Are 13a's dipole?

[jimbill]

Specifically the woofer section.

 

[twich54]

No, just the stat panel

 

[sleepysurf]

The opposed woofers aren't dipoles, but they use some phase trickery to optimize overall bass performance...

From MartinLogan | Expression ESL 13A... Using two 10-inch laser-engineered low-distortion aluminum cone woofers in independently enclosed compact chambers, exclusive PoweredForce Forward™ bass alignment technology controls the interaction between the rear-firing woofer and the wall behind that woofer. With smart phase-shifting logic, we minimize the effect that wall has on bass information that might bounce back into the listening room.

IMHO, the integration of the woofers and stat panel in the newer Masterpiece series is the most seamless they've achieved to date.

 

[MisterB]

As the others have said, the woofers are not dipoles. They use what ML calls "ForceForward" technology. Here's some addition info from a press release from when the new Masterpiece lineup was announced:

"PoweredForce Forward™ Bass Technology combines two MartinLogan audio innovations: PoweredForce, which allows small enclosures to accurately produce massive amounts of bass, and ForceForward, which significantly reduces performance-robbing front-wall bass reflections. PoweredForce Forward bass technology uses an advanced crossover topology with phase timed woofers to minimize destructive reflected energy. By virtually eliminating front-wall bass reflections and working in tandem with the panel, PoweredForce Foward Bass Technology gives you more placement flexibility, and enhances the true audio realism of your sound source."

 

[Brazillnut]

Force Forward is a really useful technology and I get excellent panel/woofer integration from my 11As. IMO, having ARC room correction for the amplified woofers is a game changer. At least it was in my listening room.