They are not cleaner or tighter but the smaller subs 8inch vs 18inch within the same line have different freq responses. The -3db down on smaller subs is usually higher than that on bigger subs. Smaller subs might be able to hit a 60hz note a little easier or naturally than an 18 inch sub and an 18 inch sub would be able to play down to 20 hz a little easier. This does not mean that they both cannot play those notes but all things being equal there is a shift in freq response. Also notice that the Fs is higher on smaller drivers and lower on bigger drivers.