I'm reposting this question on the new forum - hope this is okay - just as I registered with the SOS Forum, it moved !

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hi,

I'm building an extension on to my house (approx 5m sq, single storey, pitched roof) and would like to soundproof it, to reduce noise coming out of it. Aside from internal soundproofing (room within an room etc) which I plan to do later, I was after some advice on external wall construction.

Currently, the guy who drew my plans has specified 100mm brick (can't be changed - has to match the house) 75mm of cavity insulation and then 100mm Celcon block ("aircrete").

I asked someone at Rockwool about this (as I was thinking of using Rockwool in the 75mm cavity) - and got this response ...
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> Insulation in a cavity wall construction is mainly there for enhancing the
> thermal performance of the wall construction, it does very little for the
> acoustic performance. A dense block would provide a better acoustic
> performance compared to a light weight block.
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does anybody have any advice on this ?

thanks alot

adam


had 2 useful replies on the old forum

Hugh Robjohns: SOS Technical Editor
SOS staff
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The man is absolutely correct. The gap between outer brick and inner block wall is there for construction reasons, primarily to stop damp getting through. The insualtion is a building regs requirement for thermal efficiency.

To reduce sound transmission you need as much mass as possible in the walls, and hence his suggestion of using heavy dense internal blocks instead of the very light blocks that most builders appear to prefer.

However, while you could ask you builder to use heavy blocks, I doubt there would actually be a hugely significant advantage in terms of sound insulation, and there may well be serious knock-ons in terms of foundation requirements, time to build and raw material costs.

Personally, I'd go for the conventional wall build design, but make sure you have double or tiple glazed windows, double doors (if there is an exterior door), and take great care over the internal room-in-a-room construction.

Hugh

PS, we're all over in the new forum now.... why not join us. Just click on the forum banner in the main SOS web page.

Smiffy
Active Member
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You might like to do a search on this subject in this forum. I recall this was debated in quite some details several months ago.

Picking up on Hugh's last para, I think the outcome back then was that you could invest heavily in soundproofing your walls, but sound was transferred through roofs/ceilings, doors (internal and external) and windows more efficiently than through conventional walls. Therefore wiser to invest in better materials for these than the walls.

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IN COMPANY Multimedia Productions
www.incompany.co.uk

smiffy,

thanks for your reply - I tried searching on the old forum - couldn't seem to find anything on external walls, but have only just started using this forum, so may have mis-searched

adam

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IN COMPANY Multimedia Productions
www.incompany.co.uk

There are quite a few PDF documents at http://www.rockwool.co.uk although they're not easy to link to (or even find) so you'll have to go search there.

BTW - there's a whole forum dedicated to studio design and acoustics in this new world. We have moderators now who might move your post there.

Matt

There are a number of good .PDFs on acoutics on the Rockwool web site, the main one is the Acoustic Manual - Part E (2003).

Try that for starters, then research the sections that apply to you most, their are separate documents on Wall design etc...

Hope this helps...

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Google less; read more!

Hi,
One thing you havent yet mentioned is dimensioning your extension. You really want no two walls parallel to minimise standing waves, null spots etc. This will probably be of greater benefit long term than trying to soak them up later with traps or foam...

I've never tried telling a builder that you want the walls squint though... Who knows what could happen!

Iain

hi sejen,

I'm currently planning to make the external walls parallel, but could make the inside walls non-parallel (I could just get a really bad builder - they'd soon make the walls non-parallel ! :-) )

The extension is on the back and side of (kind of "L" shaped) a 3 bedroom semi-detatched. The extension at its widest is approx 5 metres internal dimension with approx half of that width on the back of the house and the other half at the back of my driveway (which doesn't join on to any other properties apart from my own) - the bit behind the house goes back about 3.6m meteres internal dimension, the bit at the back of the driveway extends further forward than the back of the house (5 meteres length internal dimension).


I plan to divide the space up into a control room and recording room. At the moment I'm working out of two bedrooms in my house, mostly with singers rather than full bands, but would like to do louder stuff if possible - things are going quite well this year with production work (look at my website www.incompany.co.uk if you're interested) and so I wanted to build a better studio - but also keep it close to home.

thanks for your help

adam

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IN COMPANY Multimedia Productions
www.incompany.co.uk

Quote:

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Hi,
One thing you havent yet mentioned is dimensioning your extension. You really want no two walls parallel to minimise standing waves, null spots etc. This will probably be of greater benefit long term than trying to soak them up later with traps or foam...

