Today's Message Index:
----------------------
1. 12:40 AM - Microphone gain tuning (Holger Selover-Stephan)
2. 05:40 AM - Re: Microphone gain tuning (Ken)
3. 08:02 AM - Re: Microphone gain tuning (Robert L. Nuckolls, III)
4. 09:26 AM - Re: Microphone gain tuning (Robert L. Nuckolls, III)
5. 10:30 AM - Re: Pre-oiler system controls (Robert L. Nuckolls, III)
Message 1
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Subject: | Microphone gain tuning |
Hi all,
I seem to have a microphone gain tuning problem on the second DIY
headset, following these instructions:
http://n999za.com/2011/02/04/roll-your-own-in-ear-headset/
For the first headset I slaughtered an old GA headset and used its wires
and microphone. Works beautifully. Now on the second headset I am using
new shielded wires and this microphone (packed into a wind screen):
http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&categ
ory_id=0&description=1&model=1
The microphone is now overly sensitive and picks up everything. In a
quiet environment, my transmissions are crystal clear, but in flight the
surrounding noise pretty much drowns out my voice. I tried it with two
radios: an ICOM IC-A6 (on the ground) and in the air with a KX-135A
through an RST 422 intercom. In the hangar with everything quiet but a
radio playing soft music 20 feet away that music makes it into the
transmissions.
Since I bought the microphone new, I asked the vendor, and Joel writes
back:
What you will need to do is adjust the microphone gain control within
your radio to adjust it to fit the microphone properly. All radios are
different and require proper tuning when replacing the microphone.
Please refer to your radio's manual for adjustment procedures.
We do sell a microphone that allows you to tune the microphone with a
screwdriver. This is a common occurence that microphones need to be
adjusted to the radios to perform properly. Your mic currently is set
too high in sensitivity/gain.
I can see how the combination radio and microphone needs to be tuned, I
don't want to tune the radio to just this new microphone, and thus make
all other headsets unusable in my plane.
Their adjustable gain microphones apparently need a 9V power supply -
not ideal.
Should I try this trick posted to this group a while back:
Got a great idea from somebody, and the cost is free! Get the plastic
35mm
film containers. Cut an "X" in the lid and slide it on the mic arm. Then
wrap some foam around the mic and slide on the 35mm can after you have
drilled a 1/4" hole in the side. Line up the hole with your mouth.
Better
than sliced bread. Just keep the hole tight against your mouth to keep
out
engine noise.
My engine noise keeps my intercom open, but makes for a pleasant ride
with
me as the tour guide.
walt evans
NX140DL
============
Oscar Zuniga
Medford, OR
Air Camper NX41CC "Scout"
A75 power
But this probably addresses mostly wind noise, and I'm in an all
enclosed cabin.
Any other thoughts?
Thanks!
Holger
Message 2
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Subject: | Re: Microphone gain tuning |
Oscar
I've played a version of this game. I adjusted the radio to work well
with a David Clarke non adjustable mic. Then I adjusted the mic on a
Lightspeed to match. While the light speed uses batteries to power the
active noise suppression, I often did not have batteries in it and the
mic worked fine anyway. I'm suspicious of the claim that the adjustable
mic needs a separate power source. All radios feed a DC bias voltage to
the mic anyway. Makes little sense to me that any would need additional
power. I'm sure others are more familiar with that but it would greatly
curtail the usefulness of such a mic.
I have found that the foam cover on the mic helps a bit but note that
most mics also sense background noise from the backside so that they can
cancel that out of the signal going to the radio. Makes me wonder if the
film canister you mention would work all that well although it would
certainly reduce the signal strength.
Ken
On 15/05/2013 3:38 AM, Holger Selover-Stephan wrote:
> Hi all,
>
> I seem to have a microphone gain tuning problem on the second DIY
> headset, following these instructions:
>
> http://n999za.com/2011/02/04/roll-your-own-in-ear-headset/
>
> For the first headset I slaughtered an old GA headset and used its wires
> and microphone. Works beautifully. Now on the second headset I am using
> new shielded wires and this microphone (packed into a wind screen):
>
> http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&category_id=0&description=1&model=1
>
> The microphone is now overly sensitive and picks up everything. In a
> quiet environment, my transmissions are crystal clear, but in flight the
> surrounding noise pretty much drowns out my voice. I tried it with two
> radios: an ICOM IC-A6 (on the ground) and in the air with a KX-135A
> through an RST 422 intercom. In the hangar with everything quiet but a
> radio playing soft music 20 feet away that music makes it into the
> transmissions.
