Soundproofing music rooms, and why bass is the hard part

Why bass behaves differently

Transmission through a single panel follows the mass law: each doubling of mass per unit area buys roughly 6 dB, and transmission loss also rises with frequency at about the same rate per octave. Read that second clause carefully, because it is the whole problem. The same wall that removes 34 dB at 500 Hz removes only 16 dB at 125 Hz, and below 125 Hz it does less again.

Transmission loss by frequency for BB830, according to the manufacturer’s datasheet, reference BB830/20/v2. These are laboratory values for the material alone, and a finished wall normally lands 5 to 10 dB below any published figure. The shape of the curve is the point, not the individual numbers.

What actually leaves a music room

In a rehearsal room, a home studio or a karaoke room the escaping energy is rarely where people look. The floor is usually first: a bass cabinet, a drum riser or a kick pedal couples straight into the slab, and the slab carries it through the building to rooms that do not share a wall with you at all. After that comes the door, which is normally the lightest element in the room. Then the ventilation, because a sealed room needs air and a duct is a hole with a lid on it. The wall itself is often fourth on the list.

• Structure-borne energy through the floor, from cabinets, drum hardware and amplifier stands standing directly on the slab.
• The door leaf and its perimeter. A hollow-core door in an otherwise good wall sets the ceiling for the entire partition.
• Ventilation and air-conditioning penetrations, which must pass air and therefore cannot simply be blocked.
• The ceiling void, if it runs continuously over the wall into the next room.
• Sockets, switches and conduit, which are direct holes through the construction.
• The wall itself, which is the only one of these that added mass addresses directly.

Which grade, and where it goes

BB830LF is formulated for low-frequency work and is the grade to specify where bass is the stated problem — a rehearsal room, a drum room, a karaoke room, a home studio sharing a wall with a bedroom. BB830 remains sensible for the parts of the same project where the constraint is speech and general level rather than bass, and BB830FR is the grade where a fire requirement applies, which it usually does in a commercial karaoke or entertainment venue.

What none of them do on their own is deliver a low-frequency result. A limp mass layer inside a cavity is a component. The performance comes from the assembly, and the assembly figures below are manufacturer data and laboratory values.

Note the last row. Structural separation is what buys the low end, and it is also what costs floor area. A serious drum room is a room within a room: an independent frame, a real cavity, mineral wool in it, mass on both leaves, and no rigid connection between the two other than the isolators under the floating floor.

The order of work

1. Decouple the sources from the structure before anything else. Isolation pads under cabinets, a floating riser under the drum kit, amplifiers off the slab. This is the cheapest large gain available in a music room.
2. Deal with the door. A solid-core leaf with full perimeter seals and a drop seal, or two doors with a lobby between them if the target is strict.
3. Design the ventilation as an attenuated path. Never seal a supply or extract to make the room quieter.
4. Close and seal the ceiling void at the wall line.
5. Build the wall as a cavity: independent studs where the space allows, mineral wool in the cavity, BB830LF bonded with BA990 as the limp mass layer, joints overlapped and taped.
6. Seal every perimeter and penetration with BA890, back every box with BA650, then overboard and seal the board perimeter again.

What not to do

• Do not line the room with acoustic foam and expect the neighbours to notice. Foam changes how the room sounds to you; it does not change what leaves it.
• Do not build a bass trap and call it isolation. Traps control modal behaviour inside the room. They are worth having, and they are a different problem.
• Do not tie the two leaves of a double-leaf wall together with rigid fixings or a continuous plaster bead. One rigid bridge undoes most of the separation you paid floor area for.
• Do not fill a cavity with rigid board or dense material in the belief that heavier is better. The cavity needs a limp, open absorber, which is what mineral wool is.
• Do not stack layer on layer over an unsealed first layer. An open area of roughly 1% caps transmission loss at around 20 dB regardless of what is behind it.
• Do not set the target as an absolute. Specify the level that must not be exceeded in the receiving room at the frequencies that matter, and design to that.

Where mass loaded vinyl is the wrong answer

• The path is the floor slab. Nothing added to a wall reaches structure-borne bass. Treat the mounting, the riser and the level.
• The target is below roughly 50 Hz and strict. At that point the honest answer is a room within a room, or reducing the source level, and a sheet material of any brand will not carry the job.
• The room is already heavy masonry or concrete on all sides and the complaint persists. The remaining paths are the door, the ventilation and the structure, not the wall.
• The complaint is that the room sounds bad to play in — boomy, uneven, harsh. That is absorption and modal treatment inside the room.
• The space cannot lose the depth a cavity needs. Without cavity depth there is no low-frequency performance to buy, and adding mass alone will disappoint at a cost.
• The budget cannot cover the door and the ventilation as well. Spend it on those first; a lined wall with an unsealed hollow-core door in it is not a lined wall.

Buying in Thailand

Stock is held in Bangkok and dispatched within one working day of cleared payment. A 5 m² roll weighs about 25 kg. Delivery is free nationwide over THB 20,000 excluding VAT, otherwise THB 500 in Bangkok and the surrounding provinces or THB 900 upcountry, within Thailand only.