speaker excursion..."mo power"..and bass..Sean
I've been busy for a few days, hence the lack of response. As to my comments about "damping factor being a hoax", i'm not saying that low output impedances are a joke. What i'm saying is that how people interpret the impedance relationship between an amp and a speaker and what it means to "driver control" is mostly incorrect. The closer your speaker impedance is to the output impedance of the amp, the more that the reactance / loading characteristics of the speaker will control or "highly influence" the output of the amp. The further apart they are ( a higher damping factor ), the less influence the loudspeaker load will have on the amp. This is NOT the same thing as the amp having greater control over the speaker. The only thing that allows an amplifier to "control" a loudspeaker is voltage and current output. Cinematic: Your post saying that we are 50% wrong ( or is it 50% right? ) is 75% incorrect, but i don't have time to clarify point by point. Thanks for stopping by though... : ) Sean > |
Great thread, and very interesting to me as I am in the process of building a highly-tweaked system around the Orions. I'm almost finished building them, and I added to Linkwitz' design by building in substantial dampening aids. Here's my system as it will be in about one month: McIntosh MC-275 driving tweeters Tenor 75WP monoblocks driving midranges Butler TDB 5150 driving woofers (150watts each) Sony SCD-1 Supratek Sauvignon linestage Linkwitz active x-over Chimera labs litzbraid custom speaker cables Chimera labs litzbraid interconnects BPT 3.5 Signature Conditioner I'm a bit concerned about the synergy between amps, and I intend to be extremely careful of volume levels,but it should sound fabulous. Any thoughts re: this setup from other members would be welcome. I know this doesn't directly answer the question, Fishboat, but maybe the system's performance characteristics when done would be interesting to you or others. |
Cinematic_systems...Whoops! You are right that in a second order or higher passive crossover some power is "dumped to ground". For example, for the woofer, after the inductor rolls off the highs, a capacitor to ground rolls them off further. However, I don't believe that the "dumped" power amounts to much, as the "dumping" starts near zero at the X/O frequency and increases at 6 dB/oct, but working with an input that is already rolling off at 6 dB/octive. Perhaps there is an EE out there who still remembers how to calculate the "dumped" power in a second or third order crossover. Fourth order would involve a second "dump". If Sean is right, and we all got rid of passive crossovers, perhaps the global warming problem would be solved. |
Cinematic_systems...In a passive crossover, power does indeed "go to ground", but it goes through the drivers, which is the whole point of the thing. The power "wasted" by notch filters is minimal, unless the drivers are truly aweful. The 10 AWG air coil inductors in my MG1.6 have about the same resistance as the original iron core inductors. This is why most speakers use iron core inductors. When estimating the broadband signal equivalent to two bandlimited signals, the usual approach is to do an RSS. For example... 100^2 + 60^2 = SIGNAL^2 SIGNAL = 117 If the two band limited signals are equal, the equivalent broadband signal is maximized at 1.41 times the band limited signal. However this assumes that the two bandlimited signals are uncorrelated, and this is not typical of music, where loud low notes are often simultaneous with high frequency harmonics, not to mention cymbal clashes. As to tweeters burning out...I guess that some may be huskier than others, but I just took out two SEAS Excel T25CF-002 Millenium tweeters with about a three second burst of noise due to an interconnect problem. And these tweeters were not driven directly from the amp, but rather through a passive crossover. However, replacement voice coils are available, and Madisound even installs them for free. This suggests to me that blown out voice coils must be quite common. |
Whoa! This thread had a great technical edge and now its tumbling out of control. Passive crossovers are "voltage dividers", this is where the power goes, to ground especially in 2nd order and filters with notch filter etc. There are small losses in the components but the passive filter itself is a loss as it is addressing the fully amplified signal. Drew/Bombay & Sean your original long posts were about 75% correct but this second group is getting into the land of speculation. Again good posts but now you guys are down to about 50% correct. Sorry,I don't have time to correct the errors point for point. |
