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Subject areas


How do I connect two adjacent SLS systems to optimize sound quality?

1) Connect a signal source to both systems, preferably a sine wave
2) Connect both MASTER and SLAVE loops to both amplifiers
3) Set the output level to minimum for the SLAVE systems
4) Adjust the level for both MASTER systems to approx. -3dB
5) Listen to the sound of the loop with a loop listener (Univox Listener or Univox FSM) while shifting the phase (wires) on one of them until a correct sound is heard. One position will sound distorted whereas the other will sound clean.
6) Repeat step 3-5 in the procedure above for the SLAVE systems as well
7) After you’ve completed the above procedure, adjust/certify the systems according to the IEC 60118-4 standard

Is it possible to install loops in rooms close to each other without any overspill?

This is possible if you use Univox SLS amplifiers. Read more about Univox SLS and Hollow core slab

We will replace a broken loop amplifier in a TV-room. The loop cable installed is very thin, 1mm². Which amplifier do you recommend?

Try to use a more powerful amplifier to compensate for the thin cable.

We plan to install a loop in a sports arena. Which loop amplifier do you recommend?

It is a big area to cover and it is almost impossible to receive a smooth field strength with a standard amplifier. We recommend to use Univox SLS amplifier system to for a good sound quality. By using SLS it is possible to use different program material in different parts of the arena. Read more about Univox SLS.

It sounds like a whistling sound similar to acoustic feedback problem, when I use microphones together with a loudspeaker system. What have I done wrong?

Try first to isolate the two systems.

Is the PA and Loop Amplifier working separately without any problem?

If the Loop Amplifier self-oscillate (the input LED is emitting), reduce the output loop current or remove the loop wires. If the problem stops the cause could be

1) the loop wire could be short-circuit to safety ground somewhere
2) the loop amplifier does not work

If self-oscillation only occurred when the systems are connected together try to reduce the output loop current to minimum. If the self-oscillation disappears it is most likely that there is a feedback problem between sensitive inputs and loop wire in the system. For example, there are sensitive dynamic microphones close the loop wire. Inputs and outputs (loop-wire) shall not be placed close to each other to avoid feedback. For more information visit on site planning.

I find that the coverage area is larger in your specification than in actual installations, why?

The specification of the coverage area is calculated for a free-field (no metallic objects) with a square-loop (hardest figuration) at 1.2m height. In many installations there are metallic objects that influence the field strength. The field is therefore attenuated especially in the high frequency region. Therefore loop sides wider than 10 metres should be avoided.

Example: In a room with reinforced concrete/metal works the power demand is increased by 20 to 50%, sometimes even more. A stated 170m² maximum coverage area of an amplifier will only cover approximately 130m² in a normal reinforced concrete room.

If you use a Univox SLS, Univox Super Loop System, it is easier to estimate the coverage area.

The loop amplifier shall be moved and used in different rooms and with different loops. What do I have to pay attention to?

Inform the user(s) that the loop current must be individually adjusted in each location.

Which loop amplifier do you recommend for a new auditorium that is not yet built?

We recommend a SLS system to avoid overspill and to reach a smoother magnetic field with a better frequency response. If you use a standard loop amplifier there is a risk to get acoustic feedback if you use electric guitars or other instruments in the auditorium. Read more about Univox SLS.

Is it possible to install a loop in a level seating area?

Yes, if you use the Univox SLS system above the seating area. Please contact us for more detailed information.

We plan to install loops in an elderly home with several TV-rooms close to each other – does that work?

Univox SLS system makes it possible to install loops close to each other without overspill. Read more about Univox SLS.

How does different cables influence on the coverage area when you use the AutoLoop amplifier?

We have measured the level with different cables; 0.5, 1.0, 1.5, 3.0mm² and you do not hear the difference. But to get MAXIMUM coverage area, the cable shall not be too thin.

