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? 
128x128redstarwraith
watts are a measurement of power.  however i have owned amplifiers of the exact same measurement verified power curve yet one sounds significantly more powerful than the other.  and they are made by the same manufacturer! 
the more powerful sounding one is a dual mono configuration and has several more large capacitors per channel on the circuit board.   
Sorry typo.Teledyne 132's from the uk.
Arcam Cambridge and the best HI FI in my opinion come from the uk.
Sorry guys, but power you guys run would lead to eviction notices in sa.
Cheers from a near no internet in sa, the overseas underwater cables are damaged, i can live with candles but cant live without comms, thats why im a radio dealer with some monster hf/vhf/uhf rigs.
Latest toy an Icom IC 7100, opened up by yours truly for 11m 27555 with an antron 99 to burn some holes through the ionosphere.
Callsign 44CT357....also gun crazy since 12yrs of age, 60 now.
73's

Power means little to me.
Its the speaker system and match to the amp.
Ideal speakers should be around 60-70% of rms output of amp.
I was running a pair of 7 way bookshelf on my avr HK 5000 and they sounded horrid, hooked them up to an old HITACHI HA1 in the workshop and wow, they blow the roof off at 50% with tone to die for.
Dont need surrounds, not interested.
I love the tone/power of stereo units with integrated modules.
Put the control 1's on the hk in the lounge with ar teledyne 137's and it came to life as well.
I replaced the main drivers with a pair of speakers from an electric guitar 60 watt rms amp, the teledyne boxes were gifted to me.
The guitar speakers work as 2 way as they are ribbed and flat cone.
Flipping amazing what one can do!
My wife uses a heavy QSC 350wpc a/b power amp in a "road case" in her "home" office whenever she's working from home...it works perfectly and silently since it's being used as a foot stool. Highly recommended.
Hi redstarwraith,

From what I understand, it’s not the watts per channel that matter, it’s the ability of the amp to deliver enough current to the speakers so they are driven properly. The design of the power supply is extremely important (among other design aspects) and determines the ability of that amp to drive a more difficult load.

A great example of this would be the Pass Labs line of amps. They are all so well designed, from front to back, and are best known for their ability to drive just about any speaker on the planet. The main reason for this their power supplies. The power supplies are so well designed and so well built that they never have trouble driving a difficult load. Not only can they drive a difficult load but they always remain musical while doing so. Remember, we are talking about Nelson Pass who has been designing power amps for over 40 years.

Here is a great example of what I’m talking about.

I have a Pass Labs XA30.8 amp. For those of you who may not be familiar with this amp it’s their 30 watt per channel class A stereo amp. That amp weighs 88 lbs which is probably mostly power supply. Now most people would just laugh when you mention 30 watts per channel. I also had a pair of Magnepan 3.7i’s with two of their DWM woofers wired in parallel. Now most people will tell you that a 30 watt per channel amp will not work with the Maggies and especially with that setup. The 37.i’s with two DWM woofers wired in parallel presents a constant 2 ohm load to the amplifier! 2 ohms. That load would destroy most amps and they would just simply shut off. That little amp not only drove that load but did so effortlessly for 3 years. Not only did it drive that brutal load but, and this is the most important thing to remember, the musicality was off the charts!!! If an amp can drive a difficult load but sounds like crap doing so, it’s worthless. That amp not only drove that load but sounded fantastic as well. That’s how well designed those power supplies are.

So redstarwraith, the watts per channel, especially on paper (specs) tells you nothing. Always trust your ears. If you can find a high end audio store (remember those) in your area they will usually let you take a piece home so you can listen to it in your system. There is no substitution for auditioning a piece of gear in your own system. If you like it and can afford it, buy it. If a reviewer says it’s the best amp in the world and you don’t like it, don’t buy it. Trust your ears. A local dealer who knows what they sell and can advise you as to what they think you will like and can be trusted can be invaluable. Home auditions are the way to go. Nothing beats hearing it in your own system and hopefully for as long as the dealer will allow (within reason).

