OK - I may be crazy here... but I'm going to ask a question. I'm
building a custom mod computer. In my computer, I'm hooking up a
car-audio receiver & antenna in order to listen to the radio while I
work...

On top of this, I thought it'd be a good idea to mount (2) 3" speakers
inside of the box in order to eliminate external speakers. I've read
up a bit on this and have found out that if the speakers aren't
shielded, it will conflict with and erase the hard drive and interfere
with other drives.

I have (2) 3" Blaupunkt car audio speakers...


So here are my questions:

1) Is my experiment possible?
2) How would I shield these speakers in order to elimate interference?
3) Should I try to just get PC speakers - tear into their cases and
use those instead?
4) Do have another solution?
5) Should I just scrap this plan and use external speakers?

Thanks for your time & attention....

I think you are crazy, but you can buy magnetically shielded full range
speakers from several online sources like partsexpress.com and
madisound.com.

How are you going to power the car receiver? Computer power supplies don't
provide enough current on the 12V rail to power the amplifier in a car
receiver (unless it is under 1 watt).

Let us know what you decide to do, as this is crazy.

"flint" wrote in message
...
I think you are crazy, but you can buy magnetically shielded full range
speakers from several online sources like partsexpress.com and
madisound.com.

How are you going to power the car receiver? Computer power supplies don't
provide enough current on the 12V rail to power the amplifier in a car
receiver (unless it is under 1 watt).

Let us know what you decide to do, as this is crazy.

Your information is not correct. Power supplies in late model computers will
provide 15A and some more than 25A on the +12 volt leg. This is far more
current necessary to power a car stereo head unit. Ideally, the voltage
should be 13.8v to get more out of the amplifier, especially if he plans to
play it loudly. 3" speakers can't be very efficient.

Internal speakers at a high level may resonate on the cabinet and may be a
problem with the hard drive or CD. I recommend getting a tuner card and use
external speakers/amp.

John

"jriegle" wrote in message
...
"flint" wrote in message
...
I think you are crazy, but you can buy magnetically shielded full range
speakers from several online sources like partsexpress.com and
madisound.com.

How are you going to power the car receiver? Computer power supplies
don't
provide enough current on the 12V rail to power the amplifier in a car
receiver (unless it is under 1 watt).

Let us know what you decide to do, as this is crazy.

Your information is not correct. Power supplies in late model computers
will
provide 15A and some more than 25A on the +12 volt leg. This is far more
current necessary to power a car stereo head unit. Ideally, the voltage
should be 13.8v to get more out of the amplifier, especially if he plans
to
play it loudly. 3" speakers can't be very efficient.

Internal speakers at a high level may resonate on the cabinet and may be a
problem with the hard drive or CD. I recommend getting a tuner card and
use
external speakers/amp.

John



You are correct. The 12V rail can supply as much as 26 AMPS in certain
systems.

However, the 12V rail is used to drive the all the 5V, 3.3V, 2.5V and 1.8V
motherboard busses. This includes power high current components like the
memory, CPU, and logic, as well as the PCI Bus, AGP Bus (potentially a huge
draw) and any other bus on the motherboard.

The 12V rail may be over-rated for the motherboard, but not by more than an
amp or so in most cases. I would not recommend driving a car stereo receiver
with a built in amplifier using that power supply rail.

- Flint

In article ,
(AC) wrote:

OK - I may be crazy here... but I'm going to ask a question. I'm
building a custom mod computer. In my computer, I'm hooking up a
car-audio receiver & antenna in order to listen to the radio while I
work...

On top of this, I thought it'd be a good idea to mount (2) 3" speakers
inside of the box in order to eliminate external speakers. I've read
up a bit on this and have found out that if the speakers aren't
shielded, it will conflict with and erase the hard drive and interfere
with other drives.

I have (2) 3" Blaupunkt car audio speakers...


So here are my questions:

1) Is my experiment possible?

Maybe. The power supply might not like the highly variable load of an
audio amp, though.

2) How would I shield these speakers in order to elimate interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby speaker
magnets any more than a person can feel the gravity of the sun.

Sensitive components are the power supply and monitor. Too much of a
magnetic field near the power supply will cause its inductors to
half-wave saturate. The current spikes from that can blow it apart
without even triggering overload protection. A CRT, of course, can't
produce pure colors when a magnetic field is bending the electron beams
through the wrong color mask slots.

3) Should I try to just get PC speakers - tear into their cases and
use those instead?

