A broken valve spring can most certainly cause low compression.
If the valve spring can't pull the valve completely closed, the compression will be low for that cylinder.
To check for a problem with the valve springs in that cylinder, do a leak-down test.
A leak-down test is where the piston for that cylinder is brought to TDC. Then compressed air is introduced into that cylinder thru the spark plug hole.
If you hear air escape out the tail pipe, there's a problem with the exhaust valve for that cylinder. If you hear air escape out the intake, there's a problem with the intake valve for that cylinder.