DS100/DS120 OM 7/14/98 1:32 PM Page 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,Sealed enclosures exert the most control
including filling material inside the box.over the motion of a subwoofer because
Rectangular vents can be used as longthe air acts like a spring against the
as the cross-section surface areamotion of the woofer cone. Larger boxesY Study the excursion curves on the
matches the recommended port-areaY Voice-coil overheating and burning, dueallow for more excursion, thus providingenclosed JBL Decade Series data sheet
values in the enclosed data sheet. to overexcursion, are often caused bymore low-frequency output for theand note the differences for different
overdriving an amplifier into Oclipping.�amount of power used. When placed in aenclosure applications. The type and
Power-Handling LimitationsA severely clipped signal, or squaresealed box larger than its compliancesize of box used will produce different
The power-handling capability of anywave, contains nearly twice the power(Vas), the subwoofer will perform as if itexcursion demands on the enclosed
woofer is related to both its ability to dis-of a clean sine wave at the same level.were in an infinite baffle installation.subwoofer and, consequently, different
sipate heat and maximum excursion lim-Bass that sounds broken up and distort-levels of power handling. As long as
its of its cone. Once the speakerOs voiceed at higher volumes usually indicatesVented and bandpass enclosures haverecommended parameters are used,
coil moves outside the magnetic gap,that the amplifier is clipping and isthe lowest amount of excursion for thethe subwoofer will perform properly in
power can no longer be converted intobeing asked to deliver power beyondamount of sound output. This is a resultits enclosed environment. However,
motion and all the amplifierOs power isits rated power.of port tuning reinforcing the sound out-any design deviation may result in less
converted into heat in the voice coil. ThisY Infinite baffle or Ofree air� mountingput of the speaker. Vented boxes do notthan optimum performance, and may
voice-coil heating is the largest detrimentapplications allow for greater coneprovide adequate woofer control whenalso subject the subwoofer to overex-
to speaker longevity, so overexcursionexcursion than subwoofers mounted indriven below the port tuning range, socursion (i.e., where the voice coil leaves
should be avoided. Since speaker-conean enclosure. In order to compensate,proper design is important. A ventedthe gap) that can eventually damage
excursion is different for each type ofrecognize that the power-rating value ofbandpass box will have the lowest overallthe speaker. For additional help with
enclosure, power handling is different forthe subwoofer will likely be half itscone excursion at the expense of limitedthis issue, please contact your autho-
each enclosure.rated power in this application.bandwidth.rized JBL dealer.
3 |