Manufacturers use all kinds of impressive terms to describe speaker power: program power, peak power, power capacity, and so on. But what can a speaker actually handle, and how much amplifier power do you really need?
In reality, there is no speaker that can continuously handle more than about 300 watts. Surprised? The efficiency of cone speakers is only about 1 to 3%. This means that 97 to 99% of the input power is converted into heat.
This heat comes from friction in the cone suspension and the spider, heat generated in the voice coil, and air friction. For example, if you input 300 watts, about 290 watts is turned into heat—heat that is also difficult to dissipate inside the speaker enclosure.
A small portion of that heat can escape through the front of the speaker, but most of it accumulates inside the cabinet. You might say, “But what about bass reflex enclosures? Aren’t they open?” In practice, the air inside the cabinet remains mostly stationary, with only minimal exchange with outside air. With a well-designed port, this effect is nearly negligible.
So how does power really work? It’s actually quite simple. Music has a dynamic range of 10 dB or more, and that’s where the trick lies. The decibel scale is logarithmic: an increase of 10 dB requires ten times more electrical power. A 20 dB increase is perceived roughly as twice as loud.
An amplifier delivering 10 watts will sound twice as loud (in perceived volume) at 100 watts, and three times as loud at 1000 watts.
Imagine a symphony orchestra: the average level might be around 80 dB, but peaks can reach 110 dB.
To reproduce this faithfully, you need to handle a large dynamic range. If 1 watts are needed to produce 80 dB in your living room, then theoretically 10 watts are needed to reach 90 dB (twice as loud), 100 watts for 100 dB (3 times as loud) and so on. This shows how challenging accurate reproduction can be at 4 times as loud (110 db) is almost impossible to achieve with standard amplifiers.
Most above-average speakers reach their limits around 115 dB. The trick lies in the efficiency of the loudspeaker, xx db/w/meter.
The solution lies in using multiple drivers (speakers in one enclosure). For example, if one bass speaker can produce a maximum of 98 dB/w, adding a second one gives you about 3 dB more. The efficiency increases, but the amplifier must deliver twice the power because the impedance decreases “You may still remember it from physics: you can deliver twice as much power in watts when the resistance is halved.” (from 8 tot 4 ohms)
So, if you want realistic sound reproduction with sufficient headroom, (headroom: how much does my amp has left over in watts before distortion) you can assume that larger speakers and more powerful amplifiers are the way to go.
But if you are an owner of that very nice sounding 10 watt Tube amp, you need to have high efficiency loudspeakers, say: over 90db/w meter to get the best result, but, to reach that symphonicall orchestral peak of 110db, you need to buy speakers from 95/db/w to reach that peak.
“If you are a critical listener, the advice is: do not buy a powerful power amplifier combined with a small or inefficient loudspeaker. The amplifier may deliver its power to the speaker, but the speaker will mainly convert that power into heat and distortion. A sensible choice is a high-efficiency loudspeaker.”
“Every part of the high-end hi-fi chain can be optimized, and at VDH we have carefully considered this. In this case, the conductive material used in the cables can reduce the resistance of the speaker cable. This improves the power delivery of the amplifier and also benefits the so-called headroom.”
Henk Hoogeveen
Former pro-audio sound engineer.
