Why are low impedance speakers harder to drive than high impedance speakers


I don't understand the electrical reason for this. I look at it from a mechanical point of view. If I have a spring that is of less resistance, and push it with my hand, it takes little effort, and I am not working hard to push it. When I have a stiffer spring (higher resistance)  I have to work harder to push it. This is inversely proportional when we are looking at amplifier/speaker values.

So, when I look at a speaker with an 8 ohm rating, it is easier to drive than a speaker with a 4 ohm load. This does not make sense to me, although I know it to be true. I have yet been able to have it explained to me that makes it clear.  Can someone explain this to me in a manner that does not require an EE degree?

Thanks

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I've heard it described like this:  remember that the amp is not just pushing against a spring in one direction, but rather pushing and pulling back and forth.  Less impedance, e.g. a lighter spring in your analogy, means more slop, more wiggle room, that the amp must now cope with in order to control the woofer.

Almarg, please weigh in and set us all straight.  ;-)
It's about the amp.  Amps like to put out at 8 ohms.  The mechanical analogy isn't a good one.  Instead, think about your past gf's.
A low impedance speaker requires greater current from the amplifier to result in the same voltage at the output.
I ain’t Al but one of the few things I sort of understand about electronics is Ohm’s law.

From Wikipedia
Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

I (current; amps) = Voltage divided by Resistance (ohms)

At the risk of embarrassing myself, as resistance decreases the current required for a given voltage goes up.

As an example:
1 volt/8 ohms = 0.125 amps;
1 volt/6 ohms = 0.167 amps;
1 volt/4 ohms = 0.25 amps
1 volt/2 ohms = 0.5 amps

So, for a constant voltage, current requirements double going from 8 ohms to 4 ohms and quadruple going to 2 ohms. Current production is a more useful indicator of amp "grunt" than rated wattage (or so I think).

The other thing to remember is that for a given speaker design, resistance might not be constant across the frequency range. Low resistance dips occurring at different points can result in differences in how things sound between two amps with similar wattage ratings but differing in current output capability.

That’s what I think I know.

I'll embarrass myself by saying I have always thought of it as a hose with water going through it.  If you have a narrow opening at the end (say, using a nozzle), which equates with high impedance in my analogy, you can get a powerful jet of water from the hose with your normal water pressure or even less, but if you take the nozzle off (low impedance) you won't get the same powerful jet of water unless you significantly increase the water pressure (in the analogy, a much more powerful amp). 

I'm sure Al will give the best technical explanation.

Maybe unsound will see this and chime in;
"Current production is a more useful indicator of amp "grunt" than rated wattage (or so I think)."

Nice job ghosthouse.


Best to you,
Dave
And, remember most of the amps power is going to the lower frequencies. So, if the impedance dips at low frequecies, your amp will have a hard time keeping up with the demands of the speaker.
Like the water in the hose instead of being restricted by a nozzle, is now having to provide the same pressure in a larger diameter hose.
HTH
Bob
Hi crazyeddy,
I can't explain the math to you, but the inverse proportionality that you spoke of has to do with the fact that impedance is the AC version of resistance. While it is also measured in ohms, it is not the same as DC resistance.
First, I wouldn’t say that 4 ohm speakers are **necessarily** harder to drive than 8 ohm speakers, as there are many other variables involved. Including the efficiencies of the speakers; how the magnitudes of their impedances (the number of ohms) vary over the frequency range; the phase angles of their impedances at various frequencies (which describe the degree to which the impedance becomes partially inductive or partially capacitive at various frequencies, rather than purely resistive); etc.

But yes, typically a speaker having a low nominal impedance such as 4 ohms will be more difficult to drive than one having a higher nominal impedance such as 8 ohms. Adding to what has already been said, perhaps a good way to envision that is to consider a pair of extreme examples.

On the one hand let’s say that all the amp is driving is the input impedance of another amplifier, as would be the case if the amp were only connected to the speaker-level input of a powered sub. It might then be seeing a load of perhaps 100,000 ohms, which would result in the sub responding to the voltage being put out by the amp in question at any instant of time, but per Ohm’s Law (thanks for bringing that into the discussion, Ghosthouse) drawing essentially negligible current from that amp. In that situation the amp in question would hardly know that it is connected to anything at all, and the power it would be putting out would be essentially zero. (Power into a resistive load equals voltage x current).  (In saying this, btw, I'm putting aside the fact that tube amps having output transformers should not be operated unloaded while processing a signal, that being a separate issue).