Try getting shielded speakers. They're usually 8 Ohm, which is good
because they will draw less power.

4) Do have another solution?

A USB tuner, a USB card with an internal port, and a sound card with a
built-in audio amp. You'll have to compare the pros and cons.

5) Should I just scrap this plan and use external speakers?

I just built an external speaker system for my work. 150W receiver, two
small bookshelf speakers, a 6 cubic foot home made sub that can do 10Hz,
and Apple File Sharing to my home music library. It's not so bad to be
the last one at work

Thanks for your time & attention....

On Mon, 29 Sep 2003 22:22:59 -0700, Kevin McMurtrie wrote:
2) How would I shield these speakers in order to elimate interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby speaker
magnets any more than a person can feel the gravity of the sun.
Wrong. It is because the speaker magnets are far enough away and the
drive is shielded.


Sensitive components are the power supply and monitor. Too much of a
magnetic field near the power supply will cause its inductors to
half-wave saturate. The current spikes from that can blow it apart
without even triggering overload protection.
Name a single example of this occuring.
Don't you ever quit with the bull****?

You'd have to tear the speaker magnets off, rip the power supply open
and place the magnets right against the PS inductors for there to be
any effect.

TCS wrote in message news:slrnbnj6an.2g3h.The.Central.Scrutinizer@turi ng.kaosol.net...
On Mon, 29 Sep 2003 22:22:59 -0700, Kevin McMurtrie wrote:
2) How would I shield these speakers in order to elimate interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby speaker
magnets any more than a person can feel the gravity of the sun.
Wrong. It is because the speaker magnets are far enough away and the
drive is shielded.

Further: the magnetic material is not in "particles" at all, they
are thin film deposited at the molecular and atomic level. The
"particle size" is UTTERLY irrelevant and, frankly, nonsensical.
The relevant factor is the material's coercivity and other factors.
If the field is unable to exceed the material coercivity, NO reversal
takes place. It makes not the slightest difference what the size of the
"magnetic particle" is.

Sensitive components are the power supply and monitor. Too much of a
magnetic field near the power supply will cause its inductors to
half-wave saturate. The current spikes from that can blow it apart
without even triggering overload protection.

Hoy, what a load of absolute claptrap THIS is. You REALLY must be joking,
yes?

Look at the "inductors" in a switching power supply: many if not most
of them are, in fact, toroidal. Pretty immune to external fields. Further,
the saturation magnetization of these cores in in the realm of 0.1 Tesla
or greater, while the MOSTY I have EVER measured the external field of
a speaker magnet within an inch or two of the magnet is in the realm
of 0.001 Tesla, 100 times less. If your assertion is correct, the power
supply designers are running the cores within 99% of their saturation
point to begin with, so even small variations in load or line conditions
will send it into saturation. Indeed, the earth's magnetic field might
be enough.

If your patently absurd assertion were true, power supplies all over the
world should be self-destructing because someone has a refrigerator magnet
on the side of there computer tower, or the aurora borealis is a wee bit
misbehaving that day.

Sorry, Mr. McMurtrie, but it's hard to imaging a more unsubstantiated
bit of nonsense than this.

On 30 Sep 2003 12:04:06 -0700, Dick Pierce wrote:
TCS wrote in message news:slrnbnj6an.2g3h.The.Central.Scrutinizer@turi ng.kaosol.net...
On Mon, 29 Sep 2003 22:22:59 -0700, Kevin McMurtrie wrote:
2) How would I shield these speakers in order to elimate interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby speaker
magnets any more than a person can feel the gravity of the sun.
Wrong. It is because the speaker magnets are far enough away and the
drive is shielded.

Further: the magnetic material is not in "particles" at all, they
are thin film deposited at the molecular and atomic level. The
"particle size" is UTTERLY irrelevant and, frankly, nonsensical.
The relevant factor is the material's coercivity and other factors.
If the field is unable to exceed the material coercivity, NO reversal
takes place. It makes not the slightest difference what the size of the
"magnetic particle" is.

Also: ever dissasemble a drive? The magnets used for the head positioner
are *****ing* strong yet don't seem to bother the data sitting on the
disk 2" away.

"TCS" wrote in message
news:slrnbnjq1c.2hfg.The.Central.Scrutinizer@turin g.kaosol.net...
On 30 Sep 2003 12:04:06 -0700, Dick Pierce wrote:
TCS wrote in message
news:slrnbnj6an.2g3h.The.Central.Scrutinizer@turi ng.kaosol.net...
On Mon, 29 Sep 2003 22:22:59 -0700, Kevin McMurtrie
wrote:
2) How would I shield these speakers in order to elimate
interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby speaker
magnets any more than a person can feel the gravity of the sun.
Wrong. It is because the speaker magnets are far enough away and the
drive is shielded.

