I'm not sure why more speakers aren't easy to drive. I haven't personally encountered an impact on sound quality, but my audio dealer said he tends not to like very efficient loudspeakers, like some in Paradigm's Monitor range (the Monitor 11 has 97 dB in-room efficiency). My Paradigm 7se floorstanders are "compatible with 8 ohms", with 92dB quoted efficiency. The 49W Rega doesn't even break a sweat at near-deafening levels.
There seems to be a trend in the loudspeaker industry of 4-ohm impedance. The Sonus Faber Cremona, which I really enjoy, shares that specification.
It's not clear to me specifically what accounts for the resistance of a loudspeaker, so it's difficult to say why everybody isn't making easy loads, but there must be some explanation.

So, I open my fresh baked Stereophile this month, and after a quick peruse of the TOC and

The Keith Howard article is very important, and is a good example of how much remains unknown or unrecognized about the interaction of audio components. While the article may have made your head spin, the graphs showing the EPDR for each speaker are the most important to understand, and are easily understood. Phase angle has always baffled me and was therefore useless, but when it is part of an EPDR graph calculation its significance is clear.

That meaningful analyses, like EPDR or the modified FR phenomenon caused by the interaction of speaker impedance and amplifier output impedance that JA includes in his loudspeaker measurements, are ignored baffles me. Both of those results based on measurements, demonstrate the mistake made by the "measurements don't matter" philosophy. Purely subjective analysis does not provide any information regarding what is happening and why it is happening. Without that knowledge we cannot duplicate a result that is positive or avoid one that is not except by chance. There is no learning without information, and the state of the art cannot advance in a manner we can duplicate without it. If some measurements have no correlation with sound quality that does not mean that all measurements are worthless. If a measurement is worthless in determining sound quality, we have learned that we can ignore that factor, and that knowledge is not worthless.

How measurements or calculations become part of a science' knowledge base or standard procedures is unclear to me. It seems it is not simple, given that something as straightforward as the FR response modification phenomenon I mentioned above that JA includes in loudspeaker reviews, while being so important (in my opinion) is seen nowhere else I can think of. Could anyone elaborate on that topic?

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Is there any reason not to make speakers easy to drive? Is it just a matter of driver matching? Does it affect sound quality if speakers are made efficient and easy to drive?

Most loudspeaker systems are made up of multiple drivers. These drivers need to 'integrate' to produce a cohesive sound, with uniform characteristics ( eg the mid range should neither be laid back nor shout above the bass & treble ).

The drivers are 'integrated' for their sound, by using capacitors, inductors and resistors between the power amp and the speaker drivers. These components - the cross-over network also needs to be driven by the amplifier.

The speaker designer's primary objective is to get good sound, .... not easy cross-overs for the amplifier to drive. As a result, loudspeaker systems often provide a very complex and difficult load for an amplifier.

Ofcourse this is a simplistic explanation. There are various other factors too, like the driver's interaction with the cabinet it is mounted inside...

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phase angle (not quite sure what that is)

In a resistor, current and voltage flow in tandem, ie max current flows at the same instant that the max voltage is applied to the resistor. ( This is the easiest situation for the amplifier )

However, in Inductors and capacitors, the current can lag ( flow after ) or preceed the applied voltage.

The phase angle is a measure of just how much the voltage is out of sync with the current flowing ( in this case, into the crossover and speakers )

Hope this helps.

This sort of helps. I'm still a bit fuzzy about how voltage can be divorced from current. Current is just voltage with a load. So, once you introduce a load, I don't quite understand how there may be a discontinuity between voltage and current.

Tyll, I missed the point that you were trying to make. Are you saying that difficult load speakers are a bad thing and that measurements are necessary to flush that out? Please elaborate.

Thanks

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I'm still a bit fuzzy about how voltage can be divorced from current

Yes, it is an un-usual but well established concept. Power Factor errors are the bane of Power Companies and distributors worldwide.

Unfortunately basic electricity courses at the school level typically address Direct Current (DC) as available from a battery.

Alternating Current (AC) either at 50 Hz or ANY frequency behaves differently with capacitors and inductors, compared to resistors.

As a loose analogy, consider a stone on a table, ( the load ) connected to one end of a metal rod.

