21st Century Sound For Places of Worship

Speech Intelligibility for Places of Worship.

Traditional places of worship are notorious for poor acoustics degrading the intelligibility of the spoken word. Ironically, for the hard of hearing we have largely solved the problem with the development and continuous improvement of induction loop systems. However, for the majority, with apparently good hearing, little has been done to improve the intelligibility of sound in these highly reverberant environments.

Delivering services in the mother tongue of the congregation arguably increases the need for greater clarity and intelligibility of speech; the Catholic church switched from Latin to English Mass in the UK back in 1964. Slowly over the decades, we have seen the introduction of reinforced sound in these environments, but with mixed success. The classic building for worship is highly reverberant producing a vibrant cocktail of sound. Whilst this enriches the sound of music and song it has a devastating effect on speech and can destroy any intelligibility.

The issues are multifaceted. Some reverberation can be beneficial: the trained orator can take advantage of it defying the inverse square law and projecting intelligible speech to the back of the congregation without deafening those in proximity. Too much reverberation, however, and the speech is blurred lacking any clarity regardless of the volume

Sound Reflections — Speech taking a direct path to the listener will reach him first. Speech reflected from different surfaces will reach him later and later depending on just how far it has travelled. Hard surfaces such as stone are almost perfect reflectors providing little or no attenuation.

Early audio systems used in places for worship comprised of not much more than a couple of speakers, an amplifier and a microphone. Raising the volume was the prime objective; everyone could hear the service. Unfortunately, they could not necessarily decipher what was being said.

Higher volume means everyone can hear, but from a point source such as a conventional speaker the volume falls according to the inverse square law so the volume at the speaker needs to be very high for those at the back to hear. This just exacerbates the problem. Reverberation is not resolved and sound levels are too variable for comfortable listening.

Inverse Square Law — Imagine blowing up a balloon with a big red dot on it. As the balloon gets bigger the red dot stretches and becomes lighter and lighter in colour as the red pigment is stretched over the growing surface area of the balloon. Sound emanating from a conventional speaker is being stretched over an ever growing sphere, just like the balloon surface. The surface area of a sphere is proportional to r² so the power (loudness of the sound) at the surface of the sphere is reducing as the square of the radius. At a distance 2r from the speaker the power has dropped by a factor of 4 at a distance of 3r it has fallen by a factor of 9 and so on.

A solution is to use multiple speakers down the length of the building creating zones. Each speaker covers a small range, so it is not too loud for those close to, but it has sufficient level for those at the back of the zone to hear. However, using multiple speakers in this way leads to more sound blurring. The problem of reverberation is still there, and additionally, sound from the first zone spilling into the next zone will be delayed as a consequence of the distance between the speakers. It may not be reverberant sound, but it has the same result-reduced intelligibility.

To overcome this problem a delay is introduced between zones. Now the system is becoming quite complex! Each zone needs to be wired to a separate amplifier with a different (delayed) audio feed.

Shos Soujnd delay between Zones — The sound from the speaker at point A takes 87ms to reach the speaker at point B

The soundscape has been improved but nothing has been done to tackle the fundamental issue of long reverberation times typically caused by the high ceilings with reflective surfaces. Acoustic tiles and other physical remedies could be used to dampen the reflections, but these would detract from the aesthetic and impede the musical richness of the space. Instead we turn to column speakers. Long and thin, these elegant speakers easily blend into the architecture of a high-ceilinged venue and, by nature of their construction, dispersion in the vertical plane is restricted; a longer column will offer narrower dispersion in the vertical plane. By tilting the speaker, the sound reaching the ceiling is further reduced and concentrated onto the congregation. In addition, the volume of the sound no longer reduces in accordance with the inverse square law, the speakers can project sound over much longer distances meaning fewer zones or no zones at all!

Mounting the speaker at an angle can be obtrusive. By controlling the signal to each driver in the column, the sound beam can be steered and focused onto the congregation whilst the speaker remains in a vertical position. An aesthetically pleasing acoustic solution for highly reverberant environments.

Unfortunately, the challenge is not complete. With multiple

speaker drivers, zones, time delays and possibly beam steering, instead of a small twin core cable daisy chained to connect each speaker, a large multicore cable connecting each speaker back to the control room is required. Not only is this expensive to install, in listed buildings with stone and decorative plaster work it may not even be permitted

Fulgor Services are the only manufacturer providing a solution; steerable column speakers with power, signal and control all on a twin core cable.

