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Author Topic: Hearing Assistance issue  (Read 4892 times)

Rolf Baum

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Hearing Assistance issue
« on: April 24, 2011, 07:28:36 pm »

Hi,
 
We have a hearing assistance system in our church that we are having issues with and if we need to replace it then we would like to make sure we get something that we know will work. We have a person that needs to turn up the volume on their receiver almost all the way if not all the way to be able to hear. She only has 10% hearing in one ear and 20% in the other. The quality of sound is not very good, but that is not the major issue. The issue we are having with the receiver turned all the way up is causing a squeal coming from the ear peace.

I have tested this with other receivers and walking around and if I turn the volume up it will squeal. If we turn all of the mic's off there is no squeal, so there must be some feedback with the hearing system. If the person keeps their hand over the ear piece there is less of a chance of having the squeal. But, the squeal is annoying to the others. There is a yellow and red light on the transmitter and if we keep the signal level up in the blinking to solid red it seems to be a little better. This squeal only happens when there is silence, if the speaker pauses or takes a breath, once they start talking it stops.

Donít know if there is a way to increase the volume for the person without having this squeal or is there some system that will filter/stop the squeal. Can you help us determine how to resolve this issue?

Thanks,
Rolf
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Jonathan Johnson

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Re: Hearing Assistance issue
« Reply #1 on: April 25, 2011, 11:26:49 pm »

Is the squeal just coming from the earpiece, or is it also coming from the main loudspeakers?

If it's coming from the main loudspeakers, you've definitely got a feedback issue happening. If it's only coming from the earpiece, then it's being generated solely within the hearing assistance system and most likely is not a feedback loop through the main system.

Can you produce the squeal when you play a CD/tape but have the mics off?

You say that "the quality of the sound is not very good, but that is not the major issue." The sound quality may in fact contribute to the squealing issue. Many hearing assistance systems boost the highs since the majority of hearing loss is in the higher frequencies, which carry the consonant information. Without that, talking just sounds like umma ooma waama ngoo. If your system is boosting the highs more than it should, that could cause the squeal.

What is the make/model of the system?
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Rolf Baum

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Re: Hearing Assistance issue
« Reply #2 on: April 25, 2011, 11:59:03 pm »

The squeal is just coming from the earpiece.

I will have to test if we get the squeal with a CD and the micís turned off, will let you know in a few days.

We have a Personal PA FM Auditory Assistance Transmitter T20.
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Frank DeWitt

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Re: Hearing Assistance issue
« Reply #3 on: April 26, 2011, 05:03:19 pm »

The squeal is just coming from the earpiece.

I will have to test if we get the squeal with a CD and the micís turned off, will let you know in a few days.

We have a Personal PA FM Auditory Assistance Transmitter T20.

I believe it is a feedback issue.

You have two sound systems in the room.  Main system mic mixer amp speakers.  Assisted hearing system  Mic, mixer, transmitter, receiver, earphone.  That system is going into feedback.  All the usually rules apply  Turn it down (can't do that) move the speaker (earphone) further from the mics, EQ out the feedback.  Also, and probably best, you can have her use high isolation earphones.
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David Kaiser

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Re: Hearing Assistance issue
« Reply #4 on: April 27, 2011, 05:00:54 am »

I would reccommend the closed headphone route also. The use of a headphone that totally encloses the ear would mean that she could still use her own hearing aids  and have the volume on her headphones way down. I believe that Koss has some lightweight, unobtrusive totally enclosed headphones.
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Tom Young

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Re: Hearing Assistance issue
« Reply #5 on: April 27, 2011, 06:26:24 am »

I believe it is a feedback issue.

You have two sound systems in the room.  Main system mic mixer amp speakers.  Assisted hearing system  Mic, mixer, transmitter, receiver, earphone.  That system is going into feedback.  All the usually rules apply  Turn it down (can't do that) move the speaker (earphone) further from the mics, EQ out the feedback.  Also, and probably best, you can have her use high isolation earphones.