I think the damping factor issue is directly related to the speaker in question, which may very likely have a very low moving mass and very high magnetic field and very short excursion length(such as my speakers), and thus have a very significant amount of its own internal damping ability. In cases such as this, high numerical "damping factors" may actually inhibit transient response, and may not be an advantage at all. As long as the relationship between the amp's output impedance and the speaker's relative impedance at any given frequency(damping factor) remains enough to control the speaker(>5), then it is sufficient in that circumstance. It is when the speakers have poor internal damping characteristics(ie high moving mass/low magnetic field strength/very long excursion length) where problems are more likely to be "fixed" by high electrical damping factor numbers. Regarding high power being "better" than low power, we all know I'm in the "low power" camp. I think(and I'm pretty sure Sean agrees) that you are much better off to have higher efficiency speakers than to try to overcome low efficiency speakers with brute force, because of the exponential curve of power needed to add a few db to the output. Also, it has been my experience that high power amps seem to be less "delicate" in nuances and details, due to the beefy construction needed to handle all that power. And in addition, to have power like that, you simply have to go out of Class A operation, which I don't like to do. And, when you have low efficiency speakers, you have a higher "low-level detail threshold" because it simply takes more power to make the speaker move at all, so that some very low level stuff never even makes it out of the speakers, unless you have it turned up alot. If the speakers are high efficiency, you can still get pretty loud SPL, with great low level detail, with very low power amps. I do realize that this normally sacrifices some of the very low bass. I think it is not a bad trade-off. |
Hey Sean, Neither Eldartford nor I totally denied that L & C do lose power. Eldarford: "Passive crossovers do not absorb power to the degree that you suggest." & I wrote: "Inductors will dissipate some heat as a coil of wire will have some resistance. If one is using a low ESR capacitor, very little heat gets generated in a capacitor." However, I think that you are mistaken as to just how much gets dissipated in these Ls & Cs on average. Optimizing the losses in a reactive component is NOT the way biamping achieves its perceived increase in power. Separation of power amplification into multiple chassis & the constructive addition of the music signal is what gives biamping its perceived increase in power. "The comments about the active crossovers increasing the gain of the signal have little to nothing to do with amplifier capacity." True! However an amplified signal fed into an amp needs less amplification to the speaker => more headroom for dynamics. Such a setup would have more air/the music would flow easier/more transparent. The comparison is between passive & active xover cases. "Couple this with the fact that your .1 ohm output of the SS amplifier is typically fed into 40 - 120 ohm speaker cable" What???? Who in their right mind would use a 40-120 Ohm speaker cable?? Does a speaker cable with 40-120 Ohms even exist? I think that you would ripe for catching much flack for this one, Sean! :-) I think it's a typo. You really meant milli-Ohm, right?? "Reflected EMF is a reality that the amps have to deal with." Oh, it certainly is. No question about & I never denied it in my post. However, not to the degree that you mentioned in your original post. There IS the reverse isolation of the xover & their IS the output impedance of the amplifier/damping factor as only an active circuit can get rid of the back-EMF "Damping factor is a hoax and is completely taken out of context." No it certainly is not! Without a damping factor, which is really a glorified name for amplifier output impedance there'd be no "out muscling" the woofer. We can agree to disagree here, which is just fine w/ me. ============================ Anyway, I, too, am in the more power, the better camp as long as the user is careful to not overdrive the speaker. If there are transients, then they should be shorter in duration (than being longer) & if one doesn't know then it's better to listen with a slightly lower level to be conservative. Case-in-point: Last summer I fried my Green Mountain floor stander tweeter after trying to break-in the woofer by playing music too loud for 14 hrs at a stretch! What Roy Johnson told me was that tweeter can handle way more than its 100W RMS rating if I play loud music for about 3-4 minutes (1 track) every 20 minutes or so. He says that he does that all shows regularly & the tweeter survives each time. So, now I know....... More power results in the music flowing better, more air, more transparency, more lower level details. Drivers can handle many more watts of peak power even tho they are rated for lower RMS power. (Usually, the driver ratings are RMS power, which is average program power). So, yes, Fishboat, its reserve power mostly. Additionally, a large amp has more current capacity even at lower power levels, which what gives the music is ease of flow. To get that driver moving, you need current in the voice coil. |
Capacitors DO lose power. This is called "dielectric absorption". ESR is also a term used to describe the series resistance or "internal losses" of a capacitor. If the power loss is severe, the cap "cooks" itself from the inside out and doesn't last very long or changes value to the point that normal circuit operation becomes harder and harder to achieve. Inductors DO lose power i.e. it is called series resistance. Besides that, some of the energy is dissipated in the magnetic field that the inductor creates and / or through inductive coupling to other nearby parts of the circuit that they shouldn't be in. This is why proper crossover layout is important. I've seen "high end" crossover circuits that had a tremendous amount of crosstalk taking place due to this coupling. The end result is that tweeters and midranges end up being fed energy that should have gone to the