What kind of stethoscope should you use?
Acoustic stethoscopes have three common chestpiece designs. A single-sided stethoscope has one diaphragm and suits routine adult assessment. A dual-diaphragm stethoscope has an adult diaphragm on one face and a pediatric diaphragm on the other, and suits clinicians who see patients of every size. A bell and diaphragm stethoscope pairs a diaphragm with an open bell for low-pitched heart sounds such as S3, S4, and the murmur of mitral stenosis. None of the three is best. Each one solves a different problem, and the right choice depends on who you listen to and what you listen for.Flip over the stethoscopes at any nursing station, and you will find all three. New grads ask me which one is best about once a week, and I give them an answer they never like: it depends on your patients.So this is not a ranking. I want to walk through what each type of stethoscope was designed to do, what the research supports, and what each one asks of the hands holding it.Two things to get out of the way first.Sides are one variable. Other factors matter more. Maximilian Nussbaumer spent his Cambridge PhD modeling the stethoscope as one connected system, meaning the chestpiece, diaphragm, tubing, the hand on the head, and the chest under it all get treated as a single machine that either passes sound or doesn't. [1] Out of that work: chestpiece mass shapes the low end, the size of the air cavity changes how loud things come through, and your grip loads the head in ways the bench never sees. The metal itself matters mostly through the mass it adds. I already spent a whole post on mass and metal in Stethoscope Weight: Does it Matter?, so I will leave that there.Chestpiece diameter is another one. A bigger contact area changes how the head couples to the chest, and the geometry interacts with everything else in the system. I owe you a separate article on diameter and I am working on it. Today is about the three configurations and what separates them.New to the terminology? Our stethoscope anatomy post and the chest piece and diaphragm guide will get you up to speed in ten minutes.
Single-sided stethoscopes (one diaphragm)
One listening surface. On any decent modern instrument, that surface is a diaphragm, usually a tunable one. I want to say this plainly because I hear the opposite constantly: single-sided does not mean cheap. It is a legitimate design decision, and for a lot of clinical work it is all you need.I know why people think otherwise. Say "single-head" to a nurse, and she pictures the yellow disposable on the isolation cart, the one you have to press so hard to hear anything that the patient asks if you are okay. In my experience, those really are bad, and I assume it's because of budget: a bare plastic head with a thin membrane is about the cheapest thing you can mold. But that tells you about the disposable's price point, not about the design philosophy. Plenty of us dismiss a whole category of instruments because of the free one we were handed at the door of a C. diff room.The counterexample is a competitor's flagship, and I will give it its due credit. The 3M Littmann Master Cardiology is still in the current line, and it is single-sided. Littmann's own comparison chart lists a 4.8 cm chestpiece, a tunable diaphragm, dual-lumen tubing, and the top acoustic rating in its mechanical range. [2] That rating is the manufacturer grading its own work, so weigh that however you wish. The point is narrower and does not depend on the rating: a single-sided chestpiece can sit anywhere from the isolation cart to a cardiologist's pocket. The Master Cardiology also has a history in the independent literature. When Abella, Formolo, and Penney ran six stethoscopes through a frequency sweep in 1992, it was one of the six. [3]
What one good diaphragm does for you
Heart sounds, breath sounds, bowel sounds, bruits, and manual blood pressures. That is most of a shift in most specialties, and a full-size diaphragm handles that routine assessment work without complaint. If the diaphragm is tunable, lighter pressure favors the lower-pitched sounds and firmer pressure favors the higher ones, so one surface stretches further than it used to. There is also something to be said for a head you never have to rotate. Nothing to flip, no listening through the wrong side by mistake, no checking the stem with your thumb at 0300 to make sure it is indexed correctly.
Where it runs out
The most obvious practical limit of a single-sided chestpiece isn't frequency response. It is footprint. You get one size of contact patch, and it works fine on a grown adult. Then you try it on a two-year-old with bronchiolitis. In my hands, a 4 to 5 cm diaphragm on a toddler wants to bridge two ribs, rock on the intercostal space, and leak at the edge. Same story tucked up under a clavicle, or on a preemie. A diaphragm that isn't sealed to the skin is a lid over an air leak, and you hear the room more than the patient. Adult med-surg nurses can go a whole career without meeting this problem. Anyone who floats between adult and peds, or works a rig where the next call could be eight months or eighty years old, meets it on day one. For the record, footprint is not why the two-sided head was invented. Sprague combined a bell and a Bowles diaphragm in 1926 because no single chestpiece carried every pitch of heart sound well. [1] Fit across patient sizes is another reason, and it drives the modern adult-and-pediatric dual-diaphragm design.
