The Live Music Office along with Jaryd Miles, Acoustic Engineer at engineering consultancy firm Inhabit, has come up with a short article on some of the ways you can deal with sound issues in a live music venue!
Acoustics is an all too often over-looked and underappreciated discipline in the design and arrangement of music venues. I would love a dollar for every time I’ve walked into a venue that had just bought a flash, brand spanking new sound system, only to soon realise it was basically useless because the room sound was the equivalent of a concrete bunker! Bottom line is, it pays to get the acoustics right the first time. Here’s a list of must-do’s to get you started…
Acoustic ratings and what they mean?
Before getting stuck into the sound advice (pardon the pun) here’s a run-down of some typical acoustic ratings you might see along the way.
- Sound Insulation – Keeping the sound within the venue
Building materials, windows and doors will often reference a sound insulation rating, typically seen as Rw, Rw+Ctr and/or STC, which give an indication of the products sound insulation performance. Rather than getting bogged down in the complexities of how these ratings are determined and what they mean exactly, here is a few key points to consider:
- The higher the Rw, the better the airborne sound insulation performance.
- The “+Ctr” is an adjustment factor that is used to account for low frequency noise – A high Rw rating doesn’t necessarily mean good sound insulation at low frequencies, so be sure to look out for Rw+Ctr to really know what’s going on down below.
- Rw, Rw+Ctr and STC ratings are taken from laboratory measurements in a controlled environment; i.e. once installed on site, you can likely expect a reduction of approximately 6dB in specified acoustic performance!
- An increase in Rw by 1 approximates to a reduction of 1dB in sound pressure level – see below for an idea of what a dB and Rw ratings translate to:
2. “Sound Absorption – Controlling the sound in the venue”
Sound absorption is measured as a value known as an ‘Absorption Coefficient’, within a range between 0 and 1, with 1 being complete absorption. It is typically measured over a frequency range that is divided into octave bands, however a single number or rating is often given to help compare and select materials easily. See the figures below showing two different, yet commonly used rating systems; Sound Absorption Class (A to E) and NRC (Noise Reduction Coefficient). Both systems give an indication of how well the material absorbs sound energy.
Let’s get started with some common acoustic issues in live music venues and advice on how to help.
- “Know your enemy!”
Identifying the problem(s) is the first step: Is it the sound in the venue? Or is it the sound getting out (or both)? Can’t understand the singer? Bass muddy? Neighbours complaining? Recognising the difference between issues with room acoustics and sound insulation is a critical first step, as they are two very different issues, with two very different treatments and can have two VERY different budgets!
The Battle of Room Acoustics
Having trouble understanding lyrics? Everything sound like it has its own slap-delay? Feel like you’re fighting the room in every mix? Here’s a few guidelines to help you out:
- “Absorption and where to put it?”
Good room acoustics can be briefly summed up by balance and clarity. You want to be able to walk anywhere in the audience area, hearing roughly the same quality of sound everywhere. In small venues, this is often not the case and can commonly be attributed to parallel reflective surfaces. Reflective surfaces typically absorb very little sound, bouncing the energy back into the room at a delayed time to the sound coming from the speakers, reducing clarity and definition in the audience area. Parallel surfaces further emphasise this effect as the sound gets stuck between, bouncing back and forth.
To minimise this effect, absorptive surfaces can reduce the level of the reflected/delayed sound, which in turn distinguishes the direct sound (speakers) from the room sound (reflected), improving clarity and definition. Now there are a many easily accessible and cheap materials available which are good sound absorbers, however there are also many myths (don’t get me started on egg cartons). If you follow the below guidelines, you can’t go wrong:
- The Absorption Coefficient of a porous material is not the same at all frequencies and is typically dependent on material thickness and how far off a boundary it is mounted
- TIP: You can improve low frequency absorption by either increasing material thickness (the minimum recommended is 50mm), and/or mounting the material off the wall – see below:
- Key locations for absorptive material is at the wall directly opposite the speakers, as this is generally where the strongest reflections will be; and along either side of the walls parallel to the speakers.
- Most porous absorptive materials have lower Absorption Coefficients at low frequencies, however mounting thicker materials in corners (where bass frequencies tend to collect) can dramatically increase low frequency absorption.
- Good absorptive materials are: open-cell foams and fibre insulation. Basically, soft and fluffy = Good. Hard and shiny = Bad. Easy!
- Sound absorptive materials are typically not good sound insulators, they work on different energy transfer mechanisms. So, putting up curtains in the windows won’t do much for the noise annoying the neighbours.
Sound Insulation and keeping the neighbours happy
If cranky neighbours and noise complaints are your main problems, here is a few guidelines to follow:
3. You are only as strong as your weakest link
Air-tight=sound-tight. Any gaps or openings to the outside have a severely limiting effect on the sound insulation that can ultimately be achieved. The relative size of the opening compared to the wall, sets the upper limit of its effective performance. To put this in perspective, if the area of an opening is 1% of the total area, the wall would barely stop a loud talker from being heard on the other side! Think a bucket of water with a hole in it, same principle.
TIP: Make sure to seal ALL gaps and openings around perimeters properly with good quality seals and sealants. Common perpetrators are openings around windows, doors and ceiling penetrations.
