If you don't *usually* have a hearing impairment, Mia, I doubt you have developed one with a stethoscope in your ears. There was a post here several months about not being able to hear through a brand new and expensive stethoscope and lots of good tips were given at that time. One was to go to the Littmann stethoscope web site for tips on using a stethoscope and I guess I would hand that on to you. I was able to link to this web site by putting in www.littmann.com
Also, a stethoscope's ear pieces should face slightly forward (no more than 5 to 15 degreees) as you are looking down on the earpieces when they are held in front of you hanging down. It is easy to put the stethoscope on backwards because it is a little counter-intuitive to put the earpieces in to your ears this way.
Life another poster suggested, different ear pieces do help some folks and that is good. Make sure your diaphragm is clicked into place if you have a dual head stethoscope.
Someone in the other post mentioned getting focused on what you are listening to. I may close my eyes slightly and try to block out other noises or distractions.
When I have a hard to hear blood pressure, I simply palpate the brachial artery (I don't routinely do that) so that I can place the diaphragm directly over the brachial artery, slightly reposition their arm making sure it is not too rigidly hyperextended or too flexed. I move any clothing or blankets that might be interfering, [I will only rarely during the dead of winter on a "well" person even attempt a bp over clothing but what I am saying is remove anything between you and them] and then you listen very closely while or after you palpate the blood pressure. On the hard to hear patient, sometimes knowing where that systolic will kick in and repositioning your stet will give you the edge you need to hear a quiet Karotkoff sound kick in. sometimes I can improve how well I hear by looking down slightly and opening my mouth. On my stethoscope this seems to improve the seal a little better and I may hear heart sounds or karotkoff sounds I was previously unable to hear.
The bottom line is you cannot document what you did not hear and when I cannot hear a blood pressure, I try the other arm OR I document only a palpated blood pressure (documenting that it was simply a hard to hear pressure and there were no other signs of hemodynamic instability).
Doing lots of pressures on lots of patients will improve your deftness and reliability with the procedure and you will have fewer patients you cannot hear over time, but even after 23 years, I still encounter people I cannot hear well on.