speaker excursion..."mo power"..and bass..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
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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.

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
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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
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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
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