If the open end of the metal rod is pushed suddenly, the stone will move immediately.

The metal rod is similar to the Resistor.

If the metal rod is instead replaced by a spring.... a sudden push at one end of the spring will have a time lag before the push is transmitted to the other end of the spring, and to the stone.

The stone will move a touch later, after the push is applied.

The spring is like an inductor that delays the flow of current, after a voltage is applied....

Cheers

Tyll said:

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I know I’m not the likely norm, but my point is there will always be a significant sub-set of audiophiles that get a great kick out of a deeper technical viewpoint, and Stereophile should have a mission to serve them as well.

Precisely my view too.

And THANKS JA

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Yes, it is an un-usual but well established concept. Power Factor errors are the bane of Power Companies and distributors worldwide.

I've got a buddy who builds hydro plant turbines. The flowrate available to the turbine changes day to day as it is modulated either by just low water or the Army Corps of Engineers telling him what flow rates he's allowed to use. As the flowrate changes the horse power they can throw at the turbine changes. But the turbine must allways spin at the same rate because it's attached directly to an AC generator and it always has to put out 60Hz. They way they control how fast the generator spins is by varying the phase angle of the generators output from the grids 60Hz AC. The generator is slightly advanced of the 60Hz on the grid. As you increase the phase angle the generator works harder to pump the juice. On a good day the water is pushing hard and they can load the generator with a high phase angle; when they only have a trickle the phase angle is small and the generator almost free-wheels along with the grid with a small phase ange load.

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If the metal rod is instead replaced by a spring.... a sudden push at one end of the spring will have a time lag before the push is transmitted to the other end of the spring, and to the stone.

Great analogy. I been thinking how it could be explained, it is a bit of mind twister. Let me try to extend your analogy:

So, instead of a rock on a table, how about a long rigid pendulum with an iron ball on the end. Push the ball and it swings at a some natural frequency. That's a bit like a speaker in an enclosure, the speaker with it's rest mass is the iron ball, the resonant pendulum is the springy air mass in the enclosure. Now imagine swinging the ball with a stiff rod. Not so hard if your moving it at the resonant frequency, but imagine trying to swing the ball at a different rate. You'd find yourself struggling. OK but that's an oversimplification that doesn't really give much of a picture of what the artical is about.

Now imagine two iron balls, one big and one small, on two pendulums of different lengths with the small ball on the short pendulum and the big ball on the long one. And lets imagine that the longer pendulum is not a single stiff rod but one that has a couple of elbows in it and that the three rods along the pendulum between the fulcrum, ball, and elbows are different lengths. Give the big pendulum a quick shove and it will generally swing at the resonant rate but will also wobble around some as the articulated pendulum deals with all it's elbows. Then put together some Rube Goldburg contraption of springs and levers that allows you to push on the handle but dilivers energy to both balls such that quick pushes get steared to the little ball and long slow movements gets to the big ball. And imagine it's you job to push the handle in a very specific pattern to make the balls move. Let's say the pattern is a 0.5 Hertz square wave. You push the handle in exactly one foot and hold it there for a second, and then you pull it back one foot and have to hold it there for one second.

Well, you can imagine that after you push it and hold it there, the damn thing is going to start flopping around like mad and fighting you so that its hard to hard to hold it at the one foot position. And then when you move it back it'll sometimes help you and sometimes fight you.

Obviously, you are the amp, the contraption is the crossover, and the balls are the woofer and tweeter. As an amp you might be called on to move a giant complex contraption or and fairly simple contraption. And one will be harder to drive than the other.

But the gist of the artical is that if you test the contraption only at one frequency at a time, it's likely to behave a little differently than if you have to accurately put a rather randomly varying signal into it. It'll hurky jerky wobbly all over the place and some signal patterns are likely to set up some unuslually difficult situations that are markedly different than if you just put one frequency into the system. As complicated as they are, they can still be modeled, it is a finite system after all. But you don't discover the nature of the model just by looking at its impedance over a series of frequencies. It's enough data, though, to do a bit of number crunching and come up with a more comprehensive model of the load under complex conditions.

So the point of the artical was that just presenting the impedance vs frequency raw information really doesn't tell you the whole story of how difficult the load is to drive. But if you do some math, you can come up with a fuller picture of the difficulties driving the load when driven by a complex audio signal.