To confirm that it really is mic-to-speaker (ear piece) feedback, ask her to move to the rear of the sanctuary or (if you rally want to be sure) out into the narthex/lobby.

One thing seems to be missing here: running the assisted listening signal through DSP. The main reason to do this is to delay (align) the ALS signal to the FOH speakers. Since exact alignment can only be done for one point, we (who do this) align for mid way back. The point is that one of the reasons a user cranks the volume on their bodypack is to overcome the out-of-sync acoustic energy from the loudspeakers. If these are aligned (exactly or more than they would be with no delay) there is less need for more volume. Get her to sit in the "aligned" seats or align the ALS to where she is sitting.

There is also no reason you cannot also measure the feedback frequency and notch it out with the DSP. Obviously this would not be done during a service.

If you do not have a spare input and output on your DSP, look for a used one on Ebay. Shure DFR11EQ (1-in/1-out) devices go for as little as $80-$100.00   These have parametric filters and auto-feedback filters.   

Do not buy cheap (music store) DSP.
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Brad Weber

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Re: Hearing Assistance issue
« Reply #6 on: April 27, 2011, 08:36:58 am »

Everything may be corrrect but verifying all the settings on the transmitter and receiver would be a good idea as would being sure that you have good batteries in the receiver.  There are a number of switches and settings on the rear of the T20 transmitter including a mic/line/70V input selector switch for the XLR/1/4" combo jack input, a 20Hz/175Hz/725Hz high pass selector switch, a full/-6dB/-12dB RF power selector switch and two rotary switches to select the two digit code for the channel assignment.  How are all of those currently set?  Is the audio coming in on the combo jack or is it an unblanced signal connected to the ground and one of the three input screw terminals?
 
On the front of the transmitter there are the two audio level LEDs that you noted with a screwdriver adjustable pot next to them.  The audio level should be adjusted so that you ideally see the amber 'OK' LED with signal and the red 'Hi' LED only flashes on peaks.  There are also three LEDs for Transmit Status, a green LED to show the RF is active and amber WB (Wideband) and NB (Narrowband) indicators.
 
Whether the Wideband or Narrowband LED should be lit as well as which channel should be selected using the two rotary slector switches on the rear of the transmitter depends on the receivers.  With the R7 series receivers you would use one of the 10 wide band channels and tuning the receiver to match that channel is accomplished by removing the back of the receiver and using a plastic tuning tool to adjust a turn pot.  This tuning can drift over time so it could simply have drifted off channel a bit.  The R19 series receivers have a channel select switch on the receiver and use the narrowband channels.  The standard channels are apparently 33 and 53 for the R19 (two channel selector switch on the receiver), 13/23/33/53 for the R19-4 (four channel selector switch on the receiver) and 13/23/33/38/42/53 for the R19-6 (six channel selector switch on the receiver).
 
FYI, the related manuals are at http://www.williamssound.com/files/PPA300man.pdf and http://www.williamssound.com/files/PPA500man.pdf.
 
I don't think anyone has asked about how the signal feeding the transmitter is derived, so explaining what feeds the ALS transmitter and any processing in that path may also help.
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Rolf Baum

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Re: Hearing Assistance issue
« Reply #7 on: April 28, 2011, 11:02:49 pm »

Sorry, it took so long to check things and get back you all of you, but here are my findings.

Tried turning off all the mic's and playing a CD and got no feedback. Turned up the mic and started getting the feedback. Then I turned up the volume on the CD and the feedback stopped. If I turned down the volume the feedback came back.

Doesn't seem like it matters where in the sanctuary I tested I would get feedback. But, if in the narthex/lobby or in the balcony there is no feedback. We do not have a DSP, but I can see the benefits of having one.

The settings on the transmitter are line input using a 1/4" jack. It is set for 20Hz high pass, -6dB RF power and the two rotary switches are set for 0 and 5.