The difference between 1.0 and 3.0mm² is 2dB. The difference between 0.5 and 1.0mm² is 1dB.

I need your advice for a lift installation. As you can guess, it is a metallic box with a neon light at the ceiling. Please, let me now the best amplifier and figuration for this case.

We have tested several amplifiers with lifts.

The basic installation is a multi-turn loop to let the field strength pass through the metals. Typically a 4-8 turn using a 1-2mm² wire. The number of turns has to be tested and depends on amplifier and the size and metal from of the lift.


1) Normally it is connected to the phone system. But the connections must be isolated through a ground isolator transformer. (We have standard ones mainly for car radio connections which have floating output).
2) Using the Univox AC/DC it is possibly to connect both 230v AND a 24V battery backup system for obvious reasons. Univox TV-200 works also simultaneously with 230VAC and 24V.
Is it possible to install loops in rooms close to each other and have different sounds in the rooms without the loops disturbing each other?
It is possible if you use Univox SLS amplifiers. Read more about Univox SLS.

I have to connect two PLS-300 to the same sound source, but I have only one output. Can I use the LINE OUT RCA connector for feeding input to a second amplifier?

Yes, you can use the output RCA connector to feed another amplifier.

I installed a Univox SLS system with 2 x 2.5 mm², how do I decide if I need to make a 2-turn loop or 1-turn loop?

Always start with a 2-turn loop. If you do not reach an acceptable field strength level, try with a 1-turn loop.


What to keep in mind when installing hearing loops in buildings with prestressed concrete hollow core slab

Prestressed concrete hollow core slab is a type of concrete slab with longitudinal cavities/channels. It’s a relatively light-weight concrete slab which lacks the traditional metal reinforcement mesh. When planning hearing loops in building with hollow core slabs, the expected metal attenuation is much less than from the reinforcement in traditional concrete slab floors. Especially the blocking or decreased vertical overspill expected from traditional concrete slab, does not apply to this kind of material.

Planning in Univox Loop Designer (ULD)

When planning in our web-based planning tool Univox Loop Designer (ULD we recommend ”Free field – no metal (0dB)” when choosing the Environment. This will resemble the expected metal impact in a much better way than ”Standard reinforced concrete”.

Other solutions

If SLS loop systems for any reason cannot be used in the building, there are alternative solutions available such as wireless radio systems (RF systems) and IR systems (infra-red radiation) consisting of stationary transmitters and belt pack receivers with earphones or neck loops. Also small area loop systems or portable loop systems with limited field strength range can be used, for example CTC and SmartLoop/P-CTC, mainly in reception desks and for one-on-one communication settings in meeting rooms and offices.


Loop cable

We plan to place the loop cable in a ceiling with acoustic ceiling tiles (60 x 60 cm) – does that work?

To achieve a good result the cable has to be placed in the middle of the tiles, not close to the metallic frame. You should not place the cable at a height above 3m.

We plan to place the loop at floor level in a room 10 x 5 m, where shall I place the loop cable?

Always start with a 2-turn loop. If you do not reach an acceptable field strength level, try with a 1-turn loop. In small premises like this, the 2-turn loop will probably give the best result.

How shall I do to splice the copper foil cable?

We recommend to solder the cable for best result. It is also possible to splice with standard cable as long as the area is the same as the area of the copper foil cable. For termination and slicing to a standard cable, you can also use Ebeco crimping tool.

I need to install a loop in a church, and it is not possible to place a loop in the floor. What can I do?

It is possible to place the loop cable outside the church walls. Please contact us for more detailed information.

We will replace a broken loop amplifier in a TV-room. The loop cable installed is very thin, 1mm². Does it work?

Try to use a more powerful amplifier to compensate for the thin cable.

The concrete is reinforced. Is it possible to place copper foil on the concrete and use putty on the foil?

Yes, that is possible, but it is important to measure the loop installation before adding putty.

There are heating heat pipes in the floor. Is it possible to place loop cable on top of the heat pipes?

