OK, here's my opinion regarding stethoscopes.
If all you're doing is checking blood pressures and making sure somebody's got blood going 'round and 'round and air going in and out, any old stethoscope will do. However, if you're truly interested in hearing subtle cardiac murmurs and other elusive biological sounds, you should only consider stethoscopes that have a floating (not "tunable") diaphragm, a traditional bell, and dual-lumen tubing.
Interestingly, this excludes all
stethoscopes currently manufactured by 3M Littmann, the market leader. 3M has gradually incorporated the tunable diaphragm (originally offered only on the Master Cardiology) into all of its stethoscopes except the single-lumen pediatric and infant models, resulting in one of the most uniformly mediocre and overrated product lines in the industry.
Why do I dislike tunable diaphragms so much? In short, because they muffle sounds, and because most people don't know how to use them properly. In order to use a tunable diaphragm as a diaphragm (which is what you'll want to do most of the time), you have to press firmly
on the chestpiece. Uneven pressure will result in muffled sounds. Firm, even pressure is the only way to clearly hear higher-pitched sounds. This is best accomplished on a flat surface. However, most patients' bodies are not flat, making it virtually impossible to maintain firm, even pressure as you move your stethoscope around. Unfortunately, if you only apply light pressure (which is what most people do most of the time), all you'll hear are boomy, muffled sounds. Contrary to 3M's advertising, it's nothing like what you'll hear using a traditional bell, where the low-pitched sounds are crisp and distinct. To further confuse things, correct use of a traditional bell demands light pressure, as firm pressure essentially turns the skin into a diaphragm. In short, tunable diaphragms are a recipe for disaster when you're trying to learn how to listen, and (IMHO) are partly to blame for the poor auscultation skills of modern doctors.
If you can find an older (pre-tunable diaphragm) Littmann Cardiology or Cardiology II (not SE) model, grab it...they're among the best stethoscopes ever made (Abella M, Formolo J, Penney DG. Comparison of the acoustic properties of six popular stethoscopes. J Acoust Soc Am 1992 Apr;91(4 Pt 1):2224-8). 3M discontinued the Cardiology II in 1994. However, with a little patience, you should be able to find one on eBay. If it's worn, you can send it to 3M for refurbishing, and it'll come back looking like new.
The original Hewlett-Packard (later Philips) Rappaport-Sprague is an old favorite with excellent acoustics. It's a little bulky, but the sound quality is superb. Unfortunately, it's been discontinued as well. These occasionally turn up on eBay, and replacement parts are still available. The cheap Spragues offered by other vendors simply don't compare, and are to be avoided at all costs.
Here's a list of currently-manufactured stethoscopes that are worth checking out. If you can, try them out before you buy. Everyone's ears are different, and what sounds good to me might not sound good to you.
ADC 602 Cardiology (www.adctoday.com
Allen Series 5 (www.allenstethoscopes.com
DRG PureTone Cardiology (www.doctorsresearchgroup.com
GRx CD-25 Advanced Cardiology (www.grxmedical.com
Heine Gamma C (www.heine.com
Magna Fortis Metacardia LT (www.magnafortis.com
MDF 797 Classic Cardiology (www.mdfdirect.com
W.A. Baum Cardiology (www.wabaum.com
Welch-Allyn Harvey Elite (www.welchallyn.com
Welch-Allyn Harvey Double Head (www.welchallyn.com
The old saying, "The most important part of the stethoscope is what's between
your ears" is certainly true. Unless you know what you're listening to, the best stethoscope in the world isn't going to help you. However, if the sounds don't make it to your brain in the first place, your knowledge is wasted. So, if you really want to master cardiology, ditch the Master Cardiology and get yourself a proper stethoscope. You'll be glad you did.