[cshaun]

I recently bought some new speakers. And the sub that came with them had a warning to keep it at least 60cm (2 feet) away from "PC's, Monitors, TV's, etc".

Now I'm assuming this is still the case even when it's off? (seeing as it's likely to have a magnet in it)
I assume the field gets stronger the higher the volume/power? (electromagnet powering up).

Surely I don't need to keep ALL electronics away from it? What do I need to worry about?
Obviously computer HD's...
What about a routers, UPS's, LCD monitors, phones, mobile phones...?

Reading this has got me paranoid... Just been upgrading all my gear over the last 2 months, so really don't want any harm to come to it. Anyway I'd rather be much more clued up on this and put myself at ease (been four days now and I'm driving myself crazy trying to decide were to position it).

* Updated: 6cm to 60cm - typo.

 

[error401]

Your biggest worry is going to be anything with a vacuum tube, like a CRT monitor. These work by using magnetism to control an electron beam that excites phosphors on the screen. If you introduce external magnetism, the display will be messed up, possibly permanently. Keep magnetic storage media away too (credit cards, floppy disks, hard drives), but most other electronics should be fine, including all the devices you list. Hard drives should actually be okay for the most part, but of course avoid it if possible.

I believe that the majority of the field strength comes from the permanent magnet, so yes it doesn't matter if the speaker is playing or not, or at what volume, the field will be relatively constant.

 

[gjustice]

IF they are saying 6cm then there is no big deal. Any form of magnetic storage device may be at risk(aka harddrives, any old tapes or floppy disks) If you have any CRT based technology(computer moniters or TV's) you should see color distortion long before any damage occurs. As it is there is a large magnet in the middle of the voice coil for the speaker so the field will be present any time regardless of if it is on or not. Turning it up or down should have only a minimal change as the field decreases in strength relitive to the cube(distance^3) of the distance from the magnet/voice coil.

Basically what it all boils down to is they want to make sure they are not going to be sued.... Just dont put anything sensitive to magnetic fields on top of it or touching it and your safe.

 

[cshaun]

mmm yeah that's kinda what I thought (before freaking out seeing the note), only really hard drives, floppy's, cathode ray tubes and those sorts of things that are really an issue around magnetic fields (credit cards - good one didn't think of that - though I'm sure it's have to be a very strong magnet to wipe those clean).
Other electronics that aren't using magnetism should be fine... only possible issue is eddy currents - but I'm guessing the magnetic field would have to be quiet strong for that to be an issue (though yeah not sure 'how' strong).

Ok so things to keep away:
Hard Drives - 4 of them, 40cm above top of sub in computer case if I have it that side
CRT Monitor (or TV) - using an LCD
Floppies - don't have any
Cards with magnetic strips (e.g. credit cards)

Ok guessing the 40cm is sorta safe, but perhaps not worth risking (don't know how much extra buffer the lawyers put in the 60cm recommendation).

So UPS and router/adsl modem would be save right next to it - correct?

You guys don't think there's any issue having a mobile phone near?

After mulling over it the past 4 days I think I can work around having it the other side of the desk which is just further away from everything. Good to know what's safe around it and what's not.

Bastards putting a scary note like that on them and not giving more details. Should have a website address were it addresses all sorts of questions!

Any more comments anyone?

 

[cshaun]

Oh yeah and I assume I should keep my soon to be arriving BEYERDYNAMIC DT 770 PRO/80 OHM well well away from the sub...

 

[error401]

I wouldn't worry much about hard drives. The field strength required to flip the bits is really rather astronomical. It can only be achieved by the write head because it's micrometres from the surface of the disk.

 

[cshaun]

Yeah just read a bit more about that (I even remember trying to damage an old floppy with a strong magnet with no success).
But one additional piece of information I just found is that normal magnets aren't all that bad for hard drives and other magnetic storage media. What's more dangerous is changing/alternating magnetic fields. Which I guess can/would be the case with a speaker/sub.

 

[error401]

Quote:

Originally Posted by cshaun /img/forum/go_quote.gif Yeah just read a bit more about that (I even remember trying to damage an old floppy with a strong magnet with no success). But one additional piece of information I just found is that normal magnets aren't all that bad for hard drives and other magnetic storage media. What's more dangerous is changing/alternating magnetic fields. Which I guess can/would be the case with a speaker/sub.

Yup, only changing fields will cause the magnetic media to be corrupted. Static fields won't affect it. With a strong enough magnet though, just walking past it could potentially be 'changing' enough to cause corruption. I highly doubt this would be the case with any speaker.

As was mentioned above, the field strength of the permanent magnet in a speaker dwarfs the strength of the field induced by the voice coil. As I understand it, the stronger you make the permanent magnet, the less current needs to pass through the voice coil for the same speaker extension - in other words, the more powerful the magnet, the more sensitive the speaker. I believe for the speaker to be usably efficient the permanent magnet must be orders of magnitude stronger.

 

[judas391]

There's no need to worry when the speakers are off. The current flowing through them is the thing that causes the magnetic field

 

[tbonner1]

Quote:

Your biggest worry is going to be anything with a vacuum tube, like a CRT monitor.

I agree.

 

[cshaun]

Quote:

Originally Posted by judas391 /img/forum/go_quote.gif There's no need to worry when the speakers are off. The current flowing through them is the thing that causes the magnetic field

I magnetized a pin and played with it on top of the sub... definitely as a magnetic field over a certain portion of the top. Difficult testing it higher up (further up), but seems to get weak very quickly.
Couldn't get the center channel speaker to have any effect on the pin while off.

So anyway there is definitely a field when it's off, not sure how different it is when on.

But anyway when off seems weak enough to be a non issue.

 

[cshaun]

Radiation? Er that message just looks like spam.

 

[voxr3m]

Your speaker has a persistent magnetic field from the permanent magnet regardless of whether it's on or off. It's the nature of the material.

When you turn the speaker on, the speaker's voice coil becomes an electromagnet. With two magnets near each other, one of them is going to feel significant enough a force to move. You have a total of two magnetic fields here. The changing magnetic field due to the changing current flowing through it is what causes the voicecoil(and hence the cone, spider, etc.) to move within the permanent magnet.

With a changing magnetic field, you also get a time varying electric field, and that radiates outward from the voice coil. It's not 'radiation' in the nuclear sense.

Keep your sub/speaker away from sensitive objects, but HDDs as mentioned should be fine. You'll risk more danger from the vibration that the sub causes when it plays than with the actual magnetic fields.

 

[badmonkey]

Quote:

Originally Posted by cshaun /img/forum/go_quote.gif Radiation? Er that message just looks like spam.

Spam alert.

The only "radiation" coming from your sub will be infrared as it heats up... hey well it'll make a nice foot-warmer.

 

[Prozakk]

Quote:

Originally Posted by error401 /img/forum/go_quote.gif I wouldn't worry much about hard drives. The field strength required to flip the bits is really rather astronomical. It can only be achieved by the write head because it's micrometres from the surface of the disk.

But you do have to worry if the subwoofer causes too much vibration, which can ruin a hard drive. Been there, done that.

I suggest vibrapods, or similar vibration isolation products.