Noise Control Overview
The object here is to give a general overview of the problems and, hopefully, solutions to the more common noise control applications in entertainment situations. We have tried to keep technical jargon to a minimum. Full technical literature is available for further information. It is not intended to be an answer to all problems. Some situations require specialised solutions and are outside the scope of this article.
Legislation is in place to control noise and falls generally into 2 categories, briefly:-
- Health and Safety at work. In EU countries the law protecting people at work from high sound levels is based on the 1986 EU Council Directive 86/188. Each country has translated this directive into its own law. In the UK this is done by the noise at work regulations (1989). This law is based on the concept of a daily noise exposure. Loud sounds for a short period or not so loud sounds for a longer period can both give the same exposure. Entertainment venues are places of work and the rules apply here just as in factories.
- Noise nuisance. This falls under the environmental banner of noise pollution. Local authorities are empowered to control the noise levels in their locality sufficient to prevent noise nuisance; to impose any reasonable requirements by the issue of a noise nuisance notice served under section 80 of the Environmental Protection Act 1990 and to enforce compliance through the courts.
Music and entertainment noise is all considered to be "NOISE".
More and more local authorities are now insisting on noise control measures in entertainment venues before entertainment licence renewal is granted. Formula Sound currently manufactures 3 products, which were developed purely to address the problems in these areas of concern.
Guardian CX4
The
Guardian CX4 was the first to be developed and fulfils two roles:
- As a fire alarm interface, so that a sound system can be easily linked and controlled by a fire alarm.
- As a noise controlling device.
This product tends to be more applicable to fire certificate compliance.
But it also provides level control in a fixed installation.
AVC2 - Automatic Volume Control
The
Sentry,
AT1 and the
AVC2 are purely sound control products but they are used in different applications.
The AVC2 fulfills the need to control fixed or installed sound systems as opposed to temporary or mobile systems. The reasons for installing this equipment would be to address:-
- Health and Safety issues in colleges or training environments, or in professional working environments, e.g. in recording or broadcast studios to control the monitoring system. (We have supplied units to several radio stations for this application.)
- Noise pollution situations, e.g. entertainment venues which are located near residential property. This is by far the largest use of this product.
The problem with sound systems is not the equipment, but the operators. We cannot take away the knobs and controls which they need to do their job. What we can do is control the maximum level at which the system will play irrespective of what they do. The AVC2 is an Automatic Volume Control unit and as the name suggests behaves just like someone leaning over the operator's shoulder and turning the volume down each time he tries to turn it up above what is allowed.
The more the operator tries to increase the volume the more the AVC2 will decrease it, so the system will barely change in perceived volume level. Eventually the operator will run out of controls to turn up. If the AVC2 is driven to maximum the output level will be reduced by more than the increase in input level. The system will probably now sound distorted and generally not very nice but the volume will be at a lower than normal level. Turning down the volume will allow the system to return back to normal operating level. (Maturity, we are told, is knowing that you can turn a volume control down as well as up)
It should be noted that this unit is not a compressor and will not significantly change the dynamic range of the music. This is because it is fairly slow in its action and therefore has a response time of a few seconds depending on musical content. There are no user controls on the AVC2 to be tampered with, only a bar graph meter showing how much control the AVC2 is exercising.
The AVC2 works by controlling the signal level before it gets to the loudspeakers. As this signal level is directly proportional to the noise the loudspeakers produce we do not need a measuring microphone for the system to work.
This explains the AVC2 in basic simple terms. More detailed technical information is available in the brochure. Although the AVC2 will control any sound system and do so in a way that won't embarrass or upset anyone it can only perform satisfactorily if it is installed and calibrated correctly in the venue. It is not practical to use the AVC2 in a mobile situation or where visiting artistes, bands, DJs, etc. bring their own equipment. The reasons are many, such as the problems of interfacing this equipment to visiting sound systems in the time available before a performance; where to connect it; having the correct connectors available; having the time to calibrate the equipment in the venue; having technical staff available to do the work.
So how to control mobile sound systems?
The common factor to all sound systems is the mains power supply, therefore if the power is controlled the system can be controlled. Technically this is like taking a sledge hammer to crack a walnut but it is simple and effective, and as long as a few basic facts are recognised and understood a very workable system can be provided.
This is not a new concept. There have been systems around for years, which work on this principle, but some of them had inherent problems.
Some problems with existing equipment:-
- The use of a conventional measuring microphone that can be easily tampered with and its response modified.
- No indication of actual sound level - only an indication of when the sound level is too loud, which is usually too late because the power is already off.
