Amplifier Power - How Much Is Enough?

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Amplifier Power - How Much Is Enough?

This is a question that is asked almost more frequently than any other.As with most issues in audio,the answer is complex and depends upon the following:

1. Speakers being used- Sensitivity and the impedance curve being critical.

2. Personal preferences of the listener- Type of music listened to and at what output levels.

3. Size of room - To fill a larger room will take proportionally greater amplifier power.

Speakers-
Acoustical output is dependant upon the power of the amplifier used and the efficiency with which the speaker being driven can transform the electrical signal into sound.The term "sensitivity" is a speaker measurement that reveals how much sound (in decibels) is produced at a specified distance, (usually 1 meter), from the speaker when it is fed a specified input signal, (usually 2.83 volts which is equivalent to 1 watt into 8 ohms). Therefore, a more sensitive speaker that has a flat, benign impedance curve (of 8 ohms or more), will produce greater acoustical output with the same specified amplifier power than a less sensitive speaker or an equally sensitive speaker that has a reactive, low impedance modulus. For example, a speaker that is 3 db more sensitive than another will require only half the amplifier power to generate the same sound output.

If an speaker has a sensitivity rating of 85 db @1 watt - 1 meter, to achieve an output of 88 db would require double the amplifier power or 2 watts.91 db output would take 4 watts. For 100 db output of sound, would require 32 watts of power. And if this speaker was rated at 4 ohms, a 64 watt amplifier would be needed to produce 100 db.

By contrast, a 94 db sensitive speaker would require only 4 watts to achieve a 100 db output level. Since most listening in the home environment is undertaken at 85 db or less, it can be clearly seen that only a fraction of a single watt of amplifier power is all that is required for the vast majority of listening. A 100 db output, which is loud, still needs only 4 watts of power to attain. However, it must be emphasized that while listening at an average level of 100 db, during musical passages that are very dynamic with lots of low bass content, many hundreds of watts may be necessary, (albeit for only the duration of a millesecond), to avoid amplifier clipping.

The above example clearly demonstrates how significant the sensitivity and impedance curve of the loudspeaker is upon determining how much amplifier power is necessary.

Personal Preferences of the Listener-

As the above example illustrated, higher listening levels requires greater amplifier power. Therefore, the output levels the listener chooses to listen at, will be critical in determining the amount of power that will be satisfying. The listener who is content at levels of 80 db will need a fraction of a watt while someone who likes to listen at 105 db will be using almost 260 times more power!

Of equal importance is the type of music enjoyed. Full orchestral music, for example, is very demanding on amplifier power in order to reproduce the exceptionally high levels of dynamics coupled with very low bass content (which uses enormous amounts of power). Conversely, chamber music, light folk etc. is usually listened to at lower SPLs and its musical content requires far less amplifier power to accurately reproduce.

Furthermore, some listeners prefer a punchier, gutsier sound presentation than others whose priorities lie more in the area of detail retrieval, imaging etc. For some, visceral impact is mandatory or at least may represent much more of a priority than it is to others. These personal predilections must be factored into the equation of how much power is sufficient.

Room Size -

All things being equal, the larger the room, the more amplifier power required to fill it. The sensitivity rating of a speaker is the measurement of acoustical output at a distance of 1 meter. The further away the listener is from the speaker, the lower the sensitivity. Therefore, a speaker producing 94 db from 1 watt of amplifier power at a distance of 1 meter will produce less sound pressure when the listener is 2 meters away. For a speaker to energize a room of 1000 cubic feet, for example will require significantly less amplifier power than to do the same in a 2000 cubic foot space. As a real world example, at the recent 2001 CES, Coincident demonstrated in a hotel suite of 1872 cubic feet using a 24 watt amplifier. To achieve similiar sound pressure levels and bass impact in another space of 7200 cubic feet, required 3x the amplifier power.With the same 24 watt amplifier in the much larger room, the sound was not as weighty, impactful or as dynamic as it was in the aforementioned smaller environment.

Conclusion-

With easy to drive speakers, like Coincident, many are afforded the opportunity of using low powered amplifiers like SETs with completely satisfying results. For those in a compact room, who listen at moderate levels to jazz , light rock, folk etc, then the inherent superiority of the best SETs will be appreciated. That is not to suggest that SETs are for everyone.They are decidely not. If your musical tastes are focused on big orchestral music, heavy rock, etc., and you listen at high spls in a large listening space, then small tube amplifiers may not be your sonic cup of tea. It would be recommended that a more robust amplifier be used.