flanking sound- concrete floor- soundproofing- acoustics

[saltysea]

Hello hello..

I'm in the process of partially rebuilding my studio which is housed in a concrete slab commercial building.
(studio is predominately a mix room .. audio post and music)
At present the walls are drylined with 2 sheets of 1/2" plasterboard on each side.. no green glue and nailed to 3"x4" stud work. It was all built in a hurry a few years ago without much insight into soundproofing construction. Needless to say the room is not really soundproofed at this time!
So.. I'm attempting to achieve this through a partial rebuild. I had someone come in and give me advice which included the following ideas.

Remove the internal plasterboards and fit new ones on a resilient channel system.... 3 layers of different thicknesses (with green glue coverage in between them)

Build a floating floor system which comprises (top down) of 25mm plywood, Mass loaded vinyl, quietboard (cement impregnated board), another layer of mass loaded vinyl, 25mm of MDF all bonded together on a timber frame which itself is sat on a bed of rockwool.

Acoustic treatment proposed includes super chunk corners, large limp mass bass traps behind the stereo monitor positions, a number of broadband traps for other corners and walls (about 11 in total) also.. a quadratic diffusor between the stereo monitors on the front wall- centre.

I wondered if any one here had any comments on these ideas ? and as I'm just putting together a spreadsheet of costs (and thinking about new eqp costs on top!) I'm wondering if I can economise on some of the design.

specifically
1) what do you think the impact of reducing one layer of plasterboard would be? i.e. just 2 layers on the inside with green glue between them.

2)Also I read a proposal for a floating floor on the green glue website that looks quite attractive in terms of cost and effort involved.
It suggests using some sort of resilient layer (it doesn't specify what) on the concrete floor followed by a floating raft comprising 2 sheets of OSB with green glue (of course) sandwiched between.
Could this solution be anywhere near as effective as the one I was given?

I should also say that I plan on using a subwoofer some of the time (monitoring with PMC TB2s x 5 + TLE 1.. also have Dynaudio BM15a but might be retiring them after the works)
I'm concerned about how the floor will effect that too... any thoughts on this?

To put my space into context ..it is in a pretty quiet shared 2,000 sq foot space. the main unwanted sounds I hear inside at the moment are footfall .. some particularly noisy heels that people wear on the exposed concrete just the other side of my wall!

I'm attached a couple of pics of the space .. main room dimensions are 4.4 meters long (max) by 4.1 metres wide (max). Small adjoining room .. ( to be either a VO booth or monitoring space if I record people in the main space) is 2.1m x 1.8m

one last question..
I was thinking of constructing the bass traps/ absorbers myself but when I look at the costs and the time involved in making them I've been wondering about the ready made products.. would there be a massive advantage in building the traps myself? should I wait until the super chunks are installed.. do some measurements and then take it from there?

apologies for using both metric and imperial through the post.. all thoughts most welcome and very appreciative of your time!!
all best
dennis wheatley

[avare]

Number one, a floating floor that does not cause acoustic problems is expensive and 95% of the time a floating floor is not necesary.

Andre

[DanDan]

Before you dig in here, be sure this is the right premises!
Sound travels extremely well through concrete.
Also concrete walls give rise to very strong room modes.
Soundproofing is much more difficult than acoustic treatment.
Details are absolutely crucial. You could buy Rod Gervais book. There are also plenty of construction details over at john sayers site and studiotips.
You have assembled a collection of materials, some of which are quite controversial.
There are very divided opinions on MLV for instance.
Plasterboard, some say three layers of different thickness, some say the same thickness. There are denser 'acoustic' plasterboards. IMHO, the detailing is more important than these choices, e.g. fill all the gaps carefully, and carefully follow a screwing and glueing plan. Neoprene or such at all edges.

I haven't used Green Glue so I can't attest to performance. I would imagine 3 layers of it would be expensive. I would be more inclined to first find a very high performance RC e.g. WallComp, UK - CMS Acoustics


You need to find out where that footfall is coming from? You have not described your ceiling?


Floors- MLV? Hmmmm. I would be very sure of the cement impregnated MDF though. I would steer away from controversy, find the area of consensus. Find the best resilient floating material, one that won't compress or get hard. I doubt that Green Glue is the best choice here, but I would be open to experienced opinion on that. Again, seal all gaps, screw it together intelligently, and so on.

SuperChunks rock, go for the biggest ones you can. 32 inch is practical.

Sorry to repeat, but be sure you are in the right building!

DD

Sound Sound - Homepage
DD

[saltysea]

Thanks DanDan (and Andre)

I should have said that I'm at the top of the building.. no neighbours /problems above at least... concrete floor + ceiling

The footfall I can hear is just outside of my door... in the common parts of the space I share.. covering the floor to eliminate the problem at source would be ideal but its not practical (2,000 sq ft)
With a set up like this it feels like the floor will always undo even the best soundproofed wall I put up.. It really feels like I need the floor to be decoupled somehow.
I'd be very happy to not install a floating floor but I cant see how the walls alone will stop an impact sound on the concrete just behind them.

Does anyone else have opinions about the merits or otherwise of MLV vs GreenGlue for a floating floor?

I'll look into the high spec RCs that you suggest.. sounds like a good idea.. do you think 2 layers of plasterboard with those could replace 3 with normal RC?

32" superchunks were what I had in mind... so at least that's good!

Re: choice of space.. I completely understand what you're saying! .. in many ways it isn't ideal but it has a bunch of other reasons why its attractive for me at this time... some of them financial.
So I'm looking to get something workable here that'll see me through the next couple of years really.. not bedding in for 10!