The internet, as convenient as it is, has been instrumental (in my opinion) in reducing the number of brick and mortar retail stores. If a brand you are interested in has no dealers in your area, a lot of manufacturers will sell directly. Read their return policy carefully. An great example is Liner Tube Audio. They have one of the best return policies I have ever seen. First, and this is very rare, they break in All their equipment before they ship it. They give you 14 days and they will even pay the return shipping (in the USA) if you don’t like it. What more can you ask for. That, to me, speaks volumes in their confidence of the sound quality in the products they offer. Here is an example a of a ridiculous return policy. The do not fully break in what they sell, they give you 3 days, and you have to pay the return shipping (which is understandable), but because they are built in Australia the shipping charge from the USA to Australia is $200.00 and here’s the kicker, you have to wait for them to resell it before they send you your money! You could be waiting months before you get your money back. At least they tell you all this up front. Now, compare that with Linear Tube Audio’s return policy, who would you be more inclined to buy from?

Scot



Used several amps over the years.

 Some Carvin 2000W guitar amps for driving my cerwin Vegas 
they were great sounding, but their reliability were atrocious.

Crown amps used to be very good, had the studio ref I FOR A WEEK, didn’t have a 30 amp outlet, sad day that day.

used the QSC Rx amp for a couple years.

most my speakers were either 4 ohm or lower., so. The amps output was a little more than the 8 ohm output at rated power.

another great amp is the Carver sunfire amp, either the 300 or the 600,
great sounding amp all around., LOVED the 1 ohm capacitor for making the sound a bit boomy like a tube amp, killer little feature
i still love my sunfire 600 signature.

odyssey stratos or  Kismet is a great amp. 200W at 4 ohm, so about 300+wpc into 4 ohm speakers.  

Emotiva amps are a great great start into separate audio.
their gain is a bit high, but there not too bad..

a more expensive option check the audiogon for pass, McCormack, threshold, any mnay others.

good luck, auditioning gear is a blast.




hifihottie
For most speakers, the amperage is more important than the wattage. This is one area in which most class D amps fall short of a class A or AB amp with an oversized linear power supply.
Correct, and why you’ll find it hard to see specs for "doubling wattage" + distortion with Class-D into 2ohms with "comparison made" to it’s 8ohm and 4ohm figure.
They have things inhibiting it, one is the output filter and the second is that they are mosfet output, and as you say power supplies in many are average to say the least.


https://forum.audiogon.com/discussions/power-current-how-much-is-realistic/post?postid=1863634#1863634
Here’s hypothetical to ponder over (without bashing Class-D anymore), but on amperage.

Take the two 20w-8ohm amps I linked to above, give them both higher rails and higher voltageoutputs and whatever else, so they can both now do 500w!!!! into 8ohms instead of 20w.

Into speakers such as the Wilson Alexia’s the Mark Levinson ML2’s would still blow away the Nad-3020, even though now both are 500w, and it’s because of current the ML can give over the Nad down into 2ohm loading.

Cheers George
For most speakers, the amperage is more important than the wattage. This is one area in which most class D amps fall short of a class A or AB amp with an oversized linear power supply.
@listening99, Ralph (@atmasphere) clearly interpreted your initial posts as referring to powering two speakers per channel simultaneously (i.e., a total of four speakers). However it now seems apparent that you would only be powering one Tekton speaker per channel with the amp, and nothing else. So Ralph’s comments do not apply, and the response by @audiozenology is applicable and correct.

I would add to Audiozenology’s comments, though, that in addition to the potential issue he cited involving mains noise a possible concern relates to the very high gain of your amp (35 db, per the measurements in the link he provided). If the Tektons are significantly more sensitive than your present speakers you might find yourself having to operate your volume control at undesirably low settings. Although your description of the present speakers as "horn loaded" (and therefore presumably very sensitive) suggests that both potential issues (mains noise and volume control settings) are unlikely to be problems, assuming they are not problems now.

Good luck with the new speakers. Regards,
-- Al

@atmasphere and others, when I read, for example, the power rating for the parasound A 23+, it states:


  • 160 watts x 2 @ 8 Ω RMS, both channels driven
  • 240 watts x 2 @ 4 Ω RMS, both channels driven


My assumption has always been that the top 8ohm figure is relevant to the use of not one but two 8 ohm speakers, as is stated on the website. Your figuring seems to suggest that playing two 8 ohm speakers would imply the second figure, or 240 watts from the combination of the speakers, or 4 ohms?

