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Microphones and Acoustics

Frequently Asked Questions

Get your most commonly asked acoustics questions answered.

Section I: Definitions and Terminology
Section II: Microphone Recommendations
Section III: Calibration and Testing
Section IV: Specification Clarifications
Section V: Specialty Microphone Applications
Section VI: Maintenance and Handling

If you don’t see the answer to your question, call our 24/7 SensorLineSM 716-684-0001 to speak with an application engineer or visit Ask the Acoustics Experts.

What is the minimal sound pressure level (SPL) measurable with a microphone?

Inherent Noise for an acoustic microphone and preamplifier is a combination of the noise of both components. An easy way to remember it is to think of the terminology as similar to our (broadband) resolution specification for accelerometers or pressure sensors.

The minimal SPL that can be measured will be higher than the inherent self-noise of the microphone itself, defined as the cartridge thermal noise. Other considerations should be assessed when looking at the lowest signal you can measure. You have to also account for the inherent electrical self-noise of the preamplifier, along with looking at the other components in the test set-up chain including noise from cables, power supplies, software, filters, data acquisition systems and settings, background noise, etc.

For this technical tip we will focus on the microphone and preamplifier together as a system. The noise floor will be a combination of both components. The preamplifier typically dominates the noise in the lower frequencies and the microphone will at higher frequencies, as seen below.

Noise floor can be specified in dB, dBA, in 1/3rd (or other) octave bands. The larger the diaphragm or the higher the sensitivity will typically aid in reducing the noise floor of the microphones cartridge thermal noise. A common ½” free field microphone will have a noise floor system spec of between 15-20 dBA. Refer to Tip number one for what dBA is. A larger 1” mic will be around 10-15 dBA and a ¼” microphone will be between 30-60 dBA, typically. The linear (or Z-weighted) ratings in dB will be higher.

Our newly introduced 378A04 is a specialty microphone that enables a 6.5 dBA rating (5.5 dBa typical.) Below is actual test data of the noise floor of one of our 378A04 microphone and preamplifier combinations that we manufactured.

It is important for our sales engineers to note that the noise floor is defendant upon frequency. The noise floor is basically the area under the curve for all frequencies in the usable frequency range of the microphone and preamplifier model, but if you look at a specific frequency or 1/3rd band octave range, you can see above that the noise floor can be significantly lower. If you look at the 100 Hz 1/3rd octave band the A-Wt noise floor is approximately -24 dBA. That is a negative number, well below the human hearing threshold, and the linear scale at that same 100 Hz band is about -5 dB.

It is also important to know your surroundings and capabilities and match the correct mic to the application. Unless the user has an anechoic chamber (or sound proof room or environment) their background noise can likely be higher than the noise floor of microphone and preamplifier and the 378A04 will perform no better than the more cost effective 378B02. Conversely, if they are looking to measure the lowest noise and have all the other equipment to support the true low noise test. The newly introduced 378A04 offers the best low noise prepolarized option from PCB.

What is the minimal sound pressure level (SPL) measurable with a microphone?

Inherent Noise for an acoustic microphone and preamplifier is a combination of the noise of both components. An easy way to remember it is to think of the terminology as similar to our (broadband) resolution specification for accelerometers or pressure sensors.

The minimal SPL that can be measured will be higher than the inherent self-noise of the microphone itself, defined as the cartridge thermal noise. Other considerations should be assessed when looking at the lowest signal you can measure. You have to also account for the inherent electrical self-noise of the preamplifier, along with looking at the other components in the test set-up chain including noise from cables, power supplies, software, filters, data acquisition systems and settings, background noise, etc.

For this technical tip we will focus on the microphone and preamplifier together as a system. The noise floor will be a combination of both components. The preamplifier typically dominates the noise in the lower frequencies and the microphone will at higher frequencies, as seen below.

Noise floor can be specified in dB, dBA, in 1/3rd (or other) octave bands. The larger the diaphragm or the higher the sensitivity will typically aid in reducing the noise floor of the microphones cartridge thermal noise. A common ½” free field microphone will have a noise floor system spec of between 15-20 dBA. Refer to Tip number one for what dBA is. A larger 1” mic will be around 10-15 dBA and a ¼” microphone will be between 30-60 dBA, typically. The linear (or Z-weighted) ratings in dB will be higher.

Our newly introduced 378A04 is a specialty microphone that enables a 6.5 dBA rating (5.5 dBa typical.) Below is actual test data of the noise floor of one of our 378A04 microphone and preamplifier combinations that we manufactured.

It is important for our sales engineers to note that the noise floor is defendant upon frequency. The noise floor is basically the area under the curve for all frequencies in the usable frequency range of the microphone and preamplifier model, but if you look at a specific frequency or 1/3rd band octave range, you can see above that the noise floor can be significantly lower. If you look at the 100 Hz 1/3rd octave band the A-Wt noise floor is approximately -24 dBA. That is a negative number, well below the human hearing threshold, and the linear scale at that same 100 Hz band is about -5 dB.

It is also important to know your surroundings and capabilities and match the correct mic to the application. Unless the user has an anechoic chamber (or sound proof room or environment) their background noise can likely be higher than the noise floor of microphone and preamplifier and the 378A04 will perform no better than the more cost effective 378B02. Conversely, if they are looking to measure the lowest noise and have all the other equipment to support the true low noise test. The newly introduced 378A04 offers the best low noise prepolarized option from PCB.