Shocked. Need Opinions. How muck power do I need?

I think you hit the nail on the head, the issue for many speakers is not watts @ 8 Ohms, but current delivery.  It’s how well an amplifier does in the 3-4 Ohm range that’s important, especially with speakers with dual woofers as they tend to hit a low in the bass, as you point out.

Unless you are trying to shake the walls down 100W is often more than enough for most listeners.

A Luxman 509 or even a 507 for instance would probably be more than enough for you.

@erik_squires

+1

Current is the game, absolutely. But I would not start trying to find the minimum because as you already found the bass starts dropping off. Maybe in a quick listen that is ok… but it may not sounds as good at quieter levels. I would not go below 100 wpc and with solid state, more (of the same quality) generaly sounds better. Tubes are way different… much more flexible and not requiring as much power to sound good.

Brand is a personal preference. To me solid stat Luxman has accentuated treble and a bit extra bass and is attenuated in the midrange so is not that musical. It sound very “high end” and sparkly… and looks pretty. I would look at Pass, better balanced tonally, with good midrange and very musical for solid state. Ultimately your preference.

Many thanks. Good point about a quick listen vs living with it for a while and at low levels. 

I don't know your specific components, but, as a general matter, a lot of people can do with far less power than they think they need.  But, there is no reason to go lower and lower just for the sake of seeing how low you can go.  With solid state, you can achieve fairly high power levels without that much additional cost, so there is less of a reason to go very low in power unless you are taking a fundamentally different approach to design (e.g., First Watt, an offshoot of Pass Labs).

It is a different story if you are looking at tube amps.  With tube amps, there is quite a bit more variability in sound quality and achieving higher power often comes at a sonic price.  That is why low power makes more sense, if you can live with the lower maximum volume level.  Most of my favorite tube amps are under 8 watts, although there are some that I like that hit the heady rating of 100 watts per channel.

Remember, all things being equal, you need ten times the power to double the sound volume. 

In my experience the PassLabs deliver super control of speakers such as the PMC Twenty26 vs like you found with the Evo, sounds a little weak with the PMC MB2SE. The ARC D240 MKII (120W per channel, fully differential) was much better able to deliver power.

Power supply. Power supply. Power supply. 
 

Bigger amps, have bigger power supplies. Depending on how loud you are listening, as has been said above, it’s about current driving the difficult parts of the speakers load. 
 

Smaller amp could work, if it has a power supply capable of delivering the goods…

Always have much more power then you need ,good rule of thumb 

for if playing loud you don’t want to be going into transformer saturation and distortion , they say in transients you can have 10 x the power for short burst 

in transients milliseconds ,the power supplies and. Ample capacitances is very important .150 8 ohms 300 at 4 ohms is a solid amplifier double down 

if it cannot come close then average at best performance .the output-devises  such as how many Mosfets per channel will dictate current delivery to complement the transformer size ,and filter capacitance. My Coda amp 3k transformer ,almost 100 k in filter capacitances ,and 20 15 amp Mosfets  per channel , 100 amp  capability .

it has dual 16 amp slow blow fuses on the back that says a lot about current delivery and 4 more fuses inside the unit.

if tube then calibrated different for the size ,quality of the power transformers  and chokes ,power supplies. from my experiences which is over 4 decades .

With 40W it will be -2.7dB.  Perceived loudness will be 16.6% lower (still over 100dB)

I listen to Mostly Jazz and some rock and I bet I don’t go past 5 watts 90% of the time. I actually have two systems.  one has 40 watt mono blocks and it can blast you out of the room the other has 300 watt mono blocks and I bet I’ve never used 100 watts. I also have a subwoofer, that I rarely use because on the upstairs system, I rarely need it.  So it’s probably going back into the downstairs system.

I believe my Pass X250.8 pushes about 12% class A and I never had any needs to out of it. About 30W is plenty as long it is backed up with huge power supply and enormous banks of capacitors 

I haven't owned an amp over 6 watts per channel for quite a while.  My new amp weighs 300 lbs and makes 4 wpc.

--Jerry

What amp weighs 300 lbs and makes 4 watts?  

Lots of really good content here. In my opinion, there are definitely several factors, besides the more obvious speaker load, room sizes, listening levels, etc.

Current can be very important and power supply design is a major factor here. I am not of the mind that more power is always better, particularly within a designer’s range of products.

i have a Pass XA25 driving a pair of Dynaudio speakers in a decent size room (though I do only sit about 8ft from the speakers or so) and for me, the Pass may have run low on steam once. 