Vertical Dispersion and steering capability of Activo Focus Speaker — High sound pressure levels are confined within a 3m wide band and focused onto the congregation out to 22m. Now little energy is reaching the ceiling or rear wall so reflections are reduced and intelligibility is restored,

Fulgor services specialise in the design and manufacture of audio systems for places of worship and have systems installed in many of the most iconic religious venues on three continents. They offer attractively styled passive column speakers and control systems like many manufacturers, but they also have a range of active column array speakers. These speakers have built in amplifiers and signal processing providing volume control, equalisation, time delay and even beam steering. Using a unique power supply that carries both power and audio signal on just 2 wires in many venues there is often no need to install new cables as the existing speaker cables will do even if they are daisy chained. Where new cabling is required, it is only a single twin core 1mm²cable which is easy to install and conceal.

Induction Loop Systems

Your venue needs a standard compliant induction loop system to guarantee access for your hard of hearing members and guests.

Hard of hearing people find it particularly difficult to distinguish between background noise and the speech that they want to listen to. Reverberation is background noise, acceptable levels of reverberation for someone with good hearing are much higher than those for someone who is hard of hearing. No matter how much improvement we can make to the levels of reverberation and other sources of background noise it is unlikely to be good enough for the hard of hearing. Instead we rely on assistive listening technology such as induction (hearing) loops. All assistive listening technologies work on the same principle, they filter out the background noise and deliver just the wanted sound to the listener.

If you want to speak to someone in a crowded noisy room, you will get a little closer to them and speak directly into their ear, and that is exactly what happens when you use an induction (hearing) loop system. When you speak into the microphone of an induction (hearing) loop system it is like speaking directly into the persons ear.

The microphone provides a high level of rejection to the background noise and just conveys the wanted speech.

In the simplest form of induction (hearing) loop system, the speech is converted into a current which is driven round a loop of cable encompassing the venue. The current sets up a magnetic field which in turn induces a current into the pick-up coil (T-coil) of the person’s hearing aid. This current is amplified and tonally corrected for the individual’s hearing loss and fed into their ear via the speaker in the hearing aid. Induction loops are not only universal, they are the only assistive listening technology that provide a customised signal tailored to everyone’s hearing loss.

Perimeter loops are not always the best solution. There are many other loop configurations that may be more appropriate to meet the requirements in your venue eg. Figure 8, Cancellation, Super 8, super loop etc.

Perimeter Loop Performance — Perimeter loops are a low cost system, however they have several draw backs. The generated magnetic field is still of a significant strength up to 2 x the loop width away. Metal in close proximity to an induction loop can attenuate the magnetic field. Increasing the loop current is not often a viable solution as the field strength uniformity may not meet the IEC standard and without frequency compensation it will lose intelligibiity

Cancellation Loop — Cancellation loops; these are easy to install. They provide good spill control in 1 direction, but they do not provide metal loss compensation. Where the budget is small and spill control is important then often cancellation loops can often provide an economic solution

Figure 8 Loop — Figure 8 loops; these are relatively easy to install. They can provide good spill control in two direction. They will also provide moderate to good metal loss compensation by virtual of the snaller width loops. They do suffer from a null field along the centre line

Super Loop Systems — Superloops; thes are simple to install, however, since they make multiple crossings of the space sometimes it is not practiacl to use them. They will provide the best perfomance in almost all situations compared to other loop configurations. Field strength uniformity is excellent. They offer spill control in all directions and good metal loss compensation. Most modern buildings contain constructional metal so Super Loops should be the installer's first choice. For buildings where there is no metal reinforcement perimeter loops can provide a good solution depending on the size of the venue

Places of Worship — Installing 21st century sound systems in historic venues use to be too expensive and disruptive. Activo Column speakers from Fulgor Systems now makes it possible by using conventional 2 core cables to provide, power, Beam steering signal delay and equalisation.

Univox Audio Ltd is a specialist distribuotor. We believe that good communication is core to any organisation. To help you acihieve the best levels of speech intelligibiliy we have selected the best, affordable Induction loop, Infrared, FM and speaker systems available. But rather than leave anything to chance we also provide training for installers to help them specify and design.

Ask your installer about Fulgor Activo Speakers and bring your sound system into the 21st century without the inconvenience and expense of installing specialist cables.

Need Help to Find an Installer? Call or Email Us and we will put you in touch with a competent Pro Audio Installer.

