Traditionally, it's been remarkably difficult to properly find dead spots in a speaker's output, but scientists at the British National Physical Laboratory have started using lasers to accurately visualize the sound patterns. The researchers use a laser vibrometer designed for studying mechanical vibrations to shoot through the air in front of the speaker — the sound waves create minute air-pressure changes, causing deviations in the laser's path. A reflective board bounces the laser beam back, where the vibrations are scanned and analyzed at a rate of 100,000 frames per second. This produces a visual representation of how the sound comes out of the speaker, and where it's being interfered with.
A speaker runs across a wide frequency range in the video below, and you can see the sound move from the woofer to the tweeter, and how they interact — including a prominent interference spot. Companies like Audyssey deal with acoustical problems by taking a microphone all around the listening area, figuring out where there's problems, and creating a special filter — and laser system would be remarkably less labor intense. The National Physical Laboratory deals with both the public and private sector, and is actively targeting speaker manufacturers with this, so hopefully we'll see this technique commercialized soon.