At the other extreme let’s apply a load of essentially zero ohms to the amp, by shorting its + and - output terminals directly together with a heavy gauge jumper. I think most will recognize that the amp would be incapable of putting any kind of reasonable signal into that near zero ohm load, because per Ohm’s Law creating a non-zero voltage across a zero ohm resistance requires infinite current. And as the amp attempts to do that the result is likely to be either that it goes into a self-protective shutdown, or a blown fuse, or damage.

Obviously a 4 ohm load comes closer to being a direct short than an 8 ohm load, and an 8 ohm load comes closer to being a negligible load than a 4 ohm load, so there you go!

One additional point: As Ralph/Atmasphere has stated here many times, for various reasons both solid state and tube amplifiers will exhibit measurably better distortion characteristics when driving 8 ohms than when driving 4 ohms.

Regards,
-- Al

How about this simple example. A regulator on an alternator of a car stops the alternator from putting out more power than it is designed to do. If not regulated the alternator will push as much power as you demand of it until it melts.

A speaker load that has less resistance or push against it or back pressure, will allow an amp to keep putting out more than it can handle. (over heat or melt outputs.) If an amp can do 100 watts pushing against 8 ohms it will want to do 200 into 4 and 400 into 2. If the heat sinks or power supply wasn’t built to handle that it melts down.

The reason someone else in this discussion said it is not necessarily true is because other factors include efficiency of the speaker, but this is only a factor if your taking into account that your trying to fill a room with a certain SPL level, and woofer size because you need more amperage to move a larger motor.
For the same reason you lose water pressure in the shower when the toilet is flushed. More water is drawn, lowering the pressure in the tank. When the speaker has a high impedance, it’s like a faucet that is slightly open. The pressure (voltage) in the tank (amplifier) is maintained as there is little flow (amperage) through the piping (speaker cables). When the impedance drops, the faucet opens which draws more water (amps) causing the pressure (voltage) to drop. If the amplifier does not have enough ’pressure’ it cannot supply the current for the speaker driver to move.

That is why amplifiers that maintain voltage throughout the impedance swings of speakers are heavy and expensive. They have to act as a voltage source regardless of the current demands of the speaker. This requires a bigger transformer, bigger power supply capacitors and high current output devices to put it all togther.
gs5556,
That is a very good analogy!
I’ve often wondered why given the reality of Ohm’s Law, why do many speaker designers revert to 4 ohms rather than 8 ohms (or higher) speaker impedance. As Al noted in his reply, Ralph (Atmasphere) has pointed out that the higher the impedance load ,the lower the amplifier  distortion produced (which is a desirable result you'd think).

It would seem that a concerted effort to design easier to drive high impedance speakers would yield obvious benefits. The most logical explanation for the plethora of lower impedance speakers is that the higher impedance speaker is probably more difficult to implement to get things right and presents more design challenges.
Charles
In a related matter, Roger Modjeski of Music Reference recommends hooking up your speakers to a tube amp on the lowest impedance tap that provides the power you need. So if an amp puts out 45 watts at 8 ohms and 30 at 4, and 30 watts is enough for your needs (with the combination of speaker sensitivity, room size, listening level, etc.) with an 8 ohm speaker, use the 4 ohm tap for lowest power amp distortion and best sound. 

Lots of food for thought here. Thanks guys for all your responses to help me see this a little clearer. As charles1dad pointed out, in response to Ralphs explanation, it does seem to be (at least to me) in the best interest of design, to provide a speaker with a higher impedance value. So why would a designer go the other direction?

Oh, boy, where will this be leading the thread

Charles1dad, sometimes a speaker designer will add components to a cross-over to lower the impedance  in order to make the impedance flatter/smoother. Sometimes lowering the impedance allows for more current delivery in order to facilitate stronger bass response.
I think the trend towards speakers with lower impedance corresponds to the trend for speakers to be smaller yet more full range to fit into people’s lifestyle. Also as we know from experience the best sounding gear is not always the ones that measure lowest in distortion. Lower impedance tougher load speakers just means amps must work harder. Some are able do that much mbetter than others. Newer more efficient amp technologies like Class D perhaps do it best. Class D offers a much larger higher pressure "garden hose" for your speakers.   For example I have 500 w/ch class d amps that can deliver almost 40 amps of current  that are about the size of a shoebox.    My harder load speakers shine and easily surpass my smaller easier load ones with these.     