T:010707 339216 E: info@univoxaudio.co.uk

IEC 60118-4 Has Changed:Part 2 Counter Loops (2)

Guidance For Commissioning Counter Loops

Go to the end of this article to download your free Commisioning Certificate

For optimum field strength uniformity the ideal counter loop is approximately 2m x 2m and installed in front of the counter in the floor or ceiling.

The field strength variation in the vertical plane is approx. 6db from 1.2m to 1.7m. In the horizontal plane the variation is 5db from the

centre to the edge of the loop.

However, this approach is not suitable for multiple adjacent counters and can be impractical to install. Typically, smaller preformed ‘Counter Loops’ are used instead.

The latest edition of IEC 60118-4:2014 provides new guidelines for the performance of one to one loop systems such as counter loops.

It specifies a volume of space over which the field strength should be tested.

The field strength should be measured at a height of 1.2m, 1.45m and 1.7m at locations A, B and C as shown in figure 1. At these 9 points the field strength should be within a range of -6dB to +6dB.

Note:

1.The horizontal distances specified are from the counter edge (the nearest position to the loop that the user may stand) not the loop. The distance to the loop from the counter edge is the offset, d.

2.The field strength should not exceed +8dB in the area where users are expected to stand (Red shaded area). However, due to the nature of the loop it is recognised that this is often unavoidable and the user is expected to adjust there position accordingly

3. 0dB is defined as 400mA/m rms

4. Microphones should be fixed in place as close as possible to the staff speaking position.

5. The microphone gain should be carefully adjusted to avoid over sensitivity to background noise

6 The operator should be trained on the systems use and on how to check the system using a loop listener

7. Clear signage to indicate the presence of the system must be visible

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Loop Orientation

Loop Mounted Vertically

With the loop mounted vertically in the counter there is good field strength uniformity in the horizontal plane

Test Conditions

The top front edge of the loop is at 0.77m from the floor. The loop current = 1.4A. ms . There is no horizontal offset. Loop Type:- Univox preformed 30cm x 30cm multi-turn loop.

Loop Folded At Right Angle

With the loop folded at right angles there is good uniformity in the horizontal and vertical plane.

With a small horizontal offset the uniformity in the vertical plane can be improved

TestConditions

The top front edge of the loop is at 0.77m from the floor. The loop current = 1.4A. ms . There is no horizontal offset. Loop Type:- Univox preformed 30cm x 30cm multi-turn loop.

Loop Mounted Horizontally

With the loop mounted horizontally in the counter good uniformity in the vertical plane in close proximity to the loop edge is achieved However, this loop orientation exhibits a null field that may intrude in the user defined space. See

Test Conditions

The top front edge of the loop is at 0.77m from the floor. The loop current = 1.4A. ms . There is no horizontal offset. Loop Type:- Univox preformed 30cm x 30cm multi-turn loop

Counter Loop Kits And Test Equipment To Make Compliance Easy

The FSM 2.0 Field Strength Meter

And since it is programmable, its mode of operation can be updated to reflect changes to the standard as they occur. The instrument has a clear, backlit, LCD display and steps through the required measurements in a logical sequence, matching the test certificate to simplify the certification process.

With sharp, narrow band filtering and a noise spectrum display function, spill control and background noise assessments are also made easy.

With the dedicated 1.6kHz test tone available for this meter, the maximum power bandwidth is also easy to assess.

Loop Listener

The Univox® Loop Listener has an inbuilt speaker for the assessment of audio quality and power level LED's to check field strength. It is an essential tool for any facility serious in maintaining good operational loop systems.

CTC-Counter Loop Kits

The CLS-1 Compact loop amplifier is at the heart of our counter loop kits.

It has the highest output power in its class and features Univox ® Dual Action AGC technology for superior intelligibility. The amplifier has 3 inputs with volume, base and treble (Metal Loss Compensation) controls on the front panel. Once set, the unit can be dropped into the mounting bracket supplied restricting further access.

CTC-120 Counter Loop Kit

CTC-121 Counter Loop Kit

Counter Loop Test Certificate

The Counter Loop Test Certificate has been designed specifically for the purpose of commissioning Counter Loop Systems.

To get your copy Download Here

Booklet Format A4 Format

IEC 60118-4 Has Changed:Part 1 Maximum Power Bandwidth

Why is full power bandwidth to 5kHz not necessary?

Normal hearing (and hearing aids) is less sensitive to low frequencies.

This means for the perception of equivalent loudness, we need less power at high frequencies compared to what is required at low frequencies.

The blue curve on the graph above is described as A weighted and is an approximation to the sensitivity of normal hearing . The curve below shows the sensitivity of a typical hearing aid.

