Are we really sure there's no way to get a STRONG signal on an induction mic?

WDITrent

WDITrent

Member
I think I made a similar thread a while ago, but I can't find it anywhere.

So the response I got last time was no, other members had already tried hacking and experimenting with no interesting results. But are we completely, absolutely sure? And if we're not sure, then why not discuss? Would a different magnet affect it? An induction mic made by taking parts from a non-induction mic?

Just out of curiosity. :)
 
1) Get a recorder with a low noise floor so you can amplify the signal.
2) Preamp.
3) Look for a louder speaker.
 
Possibly thinner wire in the indictiuon mic, more windings?

I've got some wire, but just no time to really play much anymore.  I think I have a spool of 42 gauge and 44 gauge winding wire.  I don't know the physics behind the induction mic to know if the thinner wire will help/hurt, or if more windings will help/hurt either.  My gut tells me thinner wire will help and more widnings will as well, with thinner wire, you can get more on the spool too!  

I also have a hunch, that you really can't do much with the speaker magnet, the field that we are picking up just isn't all that strong.  I've got to guess that the field gets exponentially fainter as you move away from the magnet, so the pickup would need to get exponentially stronger.  And we don't have that kind of technology in our backpacks.

I think we may have better luck trying to find the wires that feed the speaker and recording from there.  A better pickup might help with that...

And actually, Disney has been doing a better job putting the speakers out of reach as the years have gone by as well...
 
I think you also have to realize that a poor sound signal is never going to sound good regardless of how much you fiddle around with the equipment. There's just not enough of the sound (or magnetic waves) coming through. You may be able to increase the volume but you won't get the quality.
Rubbish in, rubbish out still holds good and even a stronger induction coil won't make up for a poor signal.
Increase the sensitivity and you'll probably increase the interference as well  :(
 
Has somebody been able to do an induction recording from the typical loudspeakers in the Disneyland Paris restrooms? I tried it last week and although I pressed my microphone directly to the speaker (in different restrooms) I didn´t get any signal... Seems to me that what you see in the ceiling isn´t the speaker itself but only some kind of "front panel", which would explain why i didn´t get anything...

Has anyone experience with this?

ebbelein
 
Is there a mesh or screen in front of the speaker?  If there is, it's probably mild steel which has a decent magnetic permeability.  The steel mesh or screen is absorbing some/most of the magnetic flux from the speaker's electromagnet and not letting enough through so that the induction pickup can generate a signal that is above the recorder's own internal "hiss" or noise floor.

There is an accessible speaker in the DCA Soarin' queue that is covered with a perforated screen and I get absolutely no noticeable signal.  I can hear the hum of the nearby lights just fine but not the queue BGM even though the speaker is on the other side of the screen.

From the website of a manufacturer of magnetic shielding material:
http://www.mushield.com/faq.shtml
Can I use mild steel instead?
Mild steel can shield magnetic fields and is appropriate for applications requiring a small attenuation of a high flux density field. A quick phone call to MuShield will answer your question about mild steel for shielding. If it is likely to work, why spend your money on high permeability materials.
Click to expand...
And a page on how magnetic shielding works, with illustrations:
http://www.kjmagnetics.com/blog.asp?p=shielding-materials

What's the volume level of those speakers?  Low, moderate or high?
 
Good point. Never thought about steel mesh. Most of the speakers (external) in DLRP are rather kinder and use perforated zinc which doesn't mess the signal up. I suppose steel would rust outside.
That being said, I have a few speakers at home which only have the usual clock cover and I can't get an induction signal from them at all. When I first got my induction mic I tested it on them (one set are my main CD speakers) and was really worried it wasn't working. I have no idea why I can't get a signal from them. Just a standard elliptical speaker in a wooden box!  ???
 
actually the ones i tried didn´t look like a mesh screen - more like a round plastic cover with some grid over the speaker...
 
As 772pilot suggested in his response to the original poster of this thread, there may be a signal there but you might need a different recorder with a lower noise floor or an additional preamp in order to hear that signal and record it.  772pilot has a Zoom H1 which is a good quality digital recorder but he can't get a signal from the speakers in the landscaping at DCA's Paradise Park.  I can get a good signal from those same speakers with a Sony PCM-D50.
 
There are also those little recording practices that help a great deal in post production. Always record in a lossless format so you have control over the digital quality of your end result. Like eyore said, rubbish in rubbish out. A recording could sound fantastic yet will suffer prematurely if there's already frequency loss from mp3 encoding (or anything else of the sort). If you want to get more technical, always record 24-bit at a 48kHz sample rate. The advantages of this come from the Nyquist-shannon sampling theorem and fall into the realm of integral calculus, but simply put: a higher bit depth will allow you to record signals that are more dynamic without distortion or dithering and a higher sample rate will allow you to more accurately capture the curvature of the original analogue waveform when digitization take place.
 
The further you get from the magnet on the speakers the fainter the recording will be, as well as the angle of the induction pickup in relation to the magnet.  An inch can make all the difference...

I've had many a recording ruined becuase of the slightest movement of the pickup during a recording session.

I'd try to get the pickup in the back of the speaker, not the front if possible.
 
Yes, some speakers are more picky that others and not all speakers have the magnet near the grill. Turning up the gain can help but the quality will suffer (I took the moans coming from a tomb outside Phantom Manor and the speaker is fairly deep within it  but managed to get something. I used a Zoom H2 on hi-gain.
http://www.mediafire.com/download.php?bkuqv9w5k2fzudv

Someone may be able to tweak this for next Halloween.
I only recorded it to see if I could.
It plays out of a gatepost leading to a raised area in the middle of Boot Hill.
The one on the right with the lamp on it. The speaker is at the bottom of the pillar
.
 

Attachments

Yep, the shape of the field can tricky but sometimes it can work to your advantage.  I could pick up the exit spiel from DCA's Mulholland Madness while standing in the middle of the walkway that ran alongside the ride.  I still have no idea where that signal originated but it made recording that much easier ;D.
 
So that's where you got that recording.  ;-)  Curious... get the same luck with Goofy's exit spiel, or did they change things around so it doesn't work?
 
No, the exit spiel signal is gone now, probably the spiel speakers have been moved.  They are now above the track instead of below it.
 
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