woofer. Why did this take place? The inductors are too close together, placed in the same horizontal or vertical plane, etc... Due to their close proximity, the coils become inductively coupled via the previously mentioned magnetic field. By simply changing the horizontal and / or vertical planes of the inductors, without even moving them further apart, crosstalk can be reduced by at least -40 dB's. Not only does this result in less loss in the circuit, but better sound due to less smearing. Power handling is also improved due to having a more effective frequency dividing network with less stray coupling. The use of a Zobel network that is tuned to operate within the audible pass-band WILL attenuate energy. The capacitor selects what frequency the Zobel comes into play and the value of the resistor dictates how much energy it will consume. If one does not use a resistor of high enough power handling and / or the value is poorly chosen, you WILL burn up the resistor in the Zobel when "cranking" the volume way up on a steady-state basis. All of these parts DO rise in temperature as they are used and this is part of what "component settling" is all about. If the average power that they are passing is high enough, you would feel the heat that they were dissipating. Since most music is very low in average power consumption and very high in peak power, the energy lost / heat generated within these parts isn't very high and / or consistent. It is these very short duration, high intensity peaks that get "eaten up" in a passive crossover, hence the increase in dynamics and increased detail that one encounters from going active. All of the aforementioned losses in the passive circuit end up costing resolution while increasing the levels of inductive and capacitive reactance that the amp tries to load into. "Thus, the practical increase in effective power is more like 2X, as that 1975 article you refer to showed". Doubling the power ( X2 ) is a 100% increase. Losing half the power ( /2 ) is a 50% loss. We've said the same thing using different wording looking at things from opposite points of view. As far as the 30 / 60 wpc actively crossed amps clipping at the same appr output level as that of the 175 wpc passively crossed amplifier, i can't help you out there. I referenced this from Vance Dickason's Loudspeaker Design Cookbook and do not have access to the original article. Your own response seems to confirm these figures rather than contradict them. The comments about the active crossovers increasing the gain of the signal have little to nothing to do with amplifier capacity. The amplifier can only put out so much power prior to clipping regardless of whether it has to amplify itself is providing the gain or whether the drive levels are increased. If anything, increasing the drive levels via the active crossover would have driven the amplifier into clipping sooner and more consistently. This is because the amplifier functions at a constant rate of gain, so long as it is linear in operation. More drive means more clipping. Damping factor is a hoax and is completely taken out of context. I've explained this in the past several times. Couple this with the fact that your .1 ohm output of the SS amplifier is typically fed into 40 - 120 ohm speaker cable to get to your 4 - 12 ohm speakers and you should begin to understand why i rant about using "properly designed" low impedance speaker cables as much as i do. You guys are missing the boat on this one in tall fashion. Reflected EMF is a reality that the amps have to deal with. If it were not, microphones would not work or produce voltage and we couldn't use them to capture acoustic signals to make recordings with. Now take the microphones that produce EMF and increase their capture area ( cone size ) and motor structure by a few dozen times and tell me that they don't generate voltages, especially when their excursions are made in great amplitude and speed. Just as feeding voltage into a coil in a magnetic field causes the cone to move, moving the cone that has the coil attached to it that is placed within the magnetic field generates voltage. This is an action / reaction that is unavoidable. Obviously, one has to "out muscle" the other opposing source of voltage / current, otherwise the two would cancel each other out as heat and there would be no acoustic output what so ever. "The externally mounted 3.5mH inductors of my MG1.6 are 10 AWG air core coils with dc resistance of 0.2 ohms, which is about the same as the original equipment iron core inductors. Since the driver is 4 ohms, 0.2/4 which is 5 percent of the power will end up as heat in the inductor". Bombaywall, El just answered your "Thermal losses in a capacitor & coil????? Physics does not allow this!" comment. On top of that, he was talking about a 5% thermal loss using a 10 gauge conductor, which has very low series resistance. How much more loss is there in an inductor that is wound using a 16 - 20 gauge conductor as found in most commercially produced loudspeakers? "It is dangerous to run a tweeter directly from a power amp. Turnon and turnoff can be accompanied by "thumps" that the tweeter won't like, and a loose interconnect can be an instant disaster." If you look at some of the old Stereo Review, Audio and even Stereophile reviews of speakers, i think that you'll find that many tweeters will easily cope with transient bursts into the 100's if not 1000+ watt range, so long as they are limited