Speaker power ratings vs. aplifier power ratings?

This is probably a stupid question that has been answere here many times but her it goes anyway......

If a speaker is rated at 120 WPC at 4 ohms such as my Green Mountain Europa's how close to that power rating do I have to stay near when choosing an amplifier?

In other words, does 120WPC mean 120WPC with no room for deviation?

No. Usually a speaker manufacturer's power rating only means maximum power input for designed performance. Uusually much less power is actually required to get satifactory performance in a typical set up.

This is all kind of loosy-goosy but the simplist was of explaining what is a complex subject is to take the db rating i.e. 86db for 1 watt of power imput and for every 3db of increase in speaker output you double the amp power as such -

86db - 1 Watt
89db - 2 Watts
92db - 4 watts
95db - 8 watts
98db - 16 watts
101db - 32 watts
104db - 64 watts
107db - 128 watts
110db - 256 watts

Assuming your speakers efficiency rating was 86db then the manufacturer would be telling you that his speaker could produce sound pressure levels within a few feet of the
speaker to a maximum limit of 107db without damage to the speakers or the onset of serious driver distortion.

FWIW this is an overly simplistic, but it should give you an idea of whats involved.
While Newbee is correct with his power table, I would also add that you do not have to stay that close to the 120 WPC speaker manufacturer recommendation, to answer your question.

I would recommend that you use a higher powered amp than the 120 wpc factory recommendation. The reason being that most speaker damage occurs from over-driving an under-powered amp past it's performance envelope, causing an unstable amplifier condition called clipping. Much more speaker damage occurs during clipping, rarely is a speaker damaged with too much 'clean' power. In other words, you run a much greater risk of damaging your speakers with a 50 WPC amp than you do with a 150 WPC amp.

You should be safe with a 150-200 WPC amp, or more if you choose.


John is correct. Unless you play heavy metal at live venue volumes, it is highly unlikely that you will overdrive your speakers with too big an amp. OTOH, there are many who say that for a given amp design, the lower powered units sound better. I certainly heard that with the McCormack DNA 0.5 vs. 1.0. But the short answer is that those are just guidelines.
I agree that they are just guidelines and would further suggest that they are just arbitrarily assigned values. I doubt seriously if any speaker manufacturer "crash tests" their speakers to see what their limits are. Generally I have seen a range proposed, meaning maybe 10 watts is needed as a minmum for satisfactory results and anything over 300 watts might put your prized speakers in jeopardy.
Unless you have very unusual speakers, you can stop thinking about this topic.
Lastly, I would tell you to call GMA yourself about such things as Roy is better qualified than all of us together to comment on Europas. I'm sure you'll find he is happy to help.
I'll third that. You want plenty of power to avoid clipping if you listen loud at all. Ratings are very ambiguous and mean little as there's no standard.
One problem I've had: in my Analog phono system, I literally blew out a woofer at fairly high volume not from clipping, too much power or music transience but from amplifying a fairly warped record. the wide subsonic excursions finally did in one woofer... anyone else have this problem? Now I monitor visually the woof's while playing LP's to make sure the warps are not too out of line and if too much then lower the volume. Also have to make sure the vol. is down when lifting the tonearm. A really powerful high current amp can do some damage in these areas.