Do You Need a Bell on Your Stethoscope?
By Sam Jaquish, RN, CCRN, MBAYou don't need a stethoscope to prove a patient has a heartbeat. A couple of fingers on a radial pulse settles that, and you should be palpating pulses anyway as part of any real assessment. If confirming a heart rate were all a stethoscope did, it would be a lot of tubing for not much information.What the stethoscope is actually for is the information a pulse check can't provide. The faint, low sounds that are easy to walk right past. An S3 in a failing ventricle. The rumble of a stenotic mitral valve. A gallop that changes your read on the whole patient. The bell is the part of the chestpiece built for exactly those sounds, and the usual case against it goes something like this: those findings are rare, I'll probably never hear one, why carry specialized equipment for it?I think that mentality is horrible healthcare. The findings are rare, yes. They're also the ones with the potential to change the plan of care when they are discovered. So let me go through what the bell does, where the modern one-sided chestpiece falls short, and why the low-frequency sounds are still worth building your exam around.
What the bell actually does, in plain terms
It helps to remember that the bell is where the whole instrument started. When René Laennec improvised the first stethoscope in Paris in 1816, sheets of paper rolled into a tube, later refined into a turned wooden cylinder, what he was holding against the chest was in effect an open cup. [1] The diaphragm didn't exist yet and wouldn't for another eight decades, until Robert Bowles patented a membrane-covered chestpiece in 1894. It took until the 1920s for Howard Sprague of Boston to put a bell and a diaphragm on the same rotating head, the dual chestpiece most of us trained on. [2] So the question in this article's title is a fairly modern one. For the first century of auscultation, the bell wasn't a feature. It was the stethoscope.The diaphragm is the flat side, the one with the tight membrane. Pressed firmly, it favors higher-frequency sound: normal S1 and S2, most breath sounds, bowel sounds. The bell is the open cup, the direct descendant of Laennec's tube. Rested lightly, it leaves the skin under the rim free to vibrate, and that free skin is what passes the low, slow pressure waves up the tubing.Here is where I'll be more careful than most articles on this topic, because the acoustic evidence is thinner than the textbooks suggest. The most cited bench study put six common stethoscopes through a frequency sweep from 37.5 to 1000 Hz, the range where nearly all heart and lung sounds live. In the low band, 37.5 to 112.5 Hz, sound was in most cases amplified by the bells and attenuated by the diaphragms, but the differences between chestpiece types did not reach statistical significance. [3] You may also see a much bigger number quoted, that a diaphragm cuts the low end by as much as 30 dB. I'd leave that one alone. It came from a setup that held the chestpiece over a loudspeaker, and when researchers later measured a diaphragm during actual auscultation, using a laser vibrometer on the membrane itself, they found real differences in how the surface moved but no significant filtering effect. [4] A diaphragm resting on skin is not a diaphragm sitting on a speaker, and the difference matters.So what does hold up? The part that turns out to be experimentally validated is not the membrane. It's the pressure. [5] That distinction is the whole argument of the next section, and it's the reason I still personally prefer a stethoscope with a bell.I've gone deeper on chestpiece acoustics in how stethoscope chestpieces really work, so I'll spare you the transfer functions here.
The tunable diaphragm, and what it asks of you
Many stethoscopes people carry now don't have a separate bell at all. They use a single- or double-sided diaphragm that changes its response with pressure. Littmann calls it a tunable diaphragm, but the technology has existed for decades and is now widely available. Press lightly, and the membrane hangs loose enough to pass the low frequencies, which is bell mode. Press firmly, and it stiffens, cutting the lows so the highs stand out.This one is not marketing. Researchers measured it directly and confirmed the mechanism: the force you apply introduces stress and deformation to both the diaphragm and the tissue underneath it, and that changes the acoustic parameters of the whole sound transmission path. [5] Note what is doing the work there. It isn't only the membrane tightening. It's the skin beneath it being stretched into a drum. Press hard, and you are tuning the patient, not just the instrument.It's a good design, and I'm not here to talk you out of it. You never flip the chestpiece, never lift off and lose your spot, and the larger membrane can make a low-frequency sound land louder than the small cup of a traditional bell does.The problem is that many providers don't actually know how to manipulate the diaphragm pressure to obtain the frequency range of interest. The same research notes that an experienced examiner adjusts the force intuitively to get the best sound. [5] That's a real skill, and it's an unmonitored one. There's no indicator telling you when your pressure is wrong. Press a little too hard while you're hunting an S3 and the membrane tightens, the skin stretches, and the low frequencies get filtered out before they reach you. You don't hear the sound, and you don't hear that you've lost it either. Nothing failed, technically. You just did the filtering yourself.An open bell doesn't ask that of you. It has one job, and it does it whether or not you enjoyed an extra strong cold brew coffee on your way to work. That matters more than it sounds like it should, because the hands in question belong to someone at hour eleven of a twelve, on a loud unit, maybe halfway through a rapid response.
