HSU high pass filter question

[Mackie]

I'm using the HSU high pass filter (a modified Bass optimizer box) to filter the low frequencies from my main speakers. It has an output knob on the front. The manual says when the box is used as a high pass filter the output knob should be set at the one o'clock position. Is this box actively amplifying the signal? If not why wouldn't the output be nominally set to maximum?

[Dr_Hsu]

The volume control at 1 o'clock has unity gain. At maximum position, the high pass filter will have 14 dB of gain. Noise level will be higher with the added gain. Hence we suggest the 1 o'clock position for most people.