Hi there ONZ, and Welcome to the Forum!
There's quite a few things visible in your photos and description that are "questionable", to put it politely, and likely related to the problems you are experiencing in your room.
As Greg said, we'd need to see the REW data to get a better idea of how the room is behaving right now, and hopefully you have a series of MDAT files, showing the results at various stages in the construction and treatment of the room. Here's a link to a tutorial I wrote a while back on how to set up and use REW for these tests:
http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122 . Hopefully you did all that before, but if not then now is a good time to do so, to make sure you have things calibrated correctly. So to get started, pleas do that, and post the MDAT file so we can take a look.
Based on the dimensions in your PDF sketch, the modal issues for your room are a close match to what you are experiencing: Your 1.0.0 mode is at 42.6 Hz, and your 0.1.0 mode is at 49.2 Hz. The slight discrepancy could be due to any number of valid reasons, but it's safe to say that you have large modal resonance issues at those frequencies, due to lack of bass trapping. It's a small room, so it will need a lot of bass trapping, and there doesn't seem to be much visible in there.
There are also room layout issues that need resolving: more on that later. (Speaker locations, mix position, desk, etc.)
The listening position, at first, seemed very bass light ,but having spent a day or two mixing stuff and checking mixes in the real world, things translate better than I expected
That says more about your mixing skills, than it does about the room!
It doesn't mean that the room is "sort of OK": it just means that you are able to mix in a deficient room. That's nice, but you'd be able to mix a lot better in a good room, and your place does have the potential to be good. Even though you managed to mix in there, I'd bet that it was an effort: you really had to concentrate, and try things multiple times to get it right. And there's also the question: How much better could it have been if the room were helping you, not fighting you?
I have read that lots of bass traps can take some getting used to.
I'm not sure I'd agree with that. Once you mix in a room that has excellent bass response, there shouldn't be much "getting used to it" required! Once you hear a room like that, and experience the clean, tight, smooth, full bass, you'll be able to mix effortlessly. Good bass trapping, properly done, such that you get flat frequency response AND flat time-domain response, should not need much learning or getting used to: it just sounds natural, and right.
The listening position is very close to the nulls though
Which implies that the room is not set up correctly!
Please measure from the front wall to the spot where your ears are located at the mix position: not leaning forward or backward.... just sitting up straight at your desk, in the position you originally expected to be. Also measure the height of your ears above the floor at that location.
I've had to bring the monitors pretty close together and lean in a bit which isn't great.
Correct! It isn't great at all! That messes with your sound-stage, and also plays havoc with your psycho-acoustic perception of the sound coming from your speakers. Even though you did manage to mix a bit like that, I'd hazard a guess that the mix didn't sound naturally wide when you listened in other places: it probably sounded "squished up", for want of a better term, with not a lot of depth to it. And you'll end up with a sore neck and back if you try to mix like that every day...
I thought I'd put a fair bit of bass trapping in. I have 4 RealTraps which are membrane type traps (3 hanging above the desk at a 45 degree angle)
Membrane traps only work if you place them at the pressure peak for the problem you are trying to kill. They won't work if you tilt them at a 45° angle, since only a small part of the wave-front will be arriving at the tap face at any given time: the wave-front will sort of "wash over" the trap, reaching it bit by bit at different parts of the trap at different times, so the trap won't ever resonate well. It needs to be flat against the wall, such that all of the wave-front hits it together at the same time. That could be part of your problem, but isn't all of it by any means.
What frequency are those traps tuned to? Membrane traps have a specific frequency at which they absorb, and that must match the frequency of the problem you are trying to solve.
Speaker wall corners have bass traps (DIY).
Are you talking about the small panels across the diagonal of the front corners? They are not big enough, and not in the correct location. There's some activity in the middle of the corners, yes, but the best spot for bass traps is the "tri-corners", where the two walls meet the floor, and the two walls meet the ceiling. That's where things are the most interesting for bass traps. To get the best effect, your traps need to cover the entire room height, from floor to ceiling.
How did you build those traps? What are they made of, and what are the dimensions?
The top of the back wall (vaulted part) is slated resonator (DIY) which is tuned around 40hz with a 1200mm void behind.
Helmholtz resonators are hard to tuned accurately. Here's the predicted tuning for yours (assuming you used something like 19mm thick slats):
ONZ-predicted-slot-tuning.png
Yes, there is a "peak" at around 40 Hz, but I wouldn't call that tuned. The Q is rather low, and the calculator could not even identify the tuning. That might be doing something but only for the 1.0.0 mode. It's not doing anything at all for the 0.1.0 mode, or anything else, and it is also reflecting all other frequencies from the rear wall, straight back to your ears, arriving in less than the Haas time, and at a rather high level, I would presume.
The speaker bridge is again homemade
I'll get to your speaker setup in another post later, but the way you have your speakers and desk set up there is certainly not helping your room acoustics! That will also need fixing...
2400x1200x300 with 3 layers of 100mm RW45 with heavy sheets of vinyl between and 100mm gap behind.
For what purpose? What is the MLV meant to do in there? Where did you get that design from?
The sofa on the back wall is also stuffed with absorbent insulation.
What type of insulation?
In short, the first thing we need to see is the MDAT from how the room is right now, done according to the tutorial I linked you to above, and hopefully additional MDAT files from earlier stages in the treatment process.
There is hope for the room, but the treatment is going to need some modification...
- Stuart -