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Anyone tried things to reduce cell phone interference in speakers?

B

barythrin

Veteran Member
Joined
Oct 5, 2005
Messages
6,256
Location
Texas
I know it has to be pissing off 80% of computer users to sit there and listen to annoying buzzing noises from your cell phone coming out of any speaker we're near. I lay there at night and have to put my cell (also my on-call work pager) in a calculated position to reduce it buzzing my turned off alarm clock speaker (don't you just love this new technology hanging around your waist area?).

Even some vintage gear gets affected or some vintage TVs when I'm near a connected nintendo or Atari, etc. I've just put up with it mostly because I figure I don't have the time to figure out how to truly resolve it but I was guessing that maybe a ferrite core wrap or something around the speaker wire could do something?.. I've threatened to spray the inside of my speakers with some chopped up ferrite chunks in paint. Maybe I need lead paint inside them, I dunno.

Anyone actually gotten fed up enough to try anything that you could share with us?

- John
 
Huh? Never heard of this problem and with the FCC/CE/TUV all over everything I'm surprised you have a problem.

Clearly the signal is getting into the amplifier input, the only contribution from the speaker could be from the wire providing the antenna.
 
When I lived in TX(my family up here doesn't have cell-phones) I had that problem all the time. Before the phone would even ring my speakers would start making this pulsing sound. Very annoying. Luckily they were always going places, and I don't have a cell phone. When I turned off the power to my speakers, though, the problem did not occour. Fix: destroy all cellular devices. Maybe wrap them in foil.

--Jack
 
We call them Mobile Phones around here, though generally we get that buzzy sound - I first discovered this when I was in the car and my Dad's mobile phone was doing it to the speakers, at first I had no idea what this was until the phone started ringing - which is what the speakers do before it gets to the phone. Not sure this problem occurred when my Dad had one of those old Analog phones - though the signal for those phones were switched off back in 2000! When I'm at home though I usually keep the darn thing switched off and where I work I don't have the problem of buzzy sounds in the speakers. :-D
 
I actually find it kind of useful. In the summer I work outside a lot in a noise filled environment. While wearing headphones tuned to local AM frequency, it is a great way to ensure I do not miss any calls which I may not hear otherwise.

Haven't tried it, but now I'm wondering if this works on FM too? Seems I'll have to experiment.
 
Ok, I just tried it. I set the cell phone fairly close (6 - 8 inches) to my stereo receiver and called it.

AM - Very loud, very noticeable.
FM - About 1/3 the volume but still noticeable.
 
My Nokia phones cause notable interference in my computer speakers, especially when a call is coming in. Strangely, it is before the phone rings and not during the call itself.

It's a fairly common occurence. iPhones do it too. And corded telephones, alarm clocks, etc. all seem to be affected.

There was a good writeup about the problem a few weeks ago. Basically, stuff is designed to be inexpensive. Part of being inexpensive is not rejecting false signals or emitting more RF than it should. But two things built to a marginal spec together, and you will hear the inteference. This is inspite of the FCC certifying all of the wireless gadgets.
 
it kindaa wud help if ya put the link

mbbrutman said:
My Nokia phones cause notable interference in my computer speakers, especially when a call is coming in. Strangely, it is before the phone rings and not during the call itself.

It's a fairly common occurence. iPhones do it too. And corded telephones, alarm clocks, etc. all seem to be affected.

There was a good writeup about the problem a few weeks ago. Basically, stuff is designed to be inexpensive. Part of being inexpensive is not rejecting false signals or emitting more RF than it should. But two things built to a marginal spec together, and you will hear the inteference. This is inspite of the FCC certifying all of the wireless gadgets.
Click to expand...
 
It seems the stray RFI is affecting the speaker coils themselves, cause mine do it even when they are turned off/disconnected. ('Specially when Art turns on his car stereo system right outside the house).

--T
 
Very cool article, Mike. Been looking for an explanation for awhile. To sum things up for ya'll, under part 15 of the FCC, devices must accept any interferance they should encounter and you will have to deal with it, no matter how undesirable. Should be on a tag on just about any electronic device; say, your clock-radio.

--Jack
Intrestingly, after looking, my Soundesign "Digital" clock-radio does not have this FCC notice. I suspected that as it looks to be made in the 70s. I was curious to check, though. I say it's "digital" because in reality it is a flip-number clock. Manual spring-actuated buttons, not membrane. Slider volume and tone adjusters, not buttons. Wheel-based tuner, not digital. Whatever, I guess it DOES plug in to the wall and DOES in fact have an orange light shining onto the numbers.
 
Actually, I thought that was an amazingly untechnical article. :)

The problem is unlikely to be in the speakers, that's just where you hear it from. In fact modern high quality speakers are remarkably insensitive and require high power. Unless the speaker wires are very long and your transmitter is quite powerful, the low impedence is likely to kill anything comming in that way. When it comes right down to it, the basic problem is cheap electronics. Better stuff is shielded and does not allow RF into the low level circuits. Miniaturized electronics can, of course, be difficult to alter. You can try some ferrite beads or similar idea on the input wires. Anything which is large enough to have room for a couple of additional parts is often easy to fix.

