4.1. The Room Structure: Traditional Room Construction
The typical British house built during the 20th Century is a solid, double brick outer wall construction with brick internal walls. Typically, it is two storey, with wooden floors supported on joists. Roofs are pitched and hung with slate. Ground floor internal walls are usually solid and plastered, though some first floor walls may be light partition or studding. In some areas (South and West England) single storey bungalows predominate and in others (towns and cities) multistorey flats, apartments and tenements are common, built in brick, stone or concrete.
These construction methods, though producing different sound characters, present few problems and generally sound acceptable. The exception is the 'concrete box' construction of modern flats or apartments, where 'flutter' echoes can be quite troublesome (see Modern Room Construction later).
Floor Problems
The main structural problem encountered by the Hi-Fi enthusiast in the traditional house is bouncy wooden floors. Though originally probably very solid, the wooden wedges and packing pieces will have deteriorated with age and fungal or insect attack. The floor 'boom' and colouration feeds back into the loudspeaker, back to the amplifier where it is further amplified in a classic feedback loop. The solution to the problem is simpler and easier than you might expect, but will involve lifting floorboards and crawling about in the space under the floor. Better to get a competent builder or joiner to do this simple job for you. There follows details about what you need to do depending on the construction of your floor.
Floor boards or flooring chipboard (Weyroc) nailed to joists.
If yours is a ground floor room, the usual cause of bounciness is that the joists have become unsupported at their centres - and sometimes at the ends.
It is usually necessary to remove a few floorboards (or small areas of flooring chipboard) to allow access to the underfloor space. Replace the wedges supporting the centre of the joist and/or pack out the ends of the joists if they are 'floating'. It is usually only a couple of hours work for a competent builder. When the joists are solid again, screw down the floorboards / chipboard in the area where your Hi-Fi system is situated. This will eliminate board 'rattle'. You may need to do this elsewhere if other boards are no longer tight to the joists.
Diagram 5.6: Ground floor room with wooden floor
If you have a ground floor with a cellar or basement beneath it, you can support the rafters with wooden pillars. Use at least 3"x 4" (76mm x 102mm )section timber. Cut the pillar short and use the overlapping wedge technique to take out the joist bounce without putting it into tension.
Suspended Floors
A common problem area, suspended floors can be stiffened by fitting 'Herring-bone Strutting' between each joist. The strutting is short lengths of 3" x 1" or 3" x 2" (76mm x 25mm or 76mm x 51mm) nailed diagonally between and to the joists spaced about 3ft (1m) apart.
Diagram 5.7: Suspended floor with 'Herringbone Strutting'
'Floating' floor on concrete
This type of floor can cause problems (i) if the battens supporting the chipboard floor are not secure to the concrete, or (ii) if the chipboard is not well nailed to
the battens.
Ideally, the battens should be nailed down with masonry nails or screwed down to the concrete. The chipboard floor panels should, in turn, be screwed to the battens.
If your floor is a real problem, you might consider lifting the boards and refixing the battens. You could also put down extra battens - say at 18" (450mm) spacings. To save time and disruption you could just do this at the system end of the room.
Diagram 5.8: Ground floor room with floating floor
Walls
Plastered walls give few problems, though there are a couple of exceptions: loose areas of plaster, blocked up windows or doors, and flutter echoes.
Loose areas of plaster held in place by wallpaper, will rattle in sympathy with low frequencies and produce some very strange sounds! They must be cut out and re-plastered. The new plaster must be carefully chosen to match the strength and hardness of the original or the new areas will sound quite different from the original. The temptation is to fill the repair with one layer of all purpose hard plaster, but don't let your plasterer do this. Make sure he fills the repairs in layers just like the original: a 'sand and cement' or 'browning' layer, and a harder 'skimming' layer.
Builders will normally use concrete blocks and a simple thin, hard, modern plaster finish when blocking up window and door openings in old brick or stone walls. The results can sound disastrous, but you can solve the problem using wall hangings and/or insulation board over the offending area.