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That said . . . from what I've read and heard from some fairly trustworthy sources (and if memory serves), building non-parallel walls mainly helps with the high mid and upper frequencies, and doesn't do quite so much for the low frequencies, as (among other things) the low frequencies are less directional.

Which means you will still need bass traps. And the other thing is that with non-parallel walls you have a more difficult time with doing the calculations.

Not to say don't do it, because this is certainly a common practice . . . but maybe it isn't quite so straightforward or as comprehensive a solution as it might seem. Could cause added complication and expense . . .

I don't claim to be any kind of expert on this . . . but I thought it might be worth bringing up. Hopefully someone with greater expertise than mine will chime in and clarify.

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Scott
--Where are we going and why am I in this handbasket?

yeah non parallel walls really over complicate things and will cause a lot of problems along the way.

as scott says they don't really affect bass frequencies unless the wall angles are quite drastic. if you just add a slight slant you get standing waves based on the average distance between surfaces. plus you still get a whole host of axial and tangenal modes. the worse thing to do is to make a parallelogram shape as this has no axis of symmetry. meaning that you stereo imaging will be innacurate. A good design would be to aim for a trapeziod shape with the monitors at the shorter parallel side. this way the angled wall aim sound away from the listening posistion. You just need to think what do with the left over space is your orignal room was cuboid. No mattery what shape room you build you will always need diffusers and absorbers

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Kasha - Picture a beautiful life

Phatriff is entirely correct, and gets awarded the 5 red balls no one else seems to have seen fit to give him....

Always a pleasure to see you Phatso

Max

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if you don't know who i am, i aint gonna tell you.

Hugh is right, denser blocks are far better for sound insulation - however your builder will use Celcon blocks (otherwise known as Thermolite blocks, or aerated blocks) as these are stipulated by building regulations concerning thermal insulation.

As well as filling the cavity with Rockwool (or 2" polystyrene, its just as good) you could also batten out the internal wall and add more fibreglass or polystyrene in between before it is covered with plaster boards.

Also, which I did in my cellar, cover the walls with a ROUGH coat of plaster, as opposed to smooth. This will help to diffuse the soundwaves. The rougher the better.

I might be pointing out the obvious but also tell your electrician to put loads of double sockets in (pref at mid-height) before plastering. You can never have too many. Put them on a seperate ring main also.

Dan

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https://itunes.apple.com/gb/album/james-bond-swagga-ski-rize/id574380007

max you are the MAC of all macs.

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Kasha - Picture a beautiful life

Thermally Polystyrene is fine, acoustically, it's next to useless.


Use Acoustic mineral wool

Higher density the better IMHO.

NORMAL pink fluffy Fibreg;lass insulation is only @30Kg/M^3 Proper AMW starts at say 60Kg.M^3 ish (some cheapo stuff is 45) and goes up.
it's dearer than The other stuff, but it's sonically a LOT more effective.


Max

(Cheers PhatRiff.... )

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if you don't know who i am, i aint gonna tell you.

>As well as filling the cavity with Rockwool (or 2" polystyrene, its just as good) you could also batten out the internal wall and add more fibreglass or polystyrene in between before it is covered with plaster boards.

I just thought I’d mention that, for thermal insulation, polystyrene is better (cheaper too) than Rockwool ‘cos polystyrene doesn’t absorb water.

If any material used for thermal insulation absorbs water its thermal properties will be severely compromised (read no insulation at all); cavity walls can sometimes harbour damp.

Tim ;o)

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Studio: www.kymatasound.com

that's right - the plans specify Celcon aircrete block, but I did notice on the Celcon website that they do a slightly denser block (750 kg/m3) as well as their standard block (620kg/m3) - but this doesn't sound a huge difference, and given the general feel of responses so far, it sounds best to stick with the "standard" construction and save money for the Room Within A Room.

thanks to everbody for replies so far - what a great forum !

