How to spec my isolation correctly

[jsrlogon]

I'm deciding whether to build a studio / meditation room in a portion of my 6mx6m steel shed or not bother at all and wait a couple of years. If I can get it silent for a reasonable $$$ then I'll do it, otherwise I will wait.

I live about 200-300 metres from a relatively busy highway used by a high proportion of diesel 4x4s and heavy semi-rigids. Also about 200m from a place where they dump rocks out of skip bins with diggers. It seems to me that low frequency will be my biggest problem.

1. Do I need a decibel meter or can I approximate with a laptop/audio interface/microphone (I have an avantone CK-6) - is an iphone app good enough?

2. Can I reasonably (without spending more than a couple of hundred bucks?) do some analysis on exactly what frequencies I have a problem with.

Cheers

Jon

[DanDan]

The iPhone will be fine. studiosixdigital and faberacoustical have very decent Acoustic Analysis tools. You would also use REW.
Your site description suggests this would be difficult and expensive. I guess it's down to what is reasonable cost?

[jsrlogon]

Thanks DanDan, that studiosix tool seems heaps better than the one I found searching the app store.

So at 9.30pm I get about 55 dbc and 45 dba, the analysis shows most of it below 100 hz and the highest read was the bottom 1/3 of an octave bar below 30 Hz. I have an oil refinery and steel works about 4-5 kilometers away - I guess even when the road is quiet there are some big pumps and other machinery that I'll never block out. Interestingly what I hear is just a low hum.

Assuming we started with a concrete slab (as opposed to the tin shed I have right now) is there any reasonable construction that would have a chance of giving me the silence I crave? I assume at those frequencies, and looking at all the curves of the wall types (double stud, triple board etc etc) that I'm never going to shut out that 20-30 hz noise? Time to move house?

[DanDan]

Yes the guy at studiosix has been doing this for a long time, previously terrasonde. To be honest I am seriously thinking of selling a Bruel and Kjaer meter and moving to iOS.
Your measurements, inside or outside?

[jsrlogon]

Outside.

[DanDan]

Ta, I have similar, a more or less constant 55dBCS outside. Valley, motorway. I don't have your VLF dominance though.
Perhaps a mad notion, but maybe an interesting experiment. How about popping the mic out the window, filtering it to just the worst octave, and feeding that into the room, playing with phase and delay to see if some cancellation is possible.

[jsrlogon]

So for a recap my problem is diesel truck engine noise 30hz-50hz @ 55-60db which I've concluded based on all the data I've looked at is, as DanDan already said, difficult and expensive to get rid of.

I've part built the room using 18mm mdf outer leaf with 90mm gap filled with earthwool with 18mm mdf on the inner leaf. Single stud pattern (i.e. not staggered). Ceiling will be the same. Built on concrete slab, will caulk the joins with sikaflex.

For a number of reasons one side of the room (that will face out through the existing roller shutter will need to have a large sliding patio style door - about 1800mm wide by 2100 high. I haven't ordered/chosen the door yet.

The default option is a 4mm + 18mm + 4mm aluminium sliding door which will set me back $1500. If I spend probably another $500 I could get some heavier laminated glass in it. Timber is also an option. I can't find any performance data on the internet for double glazing below 100hz.

Based on my existing construction how much benefit will I get buying more than the standard door - i.e. speccing thicker glass, timber, more expensive unit (UPVC is uncommon and expensive in Australia). Essentially I don't want to double the cost for a measly improvement in isolation.

It would screw up my design and my budget, but should I be looking at a pair of sliding doors 100mm apart each with single glazing?

Cheers,

Jon

[DanDan]

Your walls and roof are pretty lightweight. Therefor I don't think door choices will make any significant difference.
I'd say go for the standard and just start enjoying your room.
(Look for rejects, sometimes these places get something wrong and have to sell off the misfits)