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New member Username: MarkdUK Post Number: 5 Registered: Apr-04 | hi, don't know if i already posted this question, i couldn't find it. does anyone know what damping factor means? its listed on amplifier specifications. |
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MEXXX Unregistered guest | Put simply, its how much "control" the amp has over the speakers movement. The higher the better. Also, whenever you lower the load impedance to the amp, you also lower the damping factor. |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 2287 Registered: Dec-03 | What is damping factor? It's somewhat more technically complex than this but the "damping factor" of an amplifier is usually thought of as an indicator of how "tight" an amplifier will sound when powering large bass speakers. Here's why: A speaker is essentially a coil of wire mounted within a magnet. As it moves within the magnet's field of energy, a signal is induced back into the voice coil. This signal is called "Back EMF". It's essentially a voltage that has been generated by the loudspeaker itself. The larger the loudspeaker, the larger the voltage produced. If this Back EMF is not compensated for properly in the amplifier circuitry the result is an over accentuated or boomy bass sound as the Back EMF signal tries to oppose the signal you actually want (the one from the amplifer). Good amplifier design allows the amplifier to negate this unwanted signal and thus control the loudspeaker properly resulting in a much "tighter", controlled sound from the loudspeaker. From a technical stand point, damping factor is a reciprocal of the amplifiers output impedance and output impedance is a derivative of the amount and implementation of negative feedback within the amplifier. Beware datasheets that state damping factor values with qualifying the frequency range. A high damping factor number is only of real use at lower frequencies as high frequency devices produce very little Back EMF. Properly designed negative feedback not only corrects for Back EMF but also produces other benefits: Low distortion, low noise and flat frequency response. |
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New member Username: SoccerPost Number: 8 Registered: Apr-04 | Low damping factor = more harmonic distortion due to lack of control? My Rotel at home as a damping factor of 1500, but my car's only "greater than 5"... TIA |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 2289 Registered: Dec-03 | Damping Factor Damping factor is rarely published with low to medium grade amplifiers but it is almost always published with high end American amplifiers. And even when it is published, it is rarely published correctly. The damping factor is the ratio between the load impedance and the amplifier's internal impedance (load impedance divided by internal impedance). Like output power ratings, the damping factor is an amplifier characteristic that cannot be represented by a simple number. An impedance value is a complex number made up of a real term and an imaginary term. The real term comes from the resistance of the object being measured. For example, if you measure the resistance of an 8ohm driver with an ohmmeter, you will find that it is around 6.3 ohms. Some times, this is referred to as the DC resistance, but this is being redundant because a resistance value by its nature must be taken at DC. The imaginary term is from the inductance and reactance of the object being measured. A driver's voice coil, for example, is made up of winds of wire. The resulting effect is an inductor contributing a significant amount of inductance to the impedance value. There is also a bit of reactance caused by inherent capacitance between parallel wires in the driver assembly but it is usually small enough in a driver that its value is negligible. Those familiar with a complex value will know that its behavior is dependent on the frequency of the source signal. The impedance of a driver might be 8 ohms at say 100Hz but it could be 30 ohms at 1kHz. Thus any measurement taken that is dependent on the complex impedance of a driver will also be dependent on the frequency of the source signal. So the damping factor of an amplifier will be dependent on the frequency of the signal that the amplifier is generating, which is the reason why you can't just give a single number as the damping factor like most manufactures do. As if that isn't complicated enough, keep in mind that the impedance graph is different for each driver, the amplifier's internal impedance is also complex, and you have to figure in the impedance contributed by the wires and connectors used in the signal path. In other words, it is impossible to accurately specify a damping factor. This is all fine, but what bothers me is that most high end amplifier manufacturers just publish a number with no indication to the uselessness of such a simple representation of what is a complicated relationship between the amplifier and the load. Not all amplifier manufacturers are lazy so some come up with ways to specify the damping factor. One way manufacturers specify it is to limit the various conditions that the damping factor is dependent on. Thus they may specify a damping factor of "200 at 1kHz with a 4ohm impedance load at the amplifier output terminals". So in other words, if you put a load with an impedance of 4ohms at 1kHz across the amplifier's output terminals and the frequency generated by the amplifier is 1kHz, the ratio between the load impedance and the amplifier's internal impedance is 200. Which means that the amplifier's internal impedance at 1kHz is 0.02ohms. The amplifier's internal impedance at 1kHz will stay the same but damping factor will fluctuate depending on the load impedance used and the wires/connectors used in the signal path. For example, if you use a driver with an impedance of 8ohm at 1kHz instead, then the damping factor becomes 400. Conversely, if you use a driver with an impedance of 2ohm at 1kHz, the damping factor will be 100. For reasons that I will indicate later, the damping factor is mainly significant for amplifiers used to power sub woofers. Given that, a damping factor given at 1kHz is pretty much meaningless since sub woofers are usually limited to producing frequencies below 100Hz. How do you get around this then? Well some manufacturers publish damping factors as "greater than 200". What this means is that provided a load with a constant impedance of 4ohms across the frequency spectrum, the damping factor measured at the amplifier's output terminal is