Unsound,
That makes sense and with the advent of transistor power amplifiers I can see where the 4 ohm load speakers becomes more plausible to manufacture . One could make a case for either type of load characteristic. Higher impedance =easier load and less work for a given amplifier. Intuitively this seems to be ultimately more desirable.

There was a time when 8 to 16 ohm speakers were the norm and one could use modestly powered amps that were of high "quality ". 16 ohm speakers are quite rare these days. This would present an enormously easy load for virtually any power amplifier.
Charles
It’s all about the bass, about the bass,. Not the...

well it’s also about size and cost actually.

The reality is low power tube amp lovers have limited speaker choices at least if bass extension matters. Still good ones out there though if a low power tube amp is what one chooses to build around.

Making music especially bass is a lot of work. Somehow combo of amp and speakers must be up to the task else results suffer in comparison. A nice high pressure shower makes for a much better clean. The actual amount of water used might still vary widely though.

As watts got cheaper with ss, designers could not put as much effort into creating high imp. speakers and could also experiment with low imp. designs.

But my question is: %-wise, what contributes to impedance: the overall design (enclosure, drivers, venting, etc.) or the crossover?  I've always suspected that the crossover had a big role, and fancy crossover topologies often make for low imp. speakers (I suspect).

Ports in ported designs are always a major factor it seems. 
Because of these properties of amplifier and speaker systems:

  1. Amplifiers have a non-zero output impedance
  2. Voltage is proportional to impedance in a series circuit.
  3. Speakers usually present complex impedance, with a range of impedance magnitude and voltage / current phase angles

Let’s simplify this to a couple of statement:

Amplifiers are current limited. This limit defines the maximum voltage at any given impedance.

As the amplifier output impedance rises, or speaker impedance drops, the electrical frequency response at the speaker inputs goes from flat to tracking the speaker impedance.

Want to understand why? Read on.

As an introduction, see the first graph on my blog post on speaker impedance for a very easy to drive speaker:

https://speakermakersjourney.blogspot.com/2016/12/crossover-basics-impedance.html

We’ll ignore phase angle, as it’s hardest to grasp. Let’s assume instead:

  • Tube amp output with about 1 Ohm impedance,
  • An ESL such as a Martin Logan electrostatic, which has a panel impedance that varies from 4 Ohms at the bottom of it’s range to 0.3 Ohms at the top end.

At low frequency, say 300 Hz where the panel is 4 Ohms, the voltage at the panel is

4/(4 + 1) = 4/5ths = 80%

of the amplifier output.

At high frequencies, say 10kHz 0.3 Ohms the voltage stays at the amp, and the speaker gets

0.3 / (0.3+1) = 0.3 / 1.3 = 23%

of the amplifier output, or about 25% of the amp output!

But look what happens with an amplifier with very low impedance of 0.001 Ohms (aka high Damping Factor):

At 4 Ohms:

4/(4 + 0.001) = 4/4.001 = 99.97%

At 1/3 Ohms:

0.3 / ( 0.3 + 0.001) = 99.67%

So in the range of speaker impedance from 4 to 0.3 Ohms, the amplifier output remains nearly rock-solid.

Actually ports in ported speakers are perfect examples of why low impedance is harder to drive.     Impedance at port frequencies is always low.  Check any ported speaker impedance curve and see.   After all the port itself has little or no physical resistance/impedance.   Air blows right through largely "unimpeded".    An amp driving the ported speakers well will result in a stronger air flow. One that cannot drive it well will result in little or no air flow meaning the port is not being utilized well to move air at the lower frequencies that it is intended to enable. 
@mapman

Ahem, please see the example I posted, above. :)

The drop at resonance is no lower than Re. :)

I'm sure @Atmashpere will chime in, but depending on the amp, it's really the difference between the peaks and Re that makes a tube amp misbehave, as the high impedance will track this. If Re is high enough, it will be minor.

Best,

Erik

While a 16 ohm speaker may seem to "present an enormously easy load for virtually any power amplifier", such is not necessarily the case, as that 16 ohm rating is merely nominal. For instance, the original Quad ESL's nominal impedance was 16 ohms, but it’s impedance rose to 60 ohms at low frequencies, and fell to 1.8 ohms at high frequencies---anything but an easy load! That impedance characteristic is one reason the sound of the Quad ESL is so affected by the amp driving it, and why almost no solid state amp is a good match---it makes for overblown bass and missing highs. Ralph Karsten of Atma-Sphere has already explained this a few times.

