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Frequently asked questions - and a few brief answers

WHAT IS THE "MIXER FACILITY SOCKET?"

WHAT ARE BS.5839 and BS.7443?

WHAT IS A "DC CURRENT SINK" AND HOW CAN IT BE USED?

CAN I RUN A MUSTANG AMPLIFIER FROM BATTERIES?

WHAT IS 100V LINE, WHAT IS 4ohms, HOW DO THEY RELATE, WHY DOES IT MATTER?

CAN I USE 100V AND LOW IMPEDANCE SPEAKERS ON THE SAME AMPLIFER?

WHAT IS AN INDUCTIVE LOOP SYSTEM and HOW DOES IT WORK - what are BS6083 and BS.7594?

WHAT IS THE "MIXER FACILITY SOCKET?"

This is the connection socket on a MUSTANG amplifier, mixer, or slave amplifier where access can be gained to the signal output from the mixer section, or to the output amplifier section, or to the internal circuitry which links the two sections. The signal level at this point is normally designed to be 775mV and will be compatible with other manufacturers products requiring or delivering this signal level. Sometime this signal is referred to as being 0dB level. Not all Mustang products provide a Mixer Facility Socket.

WHAT ARE BS.5839 and BS.7443

BS.5839 is a British Standard document dating from the 1980's which originally related to fire and intruder alarm systems, only. It set out the functions and facilities to be provided by the various sounders and contacts and control circuits, power units, and indicators, etc. Later, BS.5839 was expanded by including "PART 8" in an attempt to enable it to include the broad requirements of emergency PA systems. Part 8, however is limited in that it is not a specification but a "Code of Practice" and is therefore open to interpretation and importantly does not directly cover aspects of PA system performance such as audibility or intelligibility. A BS.5839 system will always require a reserve power system (usually batteries), and a method of monitoring the integrity of the loudspeaker system.

In due course it was seen that there was a need for a new British standard, dedicated purely to emergency PA systems. So BS.7443 was was drawn up and introduced in 1991. BS.7443 covers many extra specifications that need to be met when designing sound systems for emergency purposes, in particular the matter of intelligibility. When installed, the system is measured carefully and its performance must meet a minimum speech transmission index value, referred to a the RASTI index. Because of these very much more stringent requirements, a BS.7443 system is likely to be dramatically more costly than a BS.5839 based system. Naturally, a BS.5839 system could be designed to include various aspects of a BS.7443 system to enable it to meet the requirements of a particular site.

More recently, BS7443 has been re-issued in the form of BS EN 60849.

WHAT IS A "DC CURRENT SINK" AND HOW CAN IT BE USED

This is a small circuit which is included in a MUSTANG amplifier, to enable it to control external devices such as relays, lamps, or other equipment. It operates when a certain function is called for or is triggered manually, and operates for the duration of that requirement. Electrically it behaves as a if it were a simple switch, closing a circuit to operate the relay, etc. In practice, a typical positive DC supply would be directed to the relay and the return circuit would be connected to the Current Sink. On operation, the sink would connect the return circuit to 0V, thus making the circuit and operating the relay. These sinks operate only on DC circuits, and are rated only for small switching applications up to about 50-250mA depending on the unit. Some MUSTANG units include several Current Sinks. For convenience, most MUSTANG equipment provides a typical auxiliary DC supply output of 24V for use with the sinks operated relays/lamps, etc.

CAN I RUN A MUSTANG AMPLIFIER FROM BATTERIES?

Certain ranges of MUSTANG equipment are designed to be powered from either the standard AC supply, or from batteries. The MACRO range, for example, includes models which would normally be AC mains powered, and in the event of AC failure will instantly change to powering by a 24V DC supply (batteries), and then revert once the AC supply is restored. This is most commonly used in emergency systems where an interruption to the PA system is not acceptable, such as BS.5839 or BS.7443 systems. MUSTANG equipment not designed specifically for emergency systems, can be powered from an invertor or from a UPS though BEWARE! - an unstable AC supply from such equipment could cause serious damage to the amplifier. In any case, always ensure that the MUSTANG equipment is safely earthed.

WHAT IS 100V LINE, WHAT IS 4ohms, HOW DO THEY RELATE, WHY DOES IT MATTER, CAN I CONVERT?

