Plywood over timber underfloor -- sound insulation question

Mumili

I will install 12mm laminate flooring in the three rooms upstairs. The subfloors are plywood over timber joists, so there is a lot of noise coming down when kids run around. I think it's called the drum effect due to the cavity between the joists and the plywood. Ripping all the subfloors and filling in the cavities is not an option.

I found an acoustic underlay (5mm) with good reviews. To make the floors more silent I thought about laying two sheets of underlay on top of each other and then putting the laminate flooring on. My concern is that if the underlay becomes 10mm, then it will be spongy to walk on, and the laminate sheets may even come apart. So I am undecided whether I should lay just one sheet or two sheets. Any other input with sound insulation is also welcome. 

FreeBear

Laminate is going to be noisy, even with acoustic underlay.

Put the stuff in a small upstairs room, and sound carries across the building in to rooms below - Part of the reason you often find it listed as a restriction when buying a flat. If you want to reduce the noise of small children jumping around, put down carpet with a good quality underlay.

Bigphil1474

As above, carpet will be far quieter than laminate even if you put acoustic underlay on - probably a lot cheaper as well if you can find a local carpet fitters. 

I think you're right that 2 layers of the underlay would be an issue - are you installing yourself? Best bet is to ask the people supplying the laminate or the installer if not fitting yourself.

Chickereeeee

You can get 10-13mm thick underlay, with very good acoustic and thermal insulation properties, but you would only use it for carpet. Laminate underlay should be 3-5mm thick.