4. Treat the problem, not the symptom
The most effective way to deal with noise is at the source…STAGE VOLUME! Managing your stage levels is the most effective (and by far the cheapest) way to manage your neighbours noise complaints. Must Do’s:
- If possible, try and move the source (i.e. stage/band, speakers etc) away from doors and windows to the outside. If this isn’t practical, instruct “door/window police” to keep them shut during performances, as any acoustic treatment is basically useless with them open.
- Instruct the house sound technician to keep a lid on how loud the amplifiers are (bass amplifiers are often the biggest problem, as bass frequencies are the hardest to insulate). If that won’t work, enforce limits by installing a decibel (dB) monitor at the mixing position that will flash red when the safe sound level is exceeded. Or install audio limiters before your amplifiers to limit the output level if needed; protecting both them and the audience/neighbours.
- Point speakers directly at the audience not above their heads, (believe me, I’ve seen a few that seemed to be designed for 10ft giants!) This will ensure that most of the sound energy is directed to the audience and not bouncing around the room, making it louder than it needs to be (this goes for stage monitors too).
- Use sound absorbing materials on the stage walls and ceiling. This will not only ‘soak up’ excess sound energy from the stage, but also provide a tighter, cleaner and easier to control mix.
- And last but not least, try and only include instruments in the mix which aren’t already heard. It is a sound-reinforcement-system, you’re reinforcing only what needs reinforcing. In a small venue, start with the loudest acoustic instrument (usually the drums) and build your mix around that.
5. You can’t beat physics
If the first two suggestions haven’t helped with insulating sound within the venue, then unfortunately drastic measures may be required and be warned, the laws of physics show no respect for budgets! The three key principles of effective sound insulation are as follows: mass, damping and isolation.
Mass: Generally speaking, a doubling of mass will roughly equal a 6dB improvement (in practice more like 4-5dB) in sound insulation (which is a noticeable effect). Say you had 1 layer of 13mm plasterboard and you added another, you would theoretically achieve and improvement of 6dB. However, this phenomenon is unfortunately subject to the law of diminishing returns, where to achieve the same 6dB improvement again, you would need an additional two panels. Moral of the story, if your walls/floors are mass heavy already (i.e. brick, concrete etc.) then great; if not, then adding mass is not the most cost-effective way to achieve a good sound insulation performance.
Damping: Whenever you have a cavity between two lightweight panels (e.g. a timber frame with 1 layer of plasterboard either side) there is a resonance created, which can dramatically decrease sound insulation performance (especially at low frequencies). Installing ‘fluffy’ fibre insulation within the cavity reduces this resonance effect and improves sound insulation. This one is a no-brainer; wherever you have a chance to add ‘fluffy’ insulation within a cavity between two lightweight panels (i.e. walls, ceilings, floorboards) …do it!
Isolation: The idea here is to ‘isolate’ the source of noise (i.e. the band/music) from the outside. To do this effectively, there either needs to be a physical break or resilience between the internal and external boundaries. For walls, this typically means either building an additional wall parallel to the external wall with an air gap between the two (the bigger the air gap the better – don’t forget to fill the cavity with insulation) or adding resilient clips or mounts to ensure that there is no rigid connection. For floors and ceilings, this means adding resilient clips or mounts to floorboards/ceiling. This concept is called ‘discontinuous construction’, minimizing the transmission of sound between the inside and outside by removing the path of least resistance, which is typically a physical connection. Obviously, this is the more expensive option, however it can also be the most effective.
Good acoustic treatment and design is a worthwhile investment. Technology becomes outdated, systems break down, need repair and get replaced; but good acoustics will always remain, no matter what or who plays in the venue.
To get your best bang-for-buck, hire an acoustic consultant to point out the most efficient and cost-effective ways to improve your venues acoustics.
Appendix A –Handy Hints
If you are planning on getting some new doors installed for improved sound insulation, here is a few things to look out for:
- “Mass-means-good!” Typically, the heavier the door, the better the sound insulation – check the Rw, Rw+Ctr and/or STC to be sure.
- Air-tight=Sound-tight. Any opening around the door will severely limit its acoustic performance; make sure to seal the door completely (i.e. perimeter, top and bottom) with rubber compression seals, not brush seals!
- Air-lock? If your venue has the space, 2 sealed doors with a small space in-between is an excellent solution for keeping the sound from getting outside.
Ditto for windows, see below:
- “Mass-means-good… yes, but think air-gap” Again typically, the more mass = better acoustic insulation, but adding an air-gap in between two layers of glass is also an effective way of improving sound insulation. See below for approximate Rw ratings of different glass constructions:
*Note: A 3dB reduction is considered a noticeable difference, but a 10dB reduction is perceived as half as loud!
If you’re thinking of upgrading the ceiling, here are a few pointers to improve its acoustic performance:
- When acoustic ratings are given for materials they are assuming no openings or penetrations and as you can imagine, ceilings are notorious for this (think lights, air-conditioning etc). So, when installing the new ceiling be sure to seal all penetrations completely and try and install lighting products with an acoustic rating to maintain the ceilings sound insulation performance.
- Where possible increase the ceiling cavity, use fibre insulation and install the ceiling on resilient mounts. See below for the benefits:
This information has been put together with the help of Inhabit.