Originally Posted by piotrus-g
cool! I'm not sure what your measuring equipment is, but frequency response looks pretty decent and it is probably around something I would foresee as an outcome from RAB GQ combo. I'd also suggest adding some smoothing 1/12octave is good, and also use sine sweep instead of noise. It should improve the look of the graph. I'm also not sure how accurately is calibrated your equipment but 50db level is quite low, and if you do actual measurement at that level you are getting a lot of noise from hardware, try doing graphs at around 90 or 100db.
And yes, you have to seal tubings from the inside of the monitor!
Agreed, 50dB is very low, too low to get something meaningful in terms of a FR chart. I can definitely say that the numbers on the y-axis are more of a reference than anything. I'm doing my FR testing at around 85dB, for sure.
For my Freq.Response Test Rig, here's my setup. It's a little complicated but I didn't need to buy anything as I had all this stuff in-house from previous projects:
Interface: PreSonus AudioBox 2x2 USB (http://www.presonus.com/products/AudioBox-USB)
Mic: Electro-Voice Cardinal Condenser mic (http://www.electrovoice.com/product.php?id=89)
Workstation: MacBook Pro (OSX 10.9) (http://apple.com)
Software: Electroacoustics Toolbox v3.5.2 (http://www.faberacoustical.com/products/electroacoustics_toolbox/)
Test Tones: I got all my test tones and pink and white noise, sine sweep sound clips from http://www.audiocheck.net/soundtestsaudiotesttones_index.php
Here's a look at the mic setup. It definitely doesn't looks like a Cardinal Condenser mic at all; more like a pipe bomb. Anyway, the import thing here is that I've tried to isolate the mic as best as I could see fit. I put it on a large block of lightweight foam to reduce low frequencies resonating when the mic is in contact with hard surfaces.
The white disc with the hole are made from silicon and are interchangeable in the rig. I've got a few discs I made based on the diameter of the tubes i'm trying to test.
I've isolated the back of the pipe with a layer of medium foam. There's about 2 inches of air between the foam and the back of the mic to further improve the isolation.
If I take the silicon disc off the front of the rig, you can see that there is a 20mm hole to the mic. Why 20mm? I wish I had some scientific explanation for it, but I don't. It just so happens that this large dense black foam had a 20mm smoothed hole already in it, so I used it as-is.
Taking the foam block out of the front of the rig, you can see the entire grill of the mic and also get a sense for how thick the foam actually is (about 29mm or 1.5 inches).
This mic fit perfectly inside the grey PVC tubing.
Sealed up with some electrical tape.
And here's one way I position an IEM for testing. It works surprisingly well.
If people are interested, I'll describe how I use Electroacoustic Toolbox to do FR testing. I did give ARTA a shot but need to get some more experience with it. It doesn't seem to allow me to do sine sweeps.