The also suggests, following what I think I understand of your claim, that few of the amplifiers on the market should be used for two 4 ohm speakers, as they don’t often state a 2 ohm power rating...
Repeat:

 I’ve been through a min of 7-8 amplifiers over the years, since about 1990 or so.

 Once I went beyond 300WPC @ 8 OHMs, I NEVER looked back.
during crescendos, and power chords, you will need that headroom to keep up,  o clipping. I have two setups......one is 750W @ 8 OHMS, ........second is 600W @ 8 OHMS. 

NEVER CLIP, always sounds careless, amps rarely get hot.
  I have heated up my upstairs system pretty good, while playing at a constant high volume, always sounds good,
  
 You will thank me later.

 These 2W or 150W maps are,nice for a bookshelf, if u have fullrnage speakers,get a,minimum of 200W at @ 8 ohms
  personally, I’ve had no less than a minimum of 500W/chaannel/rms into 8 ohms.

ive never looked back.

just use caution with your volume knob ;)
"2 watts of SS power to equal 1 watt of tube power"

...And it takes 2  inches on a tape measure to equal to 1 inch on a rule.


@listening99  Two 4 ohm speakers in parallel is 2 ohms.

You really want to check with the amp manufacturer to see if its OK with a load like that! But generally speaking, the lower the load impedance, the higher the distortion of the amp- and that will manifest as harshness and brightness. After spending the kind of money that high end equipment costs, this (to me) simply seems like not servicing the speaker or amplifier investment $$$$ very well.
The idea is to replace my existing speakers with two speakers that present 4ohms resistance/each. I understand the speakers are efficient, although the manufacture statistic of 98dB is probably overstated. The hope is that the amp functions well at the lower volumes I would listen to, habitually. I mean, if a speaker can produce 90dB with less than a watt of power, I should have very little difficulty, sitting about 8-9' away, and then the amplifier is basically loping along, even with two 4ohm speakers, right? I keep hearing the Moabs are amazing and no one is complaining about the 4ohm load... 
The Nuforce is stated to be suited to 8 ohms, not 4. The Moabs are efficient, running at a rated
  • 98dB 2.83V@1m sensitivity
If the speakers run easy, what am I doing to my 8ohm amp, were I to hook them up...?
If you were playing two 8 ohm speakers simultaneously, then the resulting impedance of both together is 4 ohms. If you then expect to play one 4 ohm speaker and one 8 ohm speaker in the same situation, I would check with Nuforce before proceeding as two such speakers in parallel will be 2.8 ohms.
Post removed 
listening99,

Unfortunately, I could not find much in the way of testing of the STA200, and as you probably know, the marketing literature is very sparse w.r.t. details.  There is this test on AudioScience    https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-nuforce-sta-20...
... which is all done into 4 ohms, and other than fairly high mains noise, nothing looks off. Since you have not mentioned an issue with your likely highly efficient horn loaded speakers, that does not appear to be a problem, but if the Tekton Moab's are a lot more efficient than what you have now, that could be a problem.

Take the comments made by the "reviewer", AMIRM, with a grain of salt. He is the type of "measurements" person, that gives other people who believe in measurements a bad name. His comment
"Looking at the power rating versus distortion, the STA-200 doesn't bring much to the party over the much cheaper Topping TP60 ($199)"
...  shows a lack of knowledge/experience w.r.t. what is important. At low power levels, where almost all music is, the STA200 has much lower THD than the Topping TP60, and considerably lower IMD. The STA200 though clips really hard w.r.t. IMD. With the really efficient speakers, hopefully you won't run into that issue.

