Today, with technology and the popularity of system engineering and measurement in audio, there are several popular choices in gear, especially measurement microphones. This is one of the most common questions I answer for mentees and on forums, so I’ve compiled this little guide for choosing the right microphone for your application, focusing on some of the most popular choices. These are Earthworks M30, iSEMcon EMX-7150, the Audix TM-1, and the RTA-420 by Rational Acoustics. We’ll identify some of the best applications for each mic and discuss sensitivity and price points.
Sensitivity
Before getting into the mics, let’s talk about sensitivity. What it means and why we care. Sensitivity refers to how effectively a mic converts sound into an electrical signal. The sensitivity is often recorded as the output voltage (in mV) produced when the microphone is exposed to a standardized SPL, typically 1 Pascal (Pa) at 1 kHz. High-sensitivity microphones produce a stronger signal and are better at capturing quieter sounds. Low-sensitivity microphones require louder sounds to generate the same output and are often used in high-SPL environments (live concerts, etc.). Why do we care about sensitivity? We want to ensure that we use the right microphone for our context. This matters because if I were to use a high-sensitivity microphone in a high-SPL environment like a live concert, there is a chance I could clip my preamp/interface and, therefore, be unable to measure data accurately. Of course, we also understand the importance of proper gain structure here, but we can certainly do ourselves a favor by choosing the right tool for our application.
RTA-420
Let’s start with the RTA-420 by Rational Acoustics (rationalacoustics.com). The RTA-420 is the best beginner measurement mic in this lineup, coming in at $99.99. At a great price point, this microphone allows you to accurately measure both amplitude and phase. While it doesn’t come with calibration files, unlike some of our other options, it is made of a heavy metal outer shell that allows the mic to hold up well to wear and tear. Unfortunately, I wouldn’t recommend this mic for measuring SPL as it has a fairly low max SPL. However, it can be used with the popular SC-1 calibrator if you have a 10mm adapter. This is an excellent backup mic to have one or a few of, especially for home/classroom use to be used with an RTA or any application primarily looking at frequency response. This price point is hard to beat and makes this an excellent option for students. On a personal note, this was my first measurement mic, and I still own two as backups and for home use.
Audix TM-1
Second, we have the Audix TM-1/TMI Plus (audixusa.com). Coming in at $299, this is one of two mid-level price options for a reliable measurement mic. The Audix TM-1, unlike the previous mic, comes with sensitivity data and a mic correction curve on a USB (the TM1 plus package). This mic is also made of sturdy metal housing, making it resilient against road wear and tear. It does have a barrel-like neck that can become loose, so making sure it’s fully screwed in before using it is good practice. However, this removable neck is replaceable if a capsule becomes damaged. This mic can be used with the popular SC-1 calibrator with a 6mm adapter. This microphone has a low sensitivity and is a good match for preamps with maximum input levels of about +10 dBu or less. It is also built using Switchcraft connectors. These factors make it a popular choice among production houses and engineers alike due to its 3-year manufacturer’s warranty.
iSEMcon EMX-7150
Third, we have the iSEMcon EMX-7150 (isemcon.net). At $330, it is slightly more expensive than the TM-1, but as a trade-off, the EMX-7150 is class 1 compliant. It is considered a “precision grade meter” and meets the International Electrotechnical Commission (IEC) 61672 standard. Those of us doing work that requires precise SPL measurements, such as working in countries with SPL limits enforced by law, may find this beneficial. The EMX-7150 also has sensitivity data and a correction curve specific to each microphone. However, as a generalization, this is also a low-sensitivity mic with an average sensitivity of 6 mV/Pa. The body of this microphone is made of stainless steel. This mic does have a replaceable capsule but requires the broken mic to be sent to the factory for replacement. Like the other microphones, the EMX-7150 can be used with the popular SC-1 calibrator with a 7mm adapter. This microphone has a low sensitivity and is a good match for preamps with maximum input levels of about +10 dBu or less. This EMX-7150 can operate on 9-52V DC Phantom Power, making it a popular choice for wireless measurement systems. Overall, this is one of the most common mics that touring professionals use.
Earthworks M30
Finally, we have the microphone I get asked about the most: the Earthworks M30 (earthworksaudio.com). This is the priciest of our lineup, at $699 for a single mic. However, it also has the lowest distortion and the highest sensitivity, at 34mV/Pa on average. The M30 comes with a detailed electronic calibration file and a printed frequency chart for every individual microphone. It’s also important to note that the M30 is made of a strong metal body, which allows this mic to hold up well for frequent use and travel. The only thing to consider with this microphone is that for the average user (outside of a laboratory setting), the high sensitivity will cause this microphone to clip most interfaces in high
SPL environments such as concerts. You’re good to go if you have an interface that takes at least 19dBu of input gain. The M30 is truly laboratory-grade. Due to its sensitivity, this mic is ideal for measuring low levels precisely. I have seen these mics used in various capacities, from audience mics for recording to measurement mics to tune a system.
Final Thoughts
For more information on each of these products, please see the manufacturer-specific websites for each microphone. There is no wrong choice; each application has pros and cons.
Samantha Boone is a systems engineer and audio tech with experience designing and deploying sound systems for various applications ranging from clubs to large-scale festivals and arenas. Most recently, her work has involved designing and deploying large format, low-variance systems for installs and touring productions.
