Watts and power

Can somebody break it down in layman's terms for me? Why is it that sometimes an amp that has a high watt rating (like, say, a lot of class D amps do) don't seem to always have the balls that much lower rated A or AB amps do? I have heard some people say, "It's not the watts, it's the power supply." Are they talking about big honkin' toroidal transformers? I know opinions vary on a speaker like, say, Magnepans - Maggies love power, right? A lot of people caution against using class D amps to drive them and then will turn around and say that a receiver like the Outlaw RR2160 (rated at 110 watts into 8 ohms) drives Maggies really well! I'm not really asking about differences between Class D, A, or AB so much as I am asking about how can you tell the POWER an amp has from the specs? 
I really don't like the class stereotypes. I know a lot of Class D that have got tons more balls than some class A amps.

I currently listen to Luxman. They have more bass spunk than both a Parasound and Class D amps I've listened to.  So, in this class one particular class A/B amp beats another Class A/B and a class D.

Unfortunately some will always read this as proof that a Class A/B (the Luxman) beats all Class D.
I'm not really asking about differences between Class D, A, or AB so much as I am asking about how can you tell the POWER an amp has from the specs?

Long story short, you can't. Its not only Class A, etc, but even among amps within the same class. The McCormack DNA amps for example have greater apparent power than a lot of other SS amps that test the same or higher. Its widely known that "tube watts are greater than solid state watts" simply because virtually all tube amps seem subjectively to have the power of SS amps rated twice as much. Even within tube amps there are plenty of 30 watt amps that seem as or more powerful than 60 watt tube amps- even though they may be running the same tubes!

Just a few of the many reasons why watts are one of the least important specs in all of audio.
Mainly it comes down to headroom. Many amps can cleanly play short term peaks higher and sometimes much higher than their continuous power ratings .... Except pure Class A which are limited to their rated power.

Mainly it is a factor of power supply capacitance, regulation and sometime feedback (that can negate power supply ripple). How beefy the output stage is can come into play as well.
Magnepan usually recommends getting an amp that will double its 8 ohm power at 4ohms.
No two 200wpc amps are the same. It has to do with-current.  A
200wpc Class D amp may only put out 27 amps of current per channel, while a 150wpc Odyssey Class AB amp puts out 60 amps of current per channel.  Guess which amp sounds more powerful?
27 amps is 1500 watts into 2 ohms. 60amps is 7200 watts. 60amps would require a bus voltage of 120V at 2ohms, phase-angle aside. I think the number of speakers that drop below 1.5 ohm approaches a handful and even the number that drop much below 2 ohms are uber expensive and won't be matched with a $1,500 amplifier. 60 amps at 1.5 ohms requires a 90V bus voltage (approx). Odd of the odyssey amplifier having a 90V bus supply are pretty much 0. Given it's power rating, it is much more likely to be close to 35-40V.  That 60A specification is pretty meaningless ..... not to mention 60A would drag down the power supply capacitors pretty seriously, further limiting the practicality of delivering this much current.

Tube-amps sometimes "seem" more powerful as their distortion is typically more pleasant when they clip, but they are still clipping.
After a lot of listening and reading speaker specs here is what I feel to be true:

Amps, including solid state, are a lot more susceptible to low impedance in the bass region than we should expect by the common mathematical models.

If you have a speaker that dips below 4 Ohms in the 150Hz or lower region, that is a speaker I'd expect to come out as more "discerning" of amplifier gutsiness. You can also call that speaker more challenging, and less amplifier friendly. I've even seen speaker manufacturers deliberately make their speakers dip in this region, I suppose that the idea was that by dipping the speaker would be called more transparent, because you can hear the quality of different amps. I don't know why they did it, but i know they did.

I also think this is why cables seem to matter. Amps are more susceptible to variations in impedance than we think.
Most tube amps don't have "guts" in the bass due to low damping factor. You may prefer that or you may not and that will be room / speaker dependent. 

That dip in impedance is a factor of woofer electro-electromechanical properties and sometimes a 2.5/3.5 way folding in another driver. Crossover may shunt current from woofer to tame a peak.
I doubt that audio savvy people drive tube amps to clipping when actively listening unless that listening involves heavy drinking and dancing with lampshade headwear. I used to be able to easily demonstrate where my 12Wpc tube amp clipped because my main speakers were around 90db efficiency, but now that I'm using 99db horn loaded Heresy IIIs they simply get way too loud for that sort of thing. Still, I rely on tube distortion with guitar amps, but even in a "clean" mode they are so much better sounding overall that there's no contest with the silly "modeling" amps or any SS guitar amps. Some jazz dudes still use SS amps, but many don't (John Pizzarelli borrowed a little tube amp from me at a concert last year...a 15 watt Reverend Goblin, and the brilliant Matt Munisteri used a mint 64 Fender Princeton Reverb with Katherine Russell). Tubes "seem" faster and snappier in hifi and elsewhere. Or so they say, and I agree.
Can somebody break it down in layman's terms for me?