If the loudspeaker connections to an amplifier are described as "low impedance" or "4ohms" or "8ohms" etc, then that amplifier is intended to be used with loudspeakers which are close by, and of a type which are similarly described. The loudspeaker(s) will draw the optimum power from the amplifier when the load presented by the loudspeaker matches the output rating of the amplifier. Obviously the loudspeakers must also be able to handle the power (Watts) that the amplifier will develop or there will be an expensive wisp of smoke from the speaker, the amplifier, or both. This type of arrangement is used on domestic audio, automobile audio, and PA systems for rock bands, and similar. Within the limitations above, this concept works just fine, but is absolutely no use whatever if your loudspeakers are well away from the amplifier, or if you need different audio levels from various loudspeakers dotted around a large site, simply because the power lost in the cables would be collossal with a low impedance system. You could easily waste 50% or more of amplifier power just in the cables. A 100V line system is the answer. An amplifier with an output described as "100V" or "100 Volt Line" MUST be used with 100V line speakers. The loudspeaker cable is routed round the site to cover all the areas required, and at each loudspeaker location, a 100V speaker is connected and it consumes an amount of power (watts) determined by the speaker - not the amplifier. Some speakers have an adjustment or "tapping" to fine tune the level. The inherent design of a 100V speaker also ensures that it cannot be overpowered if connected correctly, unlike a low impedance system, and there is no limit to the number of loudspeakers on the line except that the total combined consumed power must not exceed the amplifier output power rating(Watts).

However, there has to be a drawback and because the 100V system necessitates the amplifier output to be "stepped up" to 100V and then down again to low impedance at each loudspeaker, there is an element of loss introduced. Years ago this might have resulted in a problem with reduced bass or treble response, or even a "woolly" response, but modern amplifier and loudspeaker technologies now ensure that this problem is only very minimal indeed, and in most cases quite inaudible, unless you have the ears of a bat. All serious distributed sound systems use the 100V line principle (or 70V line in the USA).

HOW DO THEY RELATE? -choice will depend upon the application:

100V line for complete flexibility of locations, levels, types of speaker -mix-and-match, on a large site, and no limits to the number of loudspeakers.

Low impedance for the localised amplifier-speaker arrangement, one or two speakers per amplifier, and perhaps for the purist?

DOES IT MATTER - no, but you wouldn't plough a field with your limo, nor would you cruise off on holiday on a tractor, yet they might cost about the same. Both 4 -wheeled vehicles - just different applications. You may as well do the job correctly in the first place.

100V SAFETY Be careful when dealing with 100V technolgy as you can get an electric shock. Best switch all equipment off completely before working on the system.

CAN I CONVERT? from low impedance to 100V ? Well you might be able to, but you'd need to know the output specifications of the amplifier, its performance on inductive loads, its protection ability, calculate the bandwidth of a transformer, its saturation performance, its ratio, find one...., and by the time you've finished you might be better advised to re-plan with 100V equipment in mind. Only if you're very lucky would you stand a fighting chance of an acceptable result, and at worst you will wreck your amplifier. Do you feel lucky?

CAN I USE 100V AND LOW IMPEDANCE SPEAKERS ON THE SAME AMPLIFER?

Yes but there are limitations, and few amplifiers offer this dual aoutput facility. In practice, where the unit consists of one amplifier stage, you would consume say half the power available from the amplifier in a low impedance loudspeaker load, and then arrange for the remainder to be consumed by a 100V line loudspeaker array. You would connect the low impedance speaker to the low impedance output, and the 100V speakers to the 100V output, but the tricky aspect is ensuring that the power is shared accurately. You would connect an 8 ohm or 16 ohm loudspeaker for example to the 4 ohm amplifier output to limit the low impedance consumption, and then take up some of the remaining available power at 100V. It's very inflexible, it's messy, can jeopardise your amplifier, and we recommend that you don't try it unless there's no alternative. Most of the MUSTANG amplifier ranges offer these dual outputs.

WHAT IS AN INDUCTIVE LOOP SYSTEM and HOW DOES IT WORK

These systems are variously described as a "loop system" or "inductive loop system" or "AFILS". In the UK, the design of loop systems and equipment is covered by standards BS EN60118-4 (supercedes BS.6083) and BS.7594. Such systems are installed to enable people with a hearing impairment to hear signals picked up by a microphone or from a public address system. The user must be wearing a hearing aid which has the ability to accept signals from conventional telephones. Some aids feature a switch showing a 'T' position (for telephone) which cuts out the internal microphone of the aid itself. One of the benefits of installing a system is that users are, in effect, able to hear signals almost direct from the source, whereas without it, those signals would arrive at the hearing aid indirectly after having bounced off walls and hard furniture from several directions and being absorbed by people and soft furniture. The direct signals are dramatically clearer than indirect ones.

It works by induced magnetic fields created by a special amplifier delivering power into an "aerial" consisting of a loop of wire installed around the area to be covered. Signals fed into the amplifier vary the magnetic field and the hearing aid picks up the field and converts it back into audio.

Mustang Communications manufacture the DL.500 inductive loop amplifier which is a high power unit suitable for areas up to 500 sq. Metres such as churches, meeting rooms, public areas, etc., and will accommodate any analogue audio signal input from microphone level right up to 100V line. Once installed and adjusted, the unit is entirely automatic in operation. Installation, whilst relatively straightforward, should be carried out by an appropriately skilled contractor with knowledge of the two British Standards to ensure success.