Today I learned how to use Room EQ Wizard to tune my audio room. I had already done room tuning on my own and was happy with the results. But REW enabled me to get it even better.
Here’s the final FR measured from the listener position, 1/6 octave smoothed. Note this is 2 dB per division:
This shows a linear 1.5 db / octave slope from 40 Hz to 18 kHz. Deviations are +/- 4 dB of slope. I’m quite happy with this. I didn’t fix every little bump, but applied a few strategically located bands. The parametric EQ to get here is pretty mild. Each EQ band has amplitude of 4 dB or less, and widths range from 1 to 1/4 octave on each side of the center freq. In other words, gentle corrections and slopes. I’d rather have a few little bumps in the response, than perfectly flat response with bloated phasey sound from extreme EQ settings. Don’t let the cure be worse than the disease!
What I had before was pretty good, but this is better. Here’s how they compare:
Overall, this smoothed response throughout the range. During test listening I can switch curves instantly while the music is playing. My ears like the difference, especially noticeable on good acoustic music recordings.
Equipment & Details
- Test audio files created by REW version 5.2 beta 4, burned to DVD-A
- Oppo BDP-83 toslink PCM output
- Behringer DEQ2496 digital EQ, toslink input and output
- Oppo HA-1 DAC-preamp, toslink input, XLR output
- Adcom 5800 amp (27 years old!), XLR input
- Magnepan 3.6/R speakers (18 years old!)
- Room treatments (floor-ceiling tube traps, RPG acoustic foam, etc.)
- Rode NT1A mics
- Zoom H4 portable recorder
- Mic compensation curve
- Recorded from the listener position
Here are the rest of the REW plots:
Total distortion averaged about -50 dB (0.3%); higher in the bass, lower in the treble. That seems surprisingly low, considering it’s measured at the listener position and includes all distortion from the power amp, microphone & recorder. Many headphones, even some tube amps, have more distortion than this.
The bad news is that distortion at 40 Hz is about 10%. Yikes! But it’s down to 1% by 60 Hz, and higher bass distortion is typical of speakers, the exception being planar magnetic headphones.
I’ve always been happy with the bass response in this room. 25 Hz is audible, even if attenuated. But seeing these measurements, I’ll bet that if I got a subwoofer to handle everything below 60 Hz, it might reduce overall distortion. I don’t want more bass, but tighter cleaner bass is always A GOOD THING. I’ll have to look into that!
Impulse response is -50 dB by 100 ms and near the room noise floor by about 200 ms.
Group Delay looks pretty flat too. I had to zoom the Y azis to 5 ms per division to see the curve:
The CSD looks linear (no obvious ringing frequencies) and decently fast. The room treatment certainly helps here:
Here’s the Spectrogram, again looks linear, no obvious ringing spots except down at 30 Hz. Even that decays quickly at first, then takes longer after the initial decay. That’s the tube traps at work!
This was a fun day. It’s neat to be able to get some measurements to quantify the sound I’m getting.