Class D Amps vs. Pure Class A Amps for Subs
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Unregistered guest | I am curious as to what people's thoughts are on using high powered Class A amps on subwoofers as opposed to Class D Amps. I am well aware of the difference the amount of amps the A/B pull compared to the Ds. Having owned a class A amp or two and using them on tweets and mid speakers, I wonder how they would do on Subs. For example the Soundstream Human Reign 2 channel amp puts out 800 watts RMS @ 2 ohm. I am looking at a pair of subs in the 800 to 1000 watt RMS range with a fairly low Frequency Response. Something that is a 4 ohm DVC that can be wired down to a 2 ohm load. Any thoughts or comments will be greatly appreciated! Thanks. |
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Gold Member Username: InvainMichigan United States Post Number: 3345 Registered: Aug-04 | Not really necessary. When using subs, and dealing with low frequencies it's much harder to hear distortion. You may tell a difference between a class A and a Class D amp, but it will be a very small difference, and the normal person probably wouldn't notice. This also depends on how well built the class D amp is as well. I can't really see why you'd want to use Class A, given how ineficient they are, it's just not very practical when your talking about powering a subwoofer that can use anywhere from 250 - 2000 wrms. I guess if you were the ultimate audiohpile, and you had tons of cash to just toss around, then go ahead. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8811 Registered: Dec-03 | a pure class A amplifier, of which there are scant few in the car audio realm anyway, is only about 25% efficient. That means three quarters of the power drawn, is lost to heat due to the constant-on state of the transistors, and their full time voltage bias. Honestly I think it's a tremendous waste of power with no audible gain in SQ in a car setting. With 80+dB of road noise and engine etc, you'll never hear the difference over a class D amp with a subwoofer anyway. You probably wouldn't even hear it in a house in a quiet room to be honest. Most people can't anyway. That's why most home audio subs use a class D plate amplifier. |
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Gold Member Username: InvainMichigan United States Post Number: 3347 Registered: Aug-04 | Just a question Glass, have you yourself heard the same sub played on a class A or A/B amp, and then played on a class D, and where you able to hear any difference at all? I know distortion is very hard to hear at low frequencies, but I've always wondered if you really could hear any difference between an A and a D, any at all, even if it were barely noticeable, and took a trained ear to detect... |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8814 Registered: Dec-03 | I've done reviews on class D amplifiers in my own system, which usually uses class AB amplifiers. With a good class D amplifier, you really can't hear any difference below 60Hz, which is where my subs are filtered. |
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Gold Member Username: InvainMichigan United States Post Number: 3350 Registered: Aug-04 | Any idea as to how high you think you'd have to go, frequency wise, before you can really hear a difference? |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8824 Registered: Dec-03 | 150Hz or so maybe? |
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Gold Member Username: CarguyPost Number: 3751 Registered: Nov-04 | From my testing, you won't hear much improvements around 65Hz - 100Hz. Class D will sound just as good to human ears. However, notes below 60Hz or higher than 120Hz, then you start noticing it slightly. You almost have to switch it back and forth to detect it. |
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Gold Member Username: Jonathan_fGA USA Post Number: 4337 Registered: May-04 | To add to this, many amplifiers dubbed as a "Class A" are really closer in design to Class AB. A Class A amplifier used to be considered as an amplifier using a single output device that was turned on all the time, but now people tend to consider a Class A amplifier to simply be an amp that has enough bias applied that changing input polarity occurs within the limit of cutoff and saturation. You do this by increasing the quiescent current to just over 1/2 the peak speaker current. It is better described as more of a push-pull operation than a traditional single-ended output. Other designs use methods that have additional circuitry that is biased to the point that the output transistors never turn off. Soundstreams "Class A " amplifiers are an example of these methods, they are not your traditional class A single ended amplifier. |
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Gold Member Username: Jonathan_fGA USA Post Number: 4340 Registered: May-04 | Come on, man, it's alright that you're linking the site and all, but the picture is too inappropriate, no place for it here. My daughter is in the room, I'm sure other people have kids and wives and girlfriends that they wouldn't want seeing this either. |
