[DVV]

This must be the top audio topic regarding amps.

But I have never yet seen any serious conclusion reached. Ask as many people to get as many answers.

With my speakers (92 dB/2,83V/1m) and in my room (app. 132 sq.ft), I hardly ever use more than 4-5 watts in peaks under normal listening conditions. When I want loud, I peak out at around 35W for some mean bass notes.

Is 50W/side enough then?

Cheers,
DVV

[JoshK]

Hi Dejan,

I think many audiophools like myself have no idea how much power we are using (from our amps) when we listen to our systems.  My amp doesn't show me and I don't have any means of measuring it.

There is a difference though, at least in my mind, between playing at 92dbs and playing clearly and uncompressed without hint of strain at 92dbs.  Our audio group here in NYC has clipped 150wpc amps during our listening sessions.  

So the answer is I have no clue.

[WEEZ]

Whew...

92 db speakers in a small room peaking at 35 watts? That's loud, man.

Keep that up and you won't be enjoying music for very much longer. Seriously- 92db speakers peaking at 10 watts is loud! Your hearing will eventually suffer.

If you have an amp that clips rather gracefully like a ss mosfet; or a tube amp; your speakers should play loud enough w/ a 10-15w amp in that room with no problem. Hell, I've driven 87db speakers in a room 3-times that size to uncomfortable levels with 20wpc.

Wow

50 watts should be plenty.

WEEZ

[JLM]

My experience is that in a "normal" sized room, like 12 ft x 20 ft x 8 ft, and two speakers the sound pressure levels you obtain are roughly equal to the speaker's efficiency ratings.  In other words, sound pressure level (spl) losses from listening more than 1 meter away equals room reflective gain plus the 3 dB gain from using two speakers (doubling the power).

I recommend, especially for those interested in low powered amps, to play around with a spl meter.  Radio Shack sells one for $40, which is good enough to quickly develop a sense of how loud a given spl is.  Add in test tones, like the Stereophile test CD1, CD2, and /or CD3 and you'll also find out how deep of bass you're listening to or how high of frequencies you can hear.  If you use the RS spl meter use these corrections:  20 Hz add 6 dB; 25 Hz add 5 dB; 31 Hz add 3 dB; 40 Hz add 2 dB; 50 Hz add 2 dB; 63 Hz add 1 dB.

Public service announcement:  extended exposure to 85 dB or more will result in permanent hearing loss and possible permanent pain.  Someone, please post a chart of common sounds versus spls.

Before I played with the spl meter and test tones I thought that I was a real bass hog and spl stud.  What I found out is that I listen to an average of 70 - 80 dB average spl plus peaks for serious listening (like most other audiophiles I've hung with) and lower levels most of the rest of the time.  Jazz, folk, and other small essemble music (even rock) has only 10 dB peaks.  Classical can have 20 - 30 dB peaks.  Rock concerts run around 110 dB, classical concerts (rarely) peak around 105 dB.

So serious listening of classical averages 75 dB with typical peaks of 105 dB and jazz averages 80 dB with typical peaks around 90 dB.  Watts from your amp can converted into dB of gain:  1 watt = 0 dB gain; 2 watts = 3 dB gain; 4 watts = 6 dB of gain; 5 watts = 7 dB of gain; 8 watts = 9 dB of gain; 10 watts = 10 dB of gain; 20 watts = 13 dB of gain; 50 watts = 17 dB of gain; 100 watts = 20 dB of gain; etc.

Looking back up at the top (spls in "normal" room equal speaker efficiency rating) you can use the average/peak numbers above to come up with wattage requirements.  For instance:

80 dB efficiency speakers you'd need 1000 watts 30 dB of gain to reach rock concert levels; 350 watts to reach classical concert peaks; and 10 watts to hit jazz peaks.  

85 dB efficiency speakers you'd need 350 watts 30 dB of gain to reach rock concert levels; 100 watts to reach classical concert peaks; and 3.5 watts to hit jazz peaks.  

90 dB efficiency speakers you'd need 100 watts 30 dB of gain to reach rock concert levels; 35 watts to reach classical concert peaks; and 1 watt to hit jazz peaks.  

