Room Measurement Tutorial for Dummies Part 2: Selecting a Measurement Microphone

I hope everyone has read the first part of this tutorial on downloading and installing Room EQ Wizard. Here is the link to that if you missed it:

In there, I explained how you can use the built-in microphone in your laptop to become familiar with how REW works. I hope you have done that as it is critical to learn the program first before complicating it with external hardware and such.

For real measurements though, you want to use a purpose-built measurement microphone and that is the topic of this installment. Measurement microphones are just that: designed for room and loudspeaker measurements and not necessarily sound good for recording and such. They also tolerate high SPLs (volume).

There are a number of measurement microphones from multi-thousand dollar industry reference Brel & Kjr (B&K) (see to cheap USB Microphones and some in between. Happily for what we are going to do, even the cheapest microphone will do. Our room response variations in low frequencies are many dBs, dwarfing any small accuracy differences between measurement microphones. Now, if you are doing this for a living and want to publish papers and such, and have others be able to replicate your work, then you need to buy the B&K and have it routinely calibrated. But that is not the business we are in.

In the lower end of the market, you have a choice of buying a microphone that outputs analog signals and hence needs an adapter of sorts, usually a USB sound card, and typically one with phantom power. My strong recommendation is to not do that. Instead, get yourself an all-in-one USB microphone. These are plug-and-play. What comes out is a USB cable and both Mac and Windows PCs have built-in drivers for them.

One criticism of USB microphones is that they may not work for timing analysis in REW. As you will see, we will NOT be using timing analysis in REW. In that regard, there is no compromise in using a USB microphone and you get all the simplicity of them with no drawbacks.

The in microphone to use with REW seems to be seasonal thing. A couple of years ago when I bought mine, the Dayton Audio UMM_6 was the one to get I just looked on Amazon for it and for some strange reason, it shows a lead time of 2 to 6 months to purchase from the company. Fortunately, Parts Express also sells through Amazon and they seem to have them in stock: As you see, the discounted cost is just $88.

Another option is the Minidsp UMIK-1: I cant find a good price for that on Amazon but as you see in that link, the company itself sells it for $75.

Before you hit the buy button, let me talk about calibration. Both the UMM-6 and UMIK-1 come with a serial number that you type online and it gives you a (supposedly) a calibration file to use with REW. My recommendation is to not bother! Yes, you heard me right. You dont need a calibrated mic and these files themselves can be faulty. The difference between calibrated and non-calibrated mics is small and it is in a region that I suggest you use your ear, not an instrument, to adjust the sound.

Now, if you insist on having them calibrated, there is a very low cost way to get there and that is to buy the above microphones from Cross Spectrum Labs: For just $20 to $30, you get the same microphone but now it comes with a calibration file (or multiple for different angles). I was in a hurry when I bought mine so I bought it on Amazon. If I were not, I would have spent a few more dollars on Cross-Spectrum to support this nice service as calibration usually is a very expensive affair. But again, it is not necessary.

Once you get your microphone, then all you have to do is plug it and either tell your operating system it is the default recording device, or tell REW to use it instead of the built-in microphone. Now repeat the lessons in the first tutorial. Compare the results to the built-in microphone. You should see less low frequency roll off and more accurate overall curve.
In the next tutorial we will get into the meat of these of lessons which is to actually perform the measurements and understand what they mean.