And so one after another all he gets is a bunch of technical info. When the answer in layman's terms is actually in this case absolutely identical to the answer in technical terms: THERE IS NO ANSWER IN TECHNICAL TERMS!

Every single one of the supposed answers above, most of which sound sensible, a few of which maybe even are, nevertheless are easily proven to be nonsense. All these things are at best factors. But remember- correlation is not causation!

What happens, and OP it will really help if you can learn this one early, is someone hears an amp that sounds unusually powerful compared to its watt rating. So they look for reasons. Perfectly natural thing to do, look for reasons. Let's say they find the amp is capable of delivering a lot of current. Wow that must be the reason! Unfortunately, sorry, BS, which is demonstrated as easily as listening to another low current amp that seems to sound just as powerful, if not even more so.

The same can be done for every single one of the other technical reasons listed above, and a whole lot more we haven't yet gotten around to. Not to worry, the people incapable of noticing the request for layman's terms are equally incapable of putting a damper on their need to show off with word salad. Er, technobabble. Er I mean technical knowledge.

Oh and by the way, you can go through and replace "power" and watts with just about anything you want- liquid vs etched, 3D vs flat, dynamic vs damped, any and all of it. Sometimes there's really good causes you can point to. When faster diodes are swapped and the sound improves its fairly easy to point to the speed and recovery of the diode. Although even then its wrong to say the speed is the reason- because there are even faster diodes that sound worse, and maybe even slower ones that sound better.

Now take that one part, the lowly diode, multiply it by a thousand for all the parts in a component. Then multiply that by a hundred for all the different circuit topologies (the way the circuits are physically laid out) then multiply that by a handful more for the way the chassis and, well you get the idea. Or at least I hope you do. There's just way more variables involved than you can ever hope to understand, let alone boil down to one simple number. To then point to that number and say, "THIS is why!" Is simplistic and shortsided in the extreme.

In a way, I like @millercarbon's answer, despite leaving me with the feeling that there really are no good answers.  So far, that squares with my experience; any time I think I see a correlation between any particular amp parameter and the quality of sound I hear, along comes another amp that breaks the rule.  Having said that, I would still like to find a book that tries to address how power, output current, speaker/crossover characteristics and other factors affect what we hear from a given amp/speaker pairing.  Does anyone know if such an animal exists?
Miller as usual puts a lot of words down that mean exactly nothing. Actually your last post said absolutely nothing. Lots of snark and veiled insults but no actual info.

Tube amps may hit above their weight because they can often be driven into clipping without sounding awful and YES people with low power tube amps do this.

Other than that, looks at watts at the low of your speakers impedance. One amp that does 100 watts and 4 ohms and 200 at 2 ohms is not the same rating as 100 at 4 and 150 at 2 if your speaker dips to 2 ohms. 

Other than that, mainly comes down to headroom provided by the power suppl both the voltage and capacitance and a beefy enough output stage to deliver short term peaks. There is no magic, no ethereal effects ... Just basic low level engineering. Flowery words are meaningless.
There are few variables and they are easy to understand if you take the time to do it. Some people want it to be complex because THEY do not understand it and wish that others do not, so that keeps them on level ground.
The main usefulness of amplifier power ratings, IMO, is that they can make it possible to determine a reasonable approximation of how much volume (i.e., sound pressure level, or SPL) can be produced by a given amp/speaker combination at a given distance. In doing so they can make it possible to **rule out** candidates for purchase that would not be suitable in that respect, relative to the particular listener’s preferences.

Here is a calculator which can be used for that purpose:


In using that calculator an attempt should be made to find actual measurements of the sensitivity of the particular speakers, rather than published specifications which are often optimistic by a few db. If Stereophile has reviewed the particular speaker the measurements section of the review will provide a good indication of that.