Both graphs show a similar response.

ITU speech shown below and other test signals used to simulate speech are opposite in characteristic to the response curves shown above. More power is required at the lower frequencies

At 5kHz the signal level is approx. 24dB down on that at 1 kHz. For every 6dB reduction in field strength the loop current is halved. This implies that at 5kHz , a ¹/₁₆th of the current is required compared to that at 1kHz which is (¹/16)² of the power ( P=I²R) so the system does not need to be capable of delivering full power all the way to 5kHz

Why do we measure at 5kHz if the Maximum power bandwidth is 1.6kHz

When commissioning hearing loop systems in accordance with the IEC standard, we check the magnetic field strength at 5kHz (and 100Hz) to ensure it is no lower than what we have measured at 1kHz. This test is only to determine whether the constructional metal is absorbing the higher frequencies. It is conducted with the output of the amplifier turned down; -12dB in the case of Univox, other manufacturers choose to use less demanding test signals such as pink noise.

With the output set to deliver -12dB (small signal) and assuming the loop design is within our guidelines, the amplifier will be delivering a constant current over the full frequency range. **So if the field strength is not the same at 5kHz as measured at 1kHz the difference is due to magnetic absorption. We can compensate for this by using narrow loops or by using metal loss compensation control.

The FSM 2.0 Field Strength Meter

The FSM 2.0 is a microprocessor controlled instrument using multi-tone signals to make advanced measurements of induction loop systems quick, accurate and easy. It is the only FSM to fully satisfy the demands of the IEC60118-4 standard by being capable of measuring noise levels down to -47dB. And since it is programmable, its mode of operation can be updated to reflect changes to the standard as they occur. The instrument has a clear, backlit, LCD display and steps through the required measurements in a logical sequence, matching the test certificate to simplify the certification process. With sharp, narrow band filtering and a noise spectrum display function, spill control and background noise assessments are also made easy.

With the dedicated 1.6kHz test tone available for this meter, the maximum power bandwidth is easy to assess

Down Load the PDF for this article.

The 2015 edition of the IEC standard, IEC 60118-4:2015 includes an additional performance test, Amplifier Overload at 1.6kHz (Maximum Power Bandwidth)

The test should be carried out on the induction loop system during the commissioning process. It is aimed at checking that the amplifier is capable of delivering *full current into the load presented by the loop up to 1.6kHz.

If the amplifier is not capable of maintaining this output current, there is a possibility that voltage clipping will occur on some signal peaks which may cause audible signal distortion. (As loop systems rely on the loop current and not voltage a small amount of voltage clipping is not an issue and will not affect the perceived audio quality even though it is visible on an oscilloscope or a clip detector. So any tests on the maximum power bandwidth should be done in conjunction with a listening test.

*full current in the context of this article is the rms current at which the field strength of 0dB ±3dB is achieved using a 1kHz sine wave tone or equivalent and where metal loss correction is correctly adjusted.

** The loop cable is inductive It has both a d.c and an a.c resistance (reactance). The a.c component is frequency dependent . The higher the frequency, the higher the reactance and therefore the higher the voltage output from the amplifier required to maintain a constant current.

The Univox design software defaults to designing for Speech, 1.6kHz. So providing you follow the design and use the cable type and length specified, including feed cables, your system should automatically meet this new requirement (assuming you set the same levels as you chose in the software and all other assumptions are correct)

Testing for maximum power bandwidth to 1.6kHz

There are several methods that can be used to check the maximum power bandwidth of the system. The most accurate requires the use of an oscilloscope . This method is not covered in this document as we do not expect many installers will have access to an oscilloscope in the field.

1.) For loop amplifiers with a ‘peak voltage clip’ LED

The most recent models in the Univox range include a ‘peak voltage clip ’LED.

Method A

With the system setup to deliver the ***correct field strength (0dB±3dB) using a 1kHz tone or equivalent apply the live signal to the system and monitor the LED. It should remain off although the occasional flicker on the peaks of the signal are acceptable.

listening test is required to complete the assessment.

This is probably the least stringent of acceptable test methods. Although the input signal is not analysed and there is no confirmation that the live signal includes full power frequency components >=1.6kHz. Either the system passes because it has adequate power bandwidth or based on actual inputs, the system does not need it.

Method B

Using a 1kHz sine wave tone or equivalent set the system up to deliver the ***correct field strength (0dB ±3dB). Now apply a 1.6kHz sine wave tone. If the ‘Voltage clip’ LED remains off, the maximum power bandwidth is=> 1.6kHz.

