The diaphragm of a microphone is the primary component of the microphone transducer. Without a diaphragm to react to sound waves, a mic will not recreate produce an audio signal. Special care must be put into designing and manufacturing these diaphragms to function properly within the microphone.
What are microphone diaphragms made of? Microphone diaphragms are made of durable and flexible materials that maintain their strength under great tension and extreme thinness (only microns thick). Diaphragms (or the capsule in some condensers) must also include conductive material for the electrical mic signal to be generated.
In this article, we'll discuss the materials used to make the diaphragms of the main microphone types: the dynamic mic, the ribbon mic, and the condenser mic.
What Are Moving-Coil Dynamic Microphone Diaphragms Made Of?
Moving-coil dynamic microphone diaphragms are typically made of BoPET (biaxially-oriented polyethylene terephthalate) under the brand name Mylar.
The exact type, grade, and thicknesses of the BoPET will vary from mic to mic and from manufacturer to manufacturer.
BoPET performs very well in dynamic microphone diaphragms where the diaphragm itself doesn't need to be electrically conductive. BoPET material is a go-to choice for its high tensile strength and stability combined with its flexibility. It can be stretched tightly and still be flexible to react to sound waves with accuracy.
Strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties, and electrical insulation.
These diaphragms have conductive coils attached to their backsides. A typical moving coil is made of very small-diameter insulated copper wire that is wound many times around.
Copper is most common not only because of its price but because it helps to maximize the electromagnetic induction and produce a strong audio signal.
- Copper is very conductive (5.96×107 Siemens per meter).
- Copper is light (8.96 g/cm3) and allows the diaphragm/coil combo to be more reactive than heavier materials.
For a complete description of moving-coil dynamic microphones, check out my article The Complete Guide To Moving-Coil Dynamic Microphones.
What Are Ribbon Dynamic Microphone Diaphragms Made Of?
Ribbon microphones need to react accurately to sound waves while also being conductive and loose in terms of suspension within the ribbon mic baffle.
Ribbon microphone diaphragms are nearly always made of aluminum.
Not only is aluminum conductive, but it's also relatively strong when made so thin (ribbon diaphragms are typically less than 5 microns thick). Corrugation helps to add strength and flexibility to the diaphragm since the ribbons are typically suspended rather loosely within the baffle.
- Aluminum is conductive (3.77×107 Siemens per meter), but less so than copper (5.96×107 Siemens per meter).
- Aluminum is very light (2.7 g/cm3) and allows the diaphragm to be reactive even at lower tensions.
Some early ribbon microphone diaphragms were made of Duralumin, a then-brand name for age-hardenable aluminum alloys, namely aluminum-copper alloys. Though this material increased the durability of the ribbon diaphragm, it did so at a great cost to the performance of the diaphragm.
Duralumin did not catch on as a common ribbon material, especially as advancements in technology improved the standard corrugated aluminum ribbon.
Crowley and Tripp Ribbon Microphones developed a resilient nanomaterial for ribbon diaphragms called Roswellite. The technology never caught on, and the company has since been bought by Shure Microphones.
For a complete description of ribbon dynamic microphones, check out my article The Complete Guide To Ribbon Microphones (With Mic Examples).
What Are Condenser Microphone Diaphragms Made Of?
Condenser microphones, like dynamic mics, often have diaphragms made of BoPET (Mylar). However, these diaphragms need to be electrically conductive for the condenser capsule to work properly. Therefore, these diaphragms are often gold-sputtered.
Sputtering gold on the surface of a Mylar diaphragm, we slightly increase the strength of the diaphragm without overly affecting its responsiveness to sound. More importantly, we turn the nonconductive (even insulating) BoPET diaphragm into a conductive diaphragm.
Gold not only allows the capsule to work properly, but it helps the mic sound great. Gold-sputtering has been around for a long time in condenser diaphragms.
- Gold is conductive (4.11×107 Siemens per meter). It's more conductive than aluminum (3.77×107 Siemens per meter) but less so than copper (5.96×107 Siemens per meter).
Earlier condenser microphone capsules (like Neumann's classic M7) used PVC (Polyvinyl chloride) plastic for their diaphragm.
PVC is a synthetic plastic polymer that becomes soft and flexible when made with the addition of phthalate plasticizers. This material can maintain significant enough strength when stretched thin to act as a microphone diaphragm.
PVC is not electrically conductive and, therefore, has to be sputtered with electrically conductive material (like gold).
PVC proved to be rather stiff and not overly durable. There would often be issues of diaphragm wearing, especially around the tension ring of the capsule. So manufacturers have pretty well all switched to Mylar.
Some condenser microphone manufacturers have experimented with aluminum diaphragms. Aluminum acts as a reactive diaphragm material while also being conductive itself. However, aluminum is not as effective as the typical Mylar and gold-sputtering, so it hasn't really caught on in manufacturing.
Front electret condensers have electret material on their diaphragms or even have the diaphragms completely made of electret material.
Electret material is a dielectric material with a quasi-permanent electric charge and is used to charge the capsules of electret condenser mics. Condenser capsules, which basically act as parallel-plate capacitors, require a constant charge to work properly. This charge can be supplied via a DC biasing voltage or by electret material in the capsule.
For more information on condenser microphones, check out my article What Is A Condenser Microphone? (Detailed Answer + Examples).
What is a microphone capsule? A microphone capsule refers to the mic diaphragm and the housing around that diaphragm that act together as the microphone transducer. The term capsule typically refers to this assembly in condenser mics, though it may also be applied to dynamic mics.
For an in-depth read on microphone capsules, check out my article What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules).
What are the different types of microphones? Microphones can be divided into multiple categories, though mic “type” typically refers to the type of mic transducer. In this case, the two main microphone types and condenser and dynamic, though there are other types and sub-types, which include:
- Moving-Coil Dynamic
- Ribbon Dynamic
- Tube Condenser
- Electret Condenser
- Fibre Optic
For more information on microphone transducer types, check out the following My New Microphone articles:
• Microphone Types: The 2 Primary Transducer Types + 5 Subtypes
• How Do Microphones Work? (A Helpful Illustrated Guide)
Choosing the right microphone(s) for your applications and budget can be a challenging task. For this reason, I've created My New Microphone's Comprehensive Microphone Buyer's Guide. Check it out for help in determining your next microphone purchase.