Headphones

Judging by some MRIs, you can transport sound from a radio through a hollow tube and into headphones.

Am I right? How does this work?

Not sure but a few headphones I’ve used for in-flight movies were exactly this type. Nothing but hollow plastic tubing plugged into a jack in the armrest.

stethoscope and speaking tubes (pipes that functioned as intercom) are tubes that channel sound. works well when it feeds directly into your ear.

Never had an MRI, so can’t say for sure about that, but on the airline version the tiny speakers (transducers) are in the seat assembly and the sound is carried up the tube to your ears.

Nothing for the customer to damage or steal that’s worth much.

I’ve not flown in 12 years of so, but I believe that system is not in use much, if at all, anymore. I say that because the noise canceling headphones made by Boise and others come with adapters for airline use and would not work at all with the tube type earphone systems. Notice the link says “of the past”.

Many years ago my brother and I were asked to build just such a system for an MRI scanner. Systems used airplane issue tubular headphones, a simple closed box with a speaker and a tube. The sound is quite horrid. There are a whole heap of difficulties in propagating audio along a tube. Audio ranges in frequency from 20Hz to 20kHz. That is the full HiFi reproduction range. You can get away with a lot less than this - AM radio is a good example. But propogating even say, 100Hz to 6kHz down a tube is really messy. 100Hz is a wavelength of 3.4 metres, whilst 6kHz is a wavelength of 5.6cm. And the tube is thin - polypropylene irrigation tubeing is about 1cm. You get into all sorts of issues with the ability of the energy to propogate. Different frequencies will propagate differently, some frequencies will be subject to cancellation, and the whole thing sounds not exactly HiFi. But it is OK enough to make a patient feel a bit happier whilst in the scanner. In principle you just get compression wave propagating down the tube from the speaker, but the second order effects kill your sound. I figured that had I had the time to work out matching the line and applying resistive damping I might have improved things - but the wide variation of frequencies one needs to manage makes the problem pretty intractible.

I thought of trying a set of headphones without a magnet - and let it just work due to the feild in the scanner. Wouldn’t have be able to do it - the really huge moving magnetic fields during the scan would have made it impossible to use. Electrostatic headphones were a thought too. But in the end low tech rules. You can’t really have anything electronic anywhere near the scanner, and anything magnetic or ferro-magnetic is right out.