A listening test is required to complete the assessment.

2.) For loop amplifiers without a ‘peak voltage clip’ LED

Using a 1kHz sine wave tone or equivalent set the system up to deliver the ***correct field strength (0dB ±3dB). Now apply a 1.6kHz sine wave tone and measure the field strength. It should not have changed. Any drop in field strength indicates that the amplifier is voltage clipping and is not able to deliver the required current at this frequency.

('Squaring' of the current waveform as observed on an Oscilloscope is a more precise method)

A listening test is required to complete the assessment

***The standard does allow the field strength at 1kHz to be reduced by 1dB before applying the 1.6kHz tone, but metal loss compensation must be applied

The Univox Log Book and Commissioning Certificate now include the 1.6kHz Maximum Power Bandwidth Check.

Both documents are available as PDF Forms and can be downloaded from the knowledge centre on our website.

http://www.univoxaudio.co.uk/log-book

To access you will need to create an account and log in

Positive feedback is not always good news

Understanding Positive Feedback

We all like to receive some positive feedback, a pat on the back, a compliment, some recognition for the work we have done or for something we have achieved. However, In the audio world, things are quite different, positive feedback can lead to instability, and too much positive feedback can cause catastrophic system failure; consider pushing a child on a swing, each push is in synch with the motion of the swing requiring relatively little effort yet the child swings higher and higher . If the positive feedback continues, the system becomes unstable and eventually it breaks down ending in tears.

Audio systems are similar and grown men do cry! With an open microphone near a speaker, the output from the speaker is fed back into the system pushing the output higher and higher eventually the system self oscillates and a loud screech emanates from the speaker. If corrective action is not taken, the amplifier and possibly the speaker will self destruct.

To recover from this situation, the operator can move the microphone further away from the speaker, turn the sensitivity down on the microphone, turn the volume down on the amplifier driving the speaker, filter the oscillating frequency, a combination of these or switch the system off and start again.

Every audio system will have a point at which it becomes unstable and self oscillates. A systems integrator needs to understand where this point is and to try and maximise the dynamic range to give the best system performance.

Induction loop systems are no different except when they self oscillate it all happens in silence and invariably goes undetected until it is too late since the feedback mechanism is magnetic.

Finding the stability threshold for the loop system

The combined input and output settings at which the system begins to self oscillate is the stability threshold. To determine these points either the input level or the output level should be set to the desired position with the other control being adjusted from zero until the threshold is reached.

We suggest you set up the input level as specified in the amplifier documentation and then adjust the loop current from zero, observing the field strength generated. Increasing the current should cause the field strength to increase. If the field strength suddenly drops by 6dB the amplifier is self oscillating and the 2nd stage of the AGC has been activated. You will need to back the controls off or turn the system off to reset . An oscilloscope connected across the loop terminals (it must not be grounded) can be used to observe and measure the oscillation frequencies.

For a Super Loop system, you will need to adjust both master and slave. Start with both outputs set to zero, adjust the master whilst monitoring for feedback and if it is not reached, adjust the slave. You will need to monitor both master and slave outputs as either could begin to self oscillate

Is the system self oscillating?

It is often very difficult to tell whether the system is self-oscillating until it is too late.

To check a system:

Set the field strength generated by the system to 0dB at the desired height using test signals from an independent source. Now connect the live feed and check the output level.

Has the field strength dropped by approximately 6dB?

Keep quiet so there is no input to the microphone.

Does the audio input LED stay on?

Do the drive current LED’s stay on?

The above are all indications that the system is unstable and self oscillating. The system should be turned off to avoid damage and remedial action to prevent or reduce susceptibility to self oscillation as described should be taken.

The Univox loop listener uses a peak detector so it can easily be used to check the field strength level of live signals. With test signals you would expect to see the green led lit indicating that the field strength is at least 0dB. When you connect the live signal you would expect the green LED to flicker on the peaks of the signal with the orange LED flickering occasionally too. If neither LED flickers, the field strength has dropped to below -6dB.

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Causes of Positive Feedback

1 ) A dynamic microphone is being used inside the induction loop

Dynamic microphones use a magnetic pickup.

To reduce the susceptibility to feedback:

Use a dynamic microphone with better shielding.

Only use the microphone outside the loop and if necessary add a cancelation loop to this section.

Use a Super Loop system.

Reduce the output of the loop system (turn the current down).

