Your thoughts on the sound reduction potential of this house

Hey all, For some time now I've been scouting around the outskirts of my city (Melbourne, Australia) for a place to live where, among other things, I can have myself a nice recording studio. I have found what is in many respects of very nice property with quite a charming house and very large shed. Originally, I thought I would just turn the shed into a studio but, having looked at it, I'm thinking the house itself could make a great room for recording. Here's a picture that should give you a basic feel:- Those walls are old railway sleepers and are about four inches thick. The ceiling is stramit straw board. That's what's good about it. On the negative side, there is rubber put in between the railway sleepers. From the outside this feels like quite hard rubber but from the inside it is quite spongy. Not sure if this is a result of exposure to weather. In any case, the main problem is that the rubber has shrunk away from the sleepers in quite a number of places leaving a small (maybe 1-2mm) gap. Here is a picture of the rubber to give you an idea:- Much to the real estate agent's bemusement, I took along a PA speaker and some hardcore electronic music and took a few measurements with my sound pressure level meter (unfortunately, only dBA). Here's a rough outline of the results:- Even I was surprised at how little reduction the house provided. Point B is just outside the door and point C is perhaps only 4 metres away from the edge of the house right near the edge of the property. The edge of the neighbours house is probably only five metres to the east of point C meaning that it is only 10 metres away from the house I am considering buying. I think the following points are contributing to the lack of sound reduction:- ** The gaps between the sleepers where the rubber has come away. ** Perhaps the rubber itself is not suitable for sound reduction (?) ** The front and back doors are both very flimsy. ** The front door doesn't even close properly! (I guess in the country nobody cares about that). I was able to jam it in to the doorframe, but it was by no means flush against it all round. ** The windows are very thin Now to get the point. I am hoping to get an idea of what you all think of the potential of the house in terms of sound reduction. The place is out in the country and the area is very quiet. I measured the ambient noise at about 40dBA. Assuming a band at 115dB, I reckon I would need something in the order of 70dB of sound reduction to keep the neighbours from complaining. As stated, they are only 10 metres away from the house (not ideal). There is a lot of talk on these forums about 2 leaf structures. I would want to keep this single leaf in order to preserve the charm of the construction. Here are the steps I can think to take to try and address the main problems:- ** Seal up the gaps between the sleepers and completely seal the house in general ** Get new, heavy duty front and back doors and ensure they create a proper seal ** New windows. Whatever is best from a sound reduction point of view (haven't researched this much) What are your thoughts? It seems to me that the house has quite a bit going for it (the thickness of the sleepers, stramit ceiling). Do you think the steps I have outlined will address the weaknesses? Can I achieve my sound reduction goal with a single leaf structure? Cheers, Simon

Nice looking place, Simon! That would make a pretty awesome studio.

I'm thinking the house itself could make a great room for recording.

Just one question: If you turn the studio into a house, where are you going to live? :?: :shock: :)

I was surprised at how little reduction the house provided

That's about normal for an average house. Maybe a bit on the low side. I would expect better from the 4" sleepers, but the air gaps there, the windows, doors, air vents, and generally poor sealing (typical of houses) is what destroys the isolation. But if you fix all that up, you should be able to get at least 35 and perhaps a bit closer to 40 dB of TL. Add a fully decoupled inner-leaf, and I'm betting you could get well over 50, maybe even around 60 dB.

The edge of the neighbours house is probably only five metres to the east of point C meaning that it is only 10 metres away from the house I am considering buying.

Ouch! You'll definitely need to beef that up.

Assuming a band at 115dB, I reckon I would need something in the order of 70dB of sound reduction to keep the neighbours from complaining.

Right. 70 dB is do-able, but needs pretty hefty isolation and very close attention to detail. And you won't get there with a single leaf: two leaves is what you need, both with substantial mass, well sealed, and with a large air gap between them.

I would want to keep this single leaf in order to preserve the charm of the construction. Here are the steps I can think to take to try and address the main problems:-

Unfortunately, the laws of physics are not in your favor for doing that. For a single-leaf isolation wall, the equation that defines how that works is called "mass law". Mass law is this: TL(dB)= 20log(M) + 20log(f) -47.2 Where "M" is the surface density of the wall, and "f" is the frequency that you are calculating for. Empirically, you can estimate TL for the audible spectrum like this: TL(dB) = 14.5 log (M * 0.205) + 23 dB For a TL of 70 dB, you would therefore need a wall that has a surface density of about 8,550 kg/M2 (roughly 1750 lbs/ft2). The density of reinforced concrete is about 2300 kg/m3, so a wall about 3.7 meters thick would do the trick... That's roughly 12 feet thick.... So if you want to get 70 dB of isolation with a single leaf, that's what you'd need to do: replace your 4" wood sleepers with about 12 feet of reinforced concrete, all around, (walls, floor and ceiling). If you can't afford to lose that much space, then you could substitute a more dense material, such as lead. You would only need walls about 18" thick if you did that.... :) As you can see, if you limit yourself to a single leaf, then the laws of acoustics are going to war with the laws of economics! :)