In using that calculator it should also be kept in mind that speaker sensitivities are most often specified based on an input of 2.83 volts, rather than 1 watt. 2.83 volts into 8 ohms corresponds to 1 watt, but 2.83 volts into 4 ohms corresponds to 2 watts. So in the case of a 4 ohm speaker the response to an input of 1 watt will usually be at least 3 db less than the published specification.

Regarding output current specs for amplifiers, such as 60 amps, 100 amps, or other such outlandishly high figures, those are among the most useless of specs. As explained in the following thread what they usually represent is how much current the amp can supply into a dead short (i.e., zero ohms) for an unspecified tiny fraction of a second. And as indicated by Atmasphere in that thread they might even correspond in many cases to the output of the amplifier’s power supply under such conditions, rather than to the output of the amplifier itself:


Atmasphere has also explained in other threads that one reason some very low powered amps may sound more dynamic and powerful than their power ratings would seem to suggest is related to how the distortion they produce varies as a function of output power. In particular, single-ended triode (SET) tube amps, which often have power ratings in the vicinity of 8 watts or even less, can sound much more powerful than that because our hearing mechanisms use certain harmonic distortion components as loudness cues, and the distortion produced by SET amps varies from being vanishingly small at low power levels to being very considerable as their maximum power capability is approached. The result being a subjective perception of greater dynamics and more power than the ratings would suggest.

Generally speaking, though, once candidates that can be determined to be unsuitable matches have been ruled out (such as by determining that the pairing would not be capable of producing acceptably high SPLs) the best way to determine a preference is usually by some combination of listening, trying to determine what kind of amplification the speaker manufacturer prefers, and researching what owners have found to be suitable amplification for the particular speakers.

-- Al

P.S. to my previous post: The SPL calculator I linked to assumes box-type dynamic speakers, as opposed to planars (i.e., Maggies or electrostatics) or "line source" speakers. In those cases the calculator will typically underestimate the SPLs that can be produced at a given distance for a given input power, by several db at typical listening distances. SPLs produced by planar or line source speakers fall off less rapidly as listening distance increases than in the case of box-type dynamic speakers.

-- Al

Power and hearing perception are logarithmic. Like the earthquake richter scale. A 100 watt amplifier is only twice as loud as a 10 watt amplifier. However higher the power the More relaxed is the output. Also when buying an amp always look at the power output in watts RMS into 8 ohms CONTINUOUS output. The rest is is marketing information trying to make it look better than it is. 
Read the review for this Proton that I own.  A lowly 40wpc but 6db of headroom.  It makes my DQ 10's just sing compared to the Yamaha SS receiver I was previously using at 95wpc in 2 channel mode.  I don't know a whole lot about the 'techy' stuff but I believe it's a class g/h?  Incredible sounding 'little' amp for sure..... http://www.hifi-classic.net/review/proton-d540-410.html
I really like my Magnepans.  From the on wall version up to the MGCIII(needs factory repair).  After 15 years of trying to get them to sound best.  For me hi current 200wpc amps work best.  Went from old school BGWs to MTX Soundcraftsman to JBL Synthesis to Acurus to Denon POA 6600.  I am now happy with a Digital Amp Co 4800a.  Tried a high power tube amp along the way, also.

Each amp has slightly different sound characteristics, they all do the same job-just differently.  The Denon seems to have a lock on tight accurate bass.  I am saving my money for a pair of Digital Amp Co Cherries.  The ones that can hang off the back of the speaker, They look like pretty little rats in the company pix.

Thank you millercarbon and almarge, just wished I had your engineering knowledge.  
I know that Maggies don't like 8 Ohm's and it is not recommended. At least none of the pairs I have do. I was first running them on a pioneer Elite that was 140 WPC into 8 Ohm. It was capable of dropping to 6 Ohm but not 4 and I often found it wanted more to get it humming along. Don't get me wrong it worked and sounded good but sometimes I would find a blown fuse on both sets when the volume was up. Moved to JBL AVA 7 Minimum into 8 Ohm but nice large transformers and still the same thing. I have since switched to a class D Rotel and they no longer have the fuse issue and seems to have more than enough power. I have heard that many of class D amps can be comfortable down in the two's and that maggies can sometime go there.

Note that Magnepan did have a response to it's stance on Class D here is a quote form them " 
  • 4 Ohm capacity is important in amplifier design (more on that later).

Customers are always surprised that we don't know which brands and models are the best choices. We have a very small staff and none of us have the time to test amplifiers. But, we have decades of experience with a class of amplifiers that work well with Magneplanars. If you follow these guidelines, you are in the right "ball park".

