There is a phenomenom in cellphone uplink audio on GSM systems called
"bumblebee." The problem is that the phone's transmitter modulates the
mic capsule and/or the wire connecting it to the input preamp,
resulting in a nasty 216 Hz (13E6/48 bits/second * 1 frame/ 1250 bits
= 216.67 frames/second) tone with lots of harmonics.
From this point of view, it would probably be better to get a mic
capsule that has simultaneously high output power (so that the input
preamp AGC doesn't amplify the bumblebee) and low impedance (so less
RF is induced).
--Randy
"JANA" writes:
The impedance for most of the cell phone earphones and microphones
characteristics are an industry standard. Some of the different manufactures
are using a different connector. Most of them are using a sub-sized
tip-ring-sleeve type plug and jack arrangement. For these, you can buy most
any telephone earphone device, and it should work.
I have wired up my share of cell phones to different devices and self built
devices with great success. If the impedance and sensitivity is respected,
it will work.
--
JANA
_____
"Richard Crowley" wrote in message
...
"Crazy Horse" wrote ...
Can anyone tell me the impedance specifications for a typical
cellphone?
There probably isn't a "typical" cellphone design, nor a "typical"
earphone impedance.
I'm interested in obtaining a "high-quality" headset from Sennheiser
one that's not specifically intended for use with cellphones. But I
wonder if it will work reasonably well with a cellphone anyway. Their
fact sheet on it . . . . . . . . . . . . . . . . . .
http://www.sennheiserusa.com/newsite/pdfs/HMD280.pdf
lists the following nominal impedance values:
headphone: 300 Ohms
The headphone has a reasonable expectation of working. Since
cellphones run on such a low voltage (the internal battery), the
receivers likely have a relatively low impedance to achieve
adequate sensitivity. If there were to be any problem with a
high-fidelity stereo headphone, it would be that the impedance
was too HIGH so that the cell phone couldn't generate sufficient
audio level to overcome your ambient noise.
microphone: 200 Ohms (dynamic transducer, supercardioid
pickup pattern)
The microphone may be a different matter. Since likely ALL cell
phones use electret condenser mics, there may be a problem
with the DC power (required for electrets) being applied to the
dynamic mic coil. There may also be a problem with the audio
levels (sensitivity) of the dynamic mic vs. the electret that the cell
phone is expecting.
I've already spoken with Sennheiser from whom I've received
conflicting information.
They really aren't in any position to tell you whether it would work
or not. Since they know nothing about whatever cell phone you
have, they would just be guessing along with the rest of us.
So, I thought I'd run this by you in hopes that someone
might take a look and offer an informed opinion.
The earphone/receivers would almost certainly work fine.
IMHO, there is a significant chance that the microphone might
not work as well as an electret condenser. But it is unlikely to
cause any damage to the cell phone.
Any help will be greatly appreciated.
BACKGROUND: I'm about to embark on a new career as a
trucker and a crucial piece of equipment will be a good mobile
phone headset. Because of engine and road noise I'd like to
get one with an over-the-ear headphone and a high-quality
uni-directional boom mic.
Note that over-the-ear headphones are dangerous to drive with
and actually illegal in some jurisdictions. NOT recommended.
If you really insist on noise-blocking over-the-ear headphones,
I'd use a conventional cell-phone headset (made for your cell
phone model) and put the receiver into a noise-blocking head
set like a David Clark or equivalent. DC are the kind of ear
protection they wear on the decks of aircraft carriers, etc.
You might find a better fit with a headset made for aircraft use
like this one on eBay # 280116629433 Noise blocking AND
an electret microphone.
--
% Randy Yates % "So now it's getting late,
%% Fuquay-Varina, NC % and those who hesitate
%%% 919-577-9882 % got no one..."
%%%% % 'Waterfall', *Face The Music*, ELO
http://home.earthlink.net/~yatescr