Here's BP1Fanatic's 55Hz 1/4 wave tapped pipe as the lower end of an E-drum speaker

[freddi]

GRS12PT - sealed box on top with old Beta8CX/APT50/APT3 - series network 3mH/30uF from tapped pipe to 8CX woofer - 0.47mH on 8cx woof - 3.3uF.0.3mH on APT50 - some series attenuation w. some C bypass on CD.

Source = Flamma Drum/Loop mini pedal /Fosi TPA3255 mono amp.

Don't know what forum it fits ;^)