The short answer is direct-coupled, class A/B designs with high current capability. But to learn more, you'll need to read further.

First, let's address a misconception: The more expensive Maggies require better amplifiers.

It is true that most customers use better electronics on our more expensive models. But technically, it is not because the more expensive models are more demanding on the amplifier. The loads and efficiencies are very similar. Typically, the customer has a larger budget for amplifiers and, of course, the speakers respond with better sound.

Some individuals assume we won't make product or amplifier recommendations for "political" reasons. Not true. We CAN'T make specific recommendations because WE DON'T KNOW. It is too much work to keep up with changing models and the vast number of products. As it is, our small staff is not getting all of our work done. However, the following guidelines will be helpful. Class A/B amplifier designs that come close to doubling power at 4 ohms have a long and successful track record.

The most common question is about the amount of recommended power for Magneplanars, but, first, it is important to understand the role of current and the power supply. High current and the capability of the power supply is a good indicator of the QUALITY of the amplifier. The amount of power you will need is a matter of QUANTITY. High current and total power are two separate issues. The ratio of the power at 8 ohms and 4 ohms defines the quality of the sound probably more than any other aspect of the sonic performance. Typically, if the engineers got this right, they probably did a good job in other areas of the design.

The power supply is "what separates the men from the boys." A receiver is very efficient and cost-effective way to get is all in one package, but there are "issues". Unfortunately, consumers want all the "bells and whistles" without understanding the importance of power supply. Many manufacturers offer the "bells and whistles", but, compromise the power supply to be price competitive. There are a few manufacturers that are the exception.

Everyone understands they need plenty of power, but the role of power supply is not understood. There is one important concept you need to understand when shopping for an amplifier or receiver: and it is somewhat like understanding "good" and "bad" cholesterol. The ratio is very important. An Gold Standard for an amplifier would be to double the power at 4 ohms. This concept is important even if you are buying an 8 ohm speaker. If the amplifier is rated at 80 watts at 8 ohms, it should (ideally) produce 160 watts at 4 ohms (or close to it). None of the receivers will do that. However, this is the benchmark of a good amplifier design. A 10 watt amplifier that produces 20 watts at 4 ohms "speaks volumes" about the PHILOSOPHY of the designer. (But, of course, it does not tell you if a 10 watt amplifier is enough for your room.) In the final analysis, buy an amplifier that comes as close to doubling the power at 4 ohms as your budget will allow.

A good receiver might produce 30-40% more power at 4 ohms. Most receiver manufacturers don't want to talk about 4 ohm ratings because they have cut the "guts" out of their products to keep the cost down. Some receivers produce the same power at 4 ohms as the 8 ohm ratings. Or they use a switch on the back for 4 ohms to reduce the power and to prevent the receiver from self destructing. Others warn against 4 ohm speakers and will only offer a 6 ohm power rating. Regardless of what speaker you buy, we don't recommend any of these receivers. There are a few manufacturers making receivers with good 4 ohm capability. But, we can't keep up with who's doing what. All you have to remember is to ask: "What is the 4 ohm power rating?" If the 4 ohm rating isn't available, find another model or brand. It may take some digging to find the 4 ohm rating, but there are a number of receivers on the market that are rated for 4 ohms. For example, the THX rating requires that the amplifier section must be able to drive 4 ohms continuously. Even an inexpensive receiver like the 50 watt NAD C725 BEE (suggested retail of $799) is advertised to be stable with impedances down to 1 ohm and has peak power of 200 watts. So, don't be fooled by pretty front panels. Its what is on the inside that counts.

A new type of amplifier (Class D) has become more popular because it is a "green" design and uses less power plus it is smaller in size compared to conventional amplifier designs. We have heard reports of class D amplifiers shutting down when driving 4 ohm loads or sound quality that is less-than-desirable. Quite frankly, some sound very poor on Maggies. However, more recent designs of high-end models are much better. Because we do not have the time to determine which models of class D designs are compatible with Maggies, we must take a conservative approach. Direct-coupled, class A/B designs with high current capability have proven a good choice for many decades."

I can say that I like my Rotel amps that are class D and there are some much better expensive models and some cheaper I tested a Crown XLS1500 Class D amp for a friend and it doubles it's rating at 4 ohms and it had plenty of juice to push my 1.7I's 

Why is it that sometimes an amp that has a high watt rating (like, say, a lot of class D amps do) don’t seem to always have the balls that much lower rated A or AB amps do?

