What is one way to isolate a microphone from external vibrations?

Vibration from external sources are a real problem for good quality recordings. There are many solutions, most of them costing a significant amount of money although not all solutions need to be expensive. Here are a few options and ideas.

Generally, the bigger the microphone, the more resistant it is to vibration. The same tends to be the case for heavy microphones. Hand holding most microphones will generate noise so avoid holding or touching the mic if possible. While on the choice of microphones, cheap microphones

Vibration is carried effectively through rigid connections from a floor (or other mounting point) to the microphone. Fitting the microphone into a suspension mount will break the rigid connection but to buy a commercial suspension mount can cost several hundred dollars. It's quick and effective if you have the budget.

The cheap alternatives:

Cheap idea 1

Wrap foam around the feet of the microphone stand to make a flexible support for each of the three feet. That will eliminate a large amount of the vibration although the stand is of course less stable than it was. Typical cost - 25c.

Cheap idea 2

Hang the microphone from a suitable point on a ceiling. Two suspension points will help to stop the microphone rotating. Use a slightly elastic cord as the suspension and structure borne noise will be reduced. Typical cost - the price of a bit of string.

Cheap idea 3

Make a suspension mount - Take a look at the link below for an example of them. In particular, look at the one titled "H30". To make your own, take a tube two or three times the diameter of the microphone and about 3 inches long. A short length of plastic waste pipe is ideal. At each end of the tube, drill 4 holes equally spaced around the tube (i.e. at 90 degree intervals) The holes should be about 3mm / 1/8" diameter.

You will then need a length of elastic or rubber. It needs to be fed through the holes to provide two loops at each end of the tube. The tension will need to be adjusted so that the elastic loops are stretched when the body of the microphone is slid through each pair of loops.

The last operation is to drill a final hole to allow the tube to be mounted to the microphone stand. Ideally, use a microphone clip that allows the tube to be firmly fixed but also allows adjustment of the angle.

Once the mic is in place, noise should be significantly reduced but experimentation will be needed to get the right tension on the elastic. Too tight and noise can be carried through the elastic. Too loose and the microphone won't be secure.

Typical cost - a few dollars for parts and an hour or two of time.