Bass traps behind speakers can help with dips…you will need an air gap equal to thickness of panels….GIK has bass traps with scatter plates so you don’t deaden that small room too much.

Multiple subs would need DSP help for delays and integration…and aren’t effective above crossover.

PEQ can lower peaked frequencies, making nulls less obvious.

In small home studios they put the speakers right up against the wall to minimize speaker boundary interference…or at least to push the problems to higher frequencies that are easier treated

Try sitting closer to speakers for more even bass.

You will probably need 4 larger bass traps to make much difference

Bass traps are most likely to reduce the height of the peaks, but do little to the valleys. The valleys are result of speaker-boundary interference, the reflected waveform from a wall – usually the front wall – mixing in with the speaker’s direct radiation, and canceling it. If you had very thick and large panels behind the speakers, that would reduce the level of this reflection. Dip of 20 dB suggests that the wall is bare and reflection unattenuated, and the frequency 100 Hz suggests that distance between speaker’s front baffle and the wall is about 86 cm. Halving that distance would move the cancellation up to 200 Hz which is far less objectionable.

I suspect that those narrow dips are due to first reflections off the side wall opposite each speaker (or perhaps the ceiling). So for the right speaker, there is a primary reflection off the left side wall that arrives at the MLP with a 5msec delay, which is a half wavelength at 100Hz, so the reflected wave cancels the primary wave. I had an issue like this in my listening space that was due to a ceiling reflection. If this is the case, you will get a better improvement by placing the traps at the first reflection point. As an example, I shared pictures of my installation here.

Add 1 or 2 more subwoofers in different locations (if moving your subwoofer doesn’t help).

One more comment. Since the discussion started with standing waves; the front to back standing waves in this room will be at multiples of 67 Hz. The presence of the reflection induced dip is tuning the first mode a bit, so L and R look different. The two peaks at about 134 Hz and 201 Hz in both the L and R response curves are a result of this mode. Mounting panels on the wall behind the speakers should help tame these peaks - see the photo in the post I linked in another comment for how I have my room set up. (The black panels behind the speakers are GIK monster traps. The big panel on the left wall is an Acoustimac 2" art panel.) It will also help with decay times, which will improve the listening experience.

Generally speaking, in a room this small I would focus on treating first reflection points with the panels, rather than going after corner placed traps. The wall behind the speakers is both a first reflection point and a big contributor to long decay times.

I have full height bass traps. The best way to control bass is to get multiple subs If your room is small consider kc62s or svs micro 3000

https://www.genelec.com/monitor-placement

Read under “Wall Reflections and Cancellations”. Also, do you really hear this dip?

I actually think you’re working with an overall pretty useable room.

1. Your response has a slight downward trend as you go higher in frequency. For in-room response, this is generally accepted or preferred for two (2) reasons: your ears naturally want more bass to hear it “evenly,” and your flat side and flat rear wall sum reflections will be full of >1-2k and up, so the blurred sum will add to your SPL and let you hear a flatter overall response, albeit blurred by reverberation.

2. I marked up this screenshot of your room response to show you what I feel like are your problem room modes: approximately 120hz*, 150hz, and 200hz.

• The 120hz could very likely be from your ceiling. Sitting over a very thick couch can help this. Or cloud absorbers directly overhead of your listening position.
• The 150 and 200 Hz are grouped-yet-separate in a way that makes me think it is 2 more boundary-reinforced (wall-amplified) room modes. These 2 can be DSP’d easily and without much adverse effect

edit: whatever you do, don’t go throwing -15db notch filters on servere room modes, especially if you “measure loudly and mix/listen quietly.” room EQ is volume dependent, and to do it properly you really should be EQ’ing to fixed volume and staging positions.

Looks pretty narrow. Not sure it is audible.

Wow those dips are wild.

You can’t fix this with any form of absorber, filling a dip would rather require selectively amplifying these frequencies, which is also unrealistic.

The only realistic approach is to use a parametric equalizer to attenuate all ther frequencies, by say 10dB to keep it realistic.

The size and amount of traps ud need isn’t realistic(especially for these frequencies)for a living space, id recommend smaller somewhat aestheticly pleesing sub with some boundary mode active or just one that doesn’t extended too deep to address the neighbors “issue” or just turn it down/off in the evenings

This is certainly a room mode cancellation (and is extremely common for smaller rooms). It’s a function of the speaker positions in the room as well as the listening position.

If you’re unwilling to move them out into the room, you can try moving them left/right as well as move the listening position left/right/forward/back to see what it does.

Bass traps will certainly help, but they’re not going to magically fix a 30dB null.