It’s to do with current ability, not just watts, you can get a 3000!! watt Class-D here

And into a pair of Wilson Alexia or similar speaker with low impedance’s to a given volume level, that 3000w will sound positively weak and anemic, compared to say a pair of 25 watt Mark Levinson ML2’s, yes that’s not a typo, only 25w!!

Current is just as important if not more than watts, and an amp that can almost double it’s tested 8ohm wattage for each halving of impedance 4ohm then 2ohm or even 1ohm is an amp that can do current very well

Cheers George
Your post is welcome, as it illustrates quite well this concept of "doubling into 4, doubling again into 2" is just a "lazy mans" spec. It sounds impressive, but only if the design is conventional, and even then, the only specification that matters is how many watts at your speakers lowest impedance.  300 watts into 2 ohms, and 150 into 8, is still better than 200 into 2 ohms, and 50 into 8.  The Proton, which does not increase that much into 4 / 2 ohms, has a design methodology based around real world music where peaks are short in length, and for those peaks, it can deliver significantly more power (headroom).   It's this headroom that makes an amplifier deliver above its rated continuous wattage (which you can only compare at the same impedance).

sejodiren102 posts12-21-2019 9:39pmRead the review for this Proton that I own. A lowly 40wpc but 6db of headroom. It makes my DQ 10's just sing compared to the Yamaha SS receiver I was previously using at 95wpc in 2 channel mode. I don't know a whole lot about the 'techy' stuff but I believe it's a class g/h? Incredible sounding 'little' amp for sure..... http://www.hifi-classic.net/review/proton-d540-410.html

The Behringer is 1500 watts into 2 ohms, which is about the lowest impedance of the Wilson. There will be absolutely nothing anemic about it compared to the ML2, and that is obviously spouting uninformed nonsense, nothing actually related to reality.

1500 watts into 2 ohms is 27 amps.   The ML2 is 100 watts into 2 ohms ... or 7 amps.

"Current" is nothing more than watts at a given impedance.
1500 watts into 2ohm is always more than 100 into 2 ohms, especially when the lowest impedance is 2 ohms.  I get it, you don't like Class-D, but don't make up facts.
and 150 into 8, is still better than 200 into 2 ohms,
Good luck finding a speaker that is a flat 8ohm pure resistive load, with no -phase angle

You listen to your $420 3000w Behringer Class-D’s, I’ll take the ML2’s any day of the week over the Behringer into quality speakers that are hard to drive.

There will be absolutely nothing anemic about it compared to the ML2
You listen to one on the Alexia's, then you'll know.
Listen to what your saying and we’d all using $420 3000w class-d PA amps
I am so tired on insufficient information from the manufacturers..

They only tell us power in wattage (in one or another way).
From school it is amps multiplying with voltage gives wattage.

Where we consumer only have wattage then we can not know much of each component the amp gives for example get 100 watts.

Is it 2 amp and 50 volts ?
Is it 4 amp and 25 volts ?
Something completely else?

Some speaker technology types benefits if the wattage consists of high amount of ampere.
But we will never know which amps that delivers a lot of ampere..

Just a another small factor to add to the list.. 🥰
100w pure class A into 2 Ohm ... Means 100W is all you get , no headroom. Now you are trying to change the measure because your anemic claim was fantasy? That's not too honest now is it?

Your selective cut and paste and your mention of phase angle shows you neither understand my post nor amplifier specs. You are making a claim about an amps potential performance that is impossible to make with only continuous power specs.
Optimize, yes we do know what you are asking if say they give a spec into 8, 4 and 2 ohms which many do..
I would try reading from the recognized experts.
You will find confirmations of what Oiche lays out. 
Pass has a simple weight to watt ratio
he talks about for his A and A/B gear that I found
a good tool.
Have Fun Shopping!
You mean like statements like this that ONLY apply to pure-class-A and make assumptions about heat-sink materials, power supply architecture, etc. that are not a given in all designs.

One pound of weight for every 2 watts is a good litmus test for evaluating Class A amplifiers. An amplifier weighing less might not be pure Class A. It might be almost Class A, or it might be one of the many products which achieve a Class A designation through trick circuitry.

What's funny is that people will quote the likes of Pass when it suits them, but ignore the other things he writes when it suits him, like

Large inductors in series with the transformer primaries and secondaries can be used to stretch the duration of the charge pulse to the power supply capacitors, improving regulation and reducing noise. 

... those large inductors negate heavy gauge power cords.

