What Is the Difference Between Large and Small Diaphragm Microphones?
Studio microphones are offered as small and large diaphragm types. What does that mean, and what are the sonic differences? Which type is best for your applications? Here’s all you need to know!
In most microphone books you’ll find this explanation: “Large” means the capsule’s diaphragm (or membrane) is 1 inch (25.4 mm) or more in diameter; “small” means it is ½ inch (12.7 mm) or less. But that is just a rule of thumb. In reality, many small diaphragm microphones for audio recording (as opposed to measurement mics) use slightly larger capsules. Also, there are large diaphragm microphones whose diaphragm size is slightly below 1 inch, often 22 mm. And just to confuse you, some manufacturers will give you the size of the entire capsule, which in the case of a typical large diaphragm capsule is 32-34 mm. The actual diaphragm size rarely exceeds 27 mm. None of that really matters! In practical terms, it’s enough to differentiate between large and small diaphragm microphones.
Note that the distinction between small and large diaphragm is common only to condenser microphones. There are a couple of broadcast dynamic microphones which are explicitly termed “large diaphragm”, but otherwise neither the manufacturers nor the users seem to care about the size of a dynamic capsule or diaphragm.
It’s quite interesting that the diaphragm size is often reflected in the entire construction of the microphone. Small diaphragm condensers usually are slim, pencil-shaped and operate end-fired. Large diaphragm condensers are usually much bigger and operate side addressed.
The Pros and Cons of Large and Small
Historically, large diaphragm condensers came first. Early condenser microphones of the 1930s and 40s had to use large diaphragm capsules to overcome the noise of the tube electronics. A large membrane captures more acoustic energy, thus generating a higher signal voltage. Small diaphragm condenser microphones with a decent signal-to-noise ratio only became feasible when dedicated microphone tubes and low noise transistors became available in the 1950s and 60s.
To this day, the main technical advantage of large diaphragm condenser microphones is their noise performance. The Neumann TLM 103, for instance, has a self-noise of only 7 dB-A. That’s about 6 dB lower (i.e. half the noise voltage) than the self-noise figure of a state of the art small diaphragm microphone such as the Neumann KM 184.
However, in all other respects, the small diaphragm condenser is the superior type, technically speaking. Its main advantages are:
- excellent transient response (a small diaphragm can follow the sound waves more accurately)
- extended high frequency response (even beyond human hearing)
- very consistent pickup pattern
The latter point is of particular importance. Let’s compare the polar patterns of a small diaphragm and a large diaphragm condenser microphone at various frequencies.
As you can see, the cardioid pattern of the small diaphragm KM 184 remains constant across all frequencies. The pattern only narrows at the highest measurement frequency (16 kHz).
The cardioid pattern of the U 87A large diaphragm condenser microphone already begins to narrow at 8 kHz. Also, the cardioid pattern widens considerably at low frequencies. At 125 Hz, it is almost an omni pickup pattern.
Sound Differences and Typical Applications
However, sound is much more than just technical performance. The (supposed) shortcomings of large diaphragm condenser microphones are part of what makes them so attractive, especially for vocals and spoken word. The widening pattern at low frequencies, for instance, mollifies the proximity effect. In other words, the low frequency response remains beautifully lush, even if the singer moves (and some singers need to move in order to express themselves).
Large diaphragm condenser microphones shape the sound in a pleasing way; it just feels great to hear your own voice on your headphones. A good large diaphragm condenser makes you want to sing, because it sounds like you … on a record! Also, many vocalists like the sheer size of a large diaphragm microphone, because it gives them something to focus on, in absence of an audience. Apart from vocals and spoken word, large diaphragm microphones are often used for solo instruments to make them appear vibrant, rich, and “larger than life.”
Small diaphragm condensers are your best choice when you want to capture the pure and natural sound, without added flavors. No other type of microphone will give you a more detailed sound image. Because of their neutral sound, high quality small diaphragm microphones can be used for almost anything.
In pop music, small diaphragm microphones are typically used for piano, acoustic guitar and other stringed instruments as well as drums (overheads, snare, hi-hat, cymbals) and percussion. Small diaphragm microphones can have excellent low end response and can also be used for bass instruments, although most pop engineers prefer the extra “lushness” of a large diaphragm microphone for bass-heavy sources.
Sound engineers who record classical music use small diaphragm condensers almost exclusively. Because of their consistent pickup patterns, small diaphragm condensers are excellent to capture choirs, ensembles and orchestra in stereo (or even surround).
There is no better or worse, both large and small diaphragm condenser microphones are great recording tools. It’s all about choosing the right tool for the job.
Small diaphragm condensers give you an uncolored, neutral, very detailed sound image. Small diaphragm microphones are “realists”. Use them for anything that you want to capture just like it is.
Large diaphragm condensers are part microphone, part instrument. Their aim is to make the sound source appear bigger, more engaging, more beautiful and adorable. They will give you that “sounds like a record” feeling. Large diaphragm microphones are “romantics”. Use them to put vocals and other lead instruments into the spotlight.