What are USB measurement microphones and what advantages do they offer?
A classic acoustic measurement system consists of a microphone capsule, impedance converter, preamplifier, power supply and AD converter. This setup is complex and prone to errors.
However, powerful and highly integrated USB measurement microphones have been available for some time.
The advantages of such solutions are:
Setup is much easier:
- Simply connect to the USB port.
- no phantom power or ICP power required
- no drivers for a measurement interface.
- These systems are also directly calibrated with suitable software, i.e. absolute sound levels can be measured without a sound level calibrator.
- Calibrated measuring range switchable via software
- Cable lengths up to 60m
- Signal chain is optimally matched
This is how measurement technology with a PC should be.
In general, these new USB measurement microphones work with all measurement programs on the market. Only the level calibration is only available with specially tuned systems.
The performance ranges from simple systems to systems that meet the highest requirements (B&K capsule via thread 60 UNS and optionally 200V).
For which applications are USB measurement microphones suitable?
USB measurement microphones are suitable for many acoustic measurements, e.g room-acoustics, building-acoustics, psycho-acoustics, NVH and many more
Which frequencies can be measured with USB measurement microphones?
USB measurement microphones cover a wide frequency range, from infrasound (typically 5Hz) to the ultrasonic range (approx. 90kHz)
Which manufacturers are there for USB measurement microphones?
There are now many products available on the market. You will find a selection in our webshop .
Structure of a USB measurement microphone
A USB measurement microphone consists of the following components
- Condenser Microphone Capsule
- impedance converter
- Digitally controllable attenuator
- AD converter
- USB interfaces
- voltage converter
All these components are integrated in one housing, so that the construction is very compact. Power is supplied entirely via USB. This means that the cabling effort is minimal.
Functionality of a USB measurement microphone
The sound is converted into an electrical signal in the microphone capsule by the membrane. This has a very high output resistance. The impedance is reduced by an impedance converter. This is usually a field effect transistor (FET) located directly behind the microphone capsule. This reduces electrical interference.
In the next stage, the signal is amplified. Simple systems use the integrated amplifier of a highly integrated audio IC for this. However, the dynamics are not sufficient for demanding measurements. Therefore, high quality systems (like our ATD-4 series) use a discrete preamp that is perfectly tuned.
The amplification can be controlled digitally over a wide range, which means that different measuring ranges can be implemented via the PC.
The signal is digitized via an AD converter and sent to the PC via the USB interface.
Dynamic range of a USB measurement microphone
High-quality microphone capsules have an enormous dynamic range (e.g. a 1/2" capsule typically 15-140dB). This range can only be covered to a limited extent by an AD converter.
In high-quality USB measurement microphones, the signal is also sampled with a second channel. The second channel has a different level range. The signal is thus sampled simultaneously with an insensitive and a sensitive AD converter. A very large dynamic range can be recorded in this way.
In general, a USB measurement microphone is supplied with 5V from the USB bus. Simple USB measurement microphones (e.g. the widespread UMIK-1) supply the AD converter and the preamplifier directly. However, this limits the maximum measurable sound level, since microphone capsules can deliver enormous signal voltages. We have written a separate article for this background on measuring high sound levels .
High-quality USB measurement microphones therefore use DC/DC converters and can also record signal voltages of 10V RMS. These are 28V peak/peak!. This technique can be found in our ATD5-T and in the Microtech-Gefell MV240 .
What are the disadvantages of USB measurement microphones?
USB measurement microphones are designed to perform acoustic measurements elegantly and with the highest accuracy in connection with a PC. The output of a USB measurement microphone is digital. The microphone signal cannot be captured in purely analog form. Therefore, USB measurement microphones cannot be integrated into analog measurement setups. USB measurement microphones also cannot be connected to sound level meters. Only the capsule can often be exchanged between the two systems.