No announcement yet.

How-To: Build a MMM rig for RTA purposes for $25 or less.

  • Filter
  • Time
  • Show
Clear All
new posts

  • How-To: Build a MMM rig for RTA purposes for $25 or less.

    Hey, everyone. I recently made a video discussing how to DIY your own Moving Microphone Measurement (MMM) setup to use with an RTA system to EQ your stereo system's response and thought some of you may find it useful or a jumping off point to share your own ideas. This is my second video and I'm learning how to carry some of my ideas/content from my site ( to youtube. It isn't perfect (I need better garage lighting and a better mic) but it's the journey, right?...

    Some background:
    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" because, other than headphones, I've never seen a target curve that included elements of the human body; never mind the fact they would vary from person to person.

    Therefore, I am providing a low-cost alternative: an oscillating fan to move the microphone. In REW I just let it capture the response in real-time as the mic moves. While not perfect, this helps remedy the above two issues of time and in-accuracy and will be an improvement over the typical methods we use. I am definitely not the first person to do something like this and I'm not pretending to be. And ideally this would be a 3-axis measurement that could grab the response of the entire head area (X, Y, and Z). But, that alternative would require more money and a good deal more time to build and code it up with arduino or the like. The method I've provided is at least a step in the right direction and aimed to get people started with little money and with things they can source locally.

    Before throwing negativity my way, 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.

    I hope this little video helps you all in some way. And if nothing else, encourages you guys to get up and take this to another level that you can share with the rest of us.

    Click image for larger version

Name:	DSC05744.JPG
Views:	136
Size:	834.1 KB
ID:	1434834

  • #2
    While I have admittedly not yet watched the video (but I will), I think this is an important subject and measurement method that more DIYers should be aware of and take advantage of in their speaker evaluations and voicing.

    Here is my experience. I have been using and old DBX RTA-1 and doing moving microphone measurements as part of my speaker design/evaluation/voicing process for the last 4-5 years or so and for the last few years I have been using REW as well. In my experience and research on the subject, In my opinion, for speaker evaluation, you should be looking to cover something like a 3'cube centered on your listening position. You want to reset the RTA before a measurement and it is crucial that it is set to continuously average, so it builds a response profile over the entire time you are moving the mic. I think in REW, IIRC, you want to hit Reset Averaging in the main RTA menu, then in the RTA controls menu, set it to Averages Forever. Then start your MM process. Do this before each new MM measurement you take.

    The technique that has worked best for me and I have found easiest to produce pretty repeatable results is as follows: Sit forward in a chair and reach out with the mic about head high. Move the mic in a vertical figure 8 shape, in a slow deliberate manner with the 8 centered on the head. I make 4 passes this way, then switch to a horizontal figure 8 shape centered on the head, then while the RTA is still on and averaging, slide back in the chair and repeat these steps with the mic close to your body. This allows you to cover about a 3' cube, the back of which is close to where your listening position is. The MM method of measurement, using continuous averaging can tell you much more about what you are hearing relative to the power response or full acoustic energy emitted by the speaker into the room than the typical one axis. gated measurement you see often used by DIYers.

    Don't get me wrong, one still needs good gated measurements on whatever design axis you choose to use for crossover design and simulation, but the MM method and RTA are valuable tools for evaluation of what you are hearing from the speaker as a whole in room and one all DIYers should consider adding to their toolbox.

    Again, very good idea for a thread.
    Dan N.


    • #3
      I am trying this at home. Talk To Sonic
      Last edited by Barrows325; 03-25-2020, 10:46 PM.