Further: the magnetic material is not in "particles" at all, they
are thin film deposited at the molecular and atomic level. The
"particle size" is UTTERLY irrelevant and, frankly, nonsensical.
The relevant factor is the material's coercivity and other factors.
If the field is unable to exceed the material coercivity, NO reversal
takes place. It makes not the slightest difference what the size of the
"magnetic particle" is.

Also: ever dissasemble a drive? The magnets used for the head positioner
are *****ing* strong yet don't seem to bother the data sitting on the
disk 2" away.

Yeah, Just watch your fingers when playing with a pair of those!

I had a hard drive that had enough flux leakage that I could pick up screw
drivers an other ferrous things with right through its case.. It was fully
functional.

"flint" wrote in message
. ..
"jriegle" wrote in message
...
"flint" wrote in message
...
I think you are crazy, but you can buy magnetically shielded full
range
speakers from several online sources like partsexpress.com and
madisound.com.

How are you going to power the car receiver? Computer power supplies
don't
provide enough current on the 12V rail to power the amplifier in a car
receiver (unless it is under 1 watt).

Let us know what you decide to do, as this is crazy.

Your information is not correct. Power supplies in late model computers
will
provide 15A and some more than 25A on the +12 volt leg. This is far more
current necessary to power a car stereo head unit. Ideally, the voltage
should be 13.8v to get more out of the amplifier, especially if he plans
to
play it loudly. 3" speakers can't be very efficient.

Internal speakers at a high level may resonate on the cabinet and may be
a
problem with the hard drive or CD. I recommend getting a tuner card and
use
external speakers/amp.

John



You are correct. The 12V rail can supply as much as 26 AMPS in certain
systems.

However, the 12V rail is used to drive the all the 5V, 3.3V, 2.5V and 1.8V
motherboard busses. This includes power high current components like the
memory, CPU, and logic, as well as the PCI Bus, AGP Bus (potentially a
huge
draw) and any other bus on the motherboard.

The 12V rail may be over-rated for the motherboard, but not by more than
an
amp or so in most cases. I would not recommend driving a car stereo
receiver
with a built in amplifier using that power supply rail.

- Flint

That is true. The newer power supplies usually have a example of what
current is available if the other output is under a certain amount of
amperes load.

If he is using a 350-400 watt supply, I'd guess that he is fine unless he's
got a monster of a head unit.

Most of the +12volt leg is used to spin drive motors and fans. If he's got
one hard drive, a CD and some fans, there's probably not but 2 amps being
drawn off the +12v leg.

I tried running some Athlon XP 2600 systems from 250W PSUs. They would
bluescreen or reboot during bootup. I was reusing some old cases. I had to
endup buying some 350W PSUs. There was a fourth computer with the exact same
components that was happy with a 235W PSU! My point here is that depending
on the quality of the supplies, he could be pushing the the limit by adding
the stereo. So I agree that it is risky to try this.
John

In article ,
(Dick Pierce) wrote:

TCS wrote in message
news:slrnbnj6an.2g3h.The.Central.Scrutinizer@turi ng.kaosol.net...
On Mon, 29 Sep 2003 22:22:59 -0700, Kevin McMurtrie
wrote:
2) How would I shield these speakers in order to elimate interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby speaker
magnets any more than a person can feel the gravity of the sun.
Wrong. It is because the speaker magnets are far enough away and the
drive is shielded.

Further: the magnetic material is not in "particles" at all, they
are thin film deposited at the molecular and atomic level. The
"particle size" is UTTERLY irrelevant and, frankly, nonsensical.
The relevant factor is the material's coercivity and other factors.
If the field is unable to exceed the material coercivity, NO reversal
takes place. It makes not the slightest difference what the size of the
"magnetic particle" is.

Sensitive components are the power supply and monitor. Too much of a
magnetic field near the power supply will cause its inductors to
half-wave saturate. The current spikes from that can blow it apart
without even triggering overload protection.

Hoy, what a load of absolute claptrap THIS is. You REALLY must be joking,
yes?