Thanks again.. really appreciate the response.
ddennis

( DD.. Cork's a lovely part of the World..I have very fond memories of a wedding there years ago.. a nice all week long affair.. 'twas grand' as you might say... also makes me think of Microdisney all those years ago)

[DanDan]

Dennis, I am surprised that you can remember the wedding :-)

A version of MicroDisney did a reunion gig a few months ago. I mixed it. Great fun.
Talk of reunion.

Major flooding here recently.

You are sure about your location, now lets be sure about the issues.
It can be difficult to tell where sound is coming from. Footfall can travel through the gap around the door, through the door, through the concrete floor which will rebroadcast it near you. Likely all of the above. So you need to identify the strongest paths and prioritise your attacks. If it is through the concrete, then a floating floor is needed. You probably need a good floor surface anyway, so why not do a decoupled one. Just don't bank on this working 100%. Doors are often the weakest link, solutions are difficult to construct and proven commercial products are very heavy and expensive.

The plasterboard companies have specs for the various constructions. I doubt if they go for 3 layers. I would expect another 3-6dB for each extra layer. 2 should be fine though, just use thicker, heavier, acoustic board. LaFarge look good on paper. Focus on the detail, the screwing, gluing. Check out lots of detail at john sayers and studiotips. It may be best to create internal walls using steel studding, fulling floating from floor and ceiling. This seems to slightly outperform wood and won't shrink causing gaps later. The steel itself functions as RC but I would use the channel as well.

Andre, what product do you use to decouple the ceiling and floor plate from the concrete above and below?

I noticed another couple of points on reading again. Large Limp Mass Traps on the front wall? Again controversial. I reckon the back wall would be a much better location for these.
Your front wall could be gapped out from the concrete if you have space, creating a very large damped plasterboard trap. That should help with SBIR.
Diffusion between the monitors doesn't make much sense here. Consider it behind you.

While we are making gaps, if you have the space you should optimise your internal room dimensions.

I don't want to be so negative However you have mentioned quite a few ideas which are dubious, and this job is a bear. If this doesn't work 100%, will you neighbours tolerate your presence? 'Quiet shared space' scares me.
Take some time. Research more, there is tons of stuff on the forums mentioned.
Get Rod's book. Maybe ask a pro to look at the space and your plans before proceeding.

Best, DD

[avare]

Excellent summary of the task Dan in the post above.

Isolation of the wall/ceiling from the floor if a separate base for the walls is not feasable can be achieved with PROPERLY SPEC'ED rubber or other resilent material like sylomer. The laod and deflection have to be calculateed for the material. Otherwise it is a waste of money.

A floating floor has to have resonances (yes plural) below the frequencies where isoaltion is required. Everyone seems to remember the weight/spring resonance and then forgets the (acoustically obvious) MAM resonance of the floor!

I would first investigate the fotfall noise in greater detail. As you wrote, it is probably not coming through the concrete floor.

Andre

[saltysea]

Thanks Andre + DD .. as always I really do appreciate the time and effort in replying and keeping the conversation going.

It feels like your overall advice would be to hangfire on any ideas of decoupling the floor untill its established that the walls and doors aren't the weakpoint.
That totally makes sense but leaves me a bit unsure how to proceed because I'll need to commit to a door height in order to finish the walls and find out!
annnoying.. I'm not sure how I can get round that.. the difference in height could be quite considerable if a floating floor is needed.

Andre .. I'm afraid you lost me with what you said about MAM resonances of the floor.. is there a simple way you could sugest that I can find out/ do those calculations? or is it strictly a specialists domain.

DD... Ironically this proposed rethink of the space came actually about from seeking the advice of a professional .. He spent a day with me measuring and formulating a design.
He came very highly recommended and seemed great at the time.
I take your point on the number of layers of plasterboard..
As for the stud work itself I really need to be able to leave the existing timber 3"x4" studs in place.. It wouldn't be practical to start completely afresh.
So the walls are definitely compromised because the studs aren't sitting on any neoprene and the plasterboard is nailed on the outside rather than screwed but the idea was to take off the interior plasterboard.. check the rockwool and sealant were all as good as they could be and then fit RC and plasterboard sat on neoprene inside the space.
Limp mass traps on the back wall.. the only problem is that I need to have a door there.. unless you were thinking of the middle of the wall?
Sorry If I'm being dim but what did you mean by gapping out the concrete?!.. if it means extending the area of the room then I can't do it.
my neighbours are definitely fine.. they're ok with it as it is.. it's peaceful in the overall studio space but not pindrop quiet.. there are 40 windows which give more than a little outside ambience too!
I work between 79 and 82 db spl
Definitely looking at John Slayers and just about to get my head into rod's book but would love any more thoughts you might have.. really keen to get something going over the coming weeks.

all best
dennis

[avare]

Door height is not a restriction. The price between doors of different heights is not significant in the big picture.

MAM resonance is the same as the resonance of a panel absorber. Use the same formula. It is in most books and websites dealing with studio acoustics.

Good luck!

Andre

[DanDan]

Hi Dennis, to find the paths you need only a friend and ears! Get the friend to go the other side and make all sorts of noises, footfall, conversation, lightswitches etc. A ghettoblaster would be useful too. It can be useful to block one ear. Ears should be good enough, but if there is uncertainty about the floor, mechanics have a sort of mechanical stethoscope to listen to bearings and such. Wall plan seems fine, you could put studs on studs though to increase the depth, maybe at the front wall to make a huge damped mass panel trap. Go for the best RC you can find, those ones look good to me, but I don't get to do much proper building. I am more of a guerrilla acoustician. You can take this step by step. Final acoustic treatment is the easy part.
DD