Whew! Clear as mud I suppose, but I tried. Gives you a lot more appreciation for speaker and amp designers, though.

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Tyll, I missed the point that you were trying to make. Are you saying that difficult load speakers are a bad thing and that measurements are necessary to flush that out? Please elaborate.

Sorry, I didn't address your question directly. Speaker designers have a lot of balls to juggle. One of them is the descision of how hard a load the designer will accept. If she (aww...isn't that sweet) wants the speaker to be an easy load, she has to accept certain limitations to the design. If she doesn't much care how difficult a load it is, she'll have more latitude to be innovative or address particularly difficult problems in the design. Speakers that are difficult loads are not necessarily "bad", but you do have to throw a ballsy amp at them.

Hi Tyll,

Thanks for your detailed explanation. I understand the pendulum with joints analogy. However, what confused me was your subsequent post that says that difficult load speakers aren't necessarily bad. If I understand your pendulum analogy, then it seems to met that a heavy load speaker would create resonances that an easy load speaker would not. If that's the case, then wouldn't it be better to build easy load speakers? You mention that there are limitations concerning building easy load speakers. The only limitation I can think of off hand is driver matching. Wouldn't it be better to accept that limitation vs. introducing resonances into a speaker design due to difficult loads?

Thanks.

This sort of helps. I'm still a bit fuzzy about how voltage can be divorced from current. Current is just voltage with a load. So, once you introduce a load, I don't quite understand how there may be a discontinuity between voltage and current.
==============================================================
Alex,

You get a phase angle when the load is "reactive" - that is
it has either an inductive or capacitive component.

The current for either a capacitor or an inductive won't
be in phase with the applied voltage. That's because
both capacitors and inductors store energy.

The capacitor stores charge, which gives rise to a current
when it is discharged.

The inductor stores energy in the form of a magnetic field,
that can then induce current flow when the voltage changes.

Because of the stored energy in both these devices, the
current doesn't have to flow in lock step with the voltage.

Dr. Gregory Greenman
Physicist

Inductor opposes current flow, capacitor stores a charge, an inductor doesn't store anything...Only pure resistive loads are in phase pf 100. Anything less than 90% Pf is a lpf....PF corection to bring things as close to 1 as possible. Industry it matters with large motors transformers etc.

Current/voltage is affected by many things in the ckt. Z Xl Xc R Freq.....current leads lags etc. Wood blocks have no effect on Z

The "phase" jargon is really very simple to conceptualize. Imagine a capacitor that gets connected on to a battery, for example an alkaline AA cell. If we were to measure things AT THE VERY INSTANT the capacitor poles are connected to the battery poles, then we would see that:

(a) the voltage across the capacitor plates is zero (because it hasn't charged yet), but

(b) the current starts flowing as though the battery were short-circuited, because the capacitor wants to suck all the charge it can.

Now as the current keeps flowing, charge starts to build up in the capacitor plates, and the current flow slows down accordingly.

If we measure again after things have settled down, the voltage across the capacitor plates has become the same as the battery voltage, and current flow is now zero. The capacitor has charged fully.

So, when the current was at its maximum, voltage was zero and now that voltage has reached maximum, current is zero.

If we wanted to phrase the above sequence of events in physics jargon, we would say that "across purely capacitive loads, voltage phase lags current phase by 90 degrees".

An inductor acts in the exact inverse way, because the magnetic field created by current flow wants to keep that current flow steady and "dislikes" current fluctuations.

There is nothing confusing about such a simplified, idealized situation. If, however, we try to imagine that the voltage is not just the 3 Volts DC an AA cell can produce, but an alternating mixture of all kinds of frequencies that tries to create current flow across a complex smorgasbord of real AND virtual resistances, capacitances, inductances and friggin' back-EMF's (such as a loudspeaker with multiple drivers and a crossover), now THAT'S when things can get really confusing Even from the point of view of our previously humble AA alkaline, which has now become the output stage of a power amplifier as it tries to make do with whatever cards its power supply has dealt it.

And this was the purpose of Keith Howard's excellent article: to simplify such a complex situation down to a simple x-y axis chart.

Beautifully explained ElGreco and Morbius.