General Audio and HT Information:How
much power do I need for my speakers? It
is important to have enough power to play at the volume level you desire without
distortion. If you play speakers more loudly than the volume the amplifier can
cleanly produce, the amplifier will produce overload (clipping) distortion. The
sound will become compressed, strained, and in extreme cases, obviously
distorted. This distortion is actually non-musical additional
energy and since it is concentrated in the high frequency region where the
speaker is least able to handle it, the tweeter’s voice coil can be burned in
extreme cases. Driver damage in general is usually the result of having
inadequate power rather than having too much. If your system does not play as
loudly as you would like without becoming distorted, you need a more powerful
amplifier. There
are three almost equally important factors that determine how much power is
needed for a given situation. In order of importance they are: 1.
The volume level desired Each
of these factors can make a 10 to 1 difference in the power required. In
the real world, if all 3 factors are average, about 50 watts/channel is
required. Each factor can raise or lower this amount by a factor of about 3.
Average values for each are: -
volume level of 88db SPL The
first factor is the most difficult to analyze or objectively determine. There
are different ideas about what is “loud”. Some people do want to play music
above a sound pressure level of 88db and some do not want to play music above 88db. Usually, people who like to listen only at low levels can decrease their
power by a factor of 2. People who like music at very loud levels, even if only
occasionally, should increase their power by 2 times or more. A
speaker with a low 84db/w-m efficiency will require twice the power of an 87db
speaker and one with a high rating of 90db/w-m will require only half the power
of an average speaker. Usually high efficiency can be obtained only by trading
off sonic quality-there are very few speakers that provide a very high level of
both. A
small room will need less power for a given loudness level than a large room. A
very small room of 1000 cu ft (11’x11’ x 8’ ceiling) will usually require
only half the power of an average room. A large room of 6000 cu ft (20’ x
30’ x 10’ ceiling) will usually require twice the average power. If the
listening room is connected to another room by a large open area, the required
power will increase-but not by the amount of the combined room volume. If the
room has a “dropped” ceiling with lightweight panels, the ceiling will be
almost transparent accoustically. In this case the space above the ceiling
should be added. If the panels are heavy they will act more like a solid
ceiling. With
all this in mind, a person who likes to play music only at lower levels, has a
small room, and who has fairly efficient speakers can get the performance
desired with only 20 watts. Where as a person who sometimes likes to play
loudly, has low efficiency speakers, and a large room may need 300 watts or
more. Also
remember that how loud your system plays has nothing to do with the position of
your volume knob. Source components,
such a CD players and tape decks, as well as recordings themselves, can all have
different output levels. This means that to achieve the same volume level for
each source, your preamp’s volume control may need to be set at different
position for each source. For example, when some high output CD players are used
with lower power amplifiers, maximum power can be reached with a volume knob
setting as low as 4 on a scale of 10. Also to note, there can be a large difference in the sonic performance of two amplifiers of equal power, and a smaller powered amplifier can sound superior to a larger powered amplifier. Most will be happier with a 50 watt amplifier of high sonic quality than with a 200 watt amplifier of mediocre sonic quality. There is no substitute for listening to make your amplifier decision.
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