Related to my post above, using the lowest impedance tap on a tube power amp not only usually results in the lowest distortion and best sound the amp is capable of, but the amp’s damping factor is also highest, leading to the flattest frequency response it is capable of, irrespective of speaker impedance characteristics.

Also remember the complexity of the Crossover is directly proportional 
To ohms,resistance to the drivers and demand affecting  the Amplifiers 
Constant changing ohms ,and Amplifier Load depending on demand. 
A speaker can  go from a 8ohm load to 2 ohms which Is very demanding 
For a conventional driver Loudspeaker. Panel or stats ,can dip down to 1ohm .
This  is where a Amplifier be rock solid .verify that the  amplifier you are using 
Can handle the extreme for a given Loudspeaker before purchasing it.
Hi Bdp24,
For sake of this discussion I’m referring to speaker load impedance characteristics that remain "relatively flat. So my hypothetical comparison would be a 4 ohm vs a 16 ohm. A speaker such as the Quad that you cite with its extreme fluctuations renders nominal rating meaningless lf both the 4 and 16 ohm speakers are stable, the higher ohm speaker demands less current and work from the driving amplifier as predicted by Oohm’s law.

In reality there are speakers with both reasonably flat impedance characteristics and gentle phase angles. There are also those with widely fluctuating impedance and steep phase angles. It seems that the former would be preferable as it is far less demanding on a power amplifier assuming that either provides comparable sound quality. 
Charles
Hi Charles,

Usually it comes down to approach: picking the speaker you love and then finding the right amp or vice versa, or in a fortuitous alignment of skill and circumstance, finding both without significant compromise.

Best to you Charles,
Dave
bdp24 1-8-2017
For instance, the original Quad ESL's nominal impedance was 16 ohms, but it’s impedance rose to 60 ohms at low frequencies, and fell to 1.8 ohms at high frequencies---anything but an easy load! That impedance characteristic is one reason the sound of the Quad ESL is so affected by the amp driving it, and why almost no solid state amp is a good match---it makes for overblown bass and missing highs.
BDP, a minor correction to your characteristically excellent inputs.  The last phrase should be "it makes for missing bass and overblown highs."  As you no doubt realize, and aside from some rare exceptions, in comparison with a tube amp a solid state amp will deliver more power into low impedances and less power into high impedances, for a given input signal level.

Best regards,
-- Al
 
 ^ Lest anyone get the idea that the increase/decrease of power output by ss amps into decreased/increased impedances would suggest that frequency linearity would be compromised, the opposite is actually the case, they actually provide better frequency linearity. Most typical speakers will decrease/increase their sensitivity in direct proportion to the increased/decreased impedance changes.
 Furthermore, there are many other considerations that speaker designers need to consider besides impedance. With the advent of amplification that can adjust power output to speaker impedance/sensitivity, speakers designers were now able to permit more attention on other speaker considerations such as wave form fidelity, dispersion characteristics, box resonances, etc..
Most typical speakers will decrease/increase their sensitivity in direct proportion to the increased/decreased impedance changes.
Electrostatics being a notable exception, though, including the ESL-57 which bdp24 was referring to.  Some other exceptions are referred to in the Paradigms In Amplifier Design paper Ralph has often referred to.

In the case of speakers that have been designed to sound their best when driven by tube amplification, such as the ESL-57 (which was designed before solid state amplification existed), frequency response at the output of the speaker may very well be most flat when the frequency response of the signal provided to the input of the speaker is not flat.  In voltage terms, that is.