Dual-diaphragm stethoscopes (adult and pediatric diaphragms)
A large diaphragm on one face, a smaller one on the other, sized for adults and kids, and, in the well-known examples, both of them tunable. This layout exists for clinicians whose patient population is all over the map. Think emergency rooms, or perhaps EMS providers. It also depends most on your understanding of how a tunable diaphragm works, and I will get to why.The common examples put the adult side at 4.3 cm and the pediatric side at 3.4 cm. [2] You will read that this is the most popular configuration on the market. Maybe. I have never seen sales data that would let anyone say so, so I will call it a very common one and leave it there.
Two footprints, one mode
People describe the two faces as two instruments. I would put it differently. They are two footprints for one way of listening. The wide face goes on an adult chest. The narrow face goes on a kid, an infant, or that awkward spot on an adult where the wide one won't lie flat. Flip the stem, and you are still hearing through a membrane. If both faces are tunable, you are still picking frequency emphasis by how hard you lean on it. The two sides are not acoustically identical, since diameter and cavity depth change the response in their own right, but the way you use them is the same.
Your hand is part of the instrument
A tunable diaphragm changes what it passes based on how hard you press. That much you already know. What matters is that the mechanism isn't just the membrane getting stiffer. Nowak and Nowak measured it, first at a 2016 acoustics congress and then in a 2017 Postgraduate Medical Journal paper. [4][5] Pressing harder changed which frequencies came through. How much it changed varied from patient to patient and from one spot to the next on the same patient. And the main driver was the tissue under the head deforming, not the skin or the membrane by itself. Nussbaumer lands in the same place from the modeling side: the chest doesn't behave like a spring with a fixed stiffness, so the load you apply sets up the whole system before the first heartbeat arrives. [1] Two clinicians pressing differently on the same patient are, in a fairly literal sense, listening through two different systems. I owe a correction here, because I have repeated this one myself. The line goes: studies show clinicians can't reproduce pressure on a tunable diaphragm. I went looking for that study and came up empty. Nowak and Nowak measured what happened to the signal when the force changed. They did not ask anyone to hit "light" and then "firm" twice in a row and check the match. Their abstract actually assumes an experienced examiner adjusts the force by feel. The literature does show that agreement on gallops is poor. In a blinded 1998 study, observers agreed on an S3 with a kappa of 0.18 and on an S4 with a kappa of 0.05, which is barely better than flipping a coin. [8] That is a skill problem. Nobody has tested whether it is a pressure problem. So here is what I will stand behind. Pressure selects frequency on a tunable head. How much it shifts depends on the patient and the spot. Press on purpose every time, knowing what you are pressing for. The hands-on version is in 15 Advanced Tips for Mastering Auscultation.
The tradeoff
Two diaphragms give you two contact-patch sizes. What you give up is the bell. My background is in pediatric cardiac intensive care, and you could not possibly convince me to give up my bell. There is no open cavity anywhere on the head, so when you go looking for a soft gallop at the apex, you are working with a tunable membrane, your fingertips, and the patience to wait through fifteen beats. My guess, and it is only a guess, is that most clinicians would go years without noticing the difference. I would rather not find out on the one night it counted. That is what the next section is about.
Bell and diaphragm stethoscopes (the classic cardiology chestpiece)
The classic layout splits the two jobs into two pieces of hardware. A diaphragm handles routine and higher-pitched auscultation. An open bell handles the low end. Sprague described the combined bell-and-diaphragm chestpiece in 1926, building on Bowles's diaphragm design, and Nussbaumer notes that the basic form has barely changed since. [1] I do not think that is because nobody has had a better idea. I think it is because the two faces do different work, and we now understand the physics of that division better than the people who designed it did.
The diaphragm face
You know this side. Pressed firmly, it is where you hear S1 and S2, most systolic murmurs, breath sounds, and higher-pitched cardiovascular findings. Clinical Methods, the physical-exam text a lot of us learned from, pairs the firmly applied diaphragm with higher-frequency sounds and moves on. [6] I will do the same.