Tekton is usually conservative in their impedance ratings. When they say 4 ohms, it usually will not dip much below 4 ohms. I would say you have little to worry about other than what is stated above.
Instead of starting a new thread, I thought I would drop in a question on these same issues: I've been running a Nuforce STA200 with two 8ohm speakers, horn loaded, so the sound emerges with little effort and the amp runs cool. However, now I'm buying Tekton Moabs and they push a 4 ohm load. The Nuforce is stated to be suited to 8 ohms, not 4. The Moabs are efficient, running at a rated 
  • 98dB 2.83V@1m sensitivity
If the speakers run easy, what am I doing to my 8ohm amp, were I to hook them up...?
It couldn't possibly have anything to do with amplifier architecture and pleasant soft-clipping. Nope, it couldn't possibly be that. It probably has nothing to do with the rated power at your speakers lowest impedance either.

2 watts of SS power to equal 1 watt of tube power



I earned a living for my entire adult life as an electronics technician. I have a "First Class" radio telephone operators license. Most people today don't even know what that is, but once upon a time it meant something. I go back to a time when we used "slide rules". I mention all of this for a reason, one of them is the fact that I know formulas up the "ying yang".

For years I had a 150 watt per channel SS amp. Presently I have 70 watt tube monoblocks. I can't tell the difference in power. That's because neither of them went to school and don't even know "Ohms law"

Audio pertains to what you hear, while electronics pertains to formulas you work out on paper. I could hear those amps, but I never heard a single solitary formula.

Those amps and my ears told me that it takes 2 watts of SS power to equal 1 watt of tube power. Don't blame them, they never went to school.



And this one🤷‍♂️, well what can I say but, new/old product protection mode?

Looks like we'll never see an amp from him that can give hopefully give more than 50% wattage from 4ohms down to 2ohms especially the "old amps" the "new amp" when it released "may"??  if all the stars are lined up.

The classic statement from him was,  "Our OTLs do a nice job on the Wilson Alexia"
This is what that would look like (amp being the bulge).
  https://images.boredomfiles.com/wp-content/uploads/2018/04/14-woman-sleeps-with-python-731x457.jpeg
   
Cheers George  
The idea that doubling power is important springs from the concept that loudspeakers are ’voltage driven’. What this means isn’t that the speaker is driven by voltage (despite the expression), it means that the power that drives the speaker is such that the voltage aspect of the power is constant regardless of the load. (Voltage is an aspect of power just as current is; 1 watt equals 1 volts times 1 amp.)


IOW such an amplifier is termed a ’voltage source’.


The thing is, an amplifier **DOES NOT** have to double power as impedance is halved in order to act as a voltage source!!


Tube amplifiers can behave as voltage sources (after all, the this idea was originated by MacIntosh and ElectroVoice back in the 1950s) and they certainly don’t ’double down’... But they **can** cut their power in half as impedance is *doubled* and that is how they manage being a voltage source. The thing is a solid state amp does that as well. Its only at **Full Power** where 'doubling down' might make a difference and right after that is clipping, so its not that big of a deal since the amp really should not be running anywhere near full power if its a good match with the speaker.


So in a nutshell the ability of an amplifier to double power as impedance is halved is not what makes for a good sounding amp, and it may not be important at all; certainly with most speakers on the market its not. In fact the number of speakers that have horrendous amplifier-torturing load impedances (and phase angles) is actually pretty limited. Its a simple fact that the harder you make an amplifier work, the more distortion it makes so its unlikely that a speaker that is horrible to drive is going to sound like real music regardless of the amplifier employed.


So the whole thing is a bit of red herring.
There are two types of people:

  1. Those who know how to use Google (and other references), can sift through results using sufficient knowledge to reach accurate conclusions and consult industry friends to cross-reference.
  2. Those who insult others, but cannot back up their insults.


I don't know any audiophile who would make putting 75% more power into 2 ohms than 4 ohms their defining criteria for purchasing an amplifier. Do you?

audiozenology"I do know for a fact it puts out 75% more power into 2 ohms than it does into 4 ohms."
clearthink That is a very interesting statement, assertion, and claim how do you know this to be true? This is like you’re other pronouncements where you state something as ’fact" but offer no proof


He has no idea.
If what he said were true everyone that calls themselves an audiophile would be using them, and there would be no need for Krell’s, Gryphon’s Agostino’s, ect that can come close doubling from 4 to 2ohm, we all be using this $349 3000w Behringer he’s touting or similar. Like I said, he has no idea, all he's good for is beating his chest and stalking.