Best regards,
-- Al
 

Charles and Al, absolutely correct as always!
So why would a designer go the other direction?
Lower impedances have appeared as a means to get more power out of solid state designs. But this is very different from getting lower distortion! So a lot depends on what your goals are!
I think the trend towards speakers with lower impedance corresponds to the trend for speakers to be smaller yet more full range to fit into people’s lifestyle.
The size of the speaker has nothing to do with its impedance. The two are unrelated design aspects.
Impedance at port frequencies is always low.  Check any ported speaker impedance curve and see.
This statement is mostly false. Ports are usually placed in the peak of a cabinet resonance (which will be seen by a peak in the impedance) as a means of reducing the peak and spreading it out. If properly placed, two lessor peaks with a dip in between will be seen, but overall usually represents a higher than nominal impedance.
Usually it comes down to approach: picking the speaker you love and then finding the right amp
I don't buy that this works! Often people have a preference about tubes and transistors- the speaker **must** be chosen to take that preference into account!! Otherwise you may never get satisfaction and a lot of money down the loo.
 ^ Lest anyone get the idea that the increase/decrease of power output by ss amps into decreased/increased impedances would suggest that frequency linearity would be compromised, the opposite is actually the case, they actually provide better frequency linearity. Most typical speakers will decrease/increase their sensitivity in direct proportion to the increased/decreased impedance changes.
In the specific case to which this quote refers, a Quad ESL was the speaker and most definitely does ***not*** fit this rule! The Quad has impedance curve arising from capacitance and not resonance of a driver in a box (for starters, there is no box). Planars in general don't fit that rule either.

I feel like several points need clarification and at least one needs to be made. First the clarification:

If sound quality is your goal, your amplifier investment dollar will be best served by a speaker of 8 ohms or more, all other variables being equal (and unfortunately they almost never are).

By this I mean that no matter what amp you have, its not in your best interest to make it work hard if you want the best sound out of it that is possible! It does not matter what sort of amp- tubes, transistors or class D. The problem is the same- as you decrease impedance the distortion in the amp goes up. Unfortunately the kind of distortion that is going up is the kind you really don't want- because its the kind that is pretty audible! You don't hear it as breakup or crackle though, you hear it as tonality. Usually this means that the sound will be harsher and less detailed. This is because the distortion components are usually recognized by the ear as harshness and it take a vanishingly small amount of distortion to do this!

This is because the human ear uses higher ordered harmonics to gauge how loud sounds are, and as a result is evolved to be far more sensitive to them. This is in fact why distortion can be so low as to be hard to measure, yet it can still manifest as brightness and hardness.

So to reduce distortion and make the amp sound smoother, use a higher impedance load. Steve McCormick, a well known solid state amplifier manufacturer, sent a note to Paul Speltz, who is known for the 'anticables' but also for an autoformer known as the ZERO. The ZERO allows you to drive a 4 ohm speaker while the amp is loaded at 16 ohms. What Steve said in his letter was that even though his amps had no worries doubling power into 4 ohm loads (and BTW are very well built and designed IME) that the fact of the matter is they sound better driving 4 ohms via the ZEROs.  This is simply due to reduced distortion.

One other point not previously mentioned is the effect of speaker cables! At lower impedances they tend to be far more critical, where shorter distances and much larger gauges are required to prevent loss of definition and impact. This can be a pretty big deal as the series resistance of the speaker cable can have a pretty dramatic effect on the effective output impedance of the amplifier! By contrast the speaker cables are far less critical at 16 ohms- which is why a lot of us kids got by with hardware store zip cord  in the old days.

The reason 4 ohms is such a big deal has more to do with transistors than anything else. Back when tubes were the only game in town, speakers were usually either 8 or 16 ohms. They were often a lot more efficient too, as acoustic suspension hadn't been invented (Henry Kloss, who was the inventor of that was a co-founder of Acoustic Research, who in turn made the AR-1, the world's first acoustic suspension speaker about 1958).

Obviously several things at once were happening at the end of the 1950s. Acoustic suspension (far less efficient) was getting started, and so were transistors. At first the two were not significant. But as silicon transistors (and consequently higher power) became more available (which really started in the late 60s or early 70s) the need to get a bit more output out of the amp started to take off. BTW, high efficiency loudspeakers are a **lot** harder to build, by nearly a factor of 10 over acoustic suspension, so you can see that speaker manufacturers sensed a profit motive (as did the amp manufacturers by going solid state- a similar motivation is occurring now with class D). However by getting a possible 3 db more output out of an amplifier suddenly became a big deal; acoustic suspension allowed a smaller size but paid the price in efficiency. Anything that might make them appear easier to drive was helpful.

But in the world of high end audio, where tiny little things can make a difference, the need for 4 ohms is almost non-existent (at least not if sound quality is the goal). There really isn't a speaker technology (like planars for example) that actually **need** to be 4 ohms as opposed to a higher impedance. In most cases, this simply happens because the speaker manufacturer does not realize the smoothness and transparency benefits that are possible with the same amp if the impedance is increased! 
Bruce Thigpen, designer and builder of the Eminent Technology LFT-8b magnetic-planar loudspeaker, states in the product’s literature that he could have made the speaker any impedance he wanted, and chose a nominal 8 ohms. The LFT-8b is a hybrid (employing a dynamic woofer below the 180Hz x/o frequency), the m-p drivers themselves being closer to a 12 ohm load. If you bi-amp the speaker, the m-p’s are a very easy load for a tube amp, being not only about 12 ohms, but also primarily resistive, not capacitive or reactive.

