It is very important to distinguish between sound absorption and soundproofing. It is often thought that sticking egg boxes or foam to the wall will reduce the level of sound escaping a room. It doesn't!
Sound absorbing materials like acoustic foams reduce the noise within a space. They reduce the amount of echo and general clatter, making conversations easier to hear. These materials work by allowing sound to pass through them relatively easily which turns the sound to heat so reducing the energy.
Conversely, a material or system that provides good soundproofing is usually non-porous and a good reflector of sound.
Noise will always travel through the smallest gap or crack and will always find the weakest part of a structure. Generally noise will escape through cracks around windows and doors, through thin windows and doors, through any holes in walls, through ventilation ductwork or extractor outlets, etc.
To reduce sound leaking through and around doors, install acoustic seals to the sides and top of the frame and a threshold seal for the bottom of the door. There are many types available but generally a good quality surface mounted seal is sufficient. Doors need to be solid-core fire doors not lightweight hollow-core doors for this to be effective.
If sound is escaping through front or back doors a lobby type arrangement is a good idea where there are effectively two doors in/out of the premises separated by a small lobby. Generally when one door is opened the other door will be shut so the sound is less likely to escape.
Windows are another cause for concern. Thin single glazing does not stop much sound passing through so secondary glazing is the best option. This simply involves installing a second window spaced away from the existing window (as far as possible). If this is not possible then it may be worth looking at replacing the windows with good quality double glazed units although this won't be as good as secondary glazing
Ventilation holes must have some kind of box around them or sound will spill straight out. The box needs to be lined with acoustic foam and well sealed against the wall to be effective. Ideally another box should be constructed on the outside as well for best performance.
Ductwork can carry sound from inside a club to the outside which may annoy local residents. Cover the ductwork with some form of acoustic lagging to contain the noise within the pipes. Also don't have the end of the ductwork pointing directly towards a residential property. Noise does have directional qualities so pointing the outlet duct upwards is a better option.
If speakers are mounted directly onto walls or floors then vibrations will transfer from the speaker into the structure of the building very easily and this can also cause problems. The vibrations will re-radiate on the outside of the building possibly causing a noise nuisance. The solution is to mount the speakers via something soft like neoprene rubber to reduce this interaction.
Stages that are hollow can resonate. This can cause problems so insulate underneath the stage in the empty space and add some heavy damping sheets on top of the stage to reduce vibrations.
Lightweight plasterboard stud walls don't generally stop much sound passing through them unless they are constructed with high performance acoustic materials. Blockwork or brick walls are far heavier and so much better at stopping sound especially if they are rendered rather than just dot and dabbed with plasterboard sheets.
It's also worth noting that lightweight insulation such as fibreglass is great for heat insulation but useless for sound insulation.
When lots of people start talking and they have to shout to be heard when a club gets busy, it is because the sound is bouncing off reflective hard wall, floor and ceiling surfaces. The answer here is to install acoustic panels or acoustic foam on the walls and ceiling to absorb the excessive noise. Hard wooden floors cause far more problems than soft carpeted floors.
Reducing the noise levels inside a pub will reduce the amount of noise trying to escape through the walls and windows etc. so is in a way beneficial to soundproofing.
We have a wide range of sound absorbing panels for pubs