Of course, not everything that Nelson pass says/rights is entirely accurate either:
Also, it helps if the power supply capacitors before and after the switcher are very substantial. This is typically not the case, since one of the primary motivations to use switchers is to save money.

Power supply capacitors before the switcher are not "substantial", as small values are essential to achieve good power factor and THD, a typical design goal of AC\DC switching supplies. As a matter of fact, substantial capacitance on the front end of an AC\DC switching supply will reduce the requirement for output capacitance to achieve the same performance and will reduce the overall cost to achieve the same performance.

Reading through the posts so far, the answers from @georgehifi read the most correctly to me.

Watts, or power, is equal to voltage multiplied by current. But an individual speaker may want more voltage at some frequencies, versus more current at other frequencies. And if your amplifier is limited in one of those dimensions, it will have trouble driving the speaker.

There are other amplifier considerations for sound quality, but specifically to the question of high power ratings not having drive capability, it's the current and voltage numbers you are looking for.

The SPL calculator referenced earlier assumes a simple speaker load and unlimited current/voltage capability. I use it too, but only as a guide.
Hey there @audiozenology

That dip in impedance is a factor of woofer electro-electromechanical properties and sometimes a 2.5/3.5 way folding in another driver. Crossover may shunt current from woofer to tame a peak.

The speakers in question were a pair I did a complete speaker and crossover analysis. I am confident of my conclusions. The impedance dip was deliberate and unnecessary. A simpler 3 way low pass would have duplicated the transfer function and raised the minimum impedance by 2 ohms.

However, in a lot of cases, your statement above would be true.
Define "read the most correctly". Are you am amplifier design/EE?
If you don't exceed the rated continuous or peak wattage at a given impedance, then you have enough current (and voltage).  Georgehifi is making assumptions about performance that are not supportable with the data on hand ... namely wattage at a given impedance. I won't claim a 1500 watt $500 amplifier is going to have the overall sonic performance of a high end class-A amplifier, even at 100W, but with a speaker that drop to 2 ohms (approx), an amplifier that can deliver 1500 watts at 2 ohms, is not going to sound "anemic" as long as you don't drive it into clipping.

Watts, or power, is equal to voltage multiplied by current. But an individual speaker may want more voltage at some frequencies, versus more current at other frequencies. And if your amplifier is limited in one of those dimensions, it will have trouble driving the speaker.


Did you look into resonances? It is not uncommon to use the "cross-over" to damp a resonance. Your assumption is that the cross-over designer was competent as well. Especially in boutique audio, my experience is that is often not the case. Thank you for the post. Always good to have a reasoned discussion.
Hi @audiozenology:

I did a complete speaker and crossover analysis.

This means I measured the impedance and FR of each driver in the near field to achieve quasi-anechoic measurements. I further took the crossover apart and simulated the entire speaker in XSim. I validated my simulation by matching the simulated frequency and impedance curves to actual.

I then compared the simulated original crossover to a simulated crossover using a more conventional approach. So when I write:

would have duplicated the transfer function

This means that the input of the crossover to the output of the crossover would have been the same given the measured driver impedance.

What you are describing is akin to notch filters. That’s not what was present, and if I had not taken this into account, the two transfer functions would have been different. Further, resonance filters typically appear at the top end of a driver’s range, not the bottom.


Your selective cut and paste and your mention of phase angle shows you neither understand my post nor amplifier specs.
No it is you that has no understanding sir, as the combined loading the amp sees, of -phase angle plus low impedance can look a very much harsher load to the amp than just the low impedance alone. And you need amps that can almost keep doubling their wattage for each halving of load impedance to drive them well and if the said speaker is high efficiency but has that evil loading (as Alexia ect have) then you don't need so many watts but still need the double of those watts to signify current.

Like said listen to the Alexia driver by the 3000w Behringer then with the 25w ML2's  

No, you are wrong Georghifi , and I see you have made this wrong claim many times on this forum and even though many people have told you you are wrong, you keep making it.

Phase-angle w.r.t. load impedance is only "harsh" in that it places significant thermal stress on the output devices of linear amplifiers and additional loading on the power supply. That does not impact Class-D amplifiers. It is a transient condition in real world music. In continuous power measurement, it is NOT a factor of current delivery as maximum dissipation DOES NOT occur at the peak current / lowest impedance. That goes back to my original post above w.r.t. the importance of the power supply, which can support transient peaks with capacitance, but if you want "nice" continuous measurements, you need a beefier transformer/switching supply.