Well, if high efficiency speakers are more difficult to build by a factor of 10! that pretty much confirms my suspicion as to why their numbers are much less compared to the  many 4 ohm speakers available. Why would a speaker designer "bother" with the increased difficulty particularly knowing the popularity/high usage of solid state amplifiers. This makes sense as most SS amplifier owners with gravitate to 4 ohm speakers for the most part.

Charles

Whoa, Ralph, you took my statement out of context. Here is what I actually said:

"Usually it comes down to approach: picking the speaker you love and then finding the right amp or vice versa, or in a fortuitous alignment of skill and circumstance, finding both without significant compromise."

Vice versa means "with the main items in the preceding statement the other way around", thus indicating your approach as one of two alternatives.

To say, as you did, that the first approach (speakers then amp) does not also work is counter indicated by many fine sounding audio systems selected based on that approach.

Best to you Ralph,
Dave
If one did a study of speaker size versus nominal impedance for speakers with good bass extension, I suspect an correlation would be seen between speaker size and impedance. Also a correlation between size and efficiency for certain.

Bottom line is way more people these days prefer speakers with smaller form factors that still do extended bass well to fit into their lifestyle and that puts more demand on the amps to do the work needed. Granted that there is also a motivation for makers to make speakers smaller as well to keep costs down and profits up.

Its much harder technically to get a lot of good sound out of a smaller package than a larger one. It requires higher quality drivers capable of more output with low distortion be designed. A lot of speaker innovation these days revolves around exactly that. Smaller speakers with better sound is the holy grail to a great extent. Some do it much better than others. Granted though it does COST more to make a larger speaker of certain high quality than a smaller one. more of anything always costs more.

Add in that amps are more efficient than ever and can do more work with smaller packages and less electricity and the story is complete.

Lower power tube amps SETs in particular but OTLs and others as well have to rely more on the speakers to pick up the slack and do the work more efficiently. That’s the speakers problem then, not the amps. But all buyers need is for the amp speaker combo together to be up to the task however that is achieved.

So not really a fair thing to judge the world from the perspective of low powered tube amps. Its a different paradigm as Atmasphere accurately refers to it that one can choose from if it fits their needs better, but obviously only a small % of even high end audio enthusiasts choose to go that way for good reason just as some do. Those are the facts. Its nice to have a choice of two different ways to do about things and still get excellent results. One side will never be made to see things the others way. Each is focused on doing things a different way for good reasons. Each approach will have its pros and cons compared to the other but pundits will naturally attempt to stage the comparison in terms favorable to their preferred approach.
Atmashere, the OP said nothing of ESL's. I did make mention of :  "Most typical speakers....".

Mapman,

I don't get the sense of "pundits" taking sides. The OP raised an interesting question regarding the popularity of 4 ohm speakers. This generated a very good discussion. We agree that one fine aspect of High End audio is the many choices/paths that lead to a good sounding home audio system. Your system and mine are at opposite ends of a component/system spectrum, yet we're both very happy respectively. This is a good outcome. I appreciate the multitude of perspectives provided here.

Charles

Perfectly stated Charles. Many roads...

Dave
you took my statement out of context. Here is what I actually said:
Yes- it was not to contradict you, but to use the phrase as a talking point, as I see that approach recommended a lot. Then later people sell off the gear in search of that holy grail... I think if you start with the grail first you're less likely to sell and waste the cash.
Atmashere, the OP said nothing of ESL's. I did make mention of : "Most typical speakers...."
Correct- in fact by 'most typical' is about 95% of the market. In high end, its still about 85% and so is 'mostly accurate' :)

For those outside of that percentage (Charlesdad's speakers are box speakers but they are an example) that voltage thing just does not work. This is entirely due to the designer wanting the speaker to work with a particular kind of amp. In Charlesdad's case, the speakers were originally envisioned on a set of our M-60s and later that manufacturer started making SETs, which work much the same way. SETs in general are much happier on higher impedance loads despite often having 4 ohm taps and they tend to make constant power rather than constant voltage owing to zero loop feedback.