Reduce the sensitivity of the microphone (turn the input gain down).

Limit the bandwidth of the loop input signal using DSP or other filtering techniques.

Use a combination of the above.

To avoid the Issue of feedback:

Do not use a dynamic microphone.

Use a condenser microphone or other type of microphone that does not use a magnetic transducer.

2 ) An electric guitar is being used inside an induction loop

An electric guitar uses a magnetic pick -up coil to detect the vibrating strings.

To reduce the susceptibility to feedback:

Only use the electric guitar outside the loop and if necessary add a cancelation loop to this section.

Use an SLS system.

Reduce the output of the loop system (turn the current down).

Reduce the sensitivity of the guitar pick up coil

Limit the bandwidth of the loop input signal using DSP or other filtering techniques.

Use a combination of the above.

To avoid the Issue of feedback:

Do not use an electric guitar where an induction loop system is being operated.

3 ) The Loop or loop feed cable is parallel and in close proximity to the low signal input cables

The high current in the loop and feed cable creates a magnetic field (as intended). This magnetic field will induce currents into adjacent conductors.

If the conductors are carrying input signals eg. microphone signals then the output is being coupled back into the input; positive feedback

To reduce the susceptibility to feedback:

Increase the separation distance between the cables (at least 30cm separation between cables should be maintained).

Reduce the distance over which the cables run parallel to each other.

Use twisted pair loop feed cables (star quad configured loop feed cables are best).

Use balanced connections for high common mode rejection.

Reduce the output of the loop system (turn the current down).

Reduce the level of the input signal (turn the input down).

Limit the bandwidth of the loop input signal using DSP or other filtering techniques. (5kHz knee point or 4kHz if the system is only being used for speech) .

Modify the loop Amplifier. The manufacturer my be able to suggest some modifications to the amplifier to reduce feedback sensitivity. These modifications may cause other instability issues and therefore must be applied with caution.

Use a combination of the above.

To avoid the Issue of feedback:

Do not run loop cables in parallel with input cables. (They may cross at right angles).

Damage to induction loop amplifiers caused by positive feedback is not covered under warranty.
It is the responsibility of the installer to ensure that the system is stable.

Loop Configurations Explained

Why One Size Does Not Fit All

Universal Access

Loops and telecoils have the potential to provide truly universal access for hard of hearing people here in the UK and throughout the world , but only if they all deliver the same high performance.

To realise this potential, international agreement on the performance of a loop system has been reached and is embodied in the International performance standard for Audio Frequency Induction Loop Systems , IEC60118-4:2006.

This standard defines the magnetic field strength, signal uniformity, frequency response and background magnetic noise for a system. It means that a hearing aid user using a system in a bank, at a train station , at church, in a theatre etc... here or any where else in the world can simply select the T -programme on their hearing aid to relax, participate and enjoy the moment.

An induction loop system that does not deliver standard compliant performance is a missed opportunity. It will not delight customers encouraging them to return and may render the facility in breech of its duty to provide an equal level of access to everyone as set out in the Equalities Act 2010.

Where there is a need for audio communication to inform entertain or communicate, there is most likely a need for assistive listening. By nature of the environment of each application, the demands on the induction loop system may be very different, requiring a different solution.

Large area coverage, spill control or compensation for signal loss due to metal structures can rarely be achieved with the humble perimeter loop. A knowledgeable, experienced loop designer will consider these performance requirements with installation and budget constraints to determine the most appropriate solution, always mindful that the system must comply with the international performance standard IEC 60118-4:2006. The typical options are :

Perimeter Loop
Cancellation Loop
Figure 8 Loop
Super 8 Loop
SuperLoop

Down Load the PDF for the full article.

21st Century Sound For Places of Worship

Speech Intelligibility for Places of Worship.

Induction Loop Systems

IEC 60118-4 Has Changed:Part 2 Counter Loops (2)

Guidance For Commissioning Counter Loops

Loop Orientation

Counter Loop Kits And Test Equipment To Make Compliance Easy

Counter Loop Test Certificate

IEC 60118-4 Has Changed:Part 1 Maximum Power Bandwidth

Positive feedback is not always good news

Understanding Positive Feedback

Finding the stability threshold for the loop system

Causes of Positive Feedback

1 ) A dynamic microphone is being used inside the induction loop

2 ) An electric guitar is being used inside an induction loop

3 ) The Loop or loop feed cable is parallel and in close proximity to the low signal input cables

To reduce the susceptibility to feedback:

Loop Configurations Explained

Universal Access

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