Let me know if I should try any different settings or if I should try something else.

Thanks,
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Brad Weber

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Re: Hearing Assistance issue
« Reply #8 on: April 29, 2011, 09:16:35 am »

Tried turning off all the mic's and playing a CD and got no feedback. Turned up the mic and started getting the feedback. Then I turned up the volume on the CD and the feedback stopped. If I turned down the volume the feedback came back.
So you had feedback and simply turning up the CD stopped the feedback?  When this happened were the mics and CD routed to the ALS system and the house or to only the ALS system?  What signal feeds the ALS system?
 
The ALS system includes a compression/limiting circuit thast can be set in several different ways, however the default is a compressor mode.  Perhaps the CD signal is driving the ALS transmitter hard enough that the transmitter is applying more compression and since that compression is applied to the overall signal it is also reducing the level of the signal components causing the feedback.
 
Doesn't seem like it matters where in the sanctuary I tested I would get feedback. But, if in the narthex/lobby or in the balcony there is no feedback.
Just to verify, this is with you using the receiver with earphones?  This does seem to support that it is an acoustic feedback loop, but an ALS receiver so loud that it would cause feedback from anywhere in the Sanctuary and not also cause complaints from those seated near the person using the ALS system would be unusual.
 
You mentioned that the individual involved has only 10% hearing in one ear and 20% in the other, however I don't think it was noted whether they were trying to use the ALS system by itself or in conjunction with hearing aids.  If they have hearing aids then using them with headphones for the ALS may allow them to not need to run the receiver as loud.  And even better than that, if they have hearing aids that incorporate a T-coil then using a neck loop like this http://www.williamssound.com/productdetail.aspx?product_id=79 or this http://www.williamssound.com/productdetail.aspx?product_id=81 for the ALS receiver might be the best option.
 
The settings on the transmitter are line input using a 1/4" jack. It is set for 20Hz high pass, -6dB RF power and the two rotary switches are set for 0 and 5.

Let me know if I should try any different settings or if I should try something else.
I believe there are two different receiver models used with the T20 transmitter, the R7 series and the R19 series.  The 0 and 5 settings on the transmitter are a wideband channel setting, which is what the R7 series receivers use while the R19 series should use the narrowband channels.  If you can't find the model number on the receiver, then the R7 series has the headphone jack, a power indicator and a volume control that also acts as the power switch (there are also multi-channel versions that add a rotary channel selector) and the R19 series receivers have a headphone jack, a volume/power control, a three position tone control and a slide type channel selector switch. 
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Rolf Baum

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Re: Hearing Assistance issue
« Reply #9 on: May 01, 2011, 12:42:47 am »

So you had feedback and simply turning up the CD stopped the feedback?  When this happened were the mics and CD routed to the ALS system and the house or to only the ALS system?  What signal feeds the ALS system?

Yes, don't know why it tryed this, but it did stop the feedback. Yes, both the mic's and CD were routed thru the ALS and yes, both the house and ALS. I forgot to note the model of our amp, but the Pre Amp Out goes to a Electro-Voice EVT 2230 In and the Out goes back to the Amp and the ALS.

Just to verify, this is with you using the receiver with earphones?  This does seem to support that it is an acoustic feedback loop, but an ALS receiver so loud that it would cause feedback from anywhere in the Sanctuary and not also cause complaints from those seated near the person using the ALS system would be unusual.

Yes, it is happening with a receiver using an earphone, simular to the LA-164. We getting complants from more then just those sitting around her, but even from those in the back. She sits near the front.

You mentioned that the individual involved has only 10% hearing in one ear and 20% in the other, however I don't think it was noted whether they were trying to use the ALS system by itself or in conjunction with hearing aids.

In conjuntion with her hearing aids.

We are using the R7 receivers.
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Re: Hearing Assistance issue
¬ę Reply #9 on: May 01, 2011, 12:42:47 am ¬Ľ


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