** Seal up the gaps between the sleepers and completely seal the house in general ** Get new, heavy duty front and back doors and ensure they create a proper seal ** New windows. Whatever is best from a sound reduction point of view (haven't researched this much)

Assuming that your railway sleepers are nice dense wood, such as redwood, the density would be about 500 kG/m3. For 4" thick, that's about 50 kg/m2. So doing all of that and leaving it as a single leaf, mass law says that will get you around 37 dB of isolation. That sounds about right (assuming the roof is equally dense, and the windows are also replaced with 22mm thick laminated glass).

Do you think the steps I have outlined will address the weaknesses?

They will address the weaknesses with that leaf, yes, but it won't get you anywhere near where you are hoping. There's a reason why studios are always built with two-leaf isolation walls: it simply is not practical to get high levels of isolation from single-leaf walls.

Can I achieve my sound reduction goal with a single leaf structure?

I think that's already been answered! :) The problem with decibels is that it is a logarithmic scale, not linear. So it gets exponentially harder to add one more dB as you go up higher. Going from 30 dB of isolation to 50 dB is ten times harder than going from 30 to 40. You'd think that going from 30 dB to 60 dB is twice as hard, but that simply isn't the case: it is one hundred times harder. And going from 30 dB to 70 dB is one thousand times harder than going from 30 to 40. You need to dissipate one thousand times more energy. That's the problem. The laws of physics are a real bitch when dealing with large amounts of energy, but there is no way around them. It just isn't reasonably feasible with single-leaf construction. In order to get very high levels of isolation, you need to block very large amounts of energy, and the ONLY way to do that at a reasonable cost, is with a fully-decoupled two-leaf MSM wall. A two-leaf wall can get you where you want to go, but for 70 dB it isn't easy even then.

in order to preserve the charm of the construction. ... What are your thoughts?

It might seem drastic, but if your goal is to retain that gorgeous interior exactly as it is right now and still get 70 dB of isolation, your best option would be to do everything you already outlined, and also build another shell around the existing building. That would do the trick. That new outer-leaf could be brick, or it could be wood-framed if you prefer. It would have to go on a separate foundation (to prevent flanking through the slab itself), and would need a very massive roof, but as long as you have a large enough air gap and enough mass on the walls and roof, you could get to 70 dB, or even higher. That's probably not what you wanted to hear, but it's the plain truth. - Stuart -

Hi Stuart, That was exactly what I needed (not wanted!) to hear. Thanks a lot. I'll scrap the studio in the house idea. As I said, there is a very large shed backing onto the house which I had originally thought of turning into a studio. Another option is a house for sale nearby that's on a much larger block of land without a neighbour in sight (although the house on that block is nowhere near as nice as the one above :) Cheers, Simon

Another option is a house for sale nearby that's on a much larger block of land without a neighbour in sight

That might work, but don't forget that isolation is a two-way street: you don't need it just for sound going out, but also for sound coming in. That includes things like rain, wind, thunder, hail, aircraft flying overhead (especially helicopters), nearby traffic (especially trucks, tractors, buses, and other heavy things), animals, radios, TVs, phones, people, etc. If you plan to record in there any time you feel like it, you need isolation to prevent those sounds coming in too. OK, they won't be 115 dB (except maybe for thunder, hail and low-flying helicopters), but they can still be pretty loud and ruin the perfect take, so it's important to consider those in your isolation plan. In general, most home studio builders are pleased to get 50 db of isolation from their studios, really happy to get 60, and jumping-up-down-ecstatically-insanely-happy to get 70. That's roughly the reality of home studio builds, so you get a general idea. Even most pro studios don't aim for more than about 80 or so. The very best isolated studio on the planet (Galaxy, in Belgium) managed to achieve 100 dB, but it cost them millions of dollars to do, and they had to go to major extremes, even with two-leaf construction, and hiring the best acousticians in the business. So if you aim for around 60 dB or so, you should be fine for most circumstances, and that's an achievable goal on a decent budget. Hope that helps! - Stuart -