by Neil Bauman, Ph.D.
A man wrote,
After almost 3 weeks trying out a home loop system, I conclude that the loop would not be suitable for our church. Here are my reasons.
1. Two sounds are picked-up, one from the loop, the other direct from the speaker. This is confusing and does not contribute to improved audio quality.
2. I also question the quality of the system. I hear some additional background noise.
3. I was not convinced that the higher frequencies were faithfully transmitted.
This is a disappointment as I had hoped the system would offer an approach for better understanding at church. I would appreciate hearing from you if you think I’ve missed something or if the settings on the loop amplifier are not correct.
Let’s look at your concerns one by one.
1. When you hear two sounds—one via the loop system and the other via the microphone in your hearing aids—that tells me you do not have your hearing aids set correctly. You should only hear one sound—via the loop.
This is very easy to fix. Your hearing aids are currently set up such that both the microphones and t-coils are on at the same time. Normally this is not a good idea because then, as you have discovered, the two competing sounds “interfere” with each other since there are slight differences in timing between when you hear the sound though the air and through the loop. To fix this have your audiologist set one memory (program) in your hearing aids with just your t-coils on and your microphones off. Then you’ll only hear the sounds from the loop, and you’ll hear beautiful clear sounds.
If you have open-fit ear molds and mild or moderate hearing loss, you may hear the audio directly from the speakers on the sound system as well as from the t-coils in your hearing aids. If you are in a large looped venue, the sound technicians may have to delay the sound signals to the loop by a fraction of a second, (since sound travels slower in air than it does via the loop system) so that both signals reach your ears at the same time.
2. If you hear additional background noise—typically a humming or buzzing sound—this is not the fault of the loop. What you are hearing is stray magnetic interference from the electrical system in the building being picked up by the t-coils in your hearing aids. You can easily prove this. Just leave the loop system turned off and listen with your hearing aids in t-coil mode. If you still hear a humming or buzzing sound, you know it is not the loop system.
Since this is an electrical problem, you should have an electrician or the power company (if you still hear the interference when you are outside the building) come and fix the problem.
Normally loop installers make sure that any interference present is below -32 dB and ideally, below -47 dB before they install a loop system. However, if you have a moderate to profound hearing loss, you may not even hear stray magnetic interference, even it if it is as loud as -20 dB.
Another cause of background sounds (static) is if you don’t have a loud enough signal going into your loop amplifier. For example, if your TV’s audio output is variable rather than fixed, then if you have the volume set too low on the TV you may end up hearing sound processing noise. This can also happen if you have a weak input signal to the loop amplifier and your t-coils are not oriented in the same plane as the room loop.
3. If your loop does not produce the higher frequencies properly there are several possibilities. First, if you are using a simple perimeter room loop, the loop may be too wide, you’ll notice the signal from the loop is “muddy” and not clear like it should be.
To fix this problem you can just reduce the total size of the looped area. When you can’t do that, commercial loop installers change the configuration of the loop from a simple perimeter loop to more complex shapes such as a square figure of eight shape or triple figure of eight shape (snowman shape), or they may install phased array loops. This effectively reduces the width of the looped area.
A second possibility is that you have made the room loop too large for the power of the loop amplifier you are using. In that case, you need to use a more powerful loop amplifier that has the capacity to cover the area you want covered.
This is because if you make a loop too big for the power of the amplifier, then the high frequencies tend to fall off in the center of the loop and you hear a “muddy” signal. In properly installed commercial loops, we correct for this so it does not happen.
There are a number of other possible reasons for poor frequency response such as a low quality input signal or too low an input signal level to the loop amplifier, or the loop cable may be mismatched to the loop amplifier.
Also, note that loop systems are not going to give you wonderful high-frequency response all the way up to 20,000 Hz. However, this is typically not a problem because almost no hard of hearing people can hear these high frequencies anyway.
You see, hearing loss typically first occurs in the high frequencies and works its way down the frequency spectrum. Many hard of hearing people do not even hear up to 5,000 Hz anymore. That is why the International Standards committee chose 5,000 Hz as the cut-off frequency for flat frequency response for loop systems. Note: in order to meet standards, loop systems are required to have a flat frequency response between 100 Hz and 5,000 Hz.
I think you should give loop systems another chance. Typically, home loop systems are easy to set up properly. Setting up loop systems for larger buildings such as churches and auditoriums are best left to professional loop installers because they know how to fix these kinds of problems.
When both your hearing aids and loop system are set up correctly, you will find you are in for a wonderful listening experience. Properly-installed loop systems really ARE good! Just yesterday I received an email from a church that installed a new loop system in their sanctuary under our guidance and used it for the first time on Sunday. Their assessment of their brand new loop system? “The system works awesome!”