>04-28-12: Johnnyb53
>More or less true, but bear in mind that a 12" woofer has *at least* twice the mass of a 9.5" woofer, and perhaps more because it will probably have a thicker cone to counteract breakup. All things being equal (which they're not), a 12" woofer has 3.5 times the mass of a 6.5" woofer, so by your reckoning it would need a magnet 3.5x as powerful.
The 12" driver's excursion and acceleration requirements are also scaled down to create a given frequency + SPL sound wave compared to the 6" by the ratio of their surface areas. Using the Peerless XLS12 and Seas L16RN-SL as examples it's less than 1/4 the distance and acceleration (483 cm^2 for the Peerless XLS 12 vs. 104 cm^2).
I don't have the magnet strength on the Peerless; although if you compare the Seas L26RO4Y 10" driver (BL 18, 1.1 Tesla in the gap, mms 173g, Sd 363 cm^2) to the L16RN-SL (BL 6.2, .88 Tesla, mms 14.8g, Sd 104 cm^2) with force / mass * Sd to make a meaningful comparison the big driver comes out ahead at 39.93 vs 37.44 for the small.
I could also point out that the smaller driver probably has a higher resonance which in turn means more group delay from the inherent minimum phase response of a driver+enclosure combination although all this would still remain irrelevant for purposes other than internet arguments based on inapplicable science.
Your brain needs a lot more than a fraction of a cycle to pick up a sound and assign direction, and where transients are of interest they split into low and high frequency components which are sent to the tweeter courtesy the cross-over network.
>Maybe, maybe not. However, speed aside, the the large driver still has a disadvantage in driver blending because its dispersion pattern turns into a beam at a lower frequency. A 12" cone starts beaming at 1100 Hz; a 6.5" at about 2K Hz. Guess which is easier to cross over to a tweeter at 2K Hz while maintaining uniform dispersion?
Those are arbitrary numbers (it's a continuum - you could say that the 12" driver is 6dB down at 45 degrees off axis by 1400Hz, or -3dB by 900Hz) although the 12" would work better provided that you didn't do anything contraindicated by decades of subjective listening impressions and research.
You can put the tweeter on a wave guide so the directivity matches the 12" driver at the cross-over point. This produces much smoother spectra in the side-wall first reflections which contribute to perceived timbre than the 6.5" driver with narrowing dispersion crossing to a 1" tweeter on a non-waveguide baffle which has near uniform radiation across its front hemisphere.
You can use a more conventional 3-way design with a relatively small cone or dome midrange between woofer and tweeter with a cross-over to the midrange at a few hundred hertz. This produces more nautral sounding side-wall/front-wall/ceiling reflections with improved vertical polars coming from reduced driver spacing compared to the 6.5" 2-way.
You can use a mid-tweeter that accomodates a very low cross-over point. For instance the 1.6" Aura "full range" driver does well at the sort of moderate SPLs a 6" mid-bass limits you to with a 1KHz cross-over (the big voice coil does roll-off at high frequencies, although most of us can't hear that and where we can it can be compensated for in an active cross-over).
Of course traditional 2-way cone and dome speakers aren't worth considering where your first priority is sound quality especially where you do not limit yourself to simple music at background listening levels. They vary from each other in how their mediocrity comes out (inaccurate timbre, low SPL capability, limited bass extension) but as a listener you're better off skipping the genre and building or buying something excellent. OTOH as a speaker manufacturer this is OK because people buy based on appearance and price and as a competent cabinet maker you can make building such speakers a full-time job. Cabinet/furniture makers with more refined ears do use low cross-over points with extra-beefy tweeters like the Seas Millenium for better directivity matches at the cross-over point so the results needn't as bad as they can be.
There's a lot of latitude in how you get to "excellent" with the many possibilities producing sound more similar than different. You can use acoustically small cones and domes on acoustically small baffles with uniformly broad dispersion like the B&W Nautilus or Linkwitz Pluto (still somewhat dynamically limited). Wave guides work well to bring the high frequency dispersion from acoustically small drivers in line with the lower midrange for moderate dispersion as in the Revel Salon 2 or more directivity like the Gedlee designs or Danley Synergy Horns. Acoustically small dipoles work great where cancellation from the sonic short circuit between front and rear waves brings directivity at lower frequencies in line with higher for each driver like John Krevosky's NaO Note or Siegfried Linkwitz's Orion.
FWIW, in 2004 Sean Olive produced a pair of numerical definitions for "excellent" which correlate exceedingly well with blind subjective speaker rankings. Monotonic off-axis response curves and bass extension are significant where physics dictate conventional 2-way cone and dome speakers lack at least one.
Any one interested in sound reproduction owes it to themselves to read _Sound Reproduction: Loudspeakers and Rooms_ by Floyd Toole where chapter 20 (Closing the Loop: Predicting Listener Preferences from Measurements) is especially relevant. While not "light reading" at 500 pages it's a lot more digestible and affordable than the decades of JAES and other papers it summarizes.
For more conventional designs on more finite budgets you can do better with more less expensive drivers than fewer pricier ones, especially where the speaker maker adjusts the cross-over to compensate for the manufacturing variations (Dunlavy did this) you get at lower price points since polar response has a lot more to do with how close you get to "excellent" than other metrics like on-axis response flatness and stored energy. It's nice to have a scientific explanation for what you hear or suggestion on what to audition next.
If you want a thin spouse-friendly cabinet at the same time you can do it with a side-mounted woofer or W-frame dipole.
(You can tell I'm a bit cranky - I spent my day periodically staring at the boards which will become my next two pairs of cabinets contemplating which grain and figure combinations will look best where instead of making sawdust).
