Cómo bajar la respuesta en frecuencia de un altavoz: Vented vs. Non-Vented Woofers. ¿Buena idea?

Question:

I'm looking at the new Pioneer SP-BS22-LR bookshelf speakers for a 5.1 setup. These speakers are rated from 55Hz to 20kHz using a 4-inch driver. Can a 4-inch driver really deliver that kind of low-frequency performance? ...

Another design element that extends the bass response of the speaker is the woofer's vented pole piece. For those who might not know this term, the pole piece of any dynamic-speaker driver is a cylindrical object around which a coil of wire called the voice coil is wound. The pole-piece/voice-coil assembly is attached to the rear of the dust cap at the center of the diaphragm. As an audio signal flows through the voice coil, it creates an oscillating magnetic field that interacts with the static field of the permanent magnet that surrounds the voice coil, pushing it—and the attached diaphragm—back and forth, thus converting the electrical audio signal into acoustic sound waves. The pole piece is made of a material with high magnetic permeability and serves to focus the static magnetic field.

In the SP-BS22-LR, the pole piece is vented behind the dust cap, which lowers the nominal resonant frequency of the system and increases the mechanical Q factor, a measure of the losses at resonance—a higher Q factor means less loss and improved bass. Without venting, Jones says, the trapped air behind the dust cap impedes the diaphragm's motion, reducing its efficiency and increasing its nominal resonant frequency as well as distortion...

Two P-Audio Woofers. Note the cast frame, vented pole piece and reinforced paper cone.