95 dB efficiency speakers you'd need 35 watts 30 dB of gain to reach rock concert levels; 10 watts to reach classical concert peaks; and 0.35 watts to hit jazz peaks.  

100 dB efficiency speakers you'd need 10 watts 30 dB of gain to reach rock concert levels; 3.5 watts to reach classical concert peaks; and 0.1 watts to hit jazz peaks.  

So you can see that speaker efficiency, musical genre, and listening habits each play a major role in determining how much power is needed.

[ctviggen]

Those are all continuous ratings, and don't necessarily mean that you won't need more wattage for transients.  What I find weird about the whole power thing is that the more expensive the amp is, the lower rated it typically is.  For instance, I have a Jeff Rowland that is rated at 150 w/channel into 8 ohms.  I used to have an Onkyo that was also rated the same (though maybe the Onkyo fooled around with the rating by rating it at only one frequency).  There's no way the Onkyo and the JR produce the same power (instantaneous or continuous).

[_scotty_]

I think what is being misunderstood is the amount of power necessary to reproduce dynamic  peaks in the music vs the amount of power it takes to have a sensation of loudness in reproduced music with very little actual
dynamic range. Much of the music commonly listened to has limited dynamic range. The best example is simple pink noise, it takes very little power to have a sensation of loudness on this type of signal as it has no dynamic
range at all, 2 to 5 watts might be enough to drive you from the room. On the other hand a piece of music with a wide dynamic range
will have to be recorded with a much lower average level perhaps -30db to -40db, you will typically have to turn it up to get the softest parts of the performance above the ambient noise in your listening room and when the loudest parts of the performance occur you may think something is going to break.  This sort of recording might require 100 to 500 watts or more to not clip on the peaks depending on your room and speaker efficiency.  I have a 420sq.ft. listening space with 95db efficient loudspeakers
and 110watts/ch.  I should be able to reach a 115db peak cleanly. I might  
have enough power until I need to reproduce a 116db peak.
Basically you can never have too much power. What you think you can get away with  in your system will have to be determined by you.  When you
consistently run out of steam and your music sounds like crap you will
know it is time to do something.   Scotty

[WEEZ]

I agree that in theory- one needs "headroom" power. But gee whiz, 92db speakers in a 10 x13 room with 35w peaks is ear damaging loud! And I'm an old fart who can't hear quite as well as I used to (probably from listening to rock music with 300wpc amps in small apartments in my youth) -but loud is LOUD- even for me  

WEEZ

[PhilNYC]

FWIW, Nelson Pass has been quoted saying that to accurately reproduce the sound of a single acoustic guitar string, he needed at least 600 watts.  It's not about volume, but moreso the complexity of the tone...

[markC]

I'm with Scotty on this. If you have a ton of head room and don't need it, fine; but when you do need it on a certain passage in a certain song-it's there- wham all nice and realistic. If you don't have it, you'll never know what your missing....

[JLM]

Yes, except for rock concert playback levels, the realistic (practical/reasonable) power needs are to account for peaks.  Some have said that instantaneous peaks can reach around 130 dB, but I both doubt that and don't want to try finding amps/speakers rated to reach those spls (100,000 watts with 80 dB/w/m speakers, 10,000 watts with 90 dB/w/m speakers, or 1000 watts with 100 dB/w/m speakers).  As driver efficiency goes up so does colorations (something gotta give).

Even though a 1.3 liter engine could get a 5000 pound limo up to 70 mph, the dynamic performance would be pitiful.  IMO the amp needs to have "muscle" enough to bully the speakers around, to "tell" them what to do, not "ask".  I believe that the numbers I stated above represent a practical guidelines to address this issue.

OTOH the little digital amps out there reportedly have dynamic/bass capabilities well beyond conventional expectations, allowing 6 wpc to satisfy users of 90 dB/w/m efficient speakers.  I'm gonna try this approach myself soon.

