The bell of the stethoscope should next be placed over the apical impulse using light pressure, so you can best appreciate the low frequency fourth sound preceding the higher frequency first sound. You should then use firm pressure on the bell, making the skin into a driaphragm.

This will tend to filter out a fourth sound, but still allow you to hear the higher frequency split first sounds.

Even using this technique, it is at times difficult to differentiate these findings.