Read JBL DS 120 User Guide / Operation Manual online
3
4. Use PVC or ABS pipe for ports. Keep in
mind that the openings at either end of
the port must be at least one port
diameter away from any obstructions,
including filling material inside the box.
Rectangular vents can be used as long
as the cross-section surface area
matches the recommended port-area
values in the enclosed data sheet.
the port must be at least one port
diameter away from any obstructions,
including filling material inside the box.
Rectangular vents can be used as long
as the cross-section surface area
matches the recommended port-area
values in the enclosed data sheet.
Power-Handling Limitations
The power-handling capability of any
woofer is related to both its ability to dis-
sipate heat and maximum excursion lim-
its 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.
woofer is related to both its ability to dis-
sipate heat and maximum excursion lim-
its 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.
• 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 distort-
ed at higher volumes usually indicates
that the amplifier is clipping and is
being asked to deliver power beyond
its rated power.
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 distort-
ed at higher volumes usually indicates
that the amplifier is clipping and is
being asked to deliver power beyond
its rated power.
• Infinite baffle or “free air” mounting
applications allow for greater cone
excursion than subwoofers mounted in
an enclosure. In order to compensate,
recognize that the power-rating value of
the subwoofer will likely be half its
rated power in this application.
excursion than subwoofers mounted in
an enclosure. In order to compensate,
recognize that the power-rating value of
the subwoofer will likely be half its
rated power in this application.
Sealed enclosures exert the most control
over the motion of a subwoofer because
the air 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 larger than its compliance
(Vas), the subwoofer will perform as if it
were in an infinite baffle installation.
over the motion of a subwoofer because
the air 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 larger than its compliance
(Vas), the subwoofer 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 tuning reinforcing the sound out-
put of the speaker. Vented boxes do not
provide adequate woofer control when
driven below the port tuning range, so
proper design is important. A vented
bandpass box will have the lowest overall
cone excursion at the expense of limited
bandwidth.
the lowest amount of excursion for the
amount of sound output. This is a result
of port tuning reinforcing the sound out-
put of the speaker. Vented boxes do not
provide adequate woofer control when
driven below the port tuning range, so
proper design is important. A vented
bandpass box will have the lowest overall
cone excursion at the expense of limited
bandwidth.
• Study the excursion curves on the
enclosed JBL Decade 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
recommended 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 overex-
cursion (i.e., where the voice coil leaves
the gap) that can eventually damage
the speaker. For additional help with
this issue, please contact your autho-
rized JBL dealer.
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
recommended 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 overex-
cursion (i.e., where the voice coil leaves
the gap) that can eventually damage
the speaker. For additional help with
this issue, please contact your autho-
rized JBL dealer.
DS100/DS120 OM 7/14/98 1:32 PM Page 3
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