greater than 200. Which is the same as saying that the internal impedance of the amplifier will never rise above 0.02ohms from 20Hz to 20kHz. This is the best solution to the problem that I've seen so far since it specifies everything the amplifier's manufacturer can specify. The damping factor specified this way is only dependent on variables controlled by the consumer such as the driver, wire and connectors used. Usually, a damping factor of greater than 50 is considered adequate, though most high end amplifiers have a damping factor of greater than 200. With that said, why should you care about the damping factor at all? If it is so complicated to specify, why would we want to know it in the first place? Well, the significance of the damping factor is two folds. First, and perhaps more obscure and lesser well known, the damping factor indicates the efficiency of the output device (transistors) used in the amplifier. Second, the damping factor indicates the amplifier's ability to control the motion of a driver. The load and the output device of an amplifier makes a complete circuit and whatever current flows through the load also flows through the output device. Thus if the amplifier is putting out 2 amperes of current, then the same 2 ampere of current is flowing through the load and the output device of the amplifier. The total power dissipated in the complete circuit is then the current squared multiplied by the total impedance in the circuit. Lets assume a damping factor of 200 for a load impedance of 4ohms. Thus the amplifier's internal impedance is 0.02ohms. The total impedance in the circuit is then 4.02 ohms. Multiplying 2 squared and 4.02 together we get 16.08 watts. Of this power, 0.08 watts is dissipated by the amplifier's output device and the rest is delivered to the load. Thus about 0.5 percent of the power is wasted by the amplifier's output device. Because this percentage of wasted power is rather small compared to the overall wasted power in the whole amplifier (around 50 percent), it is rarely mentioned. But it is nonetheless indicated by the amplifier's damping factor. The damping factor is most often used as an indication of the ability of an amplifier to control the motion of a driver. When a signal sent to a driver is suddenly stopped, the driver's cone continues moving back a forth for a short period after the signal has stopped. A driver with a cone that stops quickly is said to have a good transient response while a driver with a cone that does not stop quickly is said to have a bad transient response and thus is described as inaccurate. I think it goes without saying that most people would prefer a driver with good transients and thus would prefer that the cone of the driver stop quickly after the source signal stops. With tweeters and mid-bass drivers, this not a hard task since the cones of these types of drivers are relatively light and a relatively large motor structure can be used to control the motion of the cone. However, the cone of a low frequency driver is quite sizable and it is physically impractical to use a motor assembly large enough to obtain transient responses as good as that of a tweeter or a mid-bass driver. Thus low frequency drivers usually have relatively poor transient responses. This is really not too much of a problem since humans are less sensitive to distortion in the low frequencies. In fact, THD of 3 to 6 percent from a low frequency driver is considered acceptable. Low frequency distortion only becomes objectionable when it gets close to 10 percent. Since drivers are just electric motors, they become generators when their terminals are shorted. If you place an ammeter across the leads of a driver and push the cone up and down, you will see a current flowing through the ammeter. The higher that current is, the cone becomes increasingly difficult to move. Thus, if a driver's cone is moving, the quickest way to stop it is to place a dead short across its leads. The internal impedance of an amplifier is usually very small and in the absence of a source signal, it is like a short across the leads of the driver. The amplifiers with a higher damping factor will have a lower internal impedance so it will be closer to a short. Thus the amplifier with a higher damping factor will cause the driver to stop quicker than the amplifier with a lower damping factor. Since low frequency drivers need all they help they can get to stop their cone from moving when the source signal stops, a high damping factor is desirable for an amplifier intended to power low frequency drivers. The damping factor is not as relevant when the amplifier is used to power mid-bass and tweeter drivers since those drivers already have pretty good transient response due to their relatively small cone size. quoted from: http://www.leecao.com/caraudio/amplifier.html |
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New member Username: SoccerPost Number: 9 Registered: Apr-04 | Ok, I just bookmarked this forum, 'cause there's some serious discussions around here, and I just learned something, though I'll try to digest it at night! THANKS, Glasswolf, you really know what you're saying! |
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MEXXX Unregistered guest | Isn't that what I said GlassWolf? ROFL!!!!!!! No, but really, good job. I didn't feel like putting that much effort into explaining it at the time. All most people need to know about it is MORE=BETTER. |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 2303 Registered: Dec-03 | well now he can pick if he wants the easy answer or the detailed one. heh full meal or just the salad |
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Bronze Member Username: SoccerPost Number: 12 Registered: Apr-04 | I think I'll take the full meal, but just not for now, maybe at night! TKS! |
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Bronze Member Username: TimmayyyyPasadena, CA U.S. Post Number: 16 Registered: Apr-04 | full meal was great for me.. =) for a little while, i actually thought u TYPED all that glass haha.. |
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Gold Member Username: GlasswolfNorthWest, Michigan USA Post Number: 2307 Registered: Dec-03 | I try to put sources when I quote other peoples' work. I could've typed just about as much but why when someone else already did a fine job. lol |
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New member Username: MarkdUK Post Number: 6 Registered: Apr-04 | hi, thanks for the reply. very interesting reading! i went for the long answer of course, its good to learn something new! |