In a tube amp, the 4 ohm tap is not an efficient way to use the output transformer, which often means not only less power (lost due to heat) but also less bandwidth, sometimes up to an octave lost on the bottom end. So its often really worthwhile to avoid low impedance speakers with tube amps even if you have the taps on the output transformer!
atmosphere: "One other point not previously mentioned is the effect of speaker cables! At lower impedances they tend to be far more critical, where shorter distances and much larger gauges are required to prevent loss of definition and impact. This can be a pretty big deal as the series resistance of the speaker cable can have a pretty dramatic effect on the effective output impedance of the amplifier! By contrast the speaker cables are far less critical at 16 ohms- which is why a lot of us kids got by with hardware store zip cord in the old days."

At the risk of taking this thread into the contemptuous nether regions of many others (please no!), this may explain a lot regarding contrary experiences of many on this forum regarding speaker cables' impact on sound.

Good point Ralph.

Dave 

Not sure anyone cares about this, but I thought I would chime in with more information now.

In general, many good drivers are available in 4 and 8 Ohm versions. When this is true, the 4 Ohm is usually 3 dB more sensitive. The low impedance causes extra current flow which provides for increased force against the same magnet. The choice here usually has to do with whether designers will put them in parallel and matching other drivers in the system with less wasted heat.

Some speakers really can't help it. Like ESL's. Essentially they are moving capacitors. The Apogees of old were/are essentially just wires suspended n a magnetic field. Getting up to 1 Ohm impedance was as high as they could get!  Any decrease in the current (i.e. increased impedance) would cut the force down proportionately.

In some cases I have seen crossover design deliberately lower impedance to below 4 Ohms to make speakers seem more "discerning" or "demanding." This added nothing to the sound quality of them. They just added to the snobby appeal.

Best,

E (yes, I'm a snob)
This is a very informative thread. I've benefitted from it. Thanks.

When this is true, the 4 Ohm is usually 3 dB more sensitive. The low impedance causes extra current flow which provides for increased force against the same magnet.
This seems to require clarification!

Given two drivers of the same **efficiency** (1 watt, 1 meter), if one is 8 ohms and the other is 4, the 4 ohm unit will be 3 db more **sensitive** (sensitivity is measured at 2.83Volts at 1 meter; if this is 8 ohms that is one watt, at 4 ohms its two watts; two watts is double one watt and there is your 3 db ).

That current will not flow as expected by the speaker designer if the amplifier output impedance is higher than about zero ohms. This is because as the output impedance is increased, more and more power will be dissipated in the output section of the amp rather than the load- dissipated in the form of heat.

That’s a lot of amps! In particular, this is especially true of tube amps, whose output impedance can often be measured in ohms rather than fractions of an ohm. One might ask, ’what is the point of such an amplifier?’ and the answer has to do with how humans perceive sound.

In a nutshell, we perceive volume, or sound pressure, by listening for the higher-ordered harmonics. This is because pure tones do not exist in nature, and apparently nature sorted out millions of years ago that listening for the higher-ordered harmonics is more expedient, as it would millions of years before anyone invented pure fundamental tones :)

BTW this is very easy to prove with simple test equipment and is not a matter of debate. I’ve posted the way to prove this a number of times on this site.

Since this is the case, a good number of designers (myself included) prefer to design amps that by intention do not make the higher ordered harmonics. To do this often requires a higher output impedance, because to do that means avoiding loop negative feedback (which is known to enhance higher orders and generate more of them at the same time; see Norman Crowhurst). Loop feedback lowers output impedance; without it the output impedance is therefore higher.

It also happens that it is far easier to design such an amplifier by avoiding the use of semiconductors in the signal path. Semiconductors have non-linear capacitive elements inherent in their junctions (magnified by current through the junction) and these are known to create higher ordered harmonics in the distortion structure of the device (FETs and MOSFETs far less so than conventional bipolar devices; a particular device known as a varactor takes advantage of this aspect and is used as a variable capacitance to tune radio receivers).

The bottom line is that if you are dealing with an amplifier designed to not make higher ordered harmonics (as opposed to just low THD in general), the usual voltage rules as defined in the quote above simply don’t work (and I explained why in my second paragraph). Put another way as a speaker designer you have to pay attention to driver efficiency rather than sensitivity.