The skill that's supposed to save you is slipping
You could argue that a good clinician just learns the touch. Sure. But look at where the skill has actually been heading.Researchers testing 314 internal medicine residents in the United States, Canada, and England found auscultatory proficiency was poor in all three countries, and the most striking result was how consistently inaccurate the trainees were regardless of where they trained. [6] A multicenter study of 860 medical students, residents, fellows, physicians, and faculty found that cardiac examination skills stop improving after the third year of medical school and may decline after years in practice. [7] A later confidential test of cardiologists and internists at 19 teaching centers found scores falling linearly with time since training. [8] And an eleven-year run of simulation testing at one academic center watched scores drop by 0.15 points per year across trainees overall. [9] The explanation is that echocardiography got cheap and good, so the pressure to train the ear went away.Put those two facts side by side. The standard chestpiece now depends on precise, trained pressure technique, and the training behind that technique is gradually falling out of practice. A dedicated bell doesn't fix anyone's ear. But it does remove one of the factors that might cause your exam to deceive you.
The sounds that earn the bell
So what do you actually get for carrying one?Start with the third heart sound. An S3 is a soft, low, early-diastolic thud, and picking it up depends heavily on the examiner, with wide variation even among experienced physicians. [10] It's also one of the more consequential sounds in medicine. In a retrospective analysis of 2,569 patients from the SOLVD treatment trial, an S3 was independently associated with heart-failure hospitalization and death from pump failure, even after adjusting for other markers of severity. [11] In a separate study of 100 consecutive outpatients, an audible S3 was 41 percent sensitive and 97 percent specific for an elevated BNP. [12] Translated: you'll miss plenty of them, but when you hear one, it means something. And it lives in exactly the band a firm diaphragm works against.The S4 is the same story one notch later in diastole, a low gallop pointing at a stiff, poorly compliant ventricle. Then the classic bell-dependent finding, mitral stenosis: a low-pitched, rumbling, mid-diastolic murmur, usually preceded by an opening snap, that the standard references describe as heard best with the bell at the apex with the patient rolled into the left lateral decubitus position. Heard best. Not heard more conveniently. Lean on firm diaphragm pressure there, and you can pass right over a stenotic valve.None of these is the heart rate. Each one changes the story: this ventricle is failing, this one is stiff, this valve is the problem. Most shifts you won't hear any of them. The point is being ready on the shift you do.
How to actually use it
Some of this is obvious and some of it isn't. Here's what I'd tell a new grad at the station.
Rest it, don't plant it. Bell mode means just enough contact to seal against the skin. If you see the skin tent up under the rim, you've pressed your low frequencies away.
The apex is where an S3, an S4, or a mitral rumble is going to be, and the positioning matters more than people expect. Rolling the patient onto their left side brings the apex closer to the chest wall, which isn't fussiness, it's shortening the distance the sound has to travel through tissue. Settle the bell there and then wait. Longer than you think. I'll go ten or fifteen beats before I'm willing to call it negative, because a soft gallop has a way of hiding behind a few louder cycles before it surfaces. Then press down firm and listen again at the same spot before you move on. Five seconds, and you've covered both ends of the range somewhere you already know is worth listening. If you want the fuller routine, our auscultation tips walkthrough covers positioning and sequence.
And remember the chestpiece is only half the signal path. I've made the case in the stethoscope length guide that what sits between the chestpiece and your ears matters more than most people assume.
So, do you need one?
My answer comes from where I've worked. Between the cardiac ICU, the PICU, and the back of an ambulance, I never had the luxury of a single patient population, and plenty of nurses, medics, and float staff are in the same spot. The stethoscope around your neck might land on a 90-year-old with a failing ventricle at 0200 and a toddler with bronchiolitis at 0300. For that kind of week, a dual-sided chestpiece is simply the more practical instrument. The full-size diaphragm covers the routine adult exam. The open bell covers the gallops and rumbles this whole article is about. And the smaller bell side accepts a pediatric diaphragm, which means the toddler gets a membrane sized for an actual toddler instead of a dinner plate.
That's more or less the spec sheet for the Apex Harmony, which is the stethoscope we make and therefore the one I have an obvious interest in recommending. Adjust for that accordingly. It's a dual head: the familiar pressure-sensitive diaphragm on one face, an actual open bell on the other, and the bell side takes a pediatric diaphragm when your assignment turns over. And since a few of you are only still reading because the bell is the part you care about, I'll say this much. We're working on a scope built around it. More before long.
There's a cost to this and I'm not going to pretend otherwise. Two sides means a bigger chestpiece, one more surface to wipe down, and a rotating head you have to keep track of. If you work one population and you trust your pressure technique, you can decide none of that is worth it to you. I'd disagree, but not strongly enough to tell you you're wrong.
The one argument I won't concede is that the bell is optional because the findings are uncommon. Rarity is the reason the habit has to be there in the first place. You don't half-listen for eight months and then suddenly catch the gallop on the night it matters, because by then you've stopped knowing what you were listening for. So go ahead and check the pulse with two fingers. You should. Just don't mistake that for having listened to the heart.
Sam Jaquish is a critical-care RN (CCRN) and the founder of Apex Stethoscopes, with a background in cardiac ICU, pediatric intensive care, and EMS, and an ongoing habit of taking chestpieces apart to see how they move sound. Apex runs no affiliate program and links no affiliate networks; the one product recommended above is our own, which you can weigh accordingly.
Last reviewed: July 2026
References
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