Look at the "inductors" in a switching power supply: many if not most
of them are, in fact, toroidal. Pretty immune to external fields. Further,
the saturation magnetization of these cores in in the realm of 0.1 Tesla
or greater, while the MOSTY I have EVER measured the external field of
a speaker magnet within an inch or two of the magnet is in the realm
of 0.001 Tesla, 100 times less. If your assertion is correct, the power
supply designers are running the cores within 99% of their saturation
point to begin with, so even small variations in load or line conditions
will send it into saturation. Indeed, the earth's magnetic field might
be enough.

Yes, the flyback transformer does run very close to saturation. That's
how cheap and compact computer power supplies are made. Tests of PC
power supplies by computer magazines have found that some blow
themselves apart even under proper conditions.

Look up "magnetic amplifier" too. They're used to regulate the
secondary power lines.

Give it a try on your PC right now. Not with a wimpy fridge magnet, but
with car stereo speakers as the poster wants to use. We won't miss you.


If your patently absurd assertion were true, power supplies all over the
world should be self-destructing because someone has a refrigerator magnet
on the side of there computer tower, or the aurora borealis is a wee bit
misbehaving that day.

Sorry, Mr. McMurtrie, but it's hard to imaging a more unsubstantiated
bit of nonsense than this.

"Kevin McMurtrie" wrote in message
...
In article ,
(Dick Pierce) wrote:

TCS wrote in message
news:slrnbnj6an.2g3h.The.Central.Scrutinizer@turi ng.kaosol.net...
On Mon, 29 Sep 2003 22:22:59 -0700, Kevin McMurtrie
wrote:
2) How would I shield these speakers in order to elimate
interference?

The magnets won't bother the hard drives one bit. The magnetic
particles are so small these days that they don't feel nearby
speaker
magnets any more than a person can feel the gravity of the sun.
Wrong. It is because the speaker magnets are far enough away and the
drive is shielded.

Further: the magnetic material is not in "particles" at all, they
are thin film deposited at the molecular and atomic level. The
"particle size" is UTTERLY irrelevant and, frankly, nonsensical.
The relevant factor is the material's coercivity and other factors.
If the field is unable to exceed the material coercivity, NO reversal
takes place. It makes not the slightest difference what the size of the
"magnetic particle" is.

Sensitive components are the power supply and monitor. Too much of
a
magnetic field near the power supply will cause its inductors to
half-wave saturate. The current spikes from that can blow it apart
without even triggering overload protection.

Hoy, what a load of absolute claptrap THIS is. You REALLY must be
joking,
yes?

Look at the "inductors" in a switching power supply: many if not most
of them are, in fact, toroidal. Pretty immune to external fields.
Further,
the saturation magnetization of these cores in in the realm of 0.1 Tesla
or greater, while the MOSTY I have EVER measured the external field of
a speaker magnet within an inch or two of the magnet is in the realm
of 0.001 Tesla, 100 times less. If your assertion is correct, the power
supply designers are running the cores within 99% of their saturation
point to begin with, so even small variations in load or line conditions
will send it into saturation. Indeed, the earth's magnetic field might
be enough.

Yes, the flyback transformer does run very close to saturation. That's
how cheap and compact computer power supplies are made. Tests of PC
power supplies by computer magazines have found that some blow
themselves apart even under proper conditions.

Look up "magnetic amplifier" too. They're used to regulate the
secondary power lines.

Give it a try on your PC right now. Not with a wimpy fridge magnet, but
with car stereo speakers as the poster wants to use. We won't miss you.

I took up your test because I'm crazy, and wanted see what would really
happen. I know a big magnet by some electronic ballast compact flourescent
lamps will actually turn off the light untill you move it away.

I had a computer PSU that the fan stopped spinning due to bearing failure,
otherwise it was fine. I removed the board from the metal casing. Of course,
the casing would have conducted much of the magnetic flux around the
internals. With the PSU board powered in line with a 300 watt lamp to limit
current incase of catastrophic failure, I loaded the supply with a 100 watt
12v halogen bulb on the +12v output and tried putting a speaker magnet
against each of the several coils. The results were rather boring. There was
no effect on input current draw and output voltage level. Here's a pic:

http://home.att.net/~jriegle/psutst.jpg

John

If your patently absurd assertion were true, power supplies all over the
world should be self-destructing because someone has a refrigerator
magnet
on the side of there computer tower, or the aurora borealis is a wee bit
misbehaving that day.

Sorry, Mr. McMurtrie, but it's hard to imaging a more unsubstantiated
bit of nonsense than this.

"Kevin McMurtrie" wrote in message
...
Yes, the flyback transformer does run very close to saturation.
That's
how cheap and compact computer power supplies are made. Tests
of PC
power supplies by computer magazines have found that some blow
themselves apart even under proper conditions.