I've stuck a scan of my building plans online if that's any use to anyone - www.incompany.co.uk/index_extension.html


adam

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IN COMPANY Multimedia Productions
www.incompany.co.uk

"Proposed dining room extension"? You have told the wife what's going to happen to the new "dining room" ????

A few thoughts:

Don't use ordinary/acoustic type mineral wool as a cavity insulation in external cavity walls. As Tim Rainey points out, it'll bridge the cavity and provide a path for damp incursion. Once it gets damp inside the cavity it's a nightmare to do anything about it and ordinary "acoustic" mineral wool when wet will create quite a good coupling between internal and external walls for both thermal and sound transmission. Expanded polystyrene sheet or purpose designed mineral wool sheet is better in this application. The mineral wool sheets are denser than polystyrene and will increase attenuation slightly whilst maintaining thermal insulation and without bridging the cavity; check the information on the Rockwool site for suitable products.

Personally, I'd go for the heaviest blocks I could get past the building inspector/planning dept.! Thermalite/Celcon/similar blocks are the preferred medium for thermal insulation - which is a big consideration (a requirement) for much normal domestic construction. Their relatively low mass is not, however, particularly good for attenuation. If this were not on the plan as a "dining room extension" then you could argue that a different construction is permissible. (Though if you own up to it being a studio you might run into planning problems - I've found that calling it a "music room" is a good ruse ) The construction specified meets domestic attenuation levels and thermal insulation specs and would be the default expectation of the planners. If you owned up to building a studio room you should be able to substitute HD block for Celcon. If there are any queries, point out that the thermal insulation of a room within a room construction inside HD block walls with poly filled cavity will *far* exceed any thermal specs for domestic construction. The reason I'd go for the heaviest walls I could get is that unless you are going for a *really* serious internal construction (which will substantially eat into the available space), this outer shell is your primary barrier for LF attenuation - both incoming and outgoing. Anything other than a very, very, heavy/clever internal room construction will pass LF at quite appreciable levels. A heavier external shell will attenuate this more than a lighter one. If it's not too late, I'd go for a larger cavity with heavier block construction. There again - this might well be over spec for what you want to do in the room. It'd also be much better than (what appear to be) the original walls of the house that form part of the construction so it might be a waste of time - it depends upon how much noise you intend to make and how quiet you need the room to be.

Rather than using the floor construction in the drawing, why not install a proper floating floor - like the one in the link posted by Simon in the Floating Floor thread elsewhere in this forum. If you're going to build a room within a room anyway, properly floating the floor of the original construction of the extension will save you a lot of time, work, and ceiling height and reap big benefits in attenuation. It may bump up your build cost for the extension but it should work out to be a saving in the long run - particularly in time and effort when you construct the internal room. It'll also considerably increase the effectiveness of the attenuation provided by the outer walls.And you get the builders who do the extension to do the really heavy work for you.

How will you be ventilating the room? If you're sound proofing it properly then you won't be wanting/able to open the window for a bit of fresh air. It might be worth looking into air conditioning solutions or if these are too expensive, at least some kind of ventilation system. It's much easier and cheaper to consider and plan this before you start than it is to add it later.

0VU - thanks for the detailed reply and for taking the time to look at my plan JPEGs - it will probably return to be a dining room if I ever move house. And besides, eating while recording - sounds a good combination to me :-)

Is HD block a name of a brand or just a generic term (e.g. High Density) ? I'll have a look into your suggestion of getting a heavier block and larger cavity. I was a bit put off doing this by Hugh's earlier reply which seemed to suggest that using heavier blocks might be less safe from a structural point of view.

At the moment I'm working out of two bedrooms in my 3 bed semi - one room with all the equipment and one room with mics in (and those duvets!) - most of my work is with singers and acoustic guitar players at them moment (plus monitoring at fairly low levels) and when I've talked to my neighbours in the other half of the semi they say they haven't really heard anything. So I'm expecting that with a standard construction (without room within a room) it should be as good as what I've got now.

Another reason for building the extension is just to get all the gear out of the bedrooms and turn them back into .. bedrooms. And new extension would give me quite a bit more space too.