Many, many moons ago when I worked in a high end store, it was not uncommon for one company’s lower wattage products to have some qualities that bested their larger wattage amps. Sometimes this was timbre in particular, but sometimes soundstage as well. Bass control on larger speakers does usually require more wattage. 
 

Now with very sensitive speakers and very low wattage tube amps, that is a different thing of course…

That is a huge space for those speakers, and the impression of diminished bass is relative to prior powerful amps, perhaps making more bass out of those pairs of 6.5", but with more distortion than you are/were aware of.

I would want larger woofers, (I have and would want 15" in that space). I always like mid and tweet horns, then, how much power to drive them? And, you say solid state, but I would want tubes, made affordable and more practical by efficient horn speakers.

My 14 x 24 room, I use 45 wpc tubes, that never seems 'not enough', but I don't listen to cannons and crashing highs anymore.

Definitely consider more power than generally needed to have reserves for instantaneous demands.

Great points made by everyone: Current, slew rates, transient power reserves, damping rates, bass control, not sweating low impedances, and being "musical".  But there is something about a large amp just idling along happy at putting out 40W to 100W peaks compared to a smaller 40W amp that will run out of steam - if you want to go louder. And the synergy with the speakers.  As Andrew Robinson stated in his review of the new Emotiva Airmotiv XT2. That thing was a power hog. It sounded good, but he had to step it up with what amp he used to get it to play nicely. I imagine Magnepans would be the same. 

Just sitting here watching the Mac 1.2 kw meters swing 1.2 watts 70 dB on the speakers so don't need alot of watts most times. It is the amps that drive the base tweeters don't need much on the voice coil and magnets smaller compared to offer magnets and voice coil then depends on crossovers electronic dsp or coil caps then headroom if you push an amp on upper limits causes risk of clipping or distortion damaging speakers so it is nice to put the ear muffs on and rattle the walls at 110 dB and feel the music pound you chest wall.some day try the crown I tec 12000 watts on pro jbl.enjoy the music power is volts x amps

It depends. All amps and watts are not created equal, all speakers and speaker impedances are different, and our volume preferences are different. You only need enough power to drive your speakers to the volume levels you prefer in your room. Headroom is nice if you push dynamic passages to higher volumes, but most of the time I don’t come close to the limits of my amps.

Even with speakers of average sensitivity (~ 89db), over the years I’ve gone from a high of 255 watts per channel (Hafler DH500) down to about 17 watts per channel (tube triode), and my current amps sound much nicer to me than any other more powerful amps I’ve owned. In fairness, for bass heavy passages an ample size SS amp tends to handle big bass peaks on large woofers better than my small tube amps do, but that’s one aspect of the overall sound spectrum (below 80hz in my case)

one of the rare threads in which everyone seems to be making good points. my own experience, which matches other posters', is that high current delivery is by far the most critical factor--even with demanding speakers like dynaudio i've heard 50w pass amps outperform amps with much more wattage.

@loomisjohnson  - I can believe that, but also Pass I think likes big old school speakers.  See if you can find Pass' article on damping factor and whether it really should be low or not.

I once tried my little Onkyo from my bedroom system on my Maggies. It's rated at 44/70. To my amazement, it was really good! That little Onkyo is a gem.

In some ways, a high performance amplifier is like a high performance race car. It needs to accelerate instantly and then stop on a dime - without swerving off the track.

Transient response* is an important factor in amplifier design.

In audio, an example would reproducing a 96 piece orchestra that’s reaches a crescendo, then pianissimo. The finale of Gershwin’s ’Rhapsody in Blue’ would be a good example.

Other examples would include: hearing a close-mic’d plucking of a guitar string - or - the thwap of a drum stick hitting a snare drum - and then the decay that follows. Does it sound like the real thing? A good synergy between the amp and speakers will define that. Much depends on the kind of music being listened to and the priorities of the listener.

_ _ _ _ _

* In electrical engineering and mechanical systems, the transient response refers to the temporary behavior exhibited by a system when subjected to a sudden change or disturbance in its input. It encompasses the system’s reaction to a stimulus before it settles into a stable, long-term state¹. Specifically:

• Rise time: The time required for a signal to change from a specified low value to a specified high value (typically 10% to 90% of the step height).
• Overshoot: When a signal exceeds its target value.
• Settling time: The time for the output to remain within a specified error band after an ideal instantaneous step input.
• Delay time: The time required for the response to initially reach halfway to the final value.
• Peak time: The time to reach the first peak of the overshoot.
• Steady-state error: The difference between the desired final output and the actual output when the system reaches a steady state¹².