Like so:
The RF must be bypassed right where it comes in. That could be through the power supply, but is more likely the audio input. If the problem is with the power supply, it can be fixed but the whole device is probably just way too cheap. Fixing noise entering the imputs is easier. A common approach is to use a small coil in series and a shorting capacitor. I'm not so familiar with calculating coils. The required ones could probably be made with a few turns of copper on a pencil as the form. However, just adding a capacitor across the input will cut a lot of RF. I haven't played with cell phones (mobiles) but I've spent a lot of time making audio circuits quiet. Audio signals are very low frequencies so there is no problem with cutting the highs. (slightly different story in pro equipment) The input resistance is likely around 10-k or 20k or somewhere down there so a cap of .001 mf is about the absolute max. The formula is 1 over (2 pi times R times C). Ideally, you want a number just over 20k. Of course, it goes without saying that you should use good quality shielded wire and avoid plastic boxes. /2cents
 
Terry Yager said:
It seems the stray RFI is affecting the speaker coils themselves, cause mine do it even when they are turned off/disconnected. ('Specially when Art turns on his car stereo system right outside the house).
--T
Click to expand...
Actually, I have heard that effect too. I'm not sure how it happens. Perhaps older style speakers or long wires or both. I haven't tried bypassing the RF but that might work. Shielded is expensive, but if you got a cheap source (or it's a short run or low power) then that's an easy fix. I'm pretty sure that using twisted pair would cancel it too and it won't cost much to try that. I think I've see twisted bell wire even in a hardware store not too long ago.
 
As far as the FCC notices, every sticker I've ever seen says that the device:

Must not interfere with other devices, and

Must accept any incoming interference.

Who came up with that load of crap anyways? Kinda oxymoronic, ain't it? Is this an example of bureaucratic doublespeak, circular thinking, or just plain good ol' fashioned BS?

--T
 
Fcc

Fcc

Terry Yager said...Must not interfere with other devices, and Must accept any incoming interference.
Click to expand...

It kinda makes sense if you look at the phrasing in Class A digital devices:

FCC 15.105.a says...This equipment has been tested and
found to comply with the limits for a Class
A digital device, pursuant to part 15 of the
FCC Rules. These limits are designed to provide
reasonable protection against harmful
interference when the equipment is operated
in a commercial environment. This equipment
generates, uses, and can radiate radio
frequency energy and, if not installed and
used in accordance with the instruction
manual, may cause harmful interference to
radio communications. Operation of this
equipment in a residential area is likely to
cause harmful interference in which case the
user will be required to correct the interference
at his own expense.
Click to expand...

However, if you look at
FCC 15.105.b says...

NOTE: This equipment has been tested and
found to comply with the limits for a Class
B digital device, pursuant to part 15 of the
FCC Rules. These limits are designed to provide
reasonable protection against harmful
interference in a residential installation.
This equipment generates, uses and can radiate
radio frequency energy and, if not installed
and used in accordance with the instructions,
may cause harmful interference
to radio communications. However, there is
no guarantee that interference will not occur
in a particular installation. If this equipment
does cause harmful interference to
radio or television reception, which can be
determined by turning the equipment off and
on, the user is encouraged to try to correct
the interference by one or more of the following
measures:
—Reorient or relocate the receiving antenna.
—Increase the separation between the equipment
and receiver.
—Connect the equipment into an outlet on a
circuit different from that to which the receiver
is connected.
—Consult the dealer or an experienced radio/
TV technician for help.
Click to expand...

These are the "official notices" on user notification for Chapter 15 widgets in FCC lit. They do state, however, that the notice doesn't have to be exact, just in spirit, so I think is why most manufacturers have distilled it down to ...Must not interfere with other devices, and Must accept any incoming interference.

Ok, maybe sense is overstating it. FCC Part 15 deals with unlicensed transmission.

The Class A digital device stuff basically says that this doohickie can emit messy low-power rf, shouldn't be used in a non-industrial settings, and you're stuck with whatever the effects are, and, if you're using at home, resolution of problems is at your cost.

Class B digital device basically says that this doohickie can emit messy low-power rf, you're stuck with the effects, but you should try to fiddle with it on your own if it louses up your TV reception. Or, in other words, if you're WiFi (a Chapter 15 device )messes up your neighbors cordless phone( a Chapter 15 device ) {cordless phone, not cell phone), and you like your neighbor, you should do some fiddling, but if not, then sc**w them.

Note that it deals ONLY wth interference to radio communications, NOT other devices. The big part of Chapter 15 tells you that your Chapter 15 widget must give way to licensed spectrum users and suck up any interference.

Cell phones are licensed spectrum users, governed under Chapter 22, so they get to interfere with Chapter 15 stuff. Undesirable, but not much you can do about it.

For more fun Title 47 readings go to http://wireless.fcc.gov/index.htm?job=rules_and_regulations

My favourites are:
15.23 Home Built Devices
15.25 Kits
15.103 Exempted Devices (to the unintentional radiators stuff, i.e. Class A & Class B )

patscc
 
That makes a little more sense. The condensed version sounds like neither you nor your neighbor is allowed to interfere with the other's devices, but if it does occur, neither can be held responsible, cause ya both have to accept each other's nasties. Guess the devil's in the details...(not that any sane person would ever wade thru all that fine print).

--T
 
So, Terry, I take it that not only have you read the article on the link patscc put up, but you probably own a text copy of the full official FCC guidelines, AND have read through them multiple times.

Lol, but seriously, have you?
--Jack
 
FCC regs

FCC regs

Yzzerdd said...full official FCC guidelines
Click to expand...
Actually, it's the other way around. Terry is *why* they have the FCC Chapter 15 regs...
Isn't there a S-100 system in a toolbox, or something like that floating around out there somewhere, or is my memory failing ?

Seriously, though, you guys should check out 15.23 on home built doo-dads:

Sec. 15.23 Home-built devices.

(a) Equipment authorization is not required for devices that are not
marketed, are not constructed from a kit, and are built in quantities of
five or less for personal use.
(b) It is recognized that the individual builder of home-built
equipment may not possess the means to perform the measurements for
determining compliance with the regulations. In this case, the builder
is expected to employ good engineering practices to meet the specified
technical standards to the greatest extent practicable. The provisions
of Sec. 15.5 apply to this equipment.
Click to expand...

patscc
 
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