Amp power rating: Do they matter or watt?

Alonso, it took me awhile but I got it. Watts only really matter on transients, when music peaks. Power reserve AND watts matter most. eg, your 6 cylinder car "plays music_ or drives at 80kph fine, but when you put your foot down you want 8 cylinders to get you up a hill quickly. Some 6 cylinder cars run a 7000rpm at 80kph, others run at 4000rpm at 80kph, whereas a V8 runs at 2000rpm at 80kph. It is all about the power reserves to get you to 80, with plenty left in reserve. Most amp companies state 400 watts for example, yet their amp can only "run" at 350 watts at 95% of it's TOTAL power for very short periods, like a 4 cylinder screaming at 9000rpm at 80kph! It is used to make their gear sound tough and strong, but misleading. Naim have for example the 250 amp, which is rated at 125 watts per side @ 4 ohms,  the numbers on the amps are the watts @ 4 ohms x 2 sides. HOWEVER, the 250 has a TRANSIENT ability (power reserve) to pump 400 VA or 350 watts into a load. It's kinda like a well behaved small block V8, it cruises both on flat ground AND uphill at the same sound pressure level. The NAP500 is therefore rated at 250watts at 4 ohms, but it can power something like 700watts per side. So if an orchestra goes da,da DAH! and all the music booms, the amp must be able to deliver that power (V8) so that your speakers produce that wallop accurately, and put a smile on your face! Low impedance speakers require more power to drive properly, so having that electrical storage in a big engine in the amp is exactly what companies like Solution do, who make $150K amps and have a couple of thousand watts each side in their Veyron V16 amps! I hope I have made sense, I assure you, Naim do make powerful amps for most speakers. When in doubt, if cash allows - always go for a more powerful amp, you'll hear the crescendo's be it classical or rock much better.

Excellent analogy Steve! Thank you. I think I understand a little bit better now.

I used to run Thiel CS1.6s, a nominal 4 Ohm speaker but 3 Ohms around 5KHz. When I first got them I had a Rega Maia power amp rated at 80W. I was polaying Rattle and the Berlin Phil's recording of the performing version of Mahler's 10th and had turned the volume up to hear the quiet bits over some noise from outside, when the LOUD bit arrived the sound seemed to sparkle and jump forward from the speakers as the power amp ran out of juice (fortunately these were a demo pair, I was still waiting for mine). The 250 that replaced the Maia is also rated at 80W but with a much more generous and regulated power supply never had any problem driving the Thiels at any volume I could bear. (Beware of ex demo speakers though).

It might have something to do with more focus on power regulation that output devices, Naim like to Keep it simple and run them hard with less of them - hence the need to be serviced every ten years or so.

Thats a good analogy when describing Naim Power Amps, but what is the situation for example with a Naim Supernait 2 where the feature section and specification section confirm that the power out put for each channel is 80 watt.  There is no mention of 'Transient Power' in either sections, does that mean the amplifier produces 80Watt @ 8ohm and thats it?  From various users of this amp it appears it has the ability to drive and control many speakers?  Does it have a secret Transient Power that comes into play.?  Why is it implied in various reviews that the Naim watts are better than some other make of amplifier who also have the same power output for speakers, its all a bit mysterious. 

Romi, The Supernait2 is 80w@8ohms/130w@4ohms, so check your speakers impedance. The back panel shows a maximum power of 400VA which is the same as the 250, However because that ALSO powers the preamp and other features, it does not state the actual power amp ability, I'd contact Naim. I see that it can be upgraded with a HiCap or SuperCap, these would take over powering all the functions of the unit, allowing more internal power for the amp section. They also recommend using a pairing power amp as well, or a combo of both, which help separate the sensitive digital/analogue stages of the unit creating a better sound. You probably bought it as a single box unit for ease, so my guess is unless you are using big hard to drive speakers, you'll be fine. I know this unit can handle most loads and is very good. Don't sweat the upgrade paths, Naim offer those because people like to squeeze the most from their kit, and upgradeitus is addictive.

Re:  Why is it implied in various reviews that the Naim watts are better than some other make of amplifier - Naim amps have a very robust power supply that is able to control voltage & amp swings against reactive loads,  its over sized transformers & capacitance that does this together with a low output impedance.

naim always used to downplay the output of their amps, until they started making higher powered amps.

Does power matter? It depends on the efficiency of the speakers you want to drive.

I use JBLS4700 speakers which are 6 ohms and 94db efficient. I also power them with a 200 and 250.2(LF) for replay. JBL recommend 300 watts RMS, and actually suggest using twice that for dynamic headroom. Tannoys sound great on a 7watt tube amp, UNTIL you require tight dynamic bass at volume. I am a tube fan lover, they are however really great at mid range vocals, and depending on the valves and their amplication mosfet triode ect they can't really punch the way solid state can.

Putting the really good car analogies aside, i think the question remains un-answered.

Obviously a watt is a watt, but why is it that Naim's 80wpc amplifier can go head to head with the competition's 300wpc amplifiers. People have mentioned ability to handle transients and Volt-Ampere as pointers but that really does not answer the question.There is something missing in the explanation

Case in point.

SCM40: recommended power amplifier 75 to 300 Watts

Naim's flagship (non statement) power amp is bang on the middle with 140wpc and the NAP250 barely crosses the minimum barrier with 80wpc. 

Without going into car engine analysis or naim 'hidden' power reserves... why is this the case? The NAP250 has enough grunt to command the SCM40 as god intended, and only the minimum power requirement that ATC suggest... Even the NAit XS does a decent job...  So what is it? there must me something other than watts and VA that explains it in a simple way...