in duration. I've seen tests were the tweeters handled more power than the woofers did, so long as they were bandwidth limited. Other than that, the easy way to get around "turn on surges" is not to turn your gear off. "I think that it was on the Adair Audio website that I read that VCs are only about 1-2% efficient! I was shocked to read such a low number - I knew that they were largely inefficient but wasn't expecting 1-2%! If that's true, it's easy to see why "Duration" would fry a tweeter." Pretty efficient horn designs only come up around 4% - 5% or so. Almost all of the power generated within an amplifier is dissipated as thermal losses in a loudspeaker. As such, removing even several tenths of one percentage point via getting rid of "lossy" passive components between the amplifier and driver can make a sizeable difference. Increasing power transfer via proper impedance matching can also improve system efficiency AND improve transient characteristics. Sorry if this jumps around quite a bit, but i'm limited on time. Due to my increased work load ( busiest time of the year ) and changes in my personal schedule due to family health problems, i can't hang out here as much as i'd like. Hope this at least clarifies a few things. Sean > |
Sean, Good explanation overall but I think that there are a few things that might be mis-represented: * "As taken from Audio magazine September 1975 in an article entitled "Bi-Amplification - Power vs Program Material", it was demonstrated that an actively crossed two way with 30 watts on the tweeter and 60 watts on the woofer clipped at appr the same point as a 175 wpc amp driving the same speaker full range with a passive crossover. " If I had to guess, I'd say that the active xover must have had gain. So, the 30W & the 60W amps each had help from the active xover. IOW, there were 2 amplifiers in series: the active xover & the 30W & 60W amps. Needless to say, it must have been enough. The 175W amp OTOH did not have that help & performed all the gain from input to output in just 1 chassis. Hopefully that 1975 report makes some mention of this??? So, when you do 30W+60W=90W < 175W I think that one must add the active x-over gain. Just a comment here. I do agree with you on the concept of bi-amping & further that external x-overs are better. * "This is done by reducing the thermal losses that one would normally incur when running the capacitors, coils, resistors found in a typical passive crossover." Thermal losses in a capacitor & coil????? Physics does not allow this! I think Eldartford's latest post also addresses this. This I think is a fundamental error! Inductors will dissipate some heat as a coil of wire will have some resistance. If one is using a low ESR capacitor, very little heat gets generated in a capacitor. If you have an active xover, touch the C & L right after several hours of play & see how warm or hot it is!! The way that one effectively doubles the power in a biamping situation is NOT by minimizing the thermal losses(!) but it is by splitting the power into atleast 2 chassis: one for the tweeter & one for the woofer. If one adds the power linearly then one will notice that the voltage excursions have doubled. Thus, if you calculate power, which is volts squared divide by impedance, one will notice that the power has quadrupled effectively. This is the theoretical limit which is usually not achieved owing to distortions in the amp which disallows one from running the amp wide open. Thus, the practical increase in effective power is more like 2X, as that 1975 article you refer to showed. * "In order to maintain control over the driver, the amplifier not only has to generate enough power to overcome that reflected voltage that the driver itself has produced, but it has to have even more power on reserve in order to "muscle" the driver according to the intensity of the music signal that it's being fed." I feel that this is not correctly written. Yes, the woofer does produce back-EMF. Does this back-EMF hit the amp terminals directly? Not at all.....there's the reverse isolation of the x-over ckt (active or passive). The back-EMF is attenuated quite a bit before hit the amp terminals. The amp does not have to generate more power to overcome & "muscle" the woofer. What the amp has to do (if it is designed correctly) is provide a very low output impedance path into which the back-EMF can be channeled to ground potential. This merit of the amp is measured by the "damping factor" of the amp. In an actual system the impedance of the speaker wire can totally ruin the overall damping factor & disallow (an otherwise high damping factor amp) to control/damp the woofer. * "As such, the "beefier" the drivers that you're using and the louder and lower in frequency that you want them to play, the more power that you have to have to maintain control. If you don't have the power to maintain control, the driver...." I really don't think that power maintains control over a woofer. Power/Current into a low impedance is what creates the woofer excursion BUT it is a high damping factor/very low output impedance that REALLY maintains woofer control. As they say often - power w/o control is largely useless. The control comes from the damping factor taking into consideration the speaker wire impedance & not just the amp. * "Having said that, it has been my experience that high quality drivers can take GOBS of power beyond their power rating. That is, so long as the power