Sound reduction on living room floor (re-visited)

red_imps_2003

A while ago some of you were kind enough to advise me on how to reduce the noisiness generated downstairs in our home (original thread here). We now have wooden flooring removed from the living room with a view to laying a carpet and I would like to take this opportunity to install some measures to 'deaden' the booming sounds generated when our boys run across it or drop their toys. The structure of our ground floor is the traditional long planks of wood screwed down onto wooden joists with a small void beneath them for ventilation. Consequently, any sharp impacts on the surface (even with a carpet and underlay) result in a booming noise akin to what you hear when dropping something heavy on the floor upstairs, presumably as the sound is transmitted to the void beneath the deck, echoes about in there and bounces back out again (a bit like banging a drum or similar light, hollow structure).

After asking around, we have decided to lay a dense sheeting called 'Phonestar' (previously known as 'Phonewell' and also sold as 'Karma Easy Panel') over the floorboards prior to fitting the carpet. This is designed to add mass to the floor (it's heavy stuff), reduce the transmission of vibrations to an extent (it's filled with sand), and impede the transmission of airborne sounds back up into the room. I have been planning on also fitting a 10cm deep quilt of Acoustic Mineral Wool under the floorboards to muffle any sounds that do still get transmitted and reduce the echo that must surely be generate down there. However, I am now having second thoughts about that part. For a start, my wife hates creaky floorboards and I have a feeling it will be hard to re-lay the floorboards as tightly as they are currently (they are screwed down and don't really creak at present). Also, I suspect we would have to remove the [oak] skirting, as the floorboards appear to extend underneath these.

If I could be confident the wool insulation would result in a further appreciable improvement in muffling over the Phonestar alone I may be happier to take the risk (and expense and effort) involved in lifting all the floorboards and fitting the wool in such a way that it sits between the joists but still leaving a void beneath it for air to circulate, which will be a faff.

Basically, what I am asking is (a) are the floorboards likely to be creakier upon after being lifted and re-fitted (or should a competent tradesperson be able to screw them down solidly again) and (b) is the presence of sound-absorbent wool likely to make any noticeable difference to the noise heard when something strikes the floorboards? Bearing in mind that I am not talking about the transmission of sounds from one room to another but the noise generated in the living room when something strikes its flooring (even with carpet fitted).

Normally Phonestar and similar products are installed on first floors to reduce the noise of footfall and other impact sounds overhead being transmitted to the floor below. Acoustic Mineral Wool is normally installed between the ceiling and the next floor's deck to further muffle the transmission of sounds between the rooms. What I want is for the ground floor to feel and sound more solid (more akin to concrete flooring) and it is not clear to me whether the presence of wool would be as effective at ground floor level as it is between floors.

DRP

I've never known a ground floor to 'boom' - I'd have thought 'booming' is only apparent if you are underneath i.e. first floor noise affecting the room below.
To stop creaking you can screw every floorboard to every joist - this should eliminate the noise.

Personally, I wouldn't bother insulating the ground floor (for sound) - it'll be a lot of work for little benefit.

I lifted my entire ground floor for the purpose of insulation & damp remedial work. It is mucky and physical, and will take quite a bit of time if you want to preserve the boards and skirting. But it isn't particularly difficult to relay the floor if you do it a bit at a time (it is more difficult if you take it all up, then relay the whole thing).

Norman_Castle

I considered putting soundproofing wool under the floor in my top floor flat and wondered if its possible to do by removing some of the floorboards. eg every 4th, 5th or 6th board. This would be much less work.

red_imps_2003

Thank you both for taking the time to read my post and reply. I appreciate it.

DRP, I have had a lot of difficulty describing the noise when communicating with soundproofing companies, builders and so forth. The best way I can think to explain it is if you strike a desk with the palm of your hand the noise is fairly loud, right? If you were to then take the top off your desk, lay it flat on the pavement outside and strike it in the same way you did before the noise would be a lot more muted. Similarly, when our boys chase each other around our living room it sounds like a herd of elephants stampeding through but when they run around my parents' living room (with solid concrete floor beneath the carpet) one only hears a faint pitter patter (the impact sound doesn't transmit through several inches of concrete as readily as it does through a couple of centimetres of wood with a substantial cavity of air beneath it). Or, if you were to stamp firmly on your bedroom floor, you don't have to be in the room directly below to hear the noise it makes. Lay a piece of carpet on the pavement outside and stamp on it the noise is a lot less noticeable.

Norman Castle, the local soundproofing specialist that visited us indicated he would fit the acoustic mineral wool by removing just a few boards at one end of the room, which sounds like what you describe. I can see how this would work in the cavity between floors, as the material would simply slide over the plasterboard that makes up your ceiling, guided laterally by the joists. I'm not sure how he planned to do that downstairs, though, where the material has to be suspended off the ground to allow air to continue to circulate. I'm sure he had his ways and means...

Ainsley1

I can understand your concern and the type of noise you experience. I have similar noise from my heavy footed herd of elephants!