- Only one mains socket controlled. Artistes simply connect to other sockets.
- Some units use the 'A' weighting scale for measurements. 'A' weighting is not suitable for measuring entertainment noise. (For more information see FAQ section on weighting).
- Mains power switched back on with no warning. This can damage audio equipment and the owners of this equipment may have grounds for compensation.
Sentry Mk2
The
Sentry system was developed after looking at existing products and addressing their shortcomings. The Sentry Mk2 is the second generation of this product offering more facilities than the original Sentry. The Sentry Mk2 incorporates a measuring microphone inside the unit making it virtually tamperproof. Provision is made to connect an external microphone if required.
A large illuminated bargraph display is incorporated into the unit. The unit should be installed in a position where it can be clearly seen so the artiste has full knowledge of the levels at which he is working. If the noise level drives the display to full scale, which is all the green, amber and red lights lit, after a period of time the power will be turned off. The time period is adjustable between 10 to 70 seconds. Power can only be restored manually by pressing a reset button.
The Sentry is used in conjunction with a contactor or relay usually to control mains power. The connection between the two is at low voltage so the contactor can be located in a fuse cupboard and wired to control all the sockets in the vicinity.
The Sentry has a security loop facility which can be connected to a relay controlled by the fire alarm or switches that detect open fire doors or windows to ensure that the soundproofing of the venue is not impaired. Magnetic reed switches similar to the ones used in intruder alarms can be used as detectors. If the loop circuit is open the Sentry will switch off and it will not be possible to reset the Sentry until the circuit is closed.
The Sentry Mk2 also has provision to operate at two different levels, which may be selected remotely or by switches operated by open doors and windows, or an optional time switch. This allows the unit to cater for changes in noise type (e.g. disco or live music) or changes in surroundings (e.g. a venue situated near offices requiring stricter control during office hours.)
The combination of the security loop to switch off completely and the second level function provides for most situations to be catered for.
A counter which is not resetable is also offered as an option. The counter records the number of times the unit has been reset.
To keep the Sentry system as versatile as possible connectors are fitted which allow the connection of several optional features, including remote reset switches, warning lamps, slave displays, etc.
The Sentry when supplied for entertainment venues can be internally selected to work on a linear or 'C' scale or on Bass. This should be used where Bass, i.e. low frequency noise is the problem. When this option is selected a 300Hz low pass filter with a 12dB per octave slope is inserted in the measuring circuit.
Industrial Applications
If units are being used for this application they should be ordered with the 'A' weighting filter fitted. (This will be fitted in place of the Bass option).
One or more units can be used as monitoring devices to give visual displays, which advise the need to wear hearing protection. The unit can also switch on extra warning devices if the noise exceeds a predetermined threshold.
Full installation details and further technical information is provided in the installation manual supplied with each unit.
Latest developments
Until recently this was the only way to control mobile or portable systems but we at Formula Sound felt there should be a better way and now there is:
The AT-1 controller.
The AT-1
The AT-1 is our latest noise control product. It has been designed to be used in conjunction with the Sentry Mk2 environmental control unit. It is a stereo unit and its purpose is to control the volume level of an audio system connected to it. It will control the connected system to the maximum level allowed as defined by the Sentry Thus removing the worry of having to continually watch levels so the system is not cut off completely.
It does this without affecting the dynamic range of the music being played very much along the same lines as the AVC2, but now the control chain is microphone driven monitoring the actual sound pressure level (SPL) in the venue so the amount of absorption that takes place when a venue is full of people is automatically catered for and (unlike the AVC2) calibration is no longer required; therefore any system may be connected and controlled.
It is in the interests of a visiting band or DJ to connect to the AT-1 so that they do not suffer the embarrassment of being cut off if they play too loudly. Obviously the visiting system has to provide a suitable connection to their system.
More than one AT-1 unit may be connected to the Sentry MK2 to control more than one audio system in the venue. This is particularly useful so that the house system and a visiting system band, etc. can be controlled to the same maximum level. The Sentry will automatically control the AT-1 that is in use.
The AT-1 will only work when connected to a Sentry. It will follow the level that the Sentry is set to therefore if the Sentry is switched to work at a different level the AT-1 will control to the new level.
If the visiting system is not connected to the AT-1 the Sentry will control it in the usual manner by switching the available mains power. We feel that this will encourage visiting systems to want to be connected to the AT-1.
Formula Sound has gained considerable experience over the past several years in the various aspects of sound system control and is always willing to discuss individual problems with clients and Environmental Health Officers. We offer telephone hotline support to installers and are available on a consultancy basis if required.