Someone summed it up quiet nicely "Why is it implied in various reviews that the Naim watts are better than some other make of amplifier"

The output impedance of the power amp is also important. The lower the better.

Thank you for your reply, another interesting explanation.  Just one slight amendment, I do not own a Supernait 2, I just used it as an example because on Naim Audio this product did not have any detail as to Transient Power which is is in contrast to the description of the NAP 250.  Now you  explained that part.  As part of my planned upgrade I have auditioned the Supernait 2 but I also plan to audition the Hegel H160 which has also captured my eye (from third hand reports this amplifier certainly controls a very wide make of speakers including ATC, Amphions and Magico's). What would be interesting is the difference in presentation of sound between the two amplifiers.  The instant bonus on paper is that the Hegel H160 includes a DAC and a reportedly useful Headphone socket.  Who knows it may be that NAIM sound that will win the day.

There are a few other factors at play here, and not all are obvious.

When specifying power output manufacturers measure the power with sine waves using test resistors in place of the speakers, this gives the most favourable result but some real world factors mean that the usable power is less than this test figure:

One is peak current

An amp needs to be able to drive 4.5A to achieve 80W into 8Ω speakers with sine waves.  However firstly music isn't sine waves, secondly real "8Ω nominal" speakers sometimes have impedances going down to as low as 4Ω at some frequencies.  Both these increase the peak current actually required in practice.

Naim amps have power supplies that can more easily meet peak demand than those used in some amps .

Another factor is how quickly the current can go from nothing to high current.  This causes difficulty with the driver transistors (the stage before the output transistors).  The reasons are quite complex (including the way feedback works to control amp gain), but if you get it wrong, then transient distortions arise (and I've heard this effect in quite a few commercial amps, but not from Naim!).  Again this isn't a problem with sine waves, but can limit real power when playing actual music into real speakers.

Naim (and some other manufacturers) concentrate much more on real world performance with 'difficult' speakers rather than making the figures look good on paper.

So for example... when a manufacturer like ATC states that a speaker of theirs requires between 75W to 300W of power, what do they mean? How do we, as consumers interpret that?

Would Naim's SuperNait 80wpc amplifier barely make it but it would actually struggle to deliver the sonic goods? or  because it is 80wpc, and that technically is 'above' ATCs minimum 75wpc requirement, the speaker would sound as good as if you fed them 300wpc? that is what is so confusing.  

Ok... those who can't be bothered, would say 'buy the most powerful amplifier you can afford' but as a consumer it does not feel right to buy the best product we could 'afford' and still not be able to see what the speaker is meant to deliver because 'what we can afford' is still below the technical ideal

The problem for speaker manufacturers, is that the sine wave power output is often the only figure quoted (as the others are more tricky to understand), so they don't really have a choice - that's the only thing they can quote to give any indication at all.  Unfortunately it's just not a reliable guide to know whether a power amp will drive a particular pair* of speakers well or not.

The 'the most powerful amplifier you can afford' is the simple answer that the manufactures of the amps that look good on paper want you to think - it just doesn't work in practice.

In the case of Naim amps, as their current drive is so good (look at the size of the transformers they use), and fast (part of the PRaT factor), 80W will drive speakers better than many 150W+ amps that just don't have enough current reserve.

After looking at power, there's also matching the sonic characteristics of all the components in the chain to get a system that's balanced overall.

Yes it's difficult to understand all this just from the paper specs, but that's what auditioning equipment is for.

*  unless you're George of course!

Let me see if I understood....

It's like selling shirts and only disclosing the number of buttons (shirts would represent amplifiers and the number of buttons their power output in watts) Customers are therefore limited by this parameter to make their choice related to matching power output suitability with regards to speakers, although in reality there are a few other measurements to consider,  these are quite subjective, measured differently and/or rarely disclosed in the spec sheets.

Do I make sense?

But yeah... auditioning equipment is the way to go.

In my personal experience (n=1) I brought home a pair of the loudspeakers in question (ATC SCM40) and hooked it up to a Naim XS. When I shared this experience, which was actually quite good, I faced a page load of comments suggesting that in now way the Nait XS was up to the task of moving the SCM40 properly... so I was a bit confused cause in my experience it was the opposite. But again, the Nait XS is 5W below the SCM40's minimum recommended power so that got me thinking

The shirt analogy sort of works (the speakers are equivalent of you chest and arms), and to ensure the shirt fitted you'd have to try it on (i.e. audition the amp with your speakers).

Overall, the ATC SCM40s are a bit demanding for a Nait XS to drive, however that doesn't necessarily mean that the combination will be worse than most other speakers connected to the XS.  Mostly it means that the XS won't be able to exploit the abilities of the speakers to their full potential.  Electrically speaking, the ATCs aren't a particularly difficult load, so they won't give a hard time to the amplifier, but an XS doesn't really have enough current capability to really make the ATCs sing as well as they can.  In other words, the ATCs will benefit a LOT from being driven by a 250 or above.  However; the XS will still do it's own thing with them connected, but because of the lower current available the ATCs won't sound particularly dynamic on an XS.  Also the clarity of the ATCs won't hide the limitations of the XS, but they won't actually degrade the fundamental sound of the amp.

Some speakers are electrically a very difficult load (some have a minimum impedance well below 3Ω ) and this will put an unfair load on a small integrated amp like the XS.  In this case the speakers won't sound good as they are actually degrading the sound of the amp by loading it too much.  To use the car analogy, this is like towing a large boat weighing 10 tonnes with a small hatchback with a 1.4l engine.