Room EQ Mystery

[Ron Texas]

My room has a mode at 180 hz. REW tells me it needs -7 db 4.9 Q of correction. I put this PEQ in Equalizer APO and measure again. REW tells me I need another 2 db of correction. What's happening here? Should I use -7 or -9 db? Is this something like quarter wave cancellation where EQ doesn't work?

 

[ernestcarl]

My room has a mode at 180 hz. REW tells me it needs -7 db 4.9 Q of correction. I put this PEQ in Equalizer APO and measure again. REW tells me I need another 2 db of correction. What's happening here? Should I use -7 or -9 db? Is this something like quarter wave cancellation where EQ doesn't work?

Were there no other variables that changed e.g. mic movement, time of measurement, door and windows closed, volume level change? I’ve taken enough measurements to know that just leaving what one was doing for a moment and coming back later to remeasure can show slight differences in the response.

Dunno about the quarter wave cancellation being the cause, but I’m just guessing better to err on the lesser cut. Though I don’t bother making things completely line up flat in the bass anymore.

One other practical thing you can do is just listen to burst tones using REW. Check if you can really hear 180Hz as being inconspicuously 2dB louder than, say, 100 or 240Hz.

 

[Ron Texas]

@ernestcarl after playing around a bit and lowering the Q to 4.0 the adjustment is 8.5 db. It could just be REW and how it uses psychoacoustic smoothing. I used 1/6 octave to fine tune it. The music isn't damaged. Maybe there's nothing to get excited about.

I'l try cutting less tomorrow and see how it sounds. It's definitely not quarter wave cancellation. Just why the room provides so much boost is a mystery too, but I've seen other members get similar results in their rooms.

 

[Erici]

Hi Ron,
I use variable smoothing in REW to create filters. It smoothes the lower frequencies less than the higher frequencies. This allows you to more accurately target the frequency peak. The REW manual says "Variable smoothing applies 1/48 octave below 100 Hz, 1/3 octave above 10 kHz and varies between 1/48 and 1/3 octave from 100 Hz to 10 kHz, reaching 1/6 octave at 1 kHz. Variable smoothing is recommended for responses that are to be equalised." To see how well the EQ worked, I use Psychoacoustic, and my ears of course. Works well for me....

 

[Blumlein 88]

Wouldn't 180 hz be a 3.15 foot or so distance for a room mode? Any dimensions twice that or 4 times that would excite that frequency as well. So any dimensions close to 12.6 feet?

 

[Hipper]

I use 'no smoothing' to measure below 300Hz. I also just tinker with REW until it's at its flattest. If that requires two or three measurements so be it. I just assume that the room and its contents behave in such a complicated way which even sophisticated measuring cannot accurately reveal.

To speed things up you could adjust the measuring to just 0-300Hz on REW.

You could try these test tones and just listen around the 180Hz area - say 175-185Hz - to hear if they sound different to your ears:

https://realtraps.com/test-cd.htm

One final point. It's easy to obsess about getting the flattest frequency response. Don't fall into that trap. REW, test tones etc. are just tools that help us get a better sound. The final arbiter though is always your music and getting an enjoyable listening experience.

 

[ernestcarl]

It could just be REW and how it uses psychoacoustic smoothing.

As others have mentioned, it's generally unnecessary/not recommended to apply smoothing when creating EQ filters specifically in the bass. I avoid too much cutting in some of these bass peaks because, from my experience, it can sometimes have the unintended consequence of making things sound "perceptually" anemic (despite ultra-flatness in graphs) instead of being naturally balanced.

 

[Ron Texas]

I have stopped using psychoacoustic.

 

[puppet]

The mic could be inside a mode.

 

[Erici]

I have stopped using psychoacoustic.

Hi Ron,
I'm interested in why you decided to stop using psychacoustic in REW?

The REW manual says this about psychoacoustic smoothing: "Psychoacoustic smoothing uses 1/3 octave below 100Hz, 1/6 octave above 1 kHz and varies from 1/3 octave to 1/6 octave between 100 Hz and 1 kHz. It also applies more weighting to peaks by using a cubic mean (cube root of the average of the cubed values) to produce a plot that more closely corresponds to the perceived frequency response."

 

[Ron Texas]

Hi Ron,
I'm interested in why you decided to stop using psychacoustic in REW?

The REW manual says this about psychoacoustic smoothing: "Psychoacoustic smoothing uses 1/3 octave below 100Hz, 1/6 octave above 1 kHz and varies from 1/3 octave to 1/6 octave between 100 Hz and 1 kHz. It also applies more weighting to peaks by using a cubic mean (cube root of the average of the cubed values) to produce a plot that more closely corresponds to the perceived frequency response."

I stopped using psychoacoustic because the 1/3 octave smoothing under 100 hz masks what's going on when trying to make eq adjustments.