New apartment mix room

[endorka]

It looks like you have the frequency / SPL chart within the range of 75 to 90 dB. For a room this size, that is a superb result. I'm afraid I have no experience of tuned traps so can't offer help there. You may well be into the point of diminishing returns with a room this size though, and the results you have are already superb.

How well does it work for mixing, especially in terms of the low end. Bass drums, bass guitar, low end of guitars and piano etc.?

Saying that, you may be able to get a little bit of improvement around the 109 Hz area by improving the bass trapping pertaining to your width dimension, i.e. the side walls. Would it be possible to space the existing traps away from the wall? For example, if they are 4" deep, leave a 4" gap.

You might also get some benefit by having some more superchunk type traps along the side wall / ceiling corner.

According to EBU Tech 3276 the nominal RT60 time for your room would be about 0.2s, so it is a bit dry sounding, as you say. The slat based traps would certainly help. I haven't built one of those, but it goes without saying you should make sure the slats are sized and spaced for a specific purpose, i.e. to address a frequency range you have identified as important.

Cheers,
Jennifer