remains clean ( non-clipped ) AND the music that one is listening to is "dynamic" in nature." A comment here - actually clipped power is not really that much of an issue in & off itself for a speaker driver 'cuz the clipped signal does not hit the driver directly. It must go thru a xover (active or passive). Remember that amps usually clip @ the top end i.e. when the volume has been turned up near-max. Remember, also, that a clipped signal is rich in harmonics - high frequency harmonics. These high frequency harmonics will be filtered by the tweeter xover ckt beyond 20KHz. The xover is a filter, they have to be filtered off. Thus the intensity of the clipped signal hitting the tweeter is much reduced. What really kills a tweeter is, as you wrote, duration. The longer one lets the clipped signal sustain, the longer it feeds the tweeter & the VC burns up. I think that it was on the Adair Audio website that I read that VCs are only about 1-2% efficient! I was shocked to read such a low number - I knew that they were largely inefficient but wasn't expecting 1-2%! If that's true, it's easy to see why "Duration" would fry a tweeter. Anyway, my intention is for this post to be viewed in a constructive way. I do hope that you view it the same. Thanks! |
Sean...Of course I am a long time believer in biamping, but I do think that the original reason (and I am talking about 50 years ago) was to avoid intermodulation distortion. Power amps have improved so that this is no longer a significant issue. As you say there are power delivery advantages also, but in this regard amplifiers have also improved about tenfold. (Back then a "big" amp was about 25 watts, and now it would be 250 watts or more). Which leaves us with the elimination of the passive crossover as the remaining advantage. I cannot understand how many people seem to think that driving two separate full range amps into the passive crossover is "biamping". I have two comments here. 1...It is dangerous to run a tweeter directly from a power amp. Turnon and turnoff can be accompanied by "thumps" that the tweeter won't like, and a loose interconnect can be an instant disaster. 2...Passive crossovers do not absorb power to the degree that you suggest. The simple test for this is to consider how hot they would get if they did absorb a lot of power, particularly since they are usually mounted inside a closed box, and surrounded by insulation. To take the scientific approach: Capacitors (ideal) dissipate zero power. EE101. Real capacitors are near ideal in this regard. Inductors will dissipate power because they cannot be made with zero resistance. The externally mounted 3.5mH inductors of my MG1.6 are 10 AWG air core coils with dc resistance of 0.2 ohms, which is about the same as the original equipment iron core inductors. Since the driver is 4 ohms, 0.2/4 which is 5 percent of the power will end up as heat in the inductor. (But they never feel warm). Resistors are used in crossovers, but not in the signal path except for the tweeter, where some power loss is usually necessary to balance SPL. If the tweeter padding resistor needs to be a large value, the wrong model of tweeter has been used. What is the basis of your suggestion that lost power will be 50 percent? |
All I can say is "wow"...thanks to all for taking the time to explain this. The big-power pathway does make sense and as usual there are always excpetions, like the Orion/active-types, to generalities. Drew...your numbers-based approach really explains it well. No surprise that Linkwitz has designed the Orions very well. The more I learn about the active approach & Linkwitz in particular the more interesting the Orions become. Sean...you are an amazing person. Your explanation makes a lot of sense. I caught a little of the past discussion on active speakers, but now that I look into them deeper it really is surprising that they are not more popular. SL's DIY approach is fairly inexpensive when you consider the parts that make them up. Undoubtedly if active types were more common (read: commercially available on wide basis) the "value-based" prices would be stiff. 6000 watts you say... :-)) Some folks warm up the house by tossing a log or two into the wood-burner...I'm guessing you just turn on an amp or two. |
Sean, execllent post and I concur with your opinion regarding "direct drive" versus passive designs. As has been explained many times on this board... the logic behind why an active design is generally better seems straight forward and convincing. Off the top of my head I'm trying to recall an active floorstanding design that's not ported and for some reason I'm drawing a blank. |
