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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.

How do I obtain enough constant current for a low noise microphone, if my Data Acquisition System limit is 2 mA?

To use the Industry Exclusive PCB Low Noise Prepolarized microphone, model 378A04, to its maximum capabilities, you must supply a minimum of 4 mA of excitation current. This can be achieved a few ways including combining 2 channels of 2mA current in parallel.

The new 378A04 microphone system measures to extremely low amplitudes. To achieve this, additional current must be supplied to the special microphone and preamplifier above the 2 mA that is commonly needed for microphones and other ICP® sensors. A minimum of 4 mA is required for the 378A04. It is important to note that not all Data Acquisition Systems (DAQs), or Sound Level Meter manufacturers supply this 4 mA of current.

Excitation voltage and current are two different things. The proper excitation voltage is needed so that the voltage output is not limited on the high side when the microphone responds to a high pressure input. The excitation voltage is determined by the signal conditioner and needs to be greater than (or equal to) the output bias voltage plus the peak output voltage for the microphone to operate properly within the full dynamic range. The excitation current is more closely related to the power that the microphone needs to operate. The microphone will draw however much current it needs based on the requirements of the preamplifier and the cable load. If the signal conditioner or DAQ is not capable of sourcing 4 mA on a single channel there are a few options.

Ways to obtain the 4 mA:

1) PCB® has a model 480M122 signal which we have added to our stock offering. This is similar to our 480E09, single channel battery operated signal conditioner which has gain. The difference is the ability to provide 4 mA standard. Being battery operated, the 480M122 has extremely low inherent noise characteristics for a signal conditioner. 


2) Purchase one of the other line powered PCB signal conditioners that handle 2 mA or greater signal conditioner. For example the 482C05, a 4 channel model has user adjustable current which is factory set at 4 mA.

3) Connect the microphone to two channels of DAQ in parallel. The current will be divided between the two channels of multichannel DAQ that has 2 mA each channel such that if each draws 2 mA then the total current sourced will be 4 mA (or whatever the mic needs…3.0 mA, 3.5 mA, etc…). This is done with a “T” connector. Below is a diagram showing a standard array mic (130E22) that requires only 2 mA of constant current, along with a 378A04 mic that requires 4 mA.



4) If you are purchasing a DAQ, make sure you request a model with 4 mA per channel capability, then you will not require a “T” combined connection

How do I obtain enough constant current for a low noise microphone, if my Data Acquisition System limit is 2 mA?

To use the Industry Exclusive PCB Low Noise Prepolarized microphone, model 378A04, to its maximum capabilities, you must supply a minimum of 4 mA of excitation current. This can be achieved a few ways including combining 2 channels of 2mA current in parallel.

The new 378A04 microphone system measures to extremely low amplitudes. To achieve this, additional current must be supplied to the special microphone and preamplifier above the 2 mA that is commonly needed for microphones and other ICP® sensors. A minimum of 4 mA is required for the 378A04. It is important to note that not all Data Acquisition Systems (DAQs), or Sound Level Meter manufacturers supply this 4 mA of current.

Excitation voltage and current are two different things. The proper excitation voltage is needed so that the voltage output is not limited on the high side when the microphone responds to a high pressure input. The excitation voltage is determined by the signal conditioner and needs to be greater than (or equal to) the output bias voltage plus the peak output voltage for the microphone to operate properly within the full dynamic range. The excitation current is more closely related to the power that the microphone needs to operate. The microphone will draw however much current it needs based on the requirements of the preamplifier and the cable load. If the signal conditioner or DAQ is not capable of sourcing 4 mA on a single channel there are a few options.

Ways to obtain the 4 mA:

1) PCB® has a model 480M122 signal which we have added to our stock offering. This is similar to our 480E09, single channel battery operated signal conditioner which has gain. The difference is the ability to provide 4 mA standard. Being battery operated, the 480M122 has extremely low inherent noise characteristics for a signal conditioner. 


2) Purchase one of the other line powered PCB signal conditioners that handle 2 mA or greater signal conditioner. For example the 482C05, a 4 channel model has user adjustable current which is factory set at 4 mA.

3) Connect the microphone to two channels of DAQ in parallel. The current will be divided between the two channels of multichannel DAQ that has 2 mA each channel such that if each draws 2 mA then the total current sourced will be 4 mA (or whatever the mic needs…3.0 mA, 3.5 mA, etc…). This is done with a “T” connector. Below is a diagram showing a standard array mic (130E22) that requires only 2 mA of constant current, along with a 378A04 mic that requires 4 mA.



4) If you are purchasing a DAQ, make sure you request a model with 4 mA per channel capability, then you will not require a “T” combined connection

How do I obtain enough constant current for a low noise microphone, if my Data Acquisition System limit is 2 mA?

To use the Industry Exclusive PCB Low Noise Prepolarized microphone, model 378A04, to its maximum capabilities, you must supply a minimum of 4 mA of excitation current. This can be achieved a few ways including combining 2 channels of 2mA current in parallel.

The new 378A04 microphone system measures to extremely low amplitudes. To achieve this, additional current must be supplied to the special microphone and preamplifier above the 2 mA that is commonly needed for microphones and other ICP® sensors. A minimum of 4 mA is required for the 378A04. It is important to note that not all Data Acquisition Systems (DAQs), or Sound Level Meter manufacturers supply this 4 mA of current.

Excitation voltage and current are two different things. The proper excitation voltage is needed so that the voltage output is not limited on the high side when the microphone responds to a high pressure input. The excitation voltage is determined by the signal conditioner and needs to be greater than (or equal to) the output bias voltage plus the peak output voltage for the microphone to operate properly within the full dynamic range. The excitation current is more closely related to the power that the microphone needs to operate. The microphone will draw however much current it needs based on the requirements of the preamplifier and the cable load. If the signal conditioner or DAQ is not capable of sourcing 4 mA on a single channel there are a few options.

Ways to obtain the 4 mA:

1) PCB® has a model 480M122 signal which we have added to our stock offering. This is similar to our 480E09, single channel battery operated signal conditioner which has gain. The difference is the ability to provide 4 mA standard. Being battery operated, the 480M122 has extremely low inherent noise characteristics for a signal conditioner. 


2) Purchase one of the other line powered PCB signal conditioners that handle 2 mA or greater signal conditioner. For example the 482C05, a 4 channel model has user adjustable current which is factory set at 4 mA.

3) Connect the microphone to two channels of DAQ in parallel. The current will be divided between the two channels of multichannel DAQ that has 2 mA each channel such that if each draws 2 mA then the total current sourced will be 4 mA (or whatever the mic needs…3.0 mA, 3.5 mA, etc…). This is done with a “T” connector. Below is a diagram showing a standard array mic (130E22) that requires only 2 mA of constant current, along with a 378A04 mic that requires 4 mA.



4) If you are purchasing a DAQ, make sure you request a model with 4 mA per channel capability, then you will not require a “T” combined connection