The bell face
The bell is meant to rest on the skin, not press into it, and the teaching has always reserved it for the lowest-pitched sounds: S3, S4, and the low diastolic rumble of mitral stenosis. The S3 is the best example of why. Clinical Methods puts it at roughly 25 to 50 Hz, near the bottom of what a human ear can register, low in intensity, audible over only a small patch of chest wall, and best sought with the bell laid lightly over the apex with the patient rolled onto the left side. [6] The S4 lives in the same neighborhood. If you want the clinical side of these sounds, I covered them in Beyond Lub-Dub and in Where to Listen to Heart Sounds.
What the bench work says
Abella, Formolo, and Penney swept six stethoscopes from 37.5 to 1000 Hz. In the 37.5 to 112.5 Hz band, the bells mostly boosted transmission and the diaphragms mostly cut it. But the low-frequency differences did not reach statistical significance, and the pattern shifted from one stethoscope to the next. [3] So that study doesn't give you a blanket rule that bells win at low frequency on every instrument ever built, and I would be suspicious of anyone who quotes it that way. Nussbaumer's dissertation is where this got interesting for me, because it explains something I had noticed taking chestpieces apart and never had a good answer for. Why is the bell side of a real chestpiece so deep and steep, while the diaphragm side is shallow? The answer is occlusion. Press an open cavity against a chest, and the tissue bulges up into it. In a shallow open cavity, the flesh reaches the port to the tubing, and almost nothing gets through. You can test this yourself: pop the diaphragm off a chestpiece, press the bare shallow cavity against your own chest with normal pressure, and listen to nearly nothing. A deep bell resists occlusion. A diaphragm prevents it entirely, and that is what lets the diaphragm-side cavity be shallow in the first place. [1] Nussbaumer points out that many studies test the same cavity with and without a membrane, conclude the diaphragm only hurts, and never account for the shallower cavity the diaphragm makes possible. Once you see that, the tradeoff falls out cleanly. A diaphragm stiffens the whole assembly, pushing its sweet spot toward higher pitches and quieting the output a little. The shallower cavity the diaphragm allows brings the volume back up. When Nussbaumer modeled a deep open cavity against a shallow covered one on a head of identical size and weight, the open bell came out ahead at low frequencies, and the diaphragm came out ahead at high ones. Where the crossover lands depends on the specific cavity and membrane, so the numbers are design-specific, but the shape of the result is not. [1]So the claim I am comfortable making is not that a bell always hears low frequencies better. It is that an open bell is a purpose-built interface for low-frequency sound, that a century of clinical teaching has used it for exactly the faintest findings we try to catch, and that the cavity physics now explains why it is shaped the way it is. I made the longer case in Do You Need a Bell on Your Stethoscope?
The bell has its own technique
Press a bell too hard, and the skin under the rim tightens into what Rappaport and Sprague, back in 1941, called a natural diaphragm. The low-frequency advantage goes with it. [7] Nussbaumer adds that skin alone is not the whole story, since deformation of the underlying tissue matters at least as much. [1] Either way, the instruction is the one in every physical-diagnosis text and in the current Merck Manual: rest it lightly. My own rule of thumb, not a validated cutoff: if I can see the skin tenting under the rim, I have already pressed away what I came for.Which brings me to the cleanest way I know to state the difference between the two double-sided designs. With two diaphragms, you change what you hear mostly by changing your pressure on the membrane. With a diaphragm and a bell, you physically select a low-frequency chestpiece, and then you still have to hold it right. I have called the bell side the audiophile's side before, and I stand by that as a description of who tends to love it. The scientific version is less romantic: a dedicated acoustic interface for low-frequency auscultation.
Which type of stethoscope is right for you?
Nussbaumer ends his dissertation with a sentence I keep coming back to whenever someone asks me which stethoscope is best. Because the response depends so heavily on the chest, the listening site, and the hand holding the head, there is no single answer to the question of what a given stethoscope's response to body sounds is. [1] The same goes for chestpiece configuration. Each design answers a different question about who you listen to and what you are listening for. Buy for the listening you actually do. If you cross age groups all week, two footprints will earn their place around your neck. If your work lives in the adult chest and you care about catching an S3, an S4, or a diastolic rumble, an open bell is a tool built for exactly that. And if one well-made diaphragm covers your practice, carry it without apology. Nobody is grading you on the number of sides. For the record, we make the second and third kinds. The Apex Harmony is the second kind: a full-size tunable diaphragm on one face and a pediatric diaphragm on the other, sitting over a bell cavity, so you can pop the small diaphragm off when you want an open bell. It is the one I would hand a student or anyone whose assignment changes every shift. The Apex Symphony is the third kind, and the one this whole bell section was building toward: a tunable diaphragm on one face and a true open bell on the other, no pediatric diaphragm option, because after my years in the PICU I would rather rest a bell on a small chest than press a membrane into it. Those are the stethoscopes we sell, so read my enthusiasm for bells with that in mind. My reasons are in this article and the bell post linked above, and you can weigh them against your own patient list.
