False ceiling - joist size?

[MadAlicesDad]

I want to put a false ceiling in the kitchen to lower the ceiling by about 6-7 inches to accomodate vents, water pipes etc. The span is 2.8m and the only weight on it will be the plasterboard, plaster and the lights.
Unless advised otherwise, I propose fixing 4x2 to the walls and using joist hangars at 400 or 450mm spacing. If necessary I can use galvanised straps to tie the joists to the floor joists above, but what size joist is needed for a continuous span?
TIA
Mike

 

[PrenticeBoyofDerry]

Over 2.8m 2x4s will be ample, space at 400mm centres not 450MM.

 

[foxhole]

Or 600mm centres and noggins to support all edges, less timber.

 

[ladylola]

It would even be possible to use smaller timbers and hang it from the exsisting ceiling joists.

 

[MadAlicesDad]

I thought of that but my daughter's bedroom is above and anything that can isolate us from the stamping and crashing (not bad behaviour, just that she walks like an elephant!) is a bonus!
To pick up on the 400 vs 450 vs 600 spacing, is 600 plus noggins acceptable if 450 without noggins is not (the inference from PrenticeBoy's post)? I would have used noggins anyway, but was suggesting 400 or 450 to give me flexibility in using either 2.4x1.2 or 1.8x0.9 boards depending on what is the most efficient coverage (the room is 2.8 x 3.8 so neither fits easily )
Thanks for all the advice and suggestions.
Mike