How to get rid of this room null at 60 Hz?

[goldark]

My PC setup: NAD D3045, KEF LS50 Meta, Rythmik L12.

The NAD's HPF options are limited to 40, 80, and 120Hz. Playing around with that along with the phase knob on the back of the Rythmik gave me an 80Hz crossover and a phase delay of 90 degrees as having the best natural response.

Using REW's auto-EQ up to 400Hz and moving my target EQ line below most of the dips (at the expense of headroom, but being nearfield, I had extra power to spare), I've managed to get a pretty flat bass response. Using variable smoothing, you can see the blue uncorrected response below compared to the purple corrected response.

There is one nasty exception to an otherwise pretty nice graph and it's that null at 60 Hz. I know moving the subwoofer around will help, but it's a really small room and placement options are extremely limited. I've heard room treatments might be able to help? What kind of treatment should I be looking at? And what locations should I try placing them?

 

[alex-z]

Acoustic treatment for a 60Hz dip either needs a lot of space or money. Porous absorption needs to be at least 1/4 wavelength for good efficiency, tuned membrane traps can be smaller but the cost is prohibitive.

https://www.gikacoustics.com/product/gik-acoustics-scopus-tuned-bass-trap-t70/ - example of what would work.

Adding a second subwoofer or adjusting your current subwoofer/seat location is the more realistic solution and certainly cheaper. If you have a rectangular room you can use the room sim feature of Room EQ Wizard to figure out what room mode is causing the 60Hz null, and which locations would not suffer from it.

PS, flat bass usually sounds mediocre. One constant of human hearing is that we like bass boost, I would try tilting up the response below 100Hz so that you reach +6dB at 40Hz then tilt the response back down so it is neutral again at 10-20Hz to prevent overloading your subwoofer.

 

[goldark]

Acoustic treatment for a 60Hz dip either needs a lot of space or money. Porous absorption needs to be at least 1/4 wavelength for good efficiency, tuned membrane traps can be smaller but the cost is prohibitive.

https://www.gikacoustics.com/product/gik-acoustics-scopus-tuned-bass-trap-t70/ - example of what would work.

Adding a second subwoofer or adjusting your current subwoofer/seat location is the more realistic solution and certainly cheaper. If you have a rectangular room you can use the room sim feature of Room EQ Wizard to figure out what room mode is causing the 60Hz null, and which locations would not suffer from it.

PS, flat bass usually sounds mediocre. One constant of human hearing is that we like bass boost, I would try tilting up the response below 100Hz so that you reach +6dB at 40Hz then tilt the response back down so it is neutral again at 10-20Hz to prevent overloading your subwoofer.

Thank you for your thoughts. A second subwoofer might be an option down the line if I move the office to a bigger room. I do plan to experiment with a room curve that will boost lower frequencies when I get the chance. Moving my seat more to the left definitely helps with the 60Hz null, but then I'm not sitting between my speakers anymore, but I'll continue to play around with it. Thanks again.

 

[Trdat]

Is your subwoofer in the corner, I mean right up tight into the corner?

 

[sigbergaudio]

I would argue that this dip isn't really all that nasty, and having at least one dip like this is very common especially with only one sub. This is likely more bothersome visually than in real life. So if it is possible for you while still sleeping at night, I would suggest not worrying to much about this.

 

[FrantzM]

Hi

The second sub doesn’t need to
match the capabilities of the main one. A cheap, circa $200, 10 or, even 8 inches, «subwoofer » could be the solution. This will require lot of work but is more likely to provide smooth bass in more than one listening position.
Also heed the advise of a slow rising slope in the bass.

Peace

 

[RayDunzl]

Listen to music where the bass is in stereo.

The dip will move around depending on the phase in the recording.

Use the RTA window with the mic at the listening position and watch music playing.

You will probably find that sometimes (mono bass) the dip is there, and sometimes (stereo bass) it isn't.

Left, right, and both speakers playing a test sweep. Deep null (due to phase)

RTA of some random music: Doesn't show the same problem.

Conclusion for my situation:

Don't worry about it.

 

[goldark]

Thanks to everyone for their suggestions. Moving the subwoofer/seating around really only introduces new dips/cancellations even if the one at 60Hz might look better. I've decided to leave it as it is. Running bass sweeps, the dip isn't actually as audible as it may seem from looking at the graphs, and with real-world content, I would've never guessed that dip was even there. I put in a room curve that provides a downward-sloping bass-to-treble tilt (same one I use for Audyssey One Evo in my home theater) and correct only to 400 Hz. Final REW measurement and room curve attached in case anyone was interested.

 

[RayDunzl]

...and with real-world content, I would've never guessed that dip was even there.

Same with me. Didn't know it was there until measured, still don't "hear" it (or not hear it, since it's a hole).

 

[RayDunzl]

RTA of some random music: Doesn't show the same problem.

And here's an RTA of some music that DOES show the dip.

The Who - Quadrophenia

It would appear to contain mono-fied bass.