I forgot to mention the "bad things" about clipping. The one thing that everyone forgets to mention when talking about clipping is amplifier stability. Mr Dartford alludes to this when he talks about instability. That is, a note may have a duration of anywhere from milliseconds to a couple of seconds. When an amplifier goes into hard clipping, the duration of that note can be drastically increased due to smearing / saturation. As such, the speaker not only has to deal with more power to dissipate and a greater percentage of power centered higher in frequency ( harmonics ), but it also has to deal with all of that over an increased amount of time ( longer duration ). It is a combo of the increased power with longer duty cycles that typically "cooks" the voice coil of dynamic drivers. As mentioned above, the driver can't dissipate the heat fast enough, so the end result is "thermal meltdown" ( literally ). As a side note, this is yet another reason why i feel that it is important to measure the efficiency of a speaker, not just the sensitivity. As most of you may know, the impedance of a speaker changes with frequency. As such, one might be pulling "X" amount of watts at 1 KHz due to the speaker being appr 8 ohms, but at lower frequencies, where it already needs more power to reproduce deep bass, the amp might be producing "XX" watts of power. This increased power comes from the demands of the music AND the demands of an impedance swing. Now if we knew that the amp was more stable ( able to deliver suitable amounts of power into various speaker loads ) and / or factored in this impedance swing in the efficiency of the speaker rating so we knew more of what we were dealing with, this wouldn't be a big deal. Given that not all amps are stable at all impedances, and not all speakers are rated properly ( efficiency vs sensitivity ), this makes our job of selecting suitable amps / speaker combo's even harder. That's because one amp may go into clipping sooner at lower impedances than another amp with identical power ratings as listed at 8 ohms. Other than that, amplifier loading characteristics and the type of load that each individual speaker presents to the amp is a very difficult thing to try and summarize briefly. What i will say is that, so long as quality is not compromised, you'll never be hurt by having more power. Not only do you reduce the risks and distortions of clipping, but your potential to achieve greater and more consisten levels of control over the driver are also improved. Sean > |
Drew covers a lot of excellent points. I can tell that he's really been doing his homework as his contributions to these forums continues to grow in quality. Kudo's to him for learning as much as he has AND for sharing his knowledge in a very useful manner : ) Having said that, i've ALWAYS promoted the benefits of "direct drive" i.e. amplifier to driver using active crossovers. The increase in clarity, liquidity, transient response, dynamics, etc... is STAGGERING compared to an equivalently designed passively crossed over speaker. Even with speakers using the simplest crossovers possible ( 6 dB / octave aka "first order" ), one can EASILY hear the benefits. The drawback to active crossovers / going "direct drive" is that you increase the number of channels of amplification required and end up with at least one more chassis in the rack ( active crossover ) for most designs. Depending on whether or not one uses one multi-channel amp or several two channel amps can also make for a big difference in the amount of real estate that your system takes up in the room. By bandwidth limiting the amp PRIOR to feeding it the signal to be amplified, the amp can now concentrate all of the available power to a much narrower frequency range. As such, efficiency is increased and so is headroom. As taken from Audio magazine September 1975 in an article entitled "Bi-Amplification - Power vs Program Material", it was demonstrated that an actively crossed two way with 30 watts on the tweeter and 60 watts on the woofer clipped at appr the same point as a 175 wpc amp driving the same speaker full range with a passive crossover. Since 60 + 30 = 90 and 175 is almost twice that, we can see that actively crossing pretty much doubles our effective power rating. This is done by reducing the thermal losses that one would normally incur when running the capacitors, coils, resistors found in a typical passive crossover. In the case of the Orion's, that "measly" ( and it IS measly ) 60 watts would be equivalent to appr 360 watts if fed into a typical passively crossed speaker design. Even with 360 wpc into that passively crossed design, it still wouldn't have the same transient response, control, transparency or liquidity that the active design is able to achieve. If it is not apparent by now, i'm a BIG fan of actively crossed multi-amp speakers. My mains are 3 way actively crossed designs using 12 channels of amplification ( 6000 watts rms ), my bedroom system is actively crossed with multiple amps ( 400 watts rms ), my office system is "direct drive" ( no passive crossovers ) with about 1500 watts rms, my Brother's system is actively crossed and quad-amped ( 1700 watts rms ), etc... Bare in mind that these are factory power ratings, not the "effecive" power ratings that one gains from actively crossing over. With all of that in mind, the more power that you have, the LESS chance that you have of "slapping" or "bottoming out" the driver due to a lack of control. That's because as the driver takes a longer excursion, it produces a greater amount of reflected EMF ( electromotive force or "voltage" ). In order to maintain control over the driver, the amplifier not only has to generate enough power to overcome that reflected voltage that the driver itself has produced, but it has to have even more power on reserve in order to "muscle" the driver according to the intensity of the music signal that it's being fed. With some very long throw ( long excursion ) drivers that have massive ( big voice coil / magnets ) motor structures, this can equate to several HUNDRED watts of reflected EMF. Bob Carver discusses this in detail in his white papers for the Sunfire subs if anyone is interested. As such, the "beefier" the drivers that you're using and the