Soprano : A 440 Hz
Bass : A 220 Hz
Contra Bass : A 110 Hz
Sub Contra Bass : A 55 Hz
This is the second lowest A you could play on the clarinet. There is an A one octave below. On the Sub Contra Bass that would be 27.5 Hz. If you concider that the clarinet descends to concert D-flat, C or even B-flat, (I don't know if this instruments really do) we would come up with a frequency of about 14-15 Hz. Not many people would be able to hear this frequency. In Sweden the mains supply is 50 Hz.
Please make sure that the plumber guy doesn't take this instrument for a pipe and install it in your bathroom. ;-)
The Sub Contra Bass is said to be constructed in both metal and wood. To my knowledge there is only one constructed. Have a look at the Contra Bass clrainet page for pictures and more details.