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Home > Archive > Hearing loss support > February 2006 > HA Puzzle for fun
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| Mason C 2006-02-25, 7:34 pm |
| This is just for fun, but instructive maybe.
I use a modified Whisper 2000 amplifer set next to my TV speaker.
A wire runs to my earbud at my chair eleven feet away.
Works great. But I have a squeal problem that only
happens when I put the earbud in my ear. It does NOT squeal
when the earbud is held in the air, even if pointed at
the Whisper microphone across the room. So I concluded
that it can't be feedback.
What's going on?
Hint: this is not a trick question, although one of my statements
of fact may mislead you. There's a good, scientific explanation.
Mason C
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| Mason C scribbled:
> This is just for fun, but instructive maybe.
>
> I use a modified Whisper 2000 amplifer set next to my TV speaker.
> A wire runs to my earbud at my chair eleven feet away.
>
> Works great. But I have a squeal problem that only
> happens when I put the earbud in my ear. It does NOT squeal
> when the earbud is held in the air, even if pointed at
> the Whisper microphone across the room. So I concluded
> that it can't be feedback.
>
> What's going on?
>
> Hint: this is not a trick question, although one of my statements
> of fact may mislead you. There's a good, scientific explanation.
>
> Mason C
1. Don't sit on the cat.
2. Remove the CIC aid before inserting earbud.
3. Tell the squealing child its perfectly normal.
:-)
--
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| 1. It's still squealing but when you take it out of your ear you can't
hear it.
OR
2. Due to the long wire the modified amplifier is on the verge of
electrical instability (not acoustic) and when you acoustically load
the earphone by putting it in your ear, you change the earphone's
electrical input impedance enough to tip the amplifier into
oscillation.
OR
3. The earbud is an open type speaker (back cavity is vented) and when
you put it in your ear you create two things:
a) A baffle that turns the earbud into a little baffled (closed back
cavity) speaker with a lot more output to the room through its vent
than when it is unbaffled.
b) A baffled speaker as above augmented by the resonance of the ear
canal cavity.
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| Mason C 2006-02-25, 7:34 pm |
| On 20 Feb 2006 17:37:46 -0800, "jim" <jwcrim@wiltontech.com> wrote:
>1. It's still squealing but when you take it out of your ear you can't
>hear it.
>OR
>2. Due to the long wire the modified amplifier is on the verge of
>electrical instability (not acoustic) and when you acoustically load
>the earphone by putting it in your ear, you change the earphone's
>electrical input impedance enough to tip the amplifier into
>oscillation.
>OR
>3. The earbud is an open type speaker (back cavity is vented) and when
>you put it in your ear you create two things:
>a) A baffle that turns the earbud into a little baffled (closed back
>cavity) speaker with a lot more output to the room through its vent
>than when it is unbaffled.
>b) A baffled speaker as above augmented by the resonance of the ear
>canal cavity.
I'll give the answer tomorrow evening.
By the way, Mrs. Henderson Presents is a very good movie -- saw it an hour ago.
The music did not overlap the speech so I could understand it.
Most movies have booming base and I understand none of the speech.
Mason C
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| Mason C 2006-02-25, 7:34 pm |
| On 20 Feb 2006 17:37:46 -0800, "jim" <jwcrim@wiltontech.com> wrote:
>1. It's still squealing but when you take it out of your ear you can't
>hear it.
Not so. It stops squealing.
>OR
>2. Due to the long wire the modified amplifier is on the verge of
>electrical instability (not acoustic) and when you acoustically load
>the earphone by putting it in your ear, you change the earphone's
>electrical input impedance enough to tip the amplifier into
>oscillation.
As a EE this rattled around my brain for a minute. I couldn't
believe a change in the load could cause the squeal.
>OR
>3. The earbud is an open type speaker (back cavity is vented) and when
>you put it in your ear you create two things:
>a) A baffle that turns the earbud into a little baffled (closed back
>cavity) speaker with a lot more output to the room through its vent
>than when it is unbaffled.
Close. But not out the back of the earbud. From the front.
>b) A baffled speaker as above augmented by the resonance of the ear
>canal cavity.
Not the canal cavity. The outer ear sound collector. It projects the
earbud output across the room to the microphone. Cupped hands
did the same thing.
Good try. Close. You get a 9.5.
My father had prominent ears and was hard of hearing after age 40.
It was family wisdom that his (outer) ears had grown to compensate.
Mason C ( My ears have not grown -- yet -- but I'm only 84.)
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