What I was hoping to do was to build a fairly standard external wall construction (maybe with slightly heavier block) - which I think would be fine to continue the kind of work I'm currently doing (singers etc) and then add more soundproofing (room within a room) at a later date to be able to work with some louder music (drums etc) - the extension is going cost around 13-15K (pounds) and I've got about 20K to play with at the moment. I was hoping then to do more work soundproofing maybe a year or two down the line when some money has accumulated.

Yes I better think about some ventilation, it gets really hot upstairs in the house with all the windows closed and the PC on.

cheers

adam

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IN COMPANY Multimedia Productions
www.incompany.co.uk

Quote:

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>As well as filling the cavity with Rockwool (or 2" polystyrene, its just as good) you could also batten out the internal wall and add more fibreglass or polystyrene in between before it is covered with plaster boards.

I just thought I’d mention that, for thermal insulation, polystyrene is better (cheaper too) than Rockwool ‘cos polystyrene doesn’t absorb water.

If any material used for thermal insulation absorbs water its thermal properties will be severely compromised (read no insulation at all); cavity walls can sometimes harbour damp.

Tim ;o)

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Top Man Tim...
I never realised the intent was inside the cavity... I was thinking inside and inner Skin wall of Resilient bars and Plasterboard......

Must be too tired... think I'll go to bed earlier form now on

(Like hell I will..... but it's a noble intention anyway... )

Max

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if you don't know who i am, i aint gonna tell you.

Had a quick look at your plans Adam…0VU has admirably covered a lot of ground in his usual thorough style.

I’d just like to add a couple more thoughts:

You have lots of empty space above to make an interestingly shaped ceiling; interesting both visually and acoustically. At the very least I’d slope the ceiling so it’s not parallel to the floor. Also, by incorporating more of that empty space into the room you would increase its cubic capacity; usually a good thing acoustically and for air.

Re double glazing. Sorry if you already know this but I’ll mention it anyway…double glazed units with glass of the same thickness on both sides can produce sympathetic resonance problems at certain frequencies. Dissimilar thickness panes also help with attenuation.

Laminated glass is also slightly better acoustically because sound doesn’t like to travel through dissimilar materials (ie glass-plastic-glass sandwich) It is also better for safety and security too.

Re ventilation. If you go for a ducted ventilation/cooling system then the ducts do need to be of sufficient diameter to facilitate slow movement of air. The smaller the ducting, the faster the flow and hence noise at the inlets/outlets.

Also, silenced ducting (essential to stop noise transmission through the ducts) needs length to be effective; when building my latest studio I experimented and found at least two metres of 30cm silenced ducting was required for worthwhile attenuation.

Flexible sound attenuating ducting:

http://www.decinternational.com/

I have some details of my studio build on the Construction page at:

http://www.kymatasound.com/

Thanks Max… I’m tired too… fact of life in this business eh

Tim ;o)

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Studio: www.kymatasound.com

Tim,

I've said nice studio before so I won't massage your ego
There is mention of the accoustically treated live room on your site but no details. What kind of treatment do you have in there? Also in the control room aside from the two bass traps on the back wall and the absorber on the ceiling do you have any other treatment on the walls?

cheers
Driller

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Don't worry, this won't hurt a bit

Thanks Driller

Before listing the live room treatments, a bit of background detail might help explain how I ended up with the final result:

The live room is (intentionally) rather an odd shape with two angled walls (one at 45 degs) and a stepped ceiling. The odd shape and angled walls made mode calculations pretty meaningless. In such a soundproofed room the bass would obviously be a problem so I first added a couple of large resonant panel bass traps at either end of the room.

I then set up the main monitors in there and listened to various tracks that I know well. The bass traps were doing there job but, with no HF treatments at all, it was not surprising to find that the room was overly bright and ringing at the higher frequencies. It was so bright that at high volumes the HFs were painful…

I used ETF5* to verify what my ears were telling me and got a picture of what was happening. ETF5 confirmed the much longer RT60s for the higher frequencies. I then started to temporarily fix one metre square acoustic foam panels to the bare walls, listening to the results and running ETF5 again to check the HF RT60s were moving closer to the lower frequencies.