@ssg308 The 250.8 does approx 16 Watts peak in class A into 8 ohms and half that into 4 (according to Pass)

Audioman58 agree it’s always good to have extra power. Anthony Michelson from musical fidelity said less than 250 w all you get is distortion.So I tried his supercharger 550 mono block to run my Red rose speakers monitors? He is right the speakers came alive.

Independent of the quality of amplification, the quantity you need is actually really small if one is listening at a close distance. The speaker sensitivity is the key metric for power requirements.

The simplified math is:

1w of power can deliver the speaker’s sensitivities volume (e.g. 86db) at 1m (3.28 ft) listening distance.

For every decibel volume increase above 86db requires double the power.

For every meter distance requires double the power.

Therefore…

If one sits 5m (16.4 ft) away from a rated 86db sensitive speakers and wanted to listen to their music at 86db, he/she would 5w of power.

If the volume is increased to 87db, 10w of power is required.

88db would require 20w

89db would require 40w

90db would required 80w and so forth.

You can see there’s an exponential growth of power required when both distance and volumes requirements grow.

That said, the rated speaker sensitivity db, typically around 84 to 96db, is a very high listening volume for most audiophiles. A lawnmower is typically around 94db. Took a measurement using a free dB phone app and I’m usually listening to music around 60db to 75db.

Is 40W enough? Yes, your 75W Cambridge EVO75 (89.5 db sensitive) is powerful enough to drive your Dali Mentor 6.

You need ~4w of power to drive the speakers at 10ft listening distance at 89.5db volume.

Unless your speaker are super hard to drive, don't get too caught up in the quantity wattage.

It's more important it's quality amplification that can actually reach up into its peak numbers with low distortion… because what's the point of the power if it's not really usable power. Pure wattage numbers is mostly useful for marketing and sales.

@swede58 well thats even better, meaning that 20W does the job 

@erik_squires, i will track down the pass article. i would add parasound as an amp which does well with challenging loads--during my brief forays with 83db planars my 125w hca1000 was surprisingly capable.

For every decibel volume increase above 86db requires double the power.

For every meter distance requires double the power.

Double the power will increase volume by 3dB (+23% perceived loudness)

Volume drops at double distance by 6dB. To keep volume the same requires 4x power.  To keep volume at 2m the same as 1m requires 4x power.

Not to sound repetitive but it is ALL about current, and damping factor! You only live once. Why go backwards? Is it just the form size? GanFeT solves that! Although that's NOT current as we all appreciate. Thats Pass Labs, Dan D, Mark Levinson, darTZeel... And many more... Hegel has unbelievable dampening factors of 2000!!!
 

@kijanki is correct. 3db not 1db.

Lots of responses about current and rightly so.

interesting isn’t power and current directly related ?

P = I x E 

just a thought 

In the context of the OP’s speakers and listening room it may not be obvious at first how much power/which amp is really needed, until the perceived experience sets in through a variety of different amps. Crank it as loud as you could possibly want, and then some, and then try and assess whether there’s a sense of headroom still (the limitation here may as well be the Dali’s). Knowing what proper headroom can do in these situations requires of one to, well, know about it through actual experience; what may seem at first like (proper) headroom, if it even registers as a priority, could easily be challenged in another, more capable speaker/amp context.

Or, maybe the proper headroom scenario turns out to be of secondary importance in the bigger scheme of things, and it really just comes down to the preferred overall sound at "normal" or more typical listening levels, even if it means giving up ultimately control and a sense of ease at higher SPL’s. If you can have both, however, that would be the preferred scenario.

Just today listened to the Leben CS-300F (~15W per channel) with a pair of hORNS Universum speakers, and it proved plenty capable and very lively in moderately sized spacings and a speaker sensitivity closing in on 100dB’s (in this case with the Eminence Kappa 15C as the woofer element; the later iteration uses a less sensitive woofer at ~95dB’s). Remember, your Dali’s would need some 20x more all-things-being-equal power here for the same perceived SPL, and even so the Leben with the Universum’s would likely seem like a small monster be comparison.

this the most interesting thread I have read in a while and such good answers to the OP's question.

I have a theory that has borne out to be true to my ears and understanding as an eleectronics tech and just the different amplifiers I have lived with. Like many people, my original audio setup was very modest, at 5 wpc using a Heathkit stereo receiver, it was replaced with a 40 wpc (Dynaco SCA80-Q) and then a Hafler DH-200 at 180 wpc into 4 ohms, then an Adcom 325 wpc amp, and finally a variety of Carvers at typically 650 wpc (1.5t) was my fave of the bunch - The Carverrs were all 450 wpc or above and always each step taken up the power scale produced to my ears better sound at any level. So my theory is if your speakers are rated at 300w continuous than an amp of double that power is sufficient. This way amp will never struggle to handle the load no matter the source material being played, and it will never go into clipping or even close to it. This protects tweeters and provides the best possibility of clean output from the speakers. Anything less is a compromise.

