Noob RTA question

Hi, all,


I recently purchased an Audiofrog UMI-1 mic, and have started tuning my system using REW, using the Audiofrog curve as a target.

I set up REW following the Audiofrog setup guide, and am using his tuning process of "one side at a time".


This is the first time I'm using RTA mic/software (always tweaked by ear in the past), so my stupid question is this: during the measurement process, does the measurement ever "settle down" while it's actively measuring pink noise?


What I mean is this: while taking the measurement, I’ve found that it will fluctuate above/below the target curve by a bit (sometimes by a lot, especially at the high end), and will never stop moving until I stop recording.


While this movement makes some sense (it's showing the pink noise, after all), it also means that it’s difficult to know how close I am to matching the target curve, since I might stop recording while the measurement lines up with the target curve, or I might not. So I'm worried I might start futzing with the EQ when I might not actually need to.

One other question while we're on the subject of measuring... I'm in the process of fabricating another enclosure for my second sub; I currently only have the left side enclosure done.

Should I wait until I have the second sub installed to measure, or will that not effect the outcome by any significant amount?


My system is:


HU: Pioneer P99 RS
Front stage: HAT L1 V2, L3s, L8SEs
Subs: Image Dynamics IDQ15 D2 v2 in sealed 1.25 cu ft enclosure
Amps: JL HD 600/4 for L1 V2s & L3s / JL 600/4 for L8SEs (bridged) / JL HD750/1 for sub(s)


Thanks for any input!

Quote:

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Originally Posted by DubScientist

Hi, all,


I recently purchased an Audiofrog UMI-1 mic, and have started tuning my system using REW, using the Audiofrog curve as a target.

I set up REW following the Audiofrog setup guide, and am using his tuning process of "one side at a time".


This is the first time I'm using RTA mic/software (always tweaked by ear in the past), so my stupid question is this: during the measurement process, does the measurement ever "settle down" while it's actively measuring pink noise?


What I mean is this: while taking the measurement, I’ve found that it will fluctuate above/below the target curve by a bit (sometimes by a lot, especially at the high end), and will never stop moving until I stop recording.


While this movement makes some sense (it's showing the pink noise, after all), it also means that it’s difficult to know how close I am to matching the target curve, since I might stop recording while the measurement lines up with the target curve, or I might not. So I'm worried I might start futzing with the EQ when I might not actually need to.

One other question while we're on the subject of measuring... I'm in the process of fabricating another enclosure for my second sub; I currently only have the left side enclosure done.

Should I wait until I have the second sub installed to measure, or will that not effect the outcome by any significant amount?


My system is:


HU: Pioneer P99 RS
Front stage: HAT L1 V2, L3s, L8SEs
Subs: Image Dynamics IDQ15 D2 v2 in sealed 1.25 cu ft enclosure
Amps: JL HD 600/4 for L1 V2s & L3s / JL 600/4 for L8SEs (bridged) / JL HD750/1 for sub(s)


Thanks for any input!

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I don't know right this second what the guide says, but you should use averaging in the rta settings, set the averaging to forever and stop the measurement when it stops changing significantly (usually around 50 averages).

Hi, Thanks for the reply.

That might be the issue; the Audiofrog guide for setting up the UMI-1 mic with REW says to use:

Mode: RTA 1/3 octave
FFT length: 16384
Averages: 16
Max overlap: 50
Update interval: 2

The explanation of averages says: "Choosing fewer samples will make the display move faster. Choosing more samples will make the display move more slowly. 16 is good for now".

So your suggestion is to use a much higher number of averages, let it run for a while, then stop recording when it DOES actually settle down... I'll give it a shot and see how different the reading is from where I started.

Thanks again!

Quote:

---

Originally Posted by DubScientist

Hi, Thanks for the reply.

That might be the issue; the Audiofrog guide for setting up the UMI-1 mic with REW says to use:

Mode: RTA 1/3 octave
FFT length: 16384
Averages: 16
Max overlap: 50
Update interval: 2

The explanation of averages says: "Choosing fewer samples will make the display move faster. Choosing more samples will make the display move more slowly. 16 is good for now".

So your suggestion is to use a much higher number of averages, let it run for a while, then stop recording when it DOES actually settle down... I'll give it a shot and see how different the reading is from where I started.

Thanks again!

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I use an update interval of 1 and max overlap of whatever the maximum is, 90-something percent. It looks like that guide is giving you the freedom to choose your preferred number of averages, do what works for you, there are many methods.

Thanks, I'll give that a try...

If you'd like to get the RTA to update faster, you can use periodic pink noise.

Open the signal generator and select "Pink PN" and choose a sequence length of 16k. There should be a save or wav button to export a wav file of that periodic pink noise. Save it to a usb drive or put it on your phone or something and use that noise when measuring.

The real trick though, is matching the RTA settings. Select no averaging, a rectangular window, no overlap (or 50% at most), and an FFT length of 16k to match the sequence length of the periodic pink noise. That should give you an instantly updating RTA that settles immediately. It's the best way I've found to do it.

When you're ready to capture a measurement, you can still benefit from averaging to infinity and moving the mic around to get a spatial average over 10'ish seconds or more.

The below picture kinda captures what I'm talking about:

https://photos.smugmug.com/photos/i-.../i-WPcJRXM.gif

Cool, Thanks Justin.

It's been a bit too chilly to work in my garage lately (I live in CT), but I'm itching to tweak some more.