louder and lower in frequency that you want them to play, the more power that you have to have to maintain control. If you don't have the power to maintain control, the driver is more likely to "overshoot" or "over-extend" its' own mechanical suspension, resulting in damage. This is completely different than what Linkwitz is discussing though, as he's talking about feeding too much power into the driver, which results in over-excursion but for different reasons. The difference here is that with this type of over-excursion, the driver is still being controlled by the amplifier, which has plenty of power and headroom to push it beyond the mechanical limits. In effect, too little power is equivalent to "understeer" in a car i.e. you turn the wheel and the car slides forward instead of turning due to a lack of control. Too much power is equivalent to "oversteer" or "torque steering" i.e. where the excess power applied actually increases the amount of steering input that one used. Having said that, it has been my experience that high quality drivers can take GOBS of power beyond their power rating. That is, so long as the power remains clean ( non-clipped ) AND the music that one is listening to is "dynamic" in nature. By "dynamic", i'm talking about music that has a lot of dynamic range. That's because the less dynamic range ( more compression ) that the music has, the higher the average power levels will be. The higher the average power levels, the more continuous heat each driver has to dissipate. As such, listening to hard rock / heavy metal type music is FAR more demanding of both amplifiers and speakers, because the average power levels are much higher than with Classical, Jazz, Blues, Country, etc... If one encounters EXTREMELY dynamic recordings and is running gobs of power, the initial dynamic bursts can cause the driver to over-extend beyond reasonable excursion levels. Such is the case with the cannon blast on the 1812 overture. This is the kind of "over excursion" that Linkwitz is worried about with "big power" and justifiably so. As a side note, vented ( ports, passive radiators, slot loaded, etc... ) speakers are FAR more likely to be damaged from over-excursion / lack of control as compared to a sealed design. That's because the air trapped inside the box of a sealed design acts as an equal but opposite "air spring", sucking the driver back into the box as it tries to take a longer excursion. At the same, this same "air spring" pushes the driver back out as it tries to compress the air in the box on the "back-stroke". This is why sealed and stuffed designs are called "acoustic suspension" i.e. the air pressure in the box acts as a linear suspension for the driver. Vented designs lack a linear suspension as the opening used for the vent allows the driver to become "undamped" in either direction. The fact that sealed boxes typically have a much lower impedance at resonance also means that the amp can deliver more power into the woofer. As stated above, more power transfer equals more amplifier control over the driver. Hope this helps clarify some things and answers your questions. Sean > PS... 22 wpc without passive crossovers would be equivalent to 40 wpc. Fourty wpc on a speaker that is 104 dB's efficient would surely roar. As it is, about half of the 22 wpc capabilities of that amp would be lost in the crossover network. Factor in that the speaker that the 22 watts was going to be run on has a 4 ohm woofer, which means that it needs a lot more current, and you'll see where the reduced power might not be enough. On top of that, most tubed amps don't do ANYWHERE near their rated power with "low" distortion. If tubed amps were rated with less than .1% THD, their power ratings would be WAY lower than what they are currently being rated at by most manufacturers. If such were the case, that 22 wpc tubed amp would probably be rated at something around 5 - 8 wpc or so. If you doubt this, go back and look at the first BAT amplifier that Stereophile reviewed. While the VK-60 is rated at 60 wpc, if the power output of this amp was rated at .1 THD ( which is pretty high for an SS design ), the VK-60 could only deliver 2.5 watts @ 8 ohms and 1 watt @ 4 ohms. That's a far cry from the rated 60 wpc. Then again, Stereophile did comment that this was a very noisy / highly distorted amplifier, so using it as an example to represent all other tubed amps may be a bit extreme. |
Fishboat; 60 watts is all the speakers will take with the equalizations SL uses with the Peerless speakers in the kit. They have nothing more to give. More power will not serve you well unless you increase the capacity of the woofers power handling by adding different woofers. You can't simply supersize this kit for $.49, what I would recommend is building a couple XLS subwoofers to help give the Orions a little more pop in the bass if that's what you're after. Resist the more is better tendency and you're in the Orion crowd, the other "crowds" are irrelevant to your situation. |
Fishboat...Mention of the MG1.6 is just to clarify what speakers I am making amp power observations about. I also have Dynaudio Gemini speakers, small (5" woofers) MTM boxes, and these also responded well to power increases up to 450 watts (4 ohms). I haven't tried them with the 600 watt amps. Drew_eckhardt...I think that the concern about clipping relates to the amp doing bad things, like oscillation, which may occur at frequencies completely unrelated to the waveform that caused the clip. Let's see what Professor Sean says. |
