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reference series
POWER HANDLING LIMITATIONS
The power handling capability of any woofer is
related to both its ability to dissipate heat and the
maximum excursion limits of its cone. Once the
speaker’s voice coil moves outside the magnetic
gap, power can no longer be converted into
motion and all the amplifier’s power is converted
into heat in the voice coil. This voice coil heating
is the largest detriment to speaker longevity, so
overexcursion should be avoided. Since speaker-
cone excursion is different for each type of
enclosure, power handling is different for each
enclosure.
Sealed enclosures exert the most control over
the motion of a subwoofer because the air inside
the box acts like a spring against the motion of
the woofer cone. Larger boxes allow for more
excursion, thus providing more low-frequency
output for the amount of power used. When
placed in a sealed box much larger than the Vas
of the subwoofer, it will perform as if it were in
an infinite-baffle installation.
Vented and bandpass enclosures have the lowest
amount of excursion for the amount of sound
output. This is a result of port output reinforcing
the sound output from the woofer. The mass of
the air contained in the port provides an acoustic
load on the woofer’s cone at the tuning frequency,
and this added mass decreases woofer-cone
excursion. Vented boxes do not provide adequate
woofer control when driven below the tuned
frequency (Fb), so proper design is important. A
vented bandpass box will have the lowest overall
cone excursion, provided a subsonic filter is used.
• Voice coil overheating and burning due to
overexcursion are often caused by overdriving
an amplifier into “clipping.” A severely clipped
signal, or square wave, contains nearly twice
the power of a clean sine wave at the same level.
Bass that sounds broken up and distorted at
higher volumes is usually indicative of an
amplifier that is clipping and being asked to
deliver power beyond its ability.
• Infinite-baffle or “free air” mounting applica-
tions allow for greater cone excursion than
subwoofers mounted in an enclosure. In order
to compensate, the power handling of the
subwoofer will likely be half its rated power
in this application.
• Study the excursion curves on the enclosed
Reference Series data sheet and note the
differences for different enclosure applications.
The type and size of box used will produce
different excursion demands on the enclosed
subwoofer and, consequently, different
levels of power handling. As long as the
recommended enclosure parameters are
used, the subwoofer will perform properly
in its enclosed environment. However, any
design deviation may result in less than
optimum performance, and may also subject
the subwoofer to overexcursion (i.e., where the
voice coil leaves the gap) that can eventually
damage the speaker. For additional help with
this issue, please contact your authorized
Infinity dealer.