First Measurement Issues

[Clover]

Hi Everyone,

I'm new here trying to learn REW and acoustics to help get some speakers sounding better in my room. I switched to dipole speakers and have struggled with setup, so I bought a UMIK-1 and took my first set of measurements. I'm thinking I did something wrong as the top end is dropping off sharply and looks to have a lot of ringing in the waterfall. I'm not sure what I got wrong for it to look like that or if that is actually how my room sounds up top. There are a couple areas that give me some pause but I'm too new to know what I did wrong or if these results are legitimate. I had some trouble calibrating my sound card and ended up not using a calibration for it, so maybe that is my issue. Does it look like I made an error with these measurements to you and does anyone know what I should change? The below is with 1/12 smoothing of both L+R + Subs. Thanks for the help and please let me know if something other than what I provided is needed.

 

[Clover]

I should have noted this is a starting point that I am looking to improve from and I do see the need to cut the gain on my sub from the initial look. I'll cut it some, but I do like a little extra bass so I'm okay with some shelf. I'm currently building six 9" thick + 3" air gap bass traps/panels to hang in my room at first reflection points. Thanks again.

 

[Keith_W]

To answer some of your questions:

1. Sound card calibration makes no sense if you are using a USB microphone. It only makes sense if you are using an interface with a physical loopback, and even then the deviations are in the order of +/- 0.5dB at the extreme ends of the frequency range, which is miniscule compared to your microphone. So this step is not needed.

2. You are sending REW's output through AirPlay. AirPlay is lossy, it is not bit perfect. I don't know exactly what AirPlay is doing, but lossy transmission typically cuts out high frequencies which is probably what is producing all that high freq noise. As a first step, STOP USING AIRPLAY and use a cabled connection.

3. None of your measurements have a timing reference.

4. You have four impulses in your IR, spaced exactly 500ms apart. There should only be one. Please show us a screenshot of your "Make a measurement" dialog box and "Preferences".

5. All your "Left" measurements have a tone at 125Hz. This same tone is missing in all your "Right" measurements. If the tone was present in both measurements, I would tell you to look for a source of noise in your room (computer fan, air-cond, neighbour playing bagpipes, etc) but since it is present in only your left measurements, one has to suspect something wrong with your left speaker or amp. Maybe a screw loose, maybe some kind of resonant vibration, maybe amplifier oscillation, etc. I suggest you use the tone generator to play a 125Hz tone and compare subjectively the sound of left and right. If you think it is a resonance, damp that surface by pushing on it. If you suspect an amplifier problem, swap left and right channels.

Interestingly, if you look at that spectrogram noise above 8kHz, you can see that it occurs in 500ms intervals (the same as those impulse peaks in your IR). Maybe John has an explanation for that, i'm not smart enough to know what is going on.

6. I wrote a free book on taking and interpreting REW measurements. I suggest you start there. Even with your flawed measurements I can already see a lot of problems with your room. But it's better to correct these mistakes first, take proper measurements, and then try to read them.

Good luck and welcome to AVNirvana.

 

[John Mulcahy]

You have four impulses in your IR, spaced exactly 500ms apart.

Very odd. Something in the replay chain must be generating that, some surround effect, perhaps.