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 speakercone 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 applications 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.
