- Calibrated receiver designed for measuring the performance of audio hearing loop systems to the international induction loop standard IEC60118:4.
- Accuracy with ± 0.25 dBu and compatible with most audio analyzers.
- Five year warranty backed by Listen’s service and support.
The CMR3 calibrated receiver is designed for measuring the performance of audio hearing loop systems. The audio output is within ±0.25 dB over the frequency range and where used with a suitable audio analyzer such as the Minilyser from Neutrik Ltd, the frequency response and field distribution of the magnetic field from any audio hearing loop system can be plotted.
Calibrated to provide 0 dBu output for a field strength of 400 mA/m RMS, in accordance with the international hearing loop standard IEC60118:4. It is an essential tool for anyone wishing to assess loop system performance for analyses or certification.
One (1) CMR3 Hearing Loop Calibrated Receiver
The hearing loop calibrated receiver shall measure the audio performance within ±0.25 dB of the frequency range of the hearing loop system. It shall include a 3.5 mm balanced connection. It shall include a switch to toggle between flat or A-weighted filter. The receiver shall include an LED to indicate battery condition. It shall include the ability to accept two (2) AA alkaline batteries. It shall have a battery life of approximately 200 hrs. The CMR3 Hearing Loop Calibrated Receiver is specified.
| ||Specifications ||CMR3 |
|Magnetic Field Response ||400 mA/m RMS ||0 dBu Audio Output (0.775 V) |
|Field Strength ||Coil orientation vertical (indicated by ↑) |
| || || |
|Frequency Response ||50 Hz to 8 kHz ||± 0.25 dB |
|30 Hz and 14 kHz ||-3 dB |
|A-weigthing Filter ||EN61672-1:2003 Sound Level Meter (Switched) |
| || || |
|Gain Stability ||Output variation over battery life ||<0.1 dB |
|Ouput variation due to loading ||<0.1 dB |
|Output variation over temperature range ||<0.25 dB |
|Over gain variation ||<0.5 dB |
| || || |
|Ouputs ||Output Type ||Active Balanced |
|Load Impedance ||>600 Ohm |
|Connector ||3.5 mm Stereo |
| || || |
|Power ||Battery ||Two (2) AA Alkaline |
|Battery Life ||Approximately 200 hrs. |
|Battery Condition ||OK when LED Illuminated |
| || || |
|Physical ||Size ||2.4 x 1.0 x 4.4 in. (62 x 26 x 112 mm) (WxDxH) |
|Weight ||.18 lbs. (.084 kg) |
|Environment ||IP20 Protection, 20 to 90% Relative Humidity, 14 F (-10 C) to 113 F (45 C) |
| || || |
|Specifications are subject to change without notification|
How do I choose which loop driver is best for my installation?
Generally, this depends on the size of the room, the construction of the building, and the type of loop system you need. Refer to the Designing an Hearing Loop System Guide and Listen support to help you specify and design your system.
When should I use a perimeter loop system and when do I need an array?
A perimeter loop is the simplest form of loop system requiring a single loop of cable around the area to be used. However perimeter loops cannot be used if (1) other loop systems or areas where t-coil receivers are used are nearer than 3 times the room width (shortest side); (2) the room width is over 15ft and there is significant metal in the plane of the loop, such as reinforcement in a concrete floor. In these cases an array system is usually required. You may be able to conduct a site survey to confirm whether an array is necessary – contact Listen for details.
What is an array system and how do I design one?
An array uses two loop drivers and an SP5 phase shifter to create two overlaid magnetic fields, capable of accurately controlling the field within and around the loop system. They can be used to prevent ‘spill’ of magnetic field allowing loops to be used in adjacent rooms, and to give good even coverage in areas with metal building structures or complex installations. Arrays need a special layout design that can be provided by Listen. Arrays will always give a better field coverage and higher certainty of excellent performance than a perimeter loop, however the installation is more demanding and requires loop cables to cross the floor or ceiling of the area of use.
What audio input should I use?
Either an existing audio system can be used, or a dedicated microphone or other audio source may need to be provided. The objective is to ensure the loop system receives the required audio source (e.g. a voice) and not any background noise. The most essential job of any assistive listening system is to increase the level of the signal (the voice) relative to the background.
Why is it important for a loop driver to be ‘constant current’?
A current drive or constant current driver will deliver a current to the loop that is independent of the loop impedance. A normal audio amplifier will not be able to deliver constant current into a loop, meaning lower output at higher frequencies where the loop impedance is higher. A constant current driver can deliver flat frequency response, essential for delivering intelligible sound and performance that meets the loop performance standard.
Which type of cable should I use?
For cable intended to go under a carpet, you should use 1.8mm2 flat copper tape. Otherwise, you should choose the cable based on the maximum total cable length in the specifications chart.
What is spill or overspill?
Overspill occurs when the magnetic field created by hearing loop can be heard outside of the looped area (such as a room). The field is “spilling” outside of the looped area and can affect other nearby loop systems.
How do you minimize overspill?
This is done by using an array, consisting of two loop drivers and a SP5 phase shifter that controls the field within the looped area and reduces it rapidly outside the loop perimeter. The overspill can be reduced to as little as 5 ft (1.5m) with a good design.
What is metal loss correction?
Many buildings have embedded metal in the structure such as reinforcements in concrete, metal computer floors or suspended ceiling grids. This metal causes a distortion of the frequency response if the metal is in the same plane as the loop cable. The metal loss correction equalizes the audio to make up for or “correct” this loss. Note that metal loss will also reduce the signal level in general, and may require additional power, or indeed an array system to achieve the right level of performance.
Why do loop drivers have extensive audio processing?
Because the people who benefit from hearing loops (individuals with t-coil hearing aids), have limited dynamic range due to hearing loss. Thus, these users require significantly reduced dynamic range so they can hear the softest of sounds and so that very loud sounds are brought to nominal level.
Should I purchase a field strength meter?
Absolutely, it’s the only way you’ll be able to determine if a loop system is operating properly. Any venue that owns and operates a loop system should also have some equipment to monitor the operation of the loop on a regular basis. This should either be a field strength meter (FSM) or a receiver with field strength indication (IR-IL-1).