It is impact noise (in my case on horrible chipboard mostly) and is primarily lower frequencies as the floor flexes with a little reflected back. The latter is probably not that significant.

To stop this you need mass and rigidity. The carpet you plan will tend to lessen the higher frequencies. Shortening the floorboard vibration time with damping will reduce the apparent effect but unlike a drum the wooden floor will be quite dampened already.

The product you mention, according to it's spec will give you a 19db improvement over 'boards only' and that is a very significant amount but will not eliminate it. Extra efforts you mention will not have much of an improvement. The Phone star has a weight of 19kg per sq metre, that is nowhere near as much as a much thicker concrete floor you are comparing with so, as you might expect, the reduction in impact noise will be less. Phone star may be very good for it's thickness but you might have to start pouring concrete to get those sort of results you perhaps desire! Not practical even if you could accept a floor 100mm higher!
You may think the cost of laying the Phone star is worth it (I have not considered price!) and there will be a significant improvement......but not as much as a bit of (self?) discipline by the youngsters!

Ainsley1

p.s. there are techniques based around balancing out resonances, too complicated to mention in detail here, often used in very high end studio loudspeakers or noise cancellation devices but that is really well beyond domestic applicability and would be exceedingly costly!!
And I thought I would mention that a second set of Phonestar flooring(two 15mm layers) would not give twice the reduction in case you think of that. It is a law of reminiscing returns:(

Norman_Castle

As suggested in your previous thread (original thread here) I think increasing the supports to the floor from underneath would stop the booming. If the floor is supported across its area in numerous places this will stop any movement. Smaller floors don't suffer from the same drum skin booming noise because the floor span is smaller. If you support your larger floor in numerous places it will act like a series of smaller floors with little flex.
You also mentioned concrete floors and mass. If the floor is well supported the floors density will, in effect, come from the ground underneath rather than the floors mass.

Ainsley1

Good reminder there from Norman.

Anything that will improve rigidity will have a reducing effect on the noise, the closer the joists (and the like) the more rigid the flooring, the higher the 'booming frequency' the easier it is to dampen out, the less it travels, the less intrusive it will be. Good point about the underfloor mass tending to be more effective too as the coupling to it is strengthened.

Eventually, if taken to extremes, you would end up with the solid floor scenario, but until then you will still fall a fair way short of the solid concrete floor effect. A pity no one can quantify exactly what and how much of it will need to be done to reach a situation that satisfies your desire! It may mean a lot of work so you maybe need to pick a solution (or combination of them) and try it.

red_imps_2003

Thank you all for your input. All the points made are very sensible. Our expectations are realistic; we know we will never achieve a reduction comparable to a concrete floor given the structures in place already. We are prepared to pay a premium for an appreciable reduction in sound but we are also realistic enough to know we will never achieve anything like silence. I guess my query goes back to the law of diminishing returns that Ainsley1 refers to. The Phonestar seems like a sensible provision because, although it's a fairly expensive product, it looks very straightforward to lay and will add considerable mass to the floor, which I hope will absorb impact a little and shorten vibrations across the floorboards and joists. It also appears to occlude airborne sounds to an extent. I just have less confidence that installing insulating wool beneath the floorboards will be worth the considerable effort involved.I can understand the theory that it absorbs the echo resonating in the cavity underneath the deck but I do not know how much of the noise we hear is actually caused by that. I can understand it muting airborne sounds travelling between floors, but am less convinced about it muting the sounds deflecting back up from beneath the house.

I do like the idea of installing braces underneath the joists perhaps mid way across the floor (a bit like propping a pillar in the middle of a drum to mute the sound made when you tap the skin). I guess this would transmit some of the vibrations into the solid ground beneath instead of deflecting most of it back. This could be just as effective as the wool but require far less flooring to be lifted. I will explore that a little more and see what our builder can do.

Thank you all again for your considered thoughts and opinions. It has really helped. I will abandon the acoustic mineral wool and either stick solely with the Phonestar layer or try lifting two or three boards in the middle of the room and fitting some bracing between the joist and the ground beneath.

Norman_Castle

In trying to stop noise from the flat beneath mine I removed the very old and tired underlay and installed two layers of the green underlay boards intended for laminate flooring under the carpet. This has reduced some airborne noise entering mine and I suspect has made a bigger difference in reducing airborne noise leaving mine. The green boards will have added mass although not a substantial amount but have made no difference to the booming noise when I walk heavily on the floor. I think a heavy foam or rubber underlay which absorbs the initial impact rather than the resulting noise would be very effective.

Furts

100mm acoustic under the floor is a risky proposition. How will it be held in place? It will slump over time and if it obstructs the air flow or makes contact with the ground there is a damp and rot issue for the floor.

I fail to see how noise is an issue. One would normally get the most dense, best quality, underlay and then the most dense, good quality, carpet. This would be deemed acceptable. Sound penetrates the smallest of gaps so you could put down a layer of hardboard first.

If the noise is children running around might a partial answer be to control the children to prevent some of the problems?