The clipping of a low wattage amplifier frying tweeters is a myth. A square wave is the sum of a sine wave plus all of its harmonics with amplitude 1/n. The third harmonic has barely 1/10th the power of the fundamental. Real world numbers are even better. Music has a disproportionate amount of power in the bass range so those notes clip first. With a low tweeter cross-over like 1440Hz as used in the Orion the tweeter won't see anything from a clipped 200Hz tone until the 7th harmonic which is 17dB down from the fundamental. More typical cross-over points will result in even less energy reaching the tweeter. When you're clipping bass notes increasing the volume setting can't make them any louder. Unfortunately this does increase the high frequency energy to far beyond what you have with music. Speakers designed with some level of power handling for music can handle a lot less when all of the energy is at high frequencies. You won't have problems if you don't act like a drunken teen ager who insists on turning up the volume on a distorting system. The SPL from a speaker is a simple function of the air it displaces, which is a function of excursion, which is proportional to the drive voltage. When you increase sensitivity you move more air with less voltage. When you're limited by excursion more power isn't going to get you any more peak output. I built and own a pair of Orions. Since they're active speakers and don't need to pad down higher sensitivity frequency ranges to match the least sensitive, sensitivity can vary with frequency. The variation is radical as a consequence of driver count differences (two low frequency drivers get you a 6dB sensitivity increase), radiation space changes (there's a full to half space transition from 200 - 100Hz which gets you another 6dB at 100Hz and below), dipole roll-off at 6dB/octave, and the extremely low Q woofers (about .2 before equalization, loosing 14dB at their resonance arround 20Hz). Dipoles also don't need baffle step compensation which can cost a conventional monopole designed for free space placement 5dB in sensitivity. At 80Hz woofer sensitivity is about 97dB/2.83V/1 meter. If you drive them with amps producing 60W into 8 ohms on the verge of clipping you'll get 114dB out of them. A 150W amp would get you to 118dB, although midrange excursion/power is going to limit how loud you can play without loosing hi-fi distortion characteristics. Things would be different on paper with most passive speakers. At a not atypical 87dB/2.83V/1 meter you'd need 600W for the same bass output and a more sensitive 90dB/2.83V/1 meter would take 300W. But you don't need the same volume - a 60W amp would still get you 105 and 108dB from such speakers. Solid state amplifiers give you enough wattage that power isn't a problem in most domestic situations. Orion sensitivity and maximum output are low in the last octave although that doesn't matter because there's little musical content and the the equalization is 6dB down at 20Hz. |
Before anyone wanders off on a tangent...It isn't my intention to run any amp at clipping for any length of time beyond the time it takes to turn the volume down..and not to go to clipping on any regular basis. SL's point was only that the amp will bottom out before the driver does. I know that clipping is harder on drivers than than clean power...my interest here is the time frame....is the extra power only needed to fill out the millisecond peaks. I don't think anyone would choose to power a driver into submission..not much point to that. Eldartford...planar speakers are a whole nuther topic. |
Boy, you've opened a potentially big can-o-worms. I have no idea who is right, but there are those who maintain that it is far easier to damage a speaker with a low powered amp that clips than with a high-powered amp. I believe the theory is that when an amp clips, it outputs something akin to a square wave. A square wave is a sine wave with a series of harmonics. In other words, a clipped wave has more energy in the upper frequencies than the original waveform, and therefore, more energy is sent to the tweeter which burns the tweeter out. I have no idea if this is true. I don't understand how anyone can run speakers so loud that they can be damaged. Long before damaging levels are reached, the woofer bottoms or the amp clips and makes a horrible sound, and any sane person backs the power down. As far as sonic concerns (i.e., aside from the damage issue) I am not in the more power is better camp. With tube amps, I don't know of any pentode amps that match the sound quality of triode amps or SETs, assuming the speaker is efficient enough to work with the lower powered amps. With solid state, I like the sound of lower-powered amps, particularly those running hot (generally class A) over a really big amp that is loafing along at a fraction of its output. Solid state amps with huge banks of multiple output devices often sound flat and uninvolving to me. Maybe they really kick ass at high volume, but I never want to go there anyway. |
I don't know why, but I have found that every increase in power (up to 600 watts) for my MG1.6 speakers has improved the sound. I don't think it is the power per se, but some other characteristic that tends to go along with high power capability. FAIR WARNING!!!!! If you follow Sean's example you will have multiKilowatt amps (and blown out speakers):-) |
