It takes more watts to amplify low frequencies that it does to amplify higher frequencies.  That is why a 35 watt guitar amp will almost make you deaf but it takes a 400 watt bass amp to make your ears bleed.  The more watts you have in your bass guitar amp the better the rich full bass sound you will achieve.  A bass guitar amp requires a rugged speaker.  When choosing a low powered practice amp, choose one with the biggest speaker.