Normally it works well, but it is important to make a test with measurement before putting the floor on top. Please contact us for more detailed information.

Is it possible to place the loop cable in pipes that will be placed in the concrete?

Yes, that is possible, but the reinforcement of the concrete can have a negative influence on the final result. Therefore it is important to measure the loop installation before casting.

Where do I place the loop cable – in the floor or in the ceiling?

That depends on the size of the loop. A room 15x15m the loop can be placed in the ceiling at 4m height with a good result. If you have a smaller room, for example 7x7m, the loop should not be placed higher than 2.4m to receive a good result.

We can’t place the loop cable in the floor, because of the existing parquet floor. What can we do?

You can place the cable plinth or in the ceiling.

Measurement / Control

We will install loops in an elderly home. Do we need to measure the loops?

The installation has to be tested and measured to confirm that it fulfils the IEC 60118-4 standard. Read more here.

Portable Loop Case

Is it possible to record from the loop?

Yes, use the “0dB Out” outlet.

How many square meters does the P-Loop 2.0 cover?

With the supplied cable reel of 35 meters it covers 75 m². If you add the extension cable, it doubles the area to 150 m².

Amplifiers Counters and Receptions

Can we connect two microphones to the loop amplifier in a CTC-system or will one cancel the other?

Yes, there are 2 microphone inputs on the CLS-1 amplifier.

Old products:

If you are using DLS-50 there is one special mic.input that has a controllable gain. Please use that for the main microphone and for the second microphone (we normally recommend only one to keep the acoustic noise down) other combined mic and line input. All the inputs have phantom voltage to the microphones.

Using DLS-70, there are two mic. Inputs with just the AGC-regulation function normally well but cannot be fine tuned for exact sensitivity and background acoustic noise.

Can we connect speakers to where the loop wires go? And still connect the loop pad? Which speaker do you recommend?

If you are using our loop pad just install it and connect speaker to the headphone socket. Active speaker works best. If not active and the speaker level is too low use the cushion or the loop output (the loop and cushion connecter are paralleled). An active speaker is easiest to use, but any normal speaker that could easily be built-in is useful.

We have information desks with no metal interference and the loops will be 1 m apart. Which amplifier do you recommend?

We recommend Univox CLS-1 with our loop pad, i.e. the CTC systems. If you use other loop pad the overspill could be more than 1m.

Speakers / PA

Does the OKAYO system have diversity?

Yes the EJ-700 series of receivers have diversity.

How many microphones can I use simultaneously if I want to have a well working system for example in a church?

You can us up to 4 microphones at the frequency 863-865 MHz. If you need to use more microphones, there are receivers on other frequencies available.

Please contact us for further information.

Sometimes the sound disappears completely. What could be wrong?

Check if the green LED on the transmitter and the yellow LED on the receiver lights up when the sound disappears. If so, it probably is wrong with the microphone.

How long can a signal cable between a mixer and a loop amplifier be?

The main issues with long cables are subdued treble and risk of induced interference from surrounding systems (loudspeaker cables, winding wires, data cables, etc.).

The maximum length can’t be specified in general, but the signal cable must always be balanced if the length is more than about 2m.

The maximum length is calculated by several combined parameters, e.g. how well shielded and balanced is the cable, how well balanced is the mixer, the level of the mixer (at least 0dBV = 0.775V, preferably + 4dBV) and also the output impedance of the mixer.

Signal cable placement is very important. It should never be near and parallel to the other long lines such as loop wire, speaker cable, computer networks, etc. A rule of thumb is at least 3dm from adjacent lines. Intersecting lines doesn’t interfere.

When ordinary general installation rules for audio and tele-technical installations are followed, then the length can amount to over 100m. In principle there is no upper limit.

Note that it is relatively rare that professional line level (signal between the mixer and the external devices) are causing the problems. Usually it’s the microphones low signal level that can interfere with other systems.