Monitor sizing / room dimensions.

[werp]

G'day illustrious members.
Time to consider nearfield monitors. My room size is 8.5 x 4.2 x 3.0 metres.
Double brick walls, concrete ceiling and carpeted concrete floor, with sliding glass doors at one end. Currently untreated.
No issue with setting up a decent distance from a wall, it's a dedicated room.
I'd prefer not to use a sub, but do like a punchy low end. I have a soft spot for JBLs. Trialling monitors isn't an option.
Any response would be greatly appreciated

[waveheavy]

You'll need acoustic treatment. Otherwise you'd be better with investing in some good headphones and relying on those along with how your mix translates elsewhere.

Best to not have the same material on parallel walls, nor floor-ceilings. Carpet on the floor might help a little with the concrete ceiling, but not if the rest of the room is left untreated.

Roxul Safe n' Sound 2'x 4' bats covered with breathable fabric in each corner floor to ceiling; an overhead cloud of same above your mix position, and same at each first reflection point on side walls, one for the front wall, and a couple for the rear wall. First reflection points easily found by sitting at your mix position with someone holding a mirror on sides walls, above your mix position, etc. Wherever you see your monitors in the mirror, that's a first reflection point.

Mix position should be on one of the short walls as your front, sitting position around 38% from front wall.

With proper room treatment, even cheap monitors will sound their best.

The word 'nearfield' is an oxymoron term. Just because it's called a nearfield monitor does not mean they're designed to prevent audio reflections in your room. Glass and concrete are major reflection material.