Log cabin wall thickness and transmission

The plan is to build a music-room/office in a log cabin in the garden. I'm currently playing around with layout ideas, but the current idea is an L-shaped cabin (6m x 6m but with a porch area with an apex roof rising to just under 4m (6m is roughly 19 1/2 ft, 4m about 13 ft). Internally this will be divided to provide a main room about 3.6 x 6 m and a smaller room/entrance lobby with a cloakroom and kitchen sink. There will be a loft area above the small room/porch with loft-ladder access. I'll produce some drawings once I'm happier with the layout. I'm in a suburban area, the cabin will be at the far end of our garden, 15m from our house and the nearest neighbour (next door) and at least 20m from other neighbours. I've not worked out how much sound control I need - the kids tell me they want to learn the drums, though - so I may make a smaller room that will allow them to practice. Anyway ... I have a choice of timber sizes for the external walls: 45mm through 110mm (1 3/4 to 4.3 in). My intuition suggests that the thicker walls will help reduce transmission, but I'm not sure how that will compare to brick walls. Can anyone shed (sorry) any light on this? Thanks. Ron.

Most woods (except for Balsa and Ironwood :=) are usually a bit less dense than gypsum wallboard, and mass is what makes most of the difference in sound isolation; with a single mass wall, like solid wood, you're limited to fairly ho-hum isolation because all you have going for you is mass law; the more mass, the more isolation, but it's a diminishing return. For every 5-6 dB more isolation you want, you have to DOUBLE the mass. Better would be a DOUBLE mass wall; one mass of, say, brick (hermetically sealed) and then a fiberglass or rockwool insulated air gap (bigger is better) and then a second mass; say, either 2-3 layers of gypsum drywall or a heavy wood layer. This type wall gets into mass-air-mass resonance, so you can improve its performance by adding mass to either layer, a wider air gap, or both - this is the least expensive method of high level sound proofing such as drums need when one isn't looking to make the acquaintance of the local constabulary... If you've not already done so, you should click on the "don't even think about" link at the very top of this forum, and follow ALL the suggestions there; you'll find a lot more info without the need for my fingers falling off... Steve

Thanks for that, Steve. I am ploughing through the information on this site (and have been lurking around for quite a time) and have downloaded some technical information from British Gypsum about their products (UK-based company, make "plasterboard" as we call it) ... thanks to this site I am starting to understand it :) When you talk about mass, I presume that it also goes with stiffness: to stop sound, you need a massive stiff structure that won't flex with the (sound) pressure wave and act like a diaphram (and thus produce a new pressure wave on the other side). In my case, brick is not an option since I'm building a log cabin. My other limitations are floor area (30 sq m approx 323 sq ft), and maximum height from the ground (<4m approx 13 ft) otherwise I will definitely require planning permission. I'm still at the planning stage on this - although I will have to make some decisions soon - my keyboards and rack need to be out of the house this summer.

When you talk about mass, I presume that it also goes with stiffness: to stop sound, you need a massive stiff structure that won't flex with the (sound) pressure wave and act like a diaphram (and thus produce a new pressure wave on the other side). Not necessarily; there are "limp mass" products that can improve wall performance, but they're all VERY expensive. Gypsum and masonry are the cheapest high-mass materials in most countries for sound walls. If your outer walls are "set in stone" (oops, I mean logs :=) then doing a fairly wide air space filled with insulation and an inner mass of plasterboard (at least two layers) will give you the best "bang for buck", or "sound for pound", so to speak... Steve

The cabin has arrived and is installed at the end of the garden (20 m from the house and the neighbours) Plans change to some extent - and this is not exception: the cabin is constructed from 110mm thick planed logs. There are three rooms - one will be divided into two once the plubing is in - some isolation for the toilet! The main room is 5m x 3m with a celing that ranges between 2.4 and 3.8m, (the apex is centered along the 5m wall. The other rooms are smaller: the entrance lobby is 3m x 2.77 m, with double glazed double doors to the outside, and single glazed panelled door (at the moment) connecting to the main room. A solid single door leads into the third room (which we can disregard for now). The smaller rooms have a ceiling at about 2.4m (the space above is for storage, and accessed via an opening in the connecting wall from the main room. The main room will be partly my synth workarea (and office), but is large enough to get some other musicians in. I don't think that I'll do a huge amount of recording here, but I need to have enough sound treatment to tame the reflections. It may be possible to treat the smaller room so that it can be used as either a vocal booth or (more likely) somewhere where we can put the drummer on the occasions when we have drums - obviously thinking aloud at this stage. I will come back with some specific questions - but it is currently mid winter in the UK - and without heating I'm not prepared to make any sound measurements at the moment!

Just an update... The cabin was delivered in January. I've started doing some basic electrical fitting out, but not had a great deal of time. My initial observation is that even if I do no other treatment, I have a lot of air gaps to fill, and now that we are getting some warmer weather, I'm quite surprised at the amount of movement there is in the frame, so a very flexible filler will be needed. My plan is to make as few holes as necessary to accomodate wiring between rooms, seal the joits with acoustic caulk, then apply some wooden trim to hide the caulk. Once that is done, I'll have a better idea of what I need to do to tame the acoustics. Incidently, Sound on Sound magazine ran an article recently (I think it was in the March 2006 issue, but I'll have to check) where they discussed using limp mass - but like you say, quite pricey in comparison to plaserboard)

knightfly wrote:

Most woods (except for Balsa and Ironwood :=) are usually a bit less dense than gypsum wallboard, and mass is what makes most of the difference in sound isolation; with a single mass wall, like solid wood, you're limited to fairly ho-hum isolation because all you have going for you is mass law; the more mass, the more isolation, but it's a diminishing return. For every 5-6 dB more isolation you want, you have to DOUBLE the mass.... Steve

I think perhaps this partly answers 'my' question (which is from another thread)... However the big part that concerns me is whether flanking can occur through the 'dead' air space -- from one part of that air space (say between the wall leaves) to another part of the air space (say between the ceiling leaves).... But finally, if the weakest part is still the ceiling, would any potential compromise in isolation due to the walls, compound (or add to) the 'total' isolation? K