Will a 47uf 100 volt cap block 100 hertz

It all depends what load to ground (speaker impedance) this cap sees.

A 47uf in series will have to see a load to ground after it of 30ohms to be -3db at 112hz.

If the load is 15ohms to ground then it's -3db at 56hz.

If the load to ground is 60ohms then it's -3db at 224hz.

For yours
If the load is 8ohms and you want -3db at 100hz you need a 200uf series cap.
If he load is 4ohms then you need 400uf.

Cheers George

Almarg

Oops! brain fart, thanks for the heads up, too late to swap.

Cheers George