The term "fast" is used a lot to describe tight, punchy response and is usually associated with 10" drivers. Conversely, "slow" is used for 15" drivers along with the terms "muddy" and "inarticulate." Joris if you are reading, what do you think of an aribtrary number representing the ratio of the Bl product (force) to the Mms (mass) as an indicator of tight response? It seems to me that a higher force-to-mass ratio would exert tighter control and improve transient response. I added a column to my Musician's Reference spread sheet for this ratio. Sorting in descending order, it is very apparent that 10" drivers have a much higher ratio (more force applied to less mass) than do the larger drivers. The first 15" driver is the JBL E-130 which doesn't surprise me, considering how efficient it is. The JBL E-140 and E-145 drivers are above both the average and median ratios, implying they are fairly punchy. The Carvin PS10 10" drivers scored much higher than average. I also noticed how the true subwoofer drivers are at the very bottom of the ratio. In my own rig, I noticed a signficant increase in punch when I added a pair of JBL E110s and crossed them over at 100 Hz. No mud.