudspeaker response is not some black art or magic science, or even excessively complex as to prevent its grasp by anyone with a reasonable grasp of high-school level math. It has been exhaustively dealt with by Thiele and Small and many others decades ago. System Q and Damping Factor The definitive measurement of such motion is a concept called . Technically, it is the ratio of the motional impedance to losses at resonance. It is a figure of merit that is intimately connected to the response of the system in both the frequency and the time domains. A loudspeaker system's response at cutoff is determined by the system's total , designated , and represents the total resistive losses in the system. Two loss components make up : the combined mechanical and acoustical losses, designated by , and the electrical losses, designated by . The total is related to each of these components as follows: is determined by the losses in the driver suspension, absorption losses in the enclosure, leakage losses, and so on. is determined by the combination of the electrical resistance from the DC resistance of the voice coil winding, lead resistance, crossover components, and amplifier source resistance. Thus, it is the electrical , , that is affected by the amplifier source resistance, and thus damping factor. The effect of source resistance on is simple and straightforward. From Small(3): where is the new electrical with the effect of source resistance, is the electrical assuming 0W source resistance (infinite damping factor), is the voice coil DC resistance, and is the combined source resistance. It's very important at this point to note two points. First, in nearly every loudspeaker system, and certainly in every loudspeaker system that has nay pretenses of high-fidelity, the majority of the losses are electrical in nature, usually by a factor of 3 to 1 or greater. Secondly, of those electrical losses, the largest part, by far, is the DC resistance of the voice coil. Now, once we know the new due to non-zero source resistances, we can then recalculate the total system as needed using eq. 2, above. The effect of the total on response at resonance is also fairly straightforward. Again, from Small, we find: This is valid for values greater than 0.707. Below that, the system response is over-damped and there is no response peak. We can also calculated how long it takes for the system to damp itself out under these various conditions. The scope of this article precludes a detailed description of the method, but the figures we'll look at later on are based on both simulations and measurements of real systems, and the resulting decay times are based on well-established principles of the audibility of reverberation times at the frequencies of interest. Practical Effects of Damping Factor on System Response With this information in hand, we can now set out to examine what the exact effect of source resistance and damping factor are on real loudspeaker systems. Let's take an example of a closed-box, acoustic suspension system, one that has been optimized for an amplifier with an infinite damping factor. This system, let's say, has a system resonance of 40 Hz and a system of 0.707 which leads to a maximally flat response with no peak at system resonance. The mechanical of such a system is typically about 3, we'll take that for our model. Rearranging Eq. 1 to derive the electrical of the system, we find that the electrical of the system, with an infinite damping factor, is 0.925. The DC resistance of the voice coil is typical at about 6.5 W . From this data and the equations above, let's generate a table that shows the effects of progressively lower damping factors on the system performance [see table in article] The first column is the damping factor using a nominal 8W load. The second is the effective amplifier source resistance that yields that damping factor. The third column is the resulting caused by the non-zero source resistance, the fourth is the new total system that results. The fifth column is the resulting peak that is the direct result of the loss of damping control because of the non-zero source resistance, and the last column is the decay time to below audibility in seconds. Analysis Several things are apparent from this table. First and foremost, any notion of severe overhang or extended "time amplitude envelopes) resulting from low damping factors simple does not exist. We see, at most, a doubling of decay time (this doubling is true no matter what criteria is selected for decay time). The figure we see here of 70 milliseconds is well over an order of magnitude lower than that suggested by one person, and this represents what I think we all agree is an absolute worst-case scenario of a damping factor of 1. Secondly, the effects of this loss of damping on system frequency response is non-existent in most cases, and minimal in all but the worst case scenario. Using the criteria that 0.1 dB is the smallest audible peak, the data in the table suggests that any damping factor over 10 is going to result in inaudible differences between that and one equal to infinity. It's highly doubtful that a response peak of 1/3 dB is going to be identifiable reliably, thus extending the limit another factor of two lower to a damping factor of 5. All this is well and good, but the argument suggesting that these minute changes may be audible suffers from even more fatal flaws. The differences that we see in figures up to the point where the damping factor is less than 10 are far less than the variations seen in normal driver-to-driver parameters in single-lot productions. Even those manufacturers who deliberately sort and match drivers are not likely to match a figure to better than 5%, and those numbers will swamp any differences in damping factor greater than 20. Further, the performance of drivers and systems is dependent upon temperature, humidity and barometric pressure, and those environmental variables will introduce performance changes on the order of those presented by damping factors of 20 or less. And we have completely ignored the effects presented by the crossover and lead resistances, which will be a constant in any of these figures, and further diminish the effects of non-zero source resistance. Frequency-Dependent Attenuation The analysis thus far deals with one very specific and narrow aspect of the effects of non-zero source resistance: damping or the dissipation and control of energy stored in the mechanical resonance of loudspeakers. This is not to suggest that there is no effect due to amplifier output resistance. Another mechanism that most certainly can have measurable and audible effects are response errors due to the frequency dependent impedance load presented by the speaker. The higher the output resistance of the source, the greater the magnitude of the response deviations. The attenuation can be approximated given the source resistance and impedance vs. frequency: where is the gain or loss due to attenuation, is the amplifier source resistance, and is the frequency dependent loudspeaker impedance. As a means of comparison, let's reexamine the effects of non-zero source resistance on a typical speaker whose impedance varies from a low of 6 ohms to a high of 40 ohms. [see table in article] As before, the first column shows the nominal 8 ohm damping factor, the second shows the corresponding output resistance of the amplifier. The second and third columns show the minimum and maximum attenuation due to the amplifier's source resistance, and the last column illustrates the resulting deviation in the frequency response caused by the output resistance. What can be seen from this analysis is that the frequency dependent attenuation due to the amplifier's output resistance is more significant than the effects on system damping. More importantly, these effects should not be confused with damping effects, as they represent two different mechanisms. However, these data do not support the assertion often made for the advantages of extremely high damping factors. Even given, again, the very conservative argument that ±0.1 dB deviation in frequency response is audible, that still suggests that damping factors in excess of 50 will not lead to audible improvements, all else being equal. And, as before, these deviations must be considered in the context of normal response variations due to manufacturing tolerances and environmental changes. Conclusions There may be audible differences that are caused by non-zero source resistance. However, this analysis and any mode of measurement and listening demonstrates conclusively that it is not due to the changes in damping the motion of the cone at the point where it's at it's most uncontrolled: system resonances. Even considering the substantially larger response variations resulting from the non-flat impedance vs. frequency function of most loudspeakers, the magnitude of the problem simply is not what is claimed. Rather, the people advocating the importance of high damping factors must look elsewhere for a culprit: motion control at resonance, or damping, simply fails to explain the claimed differences.