>
> Since I bought the microphone new, I asked the vendor, and Joel writes back:
>
> /What you will need to do is adjust the microphone gain control within
> your radio to adjust it to fit the microphone properly. All radios are
> different and require proper tuning when replacing the microphone.
> Please refer to your radio's manual for adjustment procedures.
>
> We do sell a microphone that allows you to tune the microphone with a
> screwdriver. This is a common occurence that microphones need to be
> adjusted to the radios to perform properly. Your mic currently is set
> too high in sensitivity/gain./
>
> I can see how the combination radio and microphone needs to be tuned, I
> don't want to tune the radio to just this new microphone, and thus make
> all other headsets unusable in my plane.
>
> Their adjustable gain microphones apparently need a 9V power supply -
> not ideal.
>
> Should I try this trick posted to this group a while back:
>
> /Got a great idea from somebody, and the cost is free! Get the plastic 35mm/
> /film containers. Cut an "X" in the lid and slide it on the mic arm. Then/
> /wrap some foam around the mic and slide on the 35mm can after you have/
> /drilled a 1/4" hole in the side. Line up the hole with your mouth. Better/
> /than sliced bread. Just keep the hole tight against your mouth to keep out/
> /engine noise./
> /My engine noise keeps my intercom open, but makes for a pleasant ride with/
> /me as the tour guide./
> /walt evans/
> /NX140DL/
> /=============/
> /Oscar Zuniga/
> /Medford, OR/
> /Air Camper NX41CC "Scout"/
> /A75 power /
>
> But this probably addresses mostly wind noise, and I'm in an all
> enclosed cabin.
>
> Any other thoughts?
>
> Thanks!
>
> Holger
>
> *
>
>
> *
>
Message 3
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Subject: | Re: Microphone gain tuning |
>
>I have found that the foam cover on the mic
>helps a bit but note that most mics also sense
>background noise from the backside so that they
>can cancel that out of the signal going to the
>radio. Makes me wonder if the film canister you
>mention would work all that well although it
>would certainly reduce the signal strength.
>Ken
Porous envelops and enclosures are simple
attenuators of sounds. They can also present
tailored effects upon the frequencies of
sound allowed to pass.
A 'noise canceling microphone' is another
critter entirely. The following is purloined from
Wikipedia:
The development is a special case of the
differential microphone topology most commonly
used to achieve directionality. All such
microphones have at least two ports through which
sound enters; a front port normally oriented
toward the desired sound and another port that's
more distant. The microphone's diaphragm is
placed between the two ports; sound arriving from
an ambient sound field reaches both ports more or
less equally. Sound that's much closer to the
front port than to the rear will make more of a
pressure gradient between the front and back of
the diaphragm, causing it to move more. The
microphone's
<http://en.wikipedia.org/wiki/Proximity_effect_%28audio%29>proximity
effect is adjusted so that flat frequency
response is achieved for sound sources very close
to the front of the mic ' typically 1 to 3 cm.
Sounds arriving from other angles are subject to
steep midrange and bass
<http://en.wikipedia.org/wiki/Rolloff>rolloff.
Commercially and militarily useful
noise-canceling microphones have been made since
the 1940s by
Roanwell,<http://en.wikipedia.org/wiki/Noise-canceling_microphone#cite_note-
1>[1][<http://en.wikipedia.org/wiki/Wikipedia:Link_rot>dead
link] Electro-Voice and others.
As you might guess, the mechanical differential microphone
presents some real design problems that get more difficult
as the size of the microphone is reduced. There are
electrical differential configurations that simply places
two identical microphones back to back amplified by circuits
that balance the two signals against each other in opposite
phase so as to achieve a degree of cancellation.
Then, my speaking closely to one of the two cartridges,
the differential balance is upset and the voice predominates
over background noise.
When we ran the airport, I had head-sets that could
be loaned to renters. I did some tests with the various
brands we had hanging on the pegs and found marked
differences in their ability to reject background noise.
David Clarks were always good . . . but a bit pricey
compared to the Telex Echelon headsets that were about
half the price and still quite effective in their ability
to cancel noise and only $120 a pop in 1990 dollars.
A note of caution about adding 'stuff' to the outside
of a microphone . . . if it is a true noise-cancelling
design, then adding external features may work against
the original design goals for the product. If the mic
is not noise-canceling design and achieves improvement
of signal-to-noise ratio by proximity of the speaker's
lips, then added features are less problematic . . .
Foam socks are most useful in the reduction of wind
noise . . . REALLY important for open-cockpit flight.
But the nature of the foam's 'bubbles' can produce
unexpected results. Use a 'sock' crafted by a supplier
of microphones that is advertised for the reduction
of wind noise.