Again, you are making a leap w.r.t. amplifier performance that you are NOT able to make with the limited information available. 2 amplifiers each able to deliver 100 watts cleanly at 2 ohms, can each supply the same current no matter what they may do at 4 or 8 ohms. Without knowing what the inherent limitation is of the design, you cannot make conclusions, only assumptions ... and you know what they say about assumptions.

Being able to deliver 1500 watts into 2 ohms, cleanly, does show the ability to deliver 27 amps. Being able to deliver 100 watts into 2 ohms, shows the ability to deliver 7 amps. Any other conclusions you want to attempt to come to are just conjecture.

-phase angle plus low impedance can look a very much harsher load to the amp than just the low impedance alone.

I will guarantee something you have not done ... listen to the Alexia with the Behringer. They may not be fancy, and they may not be what we traditionally think of as "hi-fi" but they are designed to drive loads every bit as harsh as the Alexia, and to do it continuously in harsh environments.

georgehifi6,476 posts12-22-2019 2:33pm

Like said listen to the Alexia driver by the 3000w Behringer then with the 25w ML2's  

I don’t care for what you say, you need amps that can almost double down for each halving of impedance, not ones that actually halve their wattage and go backwards!! with current sag limiting into hard loads.

Next you’ll be telling me that a 100w OTL tube amp will drive the Alexia better than the 25w ML2.

You stick with your $400 3000w Class-D’s, and go spruik your views on a PA sites instead where you’ll make a dent

Here is the difference between me and you. Your posts are all conjecture and hand-waving. Conjecture and hand waving is ..... well just that.
Again, let's look at facts:
  • 1500 watts into 2 ohms is 27 amps
  • 100 watts into 2 ohms is 7 amps
  • Maximum dissipation in a LINEAR amplifier with a real speaker load DOES NOT happen at the spot on the speaker impedance curve where the current delivery is highest.
  • Class-D is not impacted by phase w.r.t. power delivery in the same way a linear amplifier is, either in device dissipation or power supply loading.
  • Other than knowing an amplifier can deliver 100 watts into 2 ohms, you have no data that shows the power supply is any more capable of supporting continuous additional power delivery and the dissipation peak of the speaker load
  • You have not heard the Alexia with the Behringer, but you are making many claims that you don't have the requisite data to support.
  • You are deflecting bringing up OTL amplifiers
  • There are many reasons why power may not double with every 1/2ing of the impedance, and without knowing what that reason is, you can't made factual conclusions about an amplifier beyond that it will clip at a given wattage and load impedance (as stated in the specs). If the 2 ohm wattage is stated (and distortion components), and given that impedance doesn't drop below 2 ohms for almost all speakers, then beyond knowing where clipping will occur for 2 amplifiers, you really don't know much else. Any other conclusion you arrive at is purely assumption.

@audiozenology.....thanks for the feedback.  I don't comment on here much.....too much back and forth banter.  So I just read and form my own opinion.  I've become a lot more 'tech savvy' than I used to be.  There's a guy  on CL selling this Proton 'beast'.  What's your impression of the review?  He wants $750 for it. I know they are rare. Not trying to hijack this thread....haha  Judging from your answer, you like the Proton specs I'm guessing.  http://www.hifi-classic.net/review/proton-d1200-165.html
There’s a guy on CL selling this Proton ’beast’. What’s your impression of the review? He wants $750 for it.

This if in good working order >25 years old now (any bad caps have been renewed) it should be a good BJT (bi-polar) amp, at least if the specs are right (typo 175w should be 275w), and increases it’s wattage substantially for each halving of impedance all the way to 2ohms. BTW nice twin R-Core transformer also.
"The D1200’s output clipped at rms
155 watts into 8 ohms
275 watts into 4 ohms
350 watts into 2 ohms

With peaks of
593 watts - 8ohms
1,187watts - 4ohms
1,800 watts - 2ohms,

Here is a great video test clip this guy did.

Cheers George
@georgehifi ....thx!  Yea, I've seen that video and specs when I was researching some Proton amps.  Mind boggling!  A tech with 40+ years exp had told me about them when I was looking for info on the Dahlquists.  Said he'd owned several sets and had powered them with Bryston, Carver, PL and the Ampzilla.  Said the Proton sounded better than any of them.  I figured since we're talking low power, high current....I'd ask.  Appreciate the info

I've never heard one of these, I like that they used Bi-Polars (BJT's) to achieve this performance into low impedance's as complimentary mosfets would have trouble doing these sort of figures.
While a neat idea, I question the lower voltage rail, then high voltage rail used when even wattage is required for transients or louder passages, as the "sound" characteristics of those output transistors will be different for those two voltages used, I don't know if this is easily detectable while listening or not.