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Unregistered guest | Class D it is then. One more question...As far as amplifiers are concerned. My subs are 2 ohm DVC 800 watt RMS each. I am attempting to power them properly without spending a fortune but I am mostly concerned with quality. The sub's frequency response is 16 to 300 Hz. They are 15" MB Quart PWE 352. I got a really cheap deal on them and thought I would try them out. I would like to wire the subs parallel into a 1 ohm load. I realize this provides more power to each sub. Question being, would I be better off using two mono amps, two 2-channel amps bridged in mono, or one 4-channel amp bridged in mono? Right now I am primarily looking at some MA Audio, Soundstream, and Memphis amps. I am attempting to choose which would be best for these subs. Here is the link to the MB Quart site where specs and such are available (if needed): http://mbquart.com/2003/en_US/products/prod_detail.asp?isArchive=&cat=auto&serie s=premium%20series&strt=1&model=PWE+352%2F354 |
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Unregistered guest | I forgot to ask one other question in my last thread. Am I going to get better, clearer sound by using a 1 ohm load as opposed to a 4 ohm load? |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8829 Registered: Dec-03 | with a pair of dual 2 ohm coil subs, I'd use one big 2 ohm stable amp. the Orion 2500D or similar to drive those fifteens.. then cross them over low enough that they work properly. 60Hz would be about right any higher and you'll get resonance across the cone area that makes them sound boomy. |
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Unregistered guest | I have had problems with resonance before. I usually cross over around 55 to 75. If I use a 2 ohm amp, how should I wire the subs to the amp (being that it is a mono amp)? Each coil individually to the amp? Also, the 2500d is rated at 1700 max power at 2 ohms, I am not able to find the RMS ratings. I would assume that the RMS would be below 1200, if not lower. Which if it were and I had two subs hooked up to one channel, wouldn't that, theoretically, be only 600 RMS to each sub? I would like to power them closer to the 800-1000 watt range. Will that be possible with the Orian 2500D? If so, how? Thanks. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8843 Registered: Dec-03 | 1700 watts is RMS, not Peak.. as stated here: Orion 2500D 2500Watts Class D Mono Amplifier Whether it's more power or more channels Orion's 2003 amplifier lineup delivers. The new 2500D delivers an astounding 2500 watts into 1 ohm -- and those are real, 13.8V continuous watts, not the "if lightning strikes" watts some companies claim. Whether your goal is an SPL world record, or you just want the meanest, hardest hitting system in town, these three new class D models will get the job done. Extreme power, extreme efficiency, and extreme construction details like massive paralleled internal busses and a directed internal air flow cooling design characterize these monster amps that proudly advance Orion's legacy. Product Features : Selectable 12/24 dB/octave variable low-pass filter Intelli Q bass optimization circuit and remote gain option Separately adjustable, selectable variable high-pass filter with proprietary Copy/Master control circuit for RCA outputs Copy/Master feature supports gain and crossover adjustment matching in multiple amp Switchable phase invert function Heavy gauge direct-wire high current satin finish power and speaker terminals 1 x 1200 @ 4 Ohm 1 x 1700 @ 2 Ohm 1 x 2500 @ 1 Ohm Dimensions : 27.2" x 10.5" x 2.3" |
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Unregistered guest | Ok, I think I've got it now. Thanks, Glass. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8866 Registered: Dec-03 | and I missed this one "Am I going to get better, clearer sound by using a 1 ohm load as opposed to a 4 ohm load?" actually, at least on paper, just the opposite. 4 ohms will yield more headroom, better THD and SNR, and more damping factor than 1 ohm. At 1 ohm, you're pushing the amplifier, and thereby it's power supply closer to it's limits, thus leaving less of a "reserve" for use during peak momentary demands. You're also drawing a lot more current, and as a result pushing the internal components of the amplifier harder. Now in reality, you might not even be able to hear the difference in SQ between various loads, as long as the amplifier is operating within it's advertised specs. |
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Unregistered guest | What about wiring methods with two subs on the one channel amp and as far as the subs coils? |
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Silver Member Username: Audioguy22Post Number: 106 Registered: Jul-05 | Formatting ErrorThe formatting code png_alreadyuploaded_t does not exist or cannot be used in this context. |
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Silver Member Username: Audioguy22Post Number: 107 Registered: Jul-05 | I dont feel that the class of amp is so important, what you need to look at is the Damping factor and the rise time or slew rate. The higher the Damping factor the more contol the amp will have over the woofer. Higher damping = tighter more punchy sound. Try to find some specs close to these.  |