Frequently asked questions
What is the difference between a single-sided and a double-sided stethoscope? A single-sided stethoscope has one listening surface, almost always a diaphragm. A double-sided stethoscope has two listening surfaces on a rotating head and comes in two forms: two diaphragms of different sizes, or a diaphragm paired with an open bell.
Is a single-sided stethoscope lower quality? No. Single-sided describes the layout, not the build. Disposable isolation stethoscopes are single-sided, and so is at least one manufacturer's flagship cardiology model. The practical limit of a single-sided head is footprint, not sound quality.
What is the bell on a stethoscope for? The open bell is designed for low-pitched sounds: the third and fourth heart sounds (S3 and S4) and low diastolic murmurs such as mitral stenosis. It works best when rested lightly on the skin. Pressing hard tightens the skin into a natural diaphragm and filters out the sounds the bell exists to catch.
Do I need a bell if my diaphragm is tunable? A tunable diaphragm shifts its emphasis toward lower pitches under light pressure, and for many clinicians, that is enough. An open bell is a separate, dedicated low-frequency interface that does not depend on pressure technique to the same degree. Clinicians who listen for gallops and diastolic rumbles tend to want one.
Which stethoscope is best for nurses? It depends on the unit. Adult med-surg and clinic work is well served by a single diaphragm. Emergency, EMS, float, and pediatric roles benefit from two footprints. Cardiac, ICU, and step-down roles benefit from an open bell. See the sections above for the reasoning behind each.
Sam Jaquish is a critical-care RN (CCRN) and founder of Apex Stethoscopes, with a background in cardiac ICU, pediatric intensive care, and EMS, and a habit of taking chest pieces apart to see how they make sound. Apex runs no affiliate program and links to no affiliate networks; the two products mentioned above are our own.
Last reviewed: September 2026. Product specifications and clinical practice change; this article reflects information current as of the review date.
References
- Nussbaumer M. Stethoscope Acoustics. PhD dissertation, Department of Engineering, University of Cambridge; 2021. Freely readable through the Cambridge repository. Passages cited: chestpiece history and anatomy (Chapter 1), occlusion and the natural-diaphragm debate (Section 2.1), diaphragm stiffness, cavity volume, bell-mode versus diaphragm-mode simulation and the effect of holding (Chapter 9, Fig. 9.15), and Conclusions (Chapter 11). The peer-reviewed version is Nussbaumer M, Agarwal A. Journal of Sound and Vibration. 2022.
- 3M Littmann. Stethoscope Comparison Chart. 2024. littmann.com
- Abella M, Formolo J, Penney DG. Comparison of the acoustic properties of six popular stethoscopes. The Journal of the Acoustical Society of America. 1992;91(4 Pt 1):2224-2228. doi:10.1121/1.403655
- Nowak KM, Nowak LJ. On the relation between pressure applied to the chest piece of a stethoscope and parameters of the transmitted bioacoustic signals. Proceedings of the 22nd International Congress on Acoustics, Buenos Aires; 2016.
- Nowak KM, Nowak LJ. Experimental validation of the tuneable diaphragm effect in modern acoustic stethoscopes. Postgraduate Medical Journal. 2017;93(1103):523-527. doi:10.1136/postgradmedj-2017-134810
- Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Boston: Butterworths; 1990. Chapter 24, The Third Heart Sound. NCBI Bookshelf
- Rappaport MB, Sprague HB. Physiologic and physical laws that govern auscultation, and their clinical application. American Heart Journal. 1941;21(3):257-318.
- Lok CE, Morgan CD, Ranganathan N. The accuracy and interobserver agreement in detecting the 'gallop sounds' by cardiac auscultation. Chest. 1998;114(5):1283-1288. doi:10.1378/chest.114.5.1283
