First Order Crossovers: Pros and Cons

To many Doppelspaten's while trying to figure out the Doppler Effect! ;-)

Roy, you use an upward facing bass port on your C-3's - can you tell us if any of the air pressure principles you outline in Tannoy's design would have any negative bearing on the C-3?

Also there are some "officianados" on this site that claim ported speakers do not reproduce bass frequencies with the same level of integrity as sealed designs. The claim is that many designers use ports to exagerate bass output because; either a.) a sealed box has to be so much larger to reproduce a similar frequency level, which ultimately leads to increased cost and WAF issues b.) the designer cut costs by crafting an inferior cabinet to hold the bass driver.

At first glance there seems to be some merit to their sealed design argument, however to your knowledge is this position supported by math or physics? Did you come to a crossroads in your design theory regarding sealed vs ported designs and if so, how did you arrive at a ported design for your speakers?

Let me explain my porting question on GMA's C-3's relative to time and phase coherence. I have no idea if there is an audible issue with the C-3's design and based on Roy's published specifications there is nothing to suggest what I'm about ask actually takes place, nevertheless I thought I'd throw it out there to elicit a response regarding the porting theory behind this design.

In GMA's C-3 the bass port is firing in an upward direction, directly below and slightly behind both the midrange and tweeter, with a clearance of perhaps 4-5 inches. I'm wondering if conceptually there could be some type of Doppler effect taking place with the placement of the port relative to the midrange and tweeter that could slightly alter the phasing or timing of these drivers? Although there is no high-frequency whizzer cone riding on top the woofer; as in the Tannoy, in theory as the woofer moves backward and air is pushed out of the port, is it possible that this change in air pressure could somehow modulate the midrange and tweeter response by disturbing their wave lengths? Alternatively, when the woofer pushes forward, does the port suck in enough air to also disturb the wave length of the midrange driver and tweeter, thereby throwing off time and phase coherency?

Skrivis - Srajan Ebaen has recently written about the "Doppler Effect" in his quasi review of the Zu Cable Druid speaker. The following is an excerpt in which he mentions the Doppler Effect.

"Conceptually, single-driver loudspeakers (this one's technically a 1.5-way) are phase and time coherent though the Doppler effect could be cited when you consider how the high-frequency whizzer cone rides atop the woofer. The day-to-day observable Doppler effect occurs with police or fire sirens. They sound higher pitched as they approach (wavelengths shorten), then successively lower as they pass us and recede into the distance. Theoretically, each time the Druids' woofers move forward, they modulate the tweeter response. Once you do the math and consider the average stroke of this 10" driver -- to calculate possible tweeter response deviations in terms of how woofer distance traveled equates to wave length -- it seems more of a conceptual than audible problem. Still, it's only fair to mention in this context and avoid painting a picture of theoretical perfection. Clearly, if the single-driver ideal were the one perfect solution, nobody would bother with multi-driver designs. The market place rather demolishes any such notions in one brief instance. As usual, it's about priorities. What type of compromises are acceptable to facilitate certain concrete gains that matter more to you than that which is sacrificed?"

Here is the link: http://www.6moons.com/audioreviews/zu/druid.html