[mcgsxr]

I invite anyone in the Toronto area to contact me, and experience what 30wpc of digital amplification can do with my 86-90db efficient speakers - I have never wanted for volume, either for sustained levels or peaks - nor have I ever clipped this amp.

Guess that means I am a real low volume listening weenie, or that this combination of amp and speakers is a decent synergistic match...

Based on my 20 plus years of listening, I am suspicious that it is the latter, though the weenie comment might be accurate!  

[lcrim]

Mostly because this topic keeps coming up I saved this URL
http://www.smr-home-theatre.org/Power/
Its pretty good and I have posted it before.

[JLM]

thanks Larry

I believe with the exception of mentioning current demands, my first posting agrees quite nicely with your link.

Another factor the article mentions is speaker impedance.  All speakers exhibit an impedance rise as the woofer approaches it's low end.  Cabinet designs address this by flattening the impedance hump and pushing it into lower frequencies.  It is exactly this effect that extends bass response.  A proper design will provide roll off that matches room gain.  Without the dramatic impedance hump, speakers present far easier loads to amps.

IMO the best cabinet design for accomplishing this are transmission lines.  Until recently there was no way to mathematically predict performance from TLs.  But with the work of Martin King and guys like Bob Brines very successful designs are being designed and built.  20 years ago I had I. M. Fried TLs that were monsters (6 cu. ft. beass cabinets with a single 8 inch woofer per channel that were capable of 114 dB at 17 Hz).  They overloaded any residentally sized room, but were breathtaking in a 160 seat chapel using a 20 wpc NAD receiver.

[Bemopti123]

JLM, as an Engineer?  if I am not mistaken you are, how do you explain what people are saying about the mentioned digital amplifier with just 6 watts supposedly reproducing more accurately or satisfactorily sense of rhythm and flow than an amp that might put out 275 watts, especially with a speaker that has medium efficiency, as 87 db?  Is this feasible or really, honestly possible or do you think that the brain/ear relationship can play games with whatever we are hearing or like to hear?

I tried to run my 89db, Gershman towers, with 2 way mini monitors on top and a 10" woofer in the bottom with a 40 watts mono gainclone and it just did not happen.  

I tried to run the same with a 10 watt SS Opamp that puts out about 17 watts and it did not happen to control them well.

I am puzzled to hear what people are hearing with such digital amplifier.  6 watts at 8 ohm.  Those must be miracle watts.

BTW, I was at the bash where JoshK said, we used 150 watts/channel and I saw the amplifier, in the read out saying "clipping."  The interesting thing is that I did not hear the speakers clip much at all.

Paul from NYC

[Hantra]

Well I have a 12.5 x 14.5 room and if I have less than 300 watts per channel, I am NOT happy.  The more, the better.  

It all depends on your speakers. . .

B

[warnerwh]

Amplifier power gets used up much more than most people realize imo.  I once bought a Carver amp just to see how loud it would play when the needles hit 100 watts in peaks. This was with 90db speakers.  Not loud at all in at the time a 17x19 room if you consider the average listening level that must be kept to keep the amp from going over 100 watts.  I will stick with a bare minimum of 200wpc after that test.  Also anybody who ever thought about buying an older TFM model Carver amp, don't bother, it was the most awful thing you can imagine.  I wouldn't use one in my garage system.

[DVV]

... Even though a 1.3 liter engine could get a 5000 pound limo up to 70 mph, the dynamic performance would be pitiful. IMO the amp needs to have "muscle" enough to bully the speakers around, to "tell" them what to do, not "ask". I believe that the numbers I stated above represent a practical guidelines to address this issue. ...

Let's not confuse issues here, power capability and speaker control are two different things which need not necessarily go hand in hand.

One can have a relatively low power amp with excellent speaker control, which can subjectively sound much more powerful than it really is. A good example are Naim amps. 35 or 50 wpc are hardly stunning figures, yet they always amaze me with their big hearted, expansive sound far transcending the usual at that power rating, and I daresay, even twice their power rating.

And vice versa, ona can have an amp which has high power output level figures, which it fully substantiates on the bench tests, yet can sound both flabby and weak. Yes, this is an extreme, most are better than that, but most 100 watters will struggle to keep up with the above Naim, and even with some NAD and Rotel offerings.

