A thick 2 ply head with good low end attack. The EQ3 is very well focused and good for live playing situations.
A single ply thick head, the EQ 4 has an internal control ring and a removable muffle ring. The dry vents around the perimeter give it a very focused, low end tone.
This is a popular front bass drum head. It is single ply with dry vents and an internal control ring to help with the low register.