This is why back in the old days, many speakers had mid and tweeter level controls. They were not there to adjust the speaker to the room, they were there to adjust the speaker to an amplifier of unknown voltage response (high output impedance).

The approach is trickier, but has the advantage of less overall audible distortion (which the ear converts to tonality, often favoring that tonality over actual frequency response errors!).

In most cases this design approach is to avoid ’brightness’ and ’harshness’; two audiophile terms used to describe the presence of trace amounts of higher ordered harmonic distortion.

The way I see it, if a system **always** has brightness (which will be found to not be toned down by a treble control because it does not arise from a frequency response error) then the best it will sound will be like a nice stereo rather than real music.

Again, this all comes down to intention. Is your intention to get the system to sound as good as it can or is it more important to simply play loudly? If the former, than some of the lower impedance speakers and higher power transistor amps will be of interest; if the former, then you will be very careful to be matching the speaker to the amplifier (and not the other way ’round) and most likely avoiding lower impedances in general.
 If the former, than some of the lower impedance speakers and higher power transistor amps will be of interest; if the former, then you will be very careful to be matching the speaker to the amplifier (and not the other way ’round) and most likely avoiding lower impedances in general. 
 Ralph, you mentioned 'former' twice in the last part of your post.
Bob

So by and large, @atmasphere re-expressed my explanations for output impedance with a lot of discussion about tubes and distortion.

I may not agree with some of it, but the truth is, voltmeters don’t get pleasure from listening to music. Humans (and cats) do. So while I can say with precision that most solid state amps are more accurate, as far as measurements are concerned, I cannot tell you which you should buy instead of a boat, gun collection, or second home. :)

Tube amps behave and sound different, and some sound quite wonderful. If that’s the sound you are entranced with, you should go that route, but your range and choice of speakers will be different.

I agree that the idea of picking a speaker first is not the right way to go. You should find out which team you want to bat for first. Overall do you like very good solid state, or do you like tubes, and if either, what are their qualities you like?

Also, what is your real listening style? Do you really sit in a throne for 3 hours at a time in front of two speakers alone? Is it usually background music? Do you sit with your partner, friends, etc?

All these matter. :)

Best,


E

I think choosing speakers first has it's advantages. More so than with other components speakers need to be paired more carefully with the room in which they will be placed. More so than with other components speakers are the most colored components, and vary in sound more so than other components. As such it behooves one to make sure those colorations are the least offensive. Working backwards from the listening position will less likely box oneself into technological obstacles. 
I agree with Unsound’s post just above. And while I consider myself to be a "speakers first" kind of person, as he is, I don’t see that as being inconsistent with Ralph’s statements, including:
Often people have a preference about tubes and transistors- the speaker **must** be chosen to take that preference into account!!

Again, this all comes down to intention. Is your intention to get the system to sound as good as it can or is it more important to simply play loudly? If the latter [correction by Al], than some of the lower impedance speakers and higher power transistor amps will be of interest; if the former, then you will be very careful to be matching the speaker to the amplifier (and not the other way ’round) and most likely avoiding lower impedances in general.
As I see it this is saying essentially that what kind of amplification one anticipates using, now or in the future, is one of the major factors to consider in choosing a speaker. That is not quite the same as saying "amplifiers first," rather than "speakers first." Or so it seems to me.

It should also be noted, btw, that there are some speakers that will be equally suitable, or at least comparably suitable, for use with nearly all types of amplification. In those cases the resulting sonics will depend mainly on the intrinsic sonic characters of the speakers and the amp (as well as on speaker-room interactions, of course), with amplifier-speaker interactions contributing minimally if at all. Such speakers will typically have impedance curves that are relatively flat and do not have severely capacitive phase angles at any frequency, and combine relatively high efficiency with the ability to cleanly handle copious amounts of power.

Best regards,
-- Al

For best results, practically, in most cases, I think one has to first match speakers to the thing you have least control over changing (the room) and then match amp to speakers.

The room is the biggest determining factor IMHO that determines the viable approach or approaches for getting the best sound results. I’m technology and product agnostic when it comes to good sound from there.

Of course if one is willing or able to do extensive sound treatment and tweaking of the room that opens up even more ways to skin the cat.

Each case is different. No one solution always works or sounds best in the end.  Budget and funds are almost always a constraint.

If one is more biased towards using specific technologies, whatever that may be, that’s fine as well. The only thing that really matters is people like and enjoy their endeavors.