How to Determine the Headroom of Your SPL Measurement System

Determining the headroom of your measurement rig is an important consideration for ensuring accurate results, especially when measuring at concert levels. This will require the manufacturer specifications of both your measurement microphone and audio interface.

First, determine the audio interface maximum input level. This is typically given in dBu (0dBu = 0.775 vRMS). Exceeding this level will clip the interface, causing an "OVERLOAD" message to appear within Smaart on any SPL meter for that input. Please note that this message will appear when the interface is clipped; not the microphone.

SPL Meter Overload in Smaart.

Next, we need to determine the Max SPL specification and the sensitivity of the measurement microphone. Typically, for concert-level measurements, we are looking for the Max SPL value to be 140dB SPL or above. 

Once we have determined both our interface max input level and our microphone max SPL level. We can calculate the MAX SPL of our measurement system. Rational Acoustics has put together a spreadsheet to do much of this calculation for you, given the values requested above. Please note that these calculations are made assuming that your interface it set to the lowest gain possible.

Click here to download the Max SPL Calculator

To use the calculator, select your measurement microphone and audio interface from the dropdown. The spreadsheet will automatically populate the manufacturer specified values (As of Fall 2022) into the spreadsheet, and calculate the Max SPL and system headroom. 

If there is a measurement microphone or audio interface you use that is not included please submit a ticket with the device and link to manufacturer's webpage. Providing specification sheets is helpful. The Rational Acoustics team will add it to the list next time we update the spreadsheet.