Duke, I've heard the CAR's ( or is it KAR's ?? ). I've commented here that i thought they sounded pretty good for a vented system. I do have to say that using very efficient drivers does give you a BIG advantage though when it comes to tuning vents. This has a lot to do with the gains achieved due to a more efficient motor design and the lower excursion rate that results from it.
If one uses a lower to average efficiency driver and uses vents, the driver will go from minimum to maximum excursion capabilities over the operating volume range. This is due to the increased drive levels that one must apply to achieve the amount of pistonic displacement necessary to achieve high volumes with a low efficiency driver. As such, this changes the amount of air and the associated turbulence that occurs in a vent over a pretty wide spl range. As such, most ports / boxes are a compromise that run most efficiently at one specific volume range. Going below or above that results in too little flow velocity or too much through the port. The sonic result of such a design is sluggish bass that lacks damping and / or increased port noise and "one note thud". Being able to find optimum performance on most ported designs typically means that you have a small window of listening levels. Anything below or above that results in slightly different tuning and the decline of performance.
Sealed systems never run into that specific problem as there is always a specific amount of "air spring" or "internal pressure" inside the box. As such, damping remains pretty consistent regardless of volume levels. Sealed boxes do have their problems though in that they do typically require far greater excursion out of the driver, which typically results in greater distortion. Obviously, the driver has to handle a lot of power to make long excursions too, so that is another drawback. Like anything else in audio, we pick our trade-offs and try to minimize the damage done.
Using a high efficiency driver with a port gives you the advantage of having a driver that will not have to "throw" or produce as much excursion to play as loudly. Since the driver will not have to produce as much excursion to perform over the range of average listening levels that most people use, one can more precisely tune the port for maximum flow velocity and damping. This results in a more linear performance over a wider range than what a typical port / low to mid efficiency driver combo would offer. There are times that the high efficiency / port combo may become "destabilized", but a good designer will strive to minimize that effect and / or place that range outside of what most users will run into.
The advantages of working with a low production / high quality manufacturer can come into play IF one really wants to fine tune their system. One can literally design a vented system to perform optimally if most of the variables ( drivers being used, listening room size, spl's required, type of music, etc.. ) are known. By factoring in how much power it will take to pressurize the room to achieve the average listening level and knowing the efficiency of the speakers, one can literally calculate how much air would be moving through a port and size it accordingly. This would maximize port velocity while minimizing such variables as port noise ( chuffing ), lack of damping, etc.. Obviously, this design would be even more specialized than the average "compromise" and may not work the greatest in other rooms or listening situations. Such are the perils of using a port and trying to be as "precise" as possible.
A newer port design on the market ( it's really been out for years but is just making it into commercial products ) is the "Aeroport" or similar products. This design is exactly what its' name indicates i.e. a port that is aerodynamically designed. Rather than using a straight tube, both ends are flared. The bend radius is reduced, which increases flow velocity through the port, minimizes port stalling, DRASTICALLY reduces "chuffing" or "port noise" at high volumes, etc... One can use a slightly smaller diameter port to maintain low spl flow velocity and damping and still not run into port compression ( stalling and chuffing ) until a very high spl was achieved. Since most people are not pushing their systems that hard, it should offer marked advantages and looks like a win / win situation if properly implimented. Sean
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