Stephen Mantz on DF http://zedaudiocorp....l-GREYSCALE.pdf Damping Factor – This amplifier specification has been blown out of all proportion. What it means is the ability of the amplifier to resist a change in it’s output voltage. The formula is DF = Speaker Z/Amplifier output Z (where Z is impedance). So many manufacturers have claimed ridiculous, and often false damping factors. A damping factor of 1000 implies that the output impedance of the amplifier is .004ohm (4ohm load). The only way to attain this figure is to apply masses of negative feedback (or use positive feedback) and too much feedback makes amplifiers sound harsh and clinical. Also damping factor changes with frequency. The lower the frequency the higher the DF number. Typically the DF can be ten times larger at higher frequencies. Let us take this amplifier whose output impedance is .004 ohms (Zout). The speaker circuit is a series circuit and the following impedances (resistances) are in series with this .004 ohms. Let us assume that this DF measurement was made at the amplifier’s speaker terminal. The first extra contact resistance is the speaker wire to the speaker terminal (WT ohms). Then there is that of the wire itself for two conductors (W). Next is the contact resistance of the wire to the speaker terminal (WS). Next there is the contact resistance of the wire from the speaker terminal to the voice coil (WV) and lastly there is the DC resistance of the voice coil itself (DCR). So what we have is a series circuit with the following resistances in series and adding up. WT+W+WS+WV+DCR+Zout. WT, W, WS, WV and Zout are very small indeed. Certainly less than .1 ohms. Whoa, look what has happened the EFFECTIVE DAMPING FACTOR has been reduced from 1000 to 40 by just taking into account those pesky unavoidable contact resistances. Now for the cruncher, remember that the DCR is also in series and is typically 3.2 ohms for a nominal 4ohm speaker. So we must add 0.1+3.2 = 3.3 ohms and now EFFECTIVE DAMPING FACTOR is now a magnificent 1.212! (4 divided by 3.3). This is the real world. We see that the DCR of the speaker swamps all other resistances in the speaker circuit and the .004 ohms amplifier output impedance is almost meaningless. It has been found that a DF of about 20 is quite sufficient to dampen the voltage spikes from the speaker. An eye opener this one is it not? Good tube amps sound marvelous – low damping factors!

I am getting a recone from a high quality company, one from this site. Enough said, am not going to get nothing else from this thread so thanks to all that lend their input.

3x40fuses=120amps 120ampsx12.5 volt= no will not do rated power. probably wont even do it @14.4. search for how to do calculations yourself next time.