A beginners guide to acoustics.

[paradigm_x]

I started to write a beginners/practical guide to acoustics on subvertcentral, as Im an acoustic consultant. Have been meaning to finish, and then copy here, but not finished yet.

Ill post pt1 here now and copy the rest across soon.

[paradigm_x]

Ok.

Here goes. A guide to acoustics. Before I start I'd like to just point out that for every rule, there's always an exception, before people come steaming in with 'well ive put Marmite on the walls and its works fine' type shenanigans, so lets not bother. Also, Im going to use a lot of terms you might not know, so youll have to google things, otherwise this will be a dissertation ! THIS PAGE is very helpful. Ive deliberately tried to make it simple!

Ok then. Before we start, id like to define sound insulation and room acoustics.

Sound Insulation is what separates you from other buildings/rooms, acoustically. It is (very simply) measured by making a noise in one room, then going next door, and measuring the difference. This is whats called the level difference, D. There are lots of variations on this, but this will do for now. ISO 140 deals with this if you are interested.

Room acoustics is the internal acoustic conditions of a room. The room's sound quality if you like. You've probably all moved house only to find your speakers change sound totally. This is because the speakers are only really exciting the air in your room. This will obviously change when the room size changes. This is explained later (much better :hahaha:!).

Sound Insulation

Sound Insulation is what separates you from other buildings, acoustically Ie the performance of the wall/floor/ceiling. The performance of this is determined (for a single element) by its mass and density. IE a solid brick wall performs much better than a single sheet of plasterboard. The mass law for acoustics say that for a doubling in mass, you only get a 6dB increase in sound insulation. This is not a huge difference. So 'upgrading walls' by adding mass (eg plasterboard) is not going to increase your sound insulation much at all. Compare the mass of plasterboard to brickwork. Let alone fucking eggboxes :hahaha: NB The performance of a partition is frequency dependant, as you all probably know. IF interested, you get -6dB per halving of frequency, so a sub at 50Hz will be 6dB louder next door than a kick at 100). This is unfortunately physics, and the only thing you can do to improve it is to keep doubling mass.... or is it?

There are other methods of improving sound insulation. A cavity, particularly if the inner wall is isolated from the wall, or even better, completely separate (independent linings). This will at least double the performance of an identical wall without a gap. This is much more difficult to predict tho (without special software) so finding accurate test data is very important.. Manufacturers will usually be able to provide you with this, or if not, THIS SPREADHSEET has some reliable data.

The other thing to consider is flanking. If you imagine your room, caning some music, your speakers are causing the air to vibrate. This in turn causes the structure to resonate. Since virtually all buildings are connected via either the floor joists or floor slab if concrete. Therefore all the sound will travel easily into the next room, completely bypassing your nicely upgraded wall ! Therefore, its necessary to consider other paths (depending on where you are relatively within a building). There will also be vibrations travelling through he structure i.e. from the speakers via the table to the floor. If you can, isolate the speakers from the structure by putting on mopads, or even some rubber car mats, as thick as you can (ghetto style).

In order to sort this out, you therefore would ideally (we use this word ALL the time in acoustics, as no one ever listens/wants to spend the money :hahaha:) treat all flanking paths. A perfect situation would be a floating floor (basically, another floor surface on either rubber pads, or load bearing mineral wool. This isolates the inner floor from the common floor) with independent walls supported off the floating floor, and a ceiling joined to the supported walls. Obviously this will be expensive, but it would result in the best results.

NB This all assumes there are no air gaps. Air gaps make a huge difference, even when small. A 5mm diameter hole can reduce an entire wall by 3dB or more, so seal any holes with mastic, or larger holes with plasterboard, and sealed with mastic.

Practical Measures

(NB when I say walls, it would apply to whichever surface you are talking about)

So other than all that, what can you do ? Well a reasonably quick and easy job would be to add another layer of plasterboard (dense as possible, special acoustic stuff available eg British Gypsum (BG) SoundBloc - Google), with about a 25-50mm airgap, supported on what are called resilient bars (google). Fill the cavity with rockwool. Ideally (:P) youd do at least the connecting wall and the two side walls as a minimum, with ceiling next. A floor is probably hardest to do, as it would raise the floor and might make doors not work! If its just to room above, a plasterboard ceiling can be hung from resilient hangers, 50mm cavity with about 25mm rockwool on top of the pb, and give a substantial difference.

British Gypsum (and other plasterboard manufactures) publish a 'White Book' which is absolutely full of useful instructions and test data. Have a good read through that if you are thinking about it. http://www.british-gypsum.com/literatur ... _book.aspx

This will give you constructions, all the bits you need, and the likely improvement. :thumbu

Now, unfortunately, the requirements for the sound insulation dont really have any bearing to room acoustics. Ill come back to this

:thumbu

Hope this is useful.


Room acoustics

[paradigm_x]

reserved

[teqh]

nice one!! im gonna print this off and give it a proper read!

[fiziks]

Good read. My wallet got lighter just by reading that.

[ketamine]

ive put Marmite on the walls and its works fine