Weatherproof Bass Blockers for 4 Inch Speakers Installer 3 Pack Installer Jobber 3 Pack Guaranteed +/- 10% Tolerance, Weatherproof Axial Leads, Non-Polar 10% Capacitor Blocks Sounds Below 2.8kHz (14 mfd @ 4 ohm), Reduces the drive signal 4" Speaker Size Recommended although can be used for any application. The speaker size is our recommendation please be sure you want to block sounds below 2.8kHz.