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Gold Member Username: Jonathan_fGA USA Post Number: 4345 Registered: May-04 | In most amplifier designs, high damping factor equals tons of negative feedback, which causes phase shifts. Negative feedback is good if it's used to a point to smoothen frequency response and aid distortion, but it's only a good thing when necessary. Feedback also causes gain reduction and the transition from clean to distorted is much more abrupt, because the negative feedback tends to keep the amp distortion to a minimum until the output stage clips, at which point there is no "excess gain" available to keep the feedback loop operating properly. At this point, the feedback loop is broken, and the amp transitions to a full non-feedback forward gain, which means that the clipping occurs very abruptly and clips very, very HARD. In laymans terms, since a feedback amplifier causes gain reduction (less power amplified from the outputs), it will reach a point where the feedback loop becomes inactive, and since it is inactive, it also isn't limiting the amplifier's gain, which throws the amplifier that much further into clipping. For example, If you have 6dB of feedback, and it takes 2V at the phase inverter input to achieve output clipping, if you removed the feedback, it would only take 1V at the phase inverter input to achieve output clipping. There is a voltage gain reduction of 6dB, or a factor of two, in the stages enclosed by the feedback loop. This is achieved by feeding back a certain percentage of the output voltage to an earlier point in the circuit, the phase inverter. The more you feedback, the more voltage gain reduction. As long as damping is over 50, there will be no difference in the control of a subwoofer as far as the time it takes to stop the sub, this can be proven on a waterfall plot or similar test. Of course, higher is better, but it depends on how it's accomplished. Damping is not a useless spec, as it shows the efficiency of the output devices (transistors), which is a good thing, and high damping amps are almost always high current type amplifiers. But it depends on how the damping was accomplished. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8869 Registered: Dec-03 | Slew Rate: This is a term used to describe how quickly the output of an amplifier can track its input. Slew Rate is usually measured in V / usec. The higher the value (up to a point), the better the amp is at potentially reproducing the subtle nuances and dynamics associated with music reproduction. Amplifier 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 8 ohm 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 4 ohms 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 8 ohm at 1kHz instead, then the damping factor becomes 400. Conversely, if you use a driver with an impedance of 2 ohm 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 twofold. 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 more difficulr the cone becomes 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 the 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. Amplifier class matters a lot in regards to the amount of current you need to be able to supply to the amplifiers.. going all class D/class T helps ya milk more power out of the electrical system without spending boucoup bucks on a HO alternator etc. |
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Silver Member Username: Audioguy22Post Number: 108 Registered: Jul-05 | Hey Glass, thanks for that. When a switched my sub Amp(and nothing else) with a better amp with close power ratings but different damping factors, I noticed a hugh change in SQ! The bass got really tight and punchy and a lot of the noise(rattles)had gone. when I look at the specs of both amps, the big differents was the damping factors. Thats what I'm going on here, and my years of home Hi-End amps where the higher the better when it comes to DF. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8876 Registered: Dec-03 | mainly that was just to clarify the terms you'd mentioned earlier, so others coule keep up  what jon mentioned, which I didn't see till just now, basically equates to one of the problems I have with class D amplifiers. They're pretty clean amps, until you get close to peak outout and then their distortion leaps up which is why you see so many SPL competitors shred subs at competitions. They drive the amplifiers so hard they drop out of the feedback loop, distortion skyrockets suddenly, and bam, you have fried coils on the subs. The only real solution I've seen for this so far is by a few companies who digitally limit the amplifier output power to avoid reaching this point. |
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Gold Member Username: Jonathan_fGA USA Post Number: 4349 Registered: May-04 | Most "huge" differences noticed in amplifiers are either power variations, ability to handle clipping more effectively (headroom), or variations in frequency response. Damping won't do it unless you're comparing to an amp that is absolutely terrible. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8881 Registered: Dec-03 | always be careful comparing amplifiers, or any product on printed specs alone. especially if you fall into the trap of paying too much attention to any single specification, like THD for example. Specs alone can be very misleading, even when accurately stated. |
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