Just to complicate our lives and further confuse this issue, this must also be taken into account when talking about required power levels.

Cheers,
DVV

[DVV]

... Even though a 1.3 liter engine could get a 5000 pound limo up to 70 mph, the dynamic performance would be pitiful. ...

As a sideline here, I would be delighted to practically demonstrate just what a 1.3 litre engine can actually do. And a classic one at that, just one overhead cam shaft, just 8 valves in all. After some modding, it will deliver 125 bhp with about 106 lb ft torque.

And it does wonders in a car admittedly weighing not 5,000, but 1,900 lb (quite a difference, to be sure). While your above comment stands, my point is there are 1.3 litre engines and other 1.3 litre engines; they were born the same, but one evolved. And still naturally aspirated, no turbos.

Cheers,
DVV

[DVV]

Mostly because this topic keeps coming up I saved this URL
http://www.smr-home-theatre.org/Power/
Its pretty good and I have posted it before.

I must take issue with the table provided.

Many years ago, I read a paper, and in my stupidity, failed to scan it and save it, from a group from Berkley, who quoted:

* that a jet engine, going at full blast, will provide about 111 dB SPL at 3 metres. I'd call that rather loud, wouldn't you?

* that 112-114 dB SPL was the limit at which most of us will instinctively cover our ears, and

* that at about 124 dB SPL, our eardrums will probably burst, but if not, we stand an outstanding chance of going deaf or heavily impaired.

I am also baffled by some of the figures. 126 dB SPL at a rock concert - let's assume this is correct. Question - where? Where is this SPL delivered to? Assuming that SPL decreases by 3 dB/metre, on a stadium which is at least 50 m wide, delivering that kind of SPL, even in brief peaks, would require incredible power amplification.

I will readily believe this is actually being developed 1 m from the speakers, but by the time it reaches the audience, taking into account the fact that there will be many speaker clusters not just one, still boggles the mind regarding amplification - or the quoted SPL at any reasonable distance from the speaker clusters.

Work it out, take a smaller stadium as an example, assume it's 40x60 m, work out the megawatts needed. Delivering 126 dB SPL in the center of such a staion would be quite a feat, quite a feat. Even assuming speakers with an efficiency of over 100 dB/2.83V/1m. But, if the center gets 126 dB, what happens at the sides, which are nearer to the speakers? Just 10 m to any side means an extra 30 dB (sic!!!!) of loudness. At the edge of the stadion, somebody is being desintegrated by 186 dB od DPL.

Conversly, if this peak figure applies only to those nearest to the speakers, then those in the center are way below that. Would you want to sit in front of a speaker cluster and get a dB or two above your eardrum bursting level?

Cheers,
DVV

[JLM]

DVV,

Thank you for clarifying what I was trying to say with the engine/car analogy.  Yes a small displacement, say 40 hp engine could get a limo to 70 mph, but the acceleration (dynamic response) would be pitiful.  As a former F1 fan I very much appreciate what a small engine can do in a light car.

Rating the spls of different events should not be taken as science without lots of qualifiers.  I agree, you can find 100 dB/w/m speakers rated to handle up to 1000 watts, but they're not practical IMO.

Paul,

My degree is in civil engineering, but I have at least a "philosophical understanding" of the phyiscal universe.  (What in the heck does that mean?)  IMO science is a process of discovery via questioning and testing.  Engineering is about invention and application.  Dogmatic thinking, like the way we've measured distortion for the past 50 years, is hopelessly outdated and irrelevant.  And so it may be time to open our ears and shift paradigms.  That several have observed 6 wpc digital amps playing at satisfying levels with low efficiency speakers should, as you've done, question conventional wisdom.  My guess is that relatively large capacitance/current capacity of the amp with benign impedance characteristics of a given speaker may have something to do with it.  The mechanics involved with human hearing may also play a role, where improved dynamics (especially in bass frequencies) are equated (fooled) in the human ear/brain with increased sound pressure levels.