Cheers George

audiozenology
"
I do know for a fact it puts out 75% more power into 2 ohms than it does into 4 ohms."

That is a very interesting statement, assertion, and claim how do you know this to be true? This is like you're other pronouncements where you state something as 'fact" but offer no proof, documentation, or data except sometimes a link to a "source" that you Googled.
EPDR does not impact Class-D amplifiers. I do not understand why you will not communicate what you used as a current probe to measure 80 amps peaks?

Generally I would expect an amplifier that costs literally 100 times more (per channel) than another amplifier to be "superior".  However, your comment about "seriously current starved" cannot be backed up with facts. It does not go backwards into 2W, it has about 75% more power into 2W than it does into 4W. Do I have any illusions it can do 1500W into 2 ohms, even IEC bursts? Not really. But then again, you don't have proof it doesn't. I do know for a fact it puts out 75% more power into 2 ohms than it does into 4 ohms.


The Gryphon is a claimed 350W into 4 ohms continuous. The Behringer claims 750 (2x, not 17x). It also claims 3000W into 4 ohms. Will it? Doubt it, but maybe for IEC bursts. Will it do >1500W in long enough bursts to support real music at those levels? Yes it will, and yes, that is quite a bit more than the ~100 times more expensive Gryphon.


The primary limitation of it at 2 ohms, is the same as it is at 4 ohms, thermal, not current.
millercarbon
Can somebody break it down in layman's terms for me?
In a layman analogy for you.

These speakers, one of the worst load a speaker has ever measured. .9ohm EPDR
https://paragonsns2.imgix.net/wp-content/uploads/2017/05/Alexia-S2-Cove-Mariposa-Silver-5.jpg?w=1024...

Which amp will drive them the best?

This 175w Gryphon Antillion that almost doubles to 1ohm?
https://gryphon-audio.dk/wp-content/uploads/2018/10/ANTILEON_1.jpg

Or this 17 x times more powerful into 4ohms 3000w!!! Behringer Class-D that seriously get current starved and goes backwards into 2ohms
  https://www.storedj.com.au/behringer-nx3000-ultra-lightweight-3000w-class-d-power-amplifier?gclid=EAIaIQobChMIuJ-N8_fe5gIVjDgrCh1W0gqmEAQYAiABEgJjnfD_BwE

The choice is your
Cheers George
Layman’s terms:

It all comes down to "rated" power of your amplifier across the impedance of your speakers, with high emphasis over the bottom KHz or so.

Note I said across impedance, and not just at the lowest impedance as is often brought up. While a 4 ohm speaker may drop to 2 ohms (or less), it may also go up to 10 or 12 ohms (or higher) and do that over a relatively narrow frequency range. At a given volume level, not being able to deliver the required voltage at the impedance peaks or the current at impedance minimums will both cause issues in sound.

We next get into continuous ratings and peaks ratings. There are US and international standards for peak ratings. Are they good enough? Questionable, but nothing is stopping anyone from over designing beyond the standards with oversized transformers and/or large capacitor banks (or an architecture that allow more power supply droop). Of course you need high enough power supply voltages and beefy enough power supply to support the music peaks at the impedance peaks (which can be where heavy bass occurs), and a beefy enough output stage (and power supply) to support the current peaks and the minimum impedance, which are pretty much always bass.

From above .... beefy supply is the first need independent of the speaker requirements, and if your speaker dips low in impedance, you need a beefy output stage too, .... and there are many architectures that have been created to allow higher short term power bursts as is required for real music, but does not improve continuous power ratings.

So can you tell the "power" from the specs .... maybe. Depend on whether the amplifier vendor provides you enough details and you know enough about your speakers. That is about as easy as one can make it.
Can somebody break it down in layman's terms for me?


Among the many wonderful quotes attributed to the late Nobel Laureate extraordinaire Richard Feynman is this one: "If you can't explain it to a six year old that means you don't really understand it."

Probably not an exact quote. Another variant goes, "I couldn't reduce it to the freshman level. That means we really don't understand it."