@livinon2wheels while I agree with you that Amp should be about double power rating than your speakers MAX Contin. power, lately I started to think that if your speakers can deliver maximum power without the distortions and sound is way too loud to sit and listen to it than you got correctly working system.

My 250W amp is pushing enough power and staying in class A, that I have no desire to ever turn it up. 

My speakers are rated 300W max but I think 50W class A amp will do Just fine.

So it's not a power output that matters it's the current levels that count and power banks size.

Although I’m not sure about the accuracy of the VU meters on my former Vincent hybrid amp, but it  never used over 3 or 4 watts during any of my listening sessions typically up to 80 db measured at 10 feet.  This is driving 87db sensitivity KEF R11 speakers.  I’m now running a Linear Tube Amplifier (Class A/B tube amp) with 51 wpc and never have had any problems. 

this the most interesting thread I have read in a while and such good answers to the OP's question.

I have a theory that has borne out to be true to my ears and understanding as an eleectronics tech and just the different amplifiers I have lived with. Like many people, my original audio setup was very modest, at 5 wpc using a Heathkit stereo receiver, it was replaced with a 40 wpc (Dynaco SCA80-Q) and then a Hafler DH-200 at 180 wpc into 4 ohms, then an Adcom 325 wpc amp, and finally a variety of Carvers at typically 650 wpc (1.5t) was my fave of the bunch - The Carverrs were all 450 wpc or above and always each step taken up the power scale produced to my ears better sound at any level. So my theory is if your speakers are rated at 300w continuous than an amp of double that power is sufficient. This way amp will never struggle to handle the load no matter the source material being played, and it will never go into clipping or even close to it. This protects tweeters and provides the best possibility of clean output from the speakers. Anything less is a compromise.

@ssg308 - I had to laugh when you said its all class A, not because its not a great path to true hi fi, but I am gonna need to say some prayers for you in the summer time with those space heaters amping up the heat in your chilling space...and also for your monstrous electric bill. I can only imagine how much the power company loves you. But ultimately this hobby is about making decisions that are ultimately compromises in some way, some of them financial for sure with both the cost of the equipment and maintenance thereof and the power necessary to enjoy 115 db during some rock concert or movie that you want to hear at reference level or above. So many paths are valid ones to get to audio nirvana. :)

@tomaswv Others have already explained the relationship between wattage vs. db and speak efficiency. I'm only going to add my practical experience.

I used to have a pair of Hafler DH-220 kits that I installed their bridging kits into. When in bridged mode, the amps each provided 440 watts. I figured this would be a cheap way to get current to push my ESL panels easily. The problem was that the ESL are an unstable load. Eventually I switch them back to stereo mode and used only one channel from each to drive my speakers. 

The change in quality was amazing even though I went from 440 watts down to about 115 watts/side. More detail, more bloom and no loss in bottom end. This experience taught me "power" isn't everything. But the quality of the power is supremely important.

Since then I've moved on to an ARC VS-110 and am delighted with sound and still have plenty to rock the house should I choose.

Happy listening. 

@livinon2wheels lets get something straight. 

A. My amp is Pass X250.8 so by definition is not class A amp it is A/AB class amp that runs first 15-20W in class A and it working temp regardless of class operation is 119F. Its not the coolest running amp but its far cry from Pure Class A working temp.

B. It is not a STASI circuit so it does not stay on 24/7 and idling at 900W, there for my electric bills are not so bad up to date $76.92 was the highest bill since I got the amp running and opposite to my Threshold S550e it consumes less power at idle.

C. Yes it s a hobby so by definition you have to sponsor it, now, do you buy records ? CD's? if yes you know your choices are what makes that hobby yours... so are payments and all cost associated, If you are not ready to pay up, don't get in to it, like every hobby that one gets expensive as well.

The sound quality is your reward, take it or live it...

SHOCKED I tell you just SHOCKED 

Required output current at min load can be calculated.
My Benchmark AHB2 delivers continuous 100W at 8ohm requiring 3.5A current.  Let's assume even 5A to give it 100% overhead (200W).  Current will be 4x higher driving 2ohm load (8/2=4) to keep the same output voltage (perfect voltage source), resulting in 4x5A=20A.  AHB2 is specified at 29A maximum current (both channels driven) so it is OK with 2ohm loads.  “Both channels driven” is very important part of this specification showing that power supply is able to deliver total specified current (2x29A=58A).