Wireless mic/amp

[maria]

I have recently suffered hearing damage and related symptoms at an aerobics class from feedback between the wireless mic and amp at the start of the class. The amp was on far too high and the instructer walked up to the speaker creating an intense base level noise! I am planning to write an article to highlight the potential dangers if aerobics teachers have not be trained appropriately to use the wireless mic and amplifier. I am looking for a technical expert who shares my concerns and would be interested in helping me with this article.

 

Thanks

[paulears]

To be honest, Maria - I'm afraid I would be extremely doubtful if a small PA system could cause problems like this with such a short exposure without an underlying predisposition to high sound pressure levels.

 

The situation you describe is an everyday occurrence in our industry. The amp was almost certainly set to a typical level - the feedback being caused by proximity between the mic and loudspeaker, something that we have to deal with, but a phenomena that to a typical teacher appears to be a random circumstance. Most small PAs like these do not have that loud an output, but as you discovered, they are often rather bassy - but that's what the users want. The big honk when it feeds back is quite loud, but limited by the capability of the system. In most circumstances, while uncomfortable, it's not damaging when stopped quickly.

 

I really don't think we need yet another round of training. Common sense is what usually works here. After the first couple of honks, the teacher works out that they must not go near the loudspeakers without switching off/turning down.

 

I feel for your own hearing damage - but I have never come across spontaneous damage like this before. The upper limit for hearing damage is very unlikely to be exceeded by modest equipment unless you have your ears very, very close to the loudspeaker - and the nasty single frequency tone you got is no higher in level than the rated maximum power of the system, despite all being on one note. I'd imagine being at a Metallica concert would inflict much, much more volume than a feeding back small PA.

 

I am not sure that I would be able to support your article on potential danger. We do risk assessments every day, and faced with an aerobics dance class, the pre-existing risk of hearing damage from a typical system would already be low, and therefore would be difficult to reduce to zero, the next step down. If I had to risk assess this situation, I'd be more concerned with cumulative exposure to loud music - for which legislation already exists. Feedback in normal use is not considered generally to be an additional risk, it is short term and as far as I'm aware, has not been cited as an initiator of hearing damage?

 

In your example, it's sad you have been injured by this - but logic suggests that as the teacher had no problem, and was subject to the loudest feedback (being the cause), then your exposure level must have been far lower. It's sad that your problem would seem to be just one of those unfortunate examples of somebody susceptible to something others don't find an issue.

 

 

Sorry this isn't what you wanted to hear.

 

If you can find somebody who agrees with you, I'd worry that they might not be quite as experienced as they should be?

 

There seems to be no evidence whatsoever that special measure should be taken, although there's nothing wrong with raising awareness in case others with sensitive hearing could be affected. It would be wrong, however, to present your case as a danger that has technical support for it, when this doesn't exist. Hearing damage in the entertainment and music industry has been under a spotlight recently - the MU have all sorts of data on this, and have made some changes to how they do things as a result - but feedback is so short in nature, I don't think it has been a feature of any previous concerns.

 

You might not be aware that there are devices on the market to reduce feedback. However, to do this, the speakers have to feedback loudly, while the device works out what to do, and sorts it. This does not seem to have caused problems even though the users often initiate feedback on purpose, so the devices can remove it!

 

 

I hope your hearing returns to normal without permanent damage.

 

Paul

[David Duffy]

I agree that it's unlikely that your hearing has been permanently affected by this incident. As Paul said, feedback, whilst being unpleasant is temporary. Any hearing issues you now have are far more likely to have caused by prolonged high level exposure.

[Unfathomable]

Paul pretty much summed it up, just to add that we are responsible for a school hall venue with a PA system near the theatre, the kids that often operate there cause a lot of feedback due to inexperience, but I have never heard of it damaging anyone. We also have a sports centre (not our responsibility) where aerobics classes etc use a PA. They get a fair bit, but again no problems as far as I am aware.

 

Reason for edit: SPAG

[Killyp]

Further to this, low frequencies are not as damaging to the ear as higher frequencies. What's more painful to your ear - the rumble you experience when in a car, or the sound of a fire alarm?

 

That's the best example I can think of at the moment, but what I'm trying to say is, it takes a huge amount of bass to damage your hearing, but it's the high frequencies people should be wary of.

[maria]

Thanks to all for your views. The hearing loss is minimal, the associated symptoms are more of an issue - I have been left with what I would describe as a wind noise trapped in my left ear at all times and pressure similar to what you get when a plane is landing. To controls these symptoms I am taking tablets which are also given for tinnitus. The class was recorded so I am trying to get hold of a copy of the recording which would demonstrate the sound that caused this. At the moment the Health club is refusing to give me a copy, quoting copyright law!

[paulears]

I think we feel for you Maria, we really do - BUT sound is physics based, and while the nasty honk could have started something that maybe would not have naturally occured for months/years/ever, we're just doubtful if a small PA, at a distance, could do such a thing. By all the data we have, and this as we said, is a subject quite a lot is known about - we doubt that there was a problem here. I can understand the venues reluctance to give you a copy of the recording - they may have many reasons, but if it features the voice of the instructor/session leader, then there is a copyright reason that holds water. Maybe the instructor is worried about you trying to take some action (futile, in my view) and fears you will mis-use the recording. The music content of course is 100% copyright material, and making a copy as well as distributing the music are both serious issues.

 

The recording would give you a frequency that you could pass to the medical professionals, but not the loudness.

 

I'm not sure we can really help here. I'd guess that a number of people on this forum would be the kind of people called to court to act as an expert witness to refute, not support your claim. That's how we really see it.

 

We understand you believe the feedback was the source of the problem, but we would tend to find that a difficult concept to support, without far more volume than an aerobics session is capable of producing.

 

A number of us have tinnitus to some degree, and have regular hearing checks, but this doesn't change our own beliefs and opinions on the subject.

Paul

[chris4monitors]

All very elequently put by Paulears.

Maria, I sugest you see an audiologist for a frquency spectogram to see what frequencies you are deficiant at. My best guess is that it will not be in the lower regester where you say the feedback was.