The common thread being the idea that when you really do understand something you are able to explain it in very clear and simple language and even to people with no special knowledge of the subject. 

Can somebody break it down in layman's terms for me?


Apparently not. Draw your own conclusions.
From Stereophile,

https://www.stereophile.com/reference/707heavy/index.html

EPDR is simply the resistive load that would give rise to the same peak device dissipation as the speaker itself.


EPDR is not a measure of impedance, nor does it represent what the maximum current will be for a given voltage. EPDR is used as a measure for amplifier dissipation loading (not delivered power either).


EPDR is a measure of the maximum loading point of the output devices of a linear power amplifier. It is the point where the (current * voltage drop, rail to output) in the amplifier is at a maximum, hence where the dissipation is at a maximum within the amplifier. That is all it means.  It is not a direct relationship to what the maximum current draw is of an amplifier. EPDR does not occur at the impedance minimum in a reactive load, which means it also does not occur where the maximum current is delivered for a practical speaker.


Note my statement below. I specifically used 2 ohms as a minimum as that is the impedance minimum, and hence represents where the current peak would occur for any given voltage.

You did not indicate what you used for the a current probe.


P = I*I*R. Alexia's lowest impedance is 2 ohms. That means 80*80*2 = 12,800 watts (minimum) during that peak.





phase angles
EPDR = 0.9ohm load to the amp for the Alexia’s, do it for yourself, you’ll see it.
You will excuse me if I consider your 80 amp measurement suspect.
Yes, indeed it is!! Assuming a one ohm load instead of two, the maximum current would have only been 37.4 amps. A bit of a stretch to see 80!
It can be tricky to interpret oscilloscope readings off of a running loudspeaker due to the phase angles involved- the peaks may well not represent what one thinks!
P = I*I*R.  Alexia's lowest impedance is 2 ohms. That means 80*80*2 = 12,800 watts (minimum) during that peak.


V = I * R = 80 * 2 = 160 volts minimum (to achieve 80 amps).


The Antileon is 175 watts into 8 ohms suggesting a maximum rail voltage of something probably a few volts over 37.5V. Even if current and voltage were 180 degrees out of phase at the impedance peak, you only have 75 volts (not the 160 needed to drive 80 amps into 2 ohms).

You will excuse me if I consider your 80 amp measurement suspect. What were you using for a current probe?






wolf_garcia
Wolf, if you have a sample and hold oscilloscope, you can measure peaks, we did it to the Alexia’s powered up playing orchestral at normal medium level with the Gryphon Antillion, and saw amp peaks after conversion of 80amps+
Cheers George
After all of the back and forth regarding the watts issue, I was wondering if there's a simple device like my Radio Shack multimeter that could be stuck on the speaker output (or speaker input) jacks to see exactly how many watts I'm using to drive my allegedly 99db sensitive speakers at the levels I generally use. I know Nelson Pass uses something (and he likely has many bits of testing gear) like this at times while listening as it was referred to in some interview...the interviewer noted how few watts were used relative to the levels...I wanna do that...can I?
1) I have never made any claims about the SQ of the amplifier.

2) Do you have proof it cannot deliver the required current into 2 ohms to achieve 1500W?

3) What does "residue of current starvation" mean?   Are you implying they are selling an 8000W amplifier for < $400 now?  


Please explain in some detail, as you keep avoiding this, why you believe it is impossible for a Class-D amplifier to work properly into 2 ohms.


If it existed it would be PA, junk and it wouldn’t be getting it’s 1500w from a well designed amp with great current ability that can double down from 325w @ 8ohm and 750w @ 4ohms.
No, the 1500w would be the result of residue from current starvation from an amp that was originally 6000w or 8000w at 8 or 4ohms, and it would sound like junk

All of this amp conversation has me wondering what amps would best fit my pairs of Focal 936s and Focal 906s. They sure are audio file sensitive. I imagind they are also amp sensitive as they dip to 2.8ohms I believe? 

