This graph shows what happens when 370Hz is selected with different levels of boost going all the way up to +16 db’s. At 5 db’s of boost, the bandwidth affected by the boost is quite broad but tightens up as boost is increased. One way bandwidth is measured in audio is by it’s Q, which is Frequency divided by the bandwith at it’s -3db point. The lower the Q, the more broad the bandwidth. And the higher the Q number, the more narrow it is. This is in contrast to a “constant Q” design where the bell shape is always the same regardless of level.