How-To: Build a MMM rig for RTA purposes

[hardisj]

This is my second video and I'm learning. It isn't perfect (I need better garage lighting and a better mic) but it's the journey, right?...

Anyway, in this video I'll teach you how to DIY your own Moving Microphone Measurement (MMM) setup to use with an RTA system to EQ your stereo system's response.

Due to the reflective nature of car and home stereos it is often recommended users take multiple RTA measurements of their system in the "head space" (where they sit and listen). To do this you are left with two options: 1) Place the mic at different locations, measure and then average all the results together. However, this can be time-consuming and not very repeatable. 2) Sit in the listening position and hold the microphone in front of you while moving the mic around the head area. This is complicated by your own body's influence (even your hand can change the result). This is especially detrimental if you are trying to use a "target curve".

Therefore, I am providing a low-cost alternative: an oscillating fan to move the microphone. I am definitely not the first person to do something like this and I'm not pretending to be. Also, while not perfect, this solves the above two issues of time and in-accuracy and will be an improvement over the typical methods we use.

Make sure to watch the entire video for some tips on things I learned when building mine. I tried to answer all questions in advance so don't tell on yourself by asking something until you've watched.

 

[Blumlein 88]

I think your mic should be on a longer boom so it sweeps a longer arc. The academic paper on this indicated moving an arc of 1 meter radius. That was for arena and theater use (I think for arena use they used 2 meters). So maybe not that much needed in domestic listening rooms, but more than you are getting I think might be a good idea.

 

[hardisj]

I don’t disagree. But practically, that’s hard to accomplish in a car. In a home it should be easier. Also make sure you support the mic because the fan may not be able to sustain that much of a moment arm.

 

[QMuse]

Also make sure you support the mic because the fan may not be able to sustain that much of a moment arm.

Maybe aluminum arm would be a better choice to loose some weight so length can be increased (in a home usage scenario)?

 

[Blumlein 88]

Pvc tubing would be fine and have less weight. If you size it right you can even slip the mic just inside of it. I've used it that way before.

 

[hardisj]

Pvc tubing would be fine and have less weight. If you size it right you can even slip the mic just inside of it. I've used it that way before.

I have, too. My measurement system actually consisted of a mic boom with a 2 foot PVC extension (and a rod inside to keep the PVC from bending). If you watch the video you'll note where I discuss using this rig behind the seated position and using an extension to put the mic in the head space. But if you're using a long arm, say longer than a couple feet, the mic at the end will be a problem if the motor isn't built for that. I tried about 4 different fans. The one I used in the video is the only one that *might* work for a long arm like we are discussing here. I can say without a doubt the others would not, though. That's the only thing I'm cautioning against here.