Balancing the ship's audio system to the differences
between brands is a separate issue. Not all microphones
are the same but as long as the airplane is fitted
with two or more of the same model, those differences
are a wash.
>>We do sell a microphone that allows you to tune the microphone with a
>>screwdriver. This is a common occurence that microphones need to be
>>adjusted to the radios to perform properly. Your mic currently is set
>>too high in sensitivity/gain./
>>
>>I can see how the combination radio and microphone needs to be tuned, I
>>don't want to tune the radio to just this new microphone, and thus make
>>all other headsets unusable in my plane.
EXACTLY. When dealing differences between microphones,
the 'fix' is to attenuate the hotter microphones to a
level consistent with the cooler ones.
>>Their adjustable gain microphones apparently need a 9V power supply -
>>not ideal.
But the nature of the beast. If you want a mic
with the greatest applicability in the market, you
deliberately design for 'hot' and then provide
controls for attenuating the mic down to system
friendly levels.
>>/Got a great idea from somebody, and the cost is free! Get the plastic
35mm/
>>/film containers. Cut an "X" in the lid and slide it on the mic arm. Then/
>>/wrap some foam around the mic and slide on the 35mm can after you have/
>>/drilled a 1/4" hole in the side. Line up the hole with your mouth.
Better/
>>/than sliced bread. Just keep the hole tight against your mouth to keep
out/
>>/engine noise./
What ever works for you . . . assessment of
'elegance' is in the eye of the beholder. There
ARE electronic solutions transparent to the
appearance of the thing hanging out in front of
your face.
Bob . . .
Message 4
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Subject: | Re: Microphone gain tuning |
>
><http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&category_id=0&description=1&model=1>http://store.acousticom.com/m7a-amplified-electret?keyword=5720-CA&category_id=0&description=1&model=1
>
>The microphone is now overly sensitive and picks up everything. In a
>quiet environment, my transmissions are crystal clear, but in flight
>the surrounding noise pretty much drowns out my voice. I tried it
>with two radios: an ICOM IC-A6 (on the ground) and in the air with a
>KX-135A through an RST 422 intercom. In the hangar with everything
>quiet but a radio playing soft music 20 feet away that music makes
>it into the transmissions.
>
>Since I bought the microphone new, I asked the vendor, and Joel writes back:
>
>What you will need to do is adjust the microphone gain control
>within your radio to adjust it to fit the microphone properly. All
>radios are different and require proper tuning when replacing the
>microphone. Please refer to your radio's manual for adjustment procedures.
>
>We do sell a microphone that allows you to tune the microphone with
>a screwdriver. This is a common occurence that microphones need to
>be adjusted to the radios to perform properly. Your mic currently is
>set too high in sensitivity/gain.
This off-the-shelf cartridge is a two-wire 'electret'
device that contains what ever electronics are necessary
to make it look like the legacy, radio-powered, aviation carbon
microphone.
You cannot reduce it's audio output with a potentiometer
in it's leadwires. While the pot would indeed adjust
the audio output FROM this device, it would adversely
affect the DC power being conducted TO the device.
You can place a resistor-capacitor network ACROSS the
microphone's leads thusly.
Emacs!
Adjust the resistor value such that the microphone produces
a signal commensurate with others in your system. The
capacitor keeps the audio attenuator resistor from shunting
the DC power.
I'm guessing that a value in the 100 to 1000 ohm
range will prove satisfactory. You might temporarily
wire a potentiometer into the resistor's slot, adjust
the pot for desired gain, then measure with ohmmeter.
Substitute a fixed resistor of the appropriate value.
Bob . . .
Message 5
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Subject: | Re: Pre-oiler system controls |
At 01:20 PM 5/8/2013, you wrote:
>Bob,
>
>Thanks for the prompt and informational response.
>I agree with your concerns, and thank you for your interest.
>My reasons for adding pump:
>Accumulator is already installed on aircraft.
>Accumulator will also provide transient protection from low oil
>pressure during maneuvering.
>Pump and plumbing will only add about 5 Lbs to gross weight.
>The a/c is a Stewart 51, 500 HP, 2 pax (I weigh 150Lbs, my
>Lady-Friend 130Lbs), minimal baggage capability. Therefore this
>addition will barely be noticeable:)
>
>The pump and the valve are both simple on-off circuits. Is there a
>wiring diagram in your book to show how to wire this switch?
>
>Thanks very much for your time and experience,
>Neville
You need a 2TL1-50 toggle switch
http://tinyurl.com/azcswed
wired thusly:
Emacs!
Emacs!
Emacs!
Bob . . .
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