A "flyback" transformer is not a transformer although it is
commonly labelled as such. It is a coupled inductor structure
since the primary and secondary windings do not simultaneously
conduct. The core for a flyback is typically a ferrite and has a
significant air gap which dominates the reluctance. As such, the
saturation is very soft and predictable. AC flux dramatically
increases the saturation point well above the DC value. For
example, the common 3F3 and similar materials will start
saturating around 2kG at high temperatures (say 125C or so) under
DC but still handle of 3kG of 100kHz trapezoid.

I have biased ferrite cores with much stronger external fields
than a speaker magnet with measureable but insignificant changes
in saturation point. Much less than the difference caused by
raising the core temperature a few degrees.

It is true that most flyback designs are run very close to
saturation. However, due to the nature of the beast flybacks
require current mode control and/or peak primary limiting. By
necessity the current sensing ciruit is very fast and limits the
peak on a cycle by cycle basis. In any half way competent design
NO amount of saturation or even a dead short on the output will
allow destructive currents to flow.

There are many, many cheap PC power supplies on the market. Very
few will survive if operated anywhere near their "rated"
specifications for any length of time. I have done extensive
analysis of some of the cheaper units. At full rated power in a
25C environment many semiconductors are right at or above their
rated temperature (150C or 175C). With typical case temperatures
junction temperatures are well above their rating. Certainly not
a way to make a reliable power supply. Arrhenius would agree.
Yes, they blow up but it's due to excessive semiconductor stress
NOT core saturation even if you stick a monster magnet on the
side of the core.

Look up "magnetic amplifier" too. They're used to regulate the
secondary power lines.

Yeah, so what? Mag amps are used less often these days. Even if
you complete saturate a mag amp all that happens is you lose volt
second blocking and the regulated output voltages increase. The
power supply won't be damaged.

Give it a try on your PC right now. Not with a wimpy fridge
magnet, but
with car stereo speakers as the poster wants to use. We won't
miss you.

Been there, done that. Not a problem.

In article
,
"jriegle" wrote:

http://home.att.net/~jriegle/psutst.jpg

I stand corrected on computer PSUs. I have smaller switching power
supplies (CCFL, EL panel drivers, piezo drivers, DC-DC inverters) that
don't work near a speaker magnet.

On Wed, 01 Oct 2003 21:18:35 -0700, Kevin McMurtrie wrote:
In article
,
"jriegle" wrote:

http://home.att.net/~jriegle/psutst.jpg

I stand corrected on computer PSUs. I have smaller switching power
supplies (CCFL, EL panel drivers, piezo drivers, DC-DC inverters) that
don't work near a speaker magnet.

"stand corrected?" You were caught talking out your ass, and
you did it again!! And when caught a second time "you stand corrected?"

You're pathetic.

And you're still talking out your ass. Piezo drivers are not affected by
magnetic fields and nothing smaller than a head positioning magnet in
direct contact will affect a DC-DC convertor.

Tell us again how unshielded computer speakers will make a power supply
fail.

Kevin McMurtrie wrote in message ...
In article
,
"jriegle" wrote:

http://home.att.net/~jriegle/psutst.jpg

I stand corrected on computer PSUs. I have smaller switching power
supplies (CCFL, EL panel drivers, piezo drivers, DC-DC inverters) that
don't work near a speaker magnet.

Really? These are TRULY extraordinary claims. Precisely what is
it about piezo drivers that make them so sensitive? Have you EVER
actually DONE any of this stuff? I have just tried the experiment
with all of the above devices and the result is that there is
absolutely NO change in their behavior AT ALL.

How do you explain that your assertions seem to be at variance with
physical fact?

(helpful hint: you're wrong)

"Kevin McMurtrie" wrote in message
...
I stand corrected on computer PSUs. I have smaller switching
power
supplies (CCFL, EL panel drivers, piezo drivers, DC-DC
inverters) that
don't work near a speaker magnet.

Well let's see. Piezo is not magnetic. CCFL and EL are resonant
or flyback with immunity characteristics I posted before. DC-DC
is not an inverter. DC-AC is commonly called an inverter. Small
DC-DC are either forward or flyback topologies and larger are
commonly active clamp forward with synchronous rectification and
possibly zero voltage/current switching. None of which is
influenced by the magnitudes of fields we are talking about.

Me thinks you're trying to save a little face instead of
admitting you were wrong.