It's a night and day difference. My v2 tweeters sounded harsh at medium volume. They were breaking up. They weren't airy either. The v4 sound very composed, dispersive and airy.
They can take more power (larger motor structure) and dissipate heat better with a die cast aluminum vs. plastic faceplate. The plate has a tapered horn built in which improves off-axis response above I think 12KHz or so. The chamber on the rear of the tweeter is larger which allows for better magnitude and phase response at the cross-over frequency.
Andrew did a great job on it. Ian did a great job with speaker integration.
