Here is an excerpt (page 3) from Stereophile John Atkinson's interview of John Dunlavy on sealed vs. ported enclosures. Many of you know of Dunlavy as one of the greatest speaker designers of all time, and his designs were known for their incredible accuracy, both in terms of flat frequency response and accurate reproduction of an impulse response.:
Atkinson: I've found that most big loudspeakers that I've measured for Stereophile do boom. I assume that trying to achieve well-damped low-frequency behavior is why you use sealed-box alignments for all your designs, without a port to be found.
Dunlavy: Pretty much so. As soon as you add a port, the Q goes sky-high. For a port to efficiently add to the direct sound being radiated by the driver, it had to delay the energy a full 180 degrees at that frequency where it's augmenting the frontal radiation. But that port can only radiate 50% of the energy per unit cycle. Then, the next half-cycle, it radiates 50% of the remaining energy, so you have this long decay time. That's why, when you look at the impulse or step responses of speakers designed according to this approach, they look terrible. In fact, would you buy a CD player, would you buy an amplifier, would you buy any other component in your system that exhibited that kind of response? Yet people do. And they love their systems!
I played string bass two to three nights a week for nearly 22 years prior to moving to Australia in 1981. And I can tell you, the biggest problem for a bass player playing along with even a four- or five-piece combo is playing the bass loud enough to where it stands out. It's just not a loud instrument. But [to accurately reproduce the sound of the string bass] you need a loudspeaker with a "solid" response, by which I mean time-coherent, very-low-Q bass with a minimum of boom. One has to avoid the use of ported enclosures. And as soon as you abandon ports, you must have damped cavities behind the woofer of sufficient size that the speaker can reproduce that low-end bass with a natural-sounding Q.
The entire article is here: http://www.stereophile.com/interviews/163/index.html