So, the final treatments ended up as: 6 square metres of acoustic foam (mounted on 6 removable MDF panels), a 2.5 metre square wall of curtain (not that the curtain makes much difference acoustically, it’s more aesthetics) and the two resonant bass traps at either end of the room. Result… a nicely balanced sounding room. I’m very happy to report that most who have played in there say it’s a lovely sounding room

Moving on the control room: There are two large (I had to climb into them to fit the Rockwool) resonant panel bass traps on the angled front walls under the main monitors. Two slotted Helmholtz traps on the rear wall (which also absorb and diffuse HFs) shelves in between the traps for more diffusion and finally, the ceiling mounted HF/mid absorber. The left and right side walls are untreated because, being much further from the listening position than the distance to the monitors, they didn’t present a problem.

Again I used listening tests supplement with ETF5 to tune the room. Without wishing to blow my own trumpet too much…many have said it’s the best reproduction they’ve heard in their lives. I’m also extremely pleased with the results too

Tim ;o)

* http://www.etfacoustic.com/

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Studio: www.kymatasound.com

Thanks for all that Tim! If I may though, the two resonant bass traps in the live room, are they a similar design to Ethan's panel traps or some other design. And is there a rear panel or are the frames simply pressed/sealed against the wall? Also, the Helmholtz's in the control room, did you just choose a "standard" frequency to have them made to absorb, or was it the software agin which told you? Finally, to realy push my luck, did you make the traps yourself or did you buy them (guessing you made them )

Thanks for indulging me!

D

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Don't worry, this won't hurt a bit

>Thanks for all that Tim!

My pleasure Driller.

>If I may though, the two resonant bass traps in the live room, are they a similar design to Ethan's panel traps or some other design.

Mine are basically airtight sealed boxes (approx: 100 x 160 x 10cm deep) made of wood and filled with Rockwool with an air gap so the front resonant plywood panel doesn’t touch the Rockwool. They also have a larger frame around them that is dressed with a thin fabric to improve looks.

They have a fairly wide resonant centre frequency (approx 40 to 100Hz) and the overall response curve looks like a parabola, or bell curve, with the top of the curve slightly flattened.

Interestingly, the control room resonant panel traps, under the main monitors, use the same plywood fronts (albeit much smaller front panels but larger cubic capacity internally) but they exhibit a definite and much narrower centre frequency of approximately 48Hz and are –2dB at 96Hz, -8dB at 160 to 315Hz and –20dB at 500 to 800Hz. The response curve looks much more like a staircase.

>And is there a rear panel or are the frames simply pressed/sealed against the wall?

They are completely dismountable self-contained units hanging on the wall; don’t know how much they weigh but they are definitely a two-man job to lift. To maintain an airtight box all joints were: glued, screwed and covered with a generous quantity of flexible mastic.

Due to space limitations (depth) the Helmholz traps in the control room are fixed directly to the wall and sealed airtight to the wall with flexible mastic.

>Also, the Helmholtz's in the control room, did you just choose a "standard" frequency to have them made to absorb, or was it the software agin which told you?

No, not the software, I made ‘em before testing the room. My aim was to make traps that would respond to frequencies not covered by the other traps. The calculated frequencies they should be responding to are: 205,322,404,450 and 491Hz

I’d forgotten (memory error ) to say previously that I also used a DSP8024 RTA and ECM8000 test mic in the control room; a couple of very capable Behringer products; as a company, their products are frequently unfairly maligned.

>Finally, to realy push my luck, did you make the traps yourself or did you buy them (guessing you made them

Living on a fairly small and distant island, importing huge ready made traps would have cost a small fortune… so, the mother of invention lent me a hand in their construction

>Thanks for indulging me!

You’re welcome sir. Now then, about those crowns…

Tim ;o)

[quote You’re welcome sir. Now then, about those crowns…

Tim ;o)

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Heh, heh. Tell you what, come and make my new basement look like your studio and I'll see what I can do

cheers
Driller

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Don't worry, this won't hurt a bit

>(approx: 100 x 160 x 10cm deep)

Ahem... sorry, user error... that should have read: approx: 100 x 160 x 18cm deep

I’d love to come and help Driller but I couldn’t find Paris on my map of Crete

Tim ;o)