Laptops at gigs, magnetic fields, etc...

rcaz

I'm just about finished putting my laptop 'rig' together for playing Ableton Live and Pure Data with my band (laptop, interface, MIDI keyboard, MIDI controller, just looking for a stand for it all now), so I'm trying to figure out the logistics of using computer equipment at gigs.

Two questions;

Should I get my own DI?

I've heard some horror stories about people leaving their computers too close to monitor speakers or something while setting up, and then having their hard drive and other bits completely wiped by the magnetic field created when the speakers are turned on. I wasn't sure if that was a very basic lesson or a bit of hysteria, sounds like it could be both. Is that a very real risk?

exaisle

Who says the speakers have to be turned on? There's a humping great magnet in bass bins..... I have never had a problem with this...but Im sure if you put your laptop close enough to a big enough magnet......

If youre just using midi files and you dont necessarily need the soundcard on your laptop, you might be better off getting a dedicated midi file player....mind you, something like a Miditemp will knock you back well over a grand, although you could keep an eye out on ebay.

rcaz

exaisle wrote: »

Who says the speakers have to be turned on? There's a humping great magnet in bass bins..... I have never had a problem with this...but Im sure if you put your laptop close enough to a big enough magnet......

If youre just using midi files and you dont necessarily need the soundcard on your laptop, you might be better off getting a dedicated midi file player....mind you, something like a Miditemp will knock you back well over a grand, although you could keep an eye out on ebay.

I figured it would be the magnetic flux, caused by current through the magnet changing (from switching it on or playing sound through it) that would wipe a hard drive from a distance, not just inanimate magnetism...

And if I were just using MIDI files, where would I get the sound from? I'm playing softsynths with a keyboard and using sampled drum tracks and things, if I were to replace my laptop with something else I'd need a sequencer and a few other synthesisers and a sampler. Probably easier this way.

krd

Some kind of shielding on the laptop might help. But if you put a laptop on top of a monitor, you're probably asking for trouble.

It might also be wise to get a special power supply that shields against spikes and noise. There's a particular power supply type you can get for laptops - I can't remember the name - there's even a special symbol. It will stop noises and spikes. A spike can cook your laptop. Noise is really bad for any audio.

Welease

Not sure if the magnet/hard disk would really be a valid concern.. but if you wanted to be 100% confident, using an SSD should eliminate any potential for issues.

deecom

No risk what so ever. I have sat on subs line array cabinets while doing predictions for hanging pa, perfectly safe.

madtheory

El Pr0n wrote: »

I figured it would be the magnetic flux, caused by current through the magnet changing

That's not what happens... do you still have your Junior cert science book? Look up electromagnetism.

rcaz

madtheory wrote: »

That's not what happens... do you still have your Junior cert science book? Look up electromagnetism.

Oh man.... It's not like I'm in the final year of a theoretical physics course or anything...

The field around an electromagnet only fluctuates when the current through the magnet's coil changes, right? So if a speaker is playing music, the current is constantly changing, the magnetic field is constantly fluctuating, which would interfere with other magnetic fields nearby, which is what I figured might be the problem for hard drives, etc. Now I've no experience with all this stuff in practice, but I thought I had a pretty sound understanding of the theory here.

Cheers anyway for all the responses!

drum!

If using a Macbook, turn off the SMS (Sudden Motion Sensor) for the duration of your gig or your hard drive could fail in the middle of your gig. Happened to me at 3 gigs in the middle of songs until i found out what the problem was. Put it back on when you're done with the gig.

To disable the Sudden Motion Sensor:

Find the current status of Sudden Motion Sensor:

From the Finder's Go menu, choose Utilities.
In the Utilities folder, open Terminal.
When the command line appears, type sudo pmset -g and press Return.
Type in the administrator password when prompted and hit Return. This command queries the computer for the current setting of the Sudden Motion Sensor, which you can determine by locating the ams entry (in Mac OS X 10.3) or the sms entry (in Mac OS X 10.4 and 10.5) and looking to the right to determine its value. The default setting is "1" (turned on).
Disabling the Sudden Motion Sensor in Mac OS X 10.3:

In Terminal, which should still be open from the previous instructions, you can disable the Sudden Motion Sensor by typing sudo pmset -a ams 0 and pressing Return (changing the setting to a zero disables the module).
Type your administrator password when you are prompted and press Return.
Type the sudo pmset -g command again to be sure that the setting has been applied.
Disabling the Sudden Motion Sensor in Mac OS X 10.4, 10.5, and 10.6:

In Terminal, which should still be open from the previous step, you can disable the Sudden Motion Sensor by typing sudo pmset -a sms 0 and pressing Return (changing the setting to a zero disables the module).
Type your administrator password when you are prompted and press Return.
Type the sudo pmset -g command again to be sure that the setting has been applied.
Any changes that you make to the Sudden Motion Sensor setting remain in effect even after you restart the computer. If you choose to disable the Sudden Motion Sensor, Apple recommends that you re-enable it as soon as possible in order to take full advantage of the feature.

To re-enable the Sudden Motion Sensor:

Find the current status of Sudden Motion Sensor:

From the Finder's Go menu, choose Utilities.
In the Utilities folder, open Terminal.
When the command line appears, type sudo pmset -g and press Return. Type your administrator password when you are prompted and press Return. If you have the Sudden Motion Sensor turned off, the value of the ams entry (in Mac OS X 10.3) or sms entry (in Mac OS X 10.4 and 10.5) will be a zero (0).
Re-enabling the Sudden Motion Sensor in Mac OS X 10.3:

If the above command returns a zero, you can re-enable the Sudden Motion Sensor by typing sudo pmset -a ams 1 and pressing Return.
Type your administrator password when you are prompted and press Return.
Type the pmset -g command again to be sure that the setting has been applied.
Re-enabling the Sudden Motion Sensor in Mac OS X 10.4, 10.5, and 10.6:

If the above command returns a zero, you can re-enable the Sudden Motion Sensor by typing sudo pmset -a sms 1 and pressing Return.
Type your administrator password when you are prompted and press Return.
Type the pmset -g command again to be sure that the setting has been applied.

madtheory

O ya, was reading that only yesterday. High SPL (causing vibrations) will set off the SMS- it parks the heads and shuts down the drive. It's designed to avoid damage from motion in transit. Doesn't do damage to the drive, but will cause "dead air" at your gig!

So eLPron, it's soundwaves not magetism. In a speaker it's a very strong fixed magnet, not an electromagnet. The distance from the outside of the speaker cab, plus the drive casing, makes it extremely unlikely that data corruption will occur- the field strength would be negligible. But stranger things have happened!

drum!

Yep, i drove a lot of bass out of the macbook. Always shook the sh*t out of the house....and my mac. Very embarrassing.I just wanted the stage to swallow me up.

Seziertisch

I've a couple of friends that have had difficulties with computers at gigs where a fog machine was in use.

Paolo_M

El Pr0n wrote: »

Oh man.... It's not like I'm in the final year of a theoretical physics course or anything...

The field around an electromagnet only fluctuates when the current through the magnet's coil changes, right? So if a speaker is playing music, the current is constantly changing, the magnetic field is constantly fluctuating, which would interfere with other magnetic fields nearby, which is what I figured might be the problem for hard drives, etc. Now I've no experience with all this stuff in practice, but I thought I had a pretty sound understanding of the theory here.

Cheers anyway for all the responses!

That's not quite what happens is this instance.
Most computers/laptops still use rotating hard-drives, though SS is being more frequently used. This hard-drives effectively uses tape disks mounted on a spindle as their form of data storage. Tape uses magnetic alignments as it's method of storing it's 1s and 0s.
The speaker in your amp is a great big permanent magnet. When a permanent magnet is in close enough proximity to a magnetic storage devices it will realign the storage devices memory in line with it's own lines of magnetic flux, thus wiping the drive. It can also affect the tape heads.
This process does not depend on the speaker producing music, a speaker is a permanent magnet and as such has a permanent magnetic field around it.

madtheory

Seziertisch wrote: »

I've a couple of friends that have had difficulties with computers at gigs where a fog machine was in use.

What, like, not being able to see anything? :P

Seziertisch

madtheory wrote: »

What, like, not being able to see anything? :P

And here was me thinking it was the music production forum, Tomás, when in fact it was the up and coming comedians forum. Mods can ye move my post

madtheory

Well you didn't say precisely what caused the problem, so I was thinking of something like this:

https://www.youtube.com/watch?v=Xlf5ucFanpY