Cheers George
Most tube amps don't have "guts" in the bass due to low damping factor. You may prefer that or you may not and that will be room / speaker dependent.
Bandwidth also plays a role, as well as the match between the amp and speaker. You can have an amplifier with very low damping factor that plays bass great, with plenty of guts. If that's a tube amp, just put it on a 16 ohm load rather than 4 and see how gutzy it gets!
Current is just as important if not more than watts

This statement is a common myth and is false. Current cannot exist without watts; they have a simple mathematical relationship. 1 Watt = 1 Volt times 1 Amp; its that simple.

So if an amplifier has the 'current' it will also have the watts- they go hand in hand.
Where we consumer only have wattage then we can not know much of each component the amp gives for example get 100 watts.

Is it 2 amp and 50 volts ?
Is it 4 amp and 25 volts ?
Something completely else?

The issue is speakers being matched to amps and this is a historical problem. Most speakers these days are meant to be played on an amplifier that acts as a 'voltage source' which is to say for a given output voltage, that voltage is invariant with regards to load impedance. No amp can actually do that but many can do perfectly well on most speakers but not all. But to further complicate matters not all loudspeakers are meant for voltage sources and these speakers will not sound right unless they get an amplifier that matches them. Some examples of loudspeakers of this type are ESLs, many horn loudspeakers, many full range single-driver loudspeakers, some box speakers both acoustic suspension and bass reflex. So you have to know the intention of the designer! For more on this see

With regards to low impedance, in the world of high end audio one of the main goals is to get things to sound real. To this end amplifier distortion is a huge deal because it is distortion that are the differences we hear in amplifiers. Higher ordered harmonics are interpreted by the ear as harshness and brightness even in very small amounts (as our ear has to be keenly sensitive to those harmonics as it uses them to determine sound pressure). Lower orders (2nd-4th) contribute to 'warmth' and 'body'. The ear converts all forms of distortion (THD, IMD, aliasing) into tonality.

With most amplifier topologies it is not possible to add enough feedback in a way that prevents the feedback itself from contributing to higher ordered harmonic distortion. This is at the root of the tubes/transistors debate; the way the industry has gotten around this problem (insufficient gain bandwidth product) is to use an old technique known as 'lying'. They simply don't measure the amps at frequencies where we can see what happens in the range where the ear is most sensitive (Fletcher Munson) so we never get to see the real score. This is why there are amps with no feedback at all and consequently much higher output impedances. The idea with such amps is that tonality caused by distortion can be more important to the ear than actual frequency response errors.
Good luck finding all this out on a simple spec sheet.

Optimize, yes we do know what you are asking if say they give a spec into 8, 4 and 2 ohms which many do..
No they do not.
No manufacturer what I have seen have been given what ampere (current) spec into 8, 4 and 2 ohms.

Only wattage and maybe the distortion. We are in the dark of how much current (and voltage) there were when we got the power (wattage).

Internet know hows and reviewers say now and then. "The speaker X need a high current amplifier"..
How would they know?! They do not have any other specifications that we all get..
There is specific amplifier designs that are primarily designed to be current sources. So they can have relatively low wattage but for producing that wattage it gives high amount of current and low voltage..
Or are missing something here? Were is the ampere and the voltage in the specifications?
Class-D and complimentary mosfets poweramps fall down miserably when asked to deliver current into 2ohms so they can double the wattage all the way.
That's why they never advertise "true" independently tested  8, 4, 2ohm wattage's just before clipping, because the 2 usually goes backward in wattage, indicating sever current starvation or limiting.

Cheers George  
Oh come on George, I don’t know any amplifier vendor that publishes independent data, only reviewer data.

Your comment about MOSFETs is ignorant. It’s easy to drive into 2 ohms with complimentary MOSFETs. Purely an architecture thing. I don’t know why you insist on this repeated ignorant. Please learn more about amplifier design before posting on this. You know the Behringer is rated into 2 Ohm ... Why would you say what you do?

  • P = v * I
  • P = v^2 / R
  • P = i^2 * R

If you know P and R, then you can calculate I and V.

I am not aware of any commerical audio amps designed as current sources ... Not practical as it would not work with off the shelf speakers as it would screw up the crossover operation.