Regardless I'm not using anything special at the moment. Rotel rx-1052 receivers with external schiit audio DACs. The 906s seem happy. It sounds good to me but the 936s seem to be missing bits of full range or any kind of real authority punch youd expect from a tower speaker. 
Post removed 
clearthink And the result, of such "modern manufacturing" is a product that sounds awful but hey it’s a "lower margin market" so that is to be anticipated and expected.

If it existed it would be PA, junk and it wouldn’t be getting it’s 1500w from a well designed amp with great current ability that can double down from 325w @ 8ohm and 750w @ 4ohms.
No, the 1500w would be the result of residue from current starvation from an amp that was originally 6000w or 8000w at 8 or 4ohms, and it would sound like junk

Cheers George

Post removed 
Post removed 
audiozenology"someone could build a Class D amp that can put 1500 watts into 2 ohms and sell it for <$400??  The benefits of modern manufacturing and a high volume sourcing chain, not to mention a lower margin market"

And the result,  of such "modern manufacturing" is a product that sounds awful but hey it's a "lower margin market" so that is to be anticipated and expected.
Post removed 
I have Acoustic Elegance 15 inch woofers. 140 Ohm impedance at Fs. Fs is 21 Hz. In the enclosure, Fs is 32 Hz. Again, 140 Ohms at 32 Hz.

The above mentioned fabulous amp. One of the most powerful available.
3000Watts @ 8 Ohms. 6000Watts @ 4 Ohms. 12,000Watts @ 2 Ohms.

Let's go the other way;
1500Watts @ 16 Ohms. 750Watts @ 32 Ohms. 375Watts @ 64 Ohms. 187.5Watts @ 128 Ohms.

Now my poor tube amps.
140Watts @ 8 Ohms. 120Watts @ 4 Ohms. ???Watts @ 2 Ohms.

The other way;
160Watts @ ....... everything above. Therefore @ 16. 32. 64. 128 etc. it just keeps on chukin'

The average 400Watt SS amp;
400 @ 8, 200 @ 16, 100 @ 32, 50 @ 64, and, are you ready? 25Watts @ 128 Ohms.

Please correct me if I made a mistake.


sfischer1

+1 you have your finger on the pulse, and know about current delivery and wattage doubling, also about bridging stereo amps.
Others here that say a $350 3000w Behringer amp solves all that are just p*****g against the wind and some just beating their own commercial drum.

Cheers George
An amplifiers watts or amps is much like a cars topspeed, just a number. It says wery little about it`s authority, it`s punch or torque.  The amp`s weight might indicate some grunt, but just that. 
Why? because it is all about how this amp are capable to deliver it`s power fast enough. And that again depends on the internal cabling, trafos included.

And while I`m on, dampinfactor calculated from output impedance is a misunderstanding, it means nuthin. But tell me the size of your secondarys..
That cos term and the ability to act as an ideal source as the load impedance drops, is what makes most of the difference when it comes to balls.
This isn't true across the board. You can have lots of drive without anything near that if you simply are careful about the load. Some speakers are easy to drive and some aren't, but one thing is true about **All** amplifiers: the harder you make them work for a living the more distortion they are going to make, so if sounding like real music is your goal then your amplifier dollar investment is best served by an easier to drive (including higher impedance) loudspeaker.
As a very general rule of thumb: I think it safe to suggest that one double the speaker manufacturers minimum power recommendation and to consider amps that can double down that power to that speakers minimum impedance. Again, just a general rule of thumb! 
The impedance curve of a speaker takes into account the reactance already and hence the current. Few speakers dip below 2 Ohm. Some do, but they are rare. If your speaker doesn’t dip below 2 ohms than having an amp that doubles in power into 1 ohms is likely paying for something you are never going to use. Their is more to doubling into 1 ohm than just beefing up the supply, and there is no guarantee that the trade-offs , like higher feedback, are going to sonically pleasing. This is why "rules of thumb", like doubling of power into 1/2 the resistance is "better", should be taken with a grain of salt.


If your speaker does not dip to low ohm, then a so called beefy amp will not sound any beefier, but one with higher voltage rails and more capacitance will, even though it can't double into 2 ohms or 1 ohm or whatever artificial metric you want to use that may not apply to your system.