Hear With Ultrasound Using a DIY Flanagan 'Neurophone'




UPDATE: Neurophone inventor Patrick Flanagan has since confirmed this design CAN produce Neurophone effects, though it's still probably not as good as the real thing. Some research suggests this is why: TL494's square-wave output gets differentiated by the piezos (which are capacitors), producing a "Lilly wave"-like signal that mimics signals produced by nerves. (The Lilly Wave, as far as I understand, is a sharp positive spike followed by an equal but negative one. The idea is the first peak transports something, I think ions, across the barrier between nerves while negative spike brings them back so the nerves can use them again.)

Overall, I did get it pretty wrong. It turns out you have to replace the leading and trailing edges of the audio waveform with ones that have a 40kHz slope, and then double differentiate it. The TL494 "Neurophone," while it does produce a tiny sliver of the real effect, is pretty far off.

Also, it turns out "earplug-style" in-ear-monitor headphones produce some of (but probably not all) of the same effects a Neurophone does. (This was not confirmed or commented on by Flanagan as far as I know.) Try playing pink noise through them! See the post at http://neurophone.wordpress.com/.

By mixing an audio signal with ultrasound, you can hear the audio as if it's inside your head... even if the 'headphones' are nowhere near your ears.

Patrick Flanagan invented the "Neurophone" over 40 years ago. His original patent (US3393279) was basically a radio transmitter that could be picked up by the human nervous system. It modulated a one-watt 40kHz transmitter with the audio signal, and used very near-field antennas to couple it to the body. It also used extremely high voltages.

Fortunately, we don't need to work with radio transmitters or high voltages. Over a decade later, Flanagan came up with a version of the "Neurophone" that didn't use radio, or high voltages. (Patent US3647970)

The second version of the "Neurophone" used ultrasound instead. By modulating an ultrasonic signal with the audio we want to listen to, it gets picked up by a little-known part of the brain and turned into something that feels like sound.

The weird thing is this works even if the ultrasound transducers are far away from the head: maybe down at your waist, or even further (depending on your body).

To make the ultrasound signal, we'll use a widely-available TL494 pulse-width modulation controller. This isn't a perfect solution, so you won't hear the signal as well as with one of Flanagan's designs. But it's a lot simpler than messing around with DSP. And it gives you a chance to experience and experiment with the "Neurophone" effect.

Have a look at the schematic. You'll see there are two adjustment potentiometers.

The first potentiometer is near the input, and it adjusts the DC bias of the input: whether the TL494 thinks the input signal is mostly positive, neutral, or mostly negative. The best way to adjust it is by connecting an oscilloscope to the circuit's output. Connect a sine wave signal generator to the input. (If you don't have a signal generator, generate a 440Hz sine wave in the open-source Audacity music editor and upload the file to an MP3 player.) You then adjust the potentiometer until the signal looks about even between top and bottom. If you don't have an oscilloscope, try with the potentiometer centered.

The second potentiometer controls the modulation frequency. Using your oscilloscope or a frequency counter, turn it until you get about a 40-50kHz signal from the output (with nothing connected to the input). If you don't have either of those, play with the control until you can hear the signal.

The 'electrodes' are actually transducers. You can pick up the piezo disks online, or at an electronics shop. Try searching for 'piezo' or 'piezo element.' You only need to connect to the piezo side on each: the disks form an electric circuit through the surface of the skin. (This may help the signal be heard, since nerves are sensitive to electricity too.) Don't worry: there's so little current flowing between the electrodes that you'll feel nothing. (And while I'm not a medical professional, I don't think there's any way it could do any harm.)

Do be careful about putting them on and taking them off, though. They're putting out a fairly high-power ultrasound signal, so if they sit too loosely on the skin they could irritate it.

Lastly, you'll probably find the signal is easiest to hear 'in your head' with the electrodes near your head. Also, and this applies double if you're putting the electrodes far away from your head, you'll probably only be able to 'hear' a very narrow range of frequencies. A signal generator where you can easily vary the signal from 20Hz to 20,000Hz is very helpful in finding what you can hear and what you can't.

Oh, and don't forget to play with the volume control on your signal generator or MP3 player: you may need to set it a lot higher or lower than with regular headphones.

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    11 Discussions


    7 years ago on Introduction

    It hasn't killed me yet! Or Flanagan, and the original one used 2000VAC. (albeit through a thicker dielectric)

    The driver may be capable of lots of current in general, but not here. The piezo elements act as picofarad-size capacitors that let barely any current through. In this case, probably on the order of microamps, though I haven't measured.

    For what it's worth, medical TENS electrostimulators use 50-100VAC at much higher levels of current to help with pain.

    And you probably don't want to put the electrodes near your ears or heart anyway! There's too much hair near your ears, and you probably won't hear a good signal putting them near your heart -- and it's better to be safe and stay away from that area anyway.


    4 years ago on Introduction

    I have actually physically heard the effect of ultrasonic speakers when the beams of each speaker interact as it strikes the target from a distance, my head for instance, and the resulting heterodyned waveform is audible. LRAD works along that principle.

    The circuit in this project, on the other hand, produces an audible signal from being in contact with target, but what I don't understand that the circuit in this project produces the same signal into both piezos. How can this produce a beat frequency (heterodyning) effect if there is only one channel output from this device? Perhaps your body is acting as a low pass filter capacitor filtering out the ultrasonic high frequency carrier wave and letting the audible low frequency modulated signal through rather than detecting the audio from some special organ in our heads that can translate ultrasonics into audible. See Dr. Flanagan's video so that you get what I mean. He claims that humans have the same sonar organ that some sea mammals use for echo-locating except that the human's organ is specialized for balance. I forget the name of that organ as I write this comment.

    2 replies

    Reply 4 months ago

    Maybe the diagram is not ok, and one output(pin 9) goes to the first transducer + and the other output (pin 10) goes to the second transducer + . Here is a link to a ultrasonic directive speaker circuit in wich the TL494 is like this one but the otputs goes like I said.
    Anyway I will build it and post the result.


    Reply 2 years ago

    I'd be more inclined to believe a simpler explanation - that the ultrasound excites nerves at the same frequencies as Flanagan's original neurophone does and frequency-modulates the affected nerves to deliver an audio signal that somehow is "heard" by the brain's auditory cortex.


    2 years ago

    milliamps (~10) are the range where you start seeing the risk of cardiac arrest and other physiological damage through the skin. If the signal in the low-microamp range, yes, I'd agree that we're talking about a medically safe signal..I'm thinking that one of those over-the-counter TENS units might be a good point to start with for a more sophisticated neurophone, but don't think the actual signal processing hardware can be adapted. You'd have to disable that and just use the amplifiers on board (if indeed, they are discrete from the signal generator chip) to drive the electrode pads that come with the TENS unit.


    4 years ago on Introduction

    Amazing to see this. Great news, visit http://NEOneurophone.com and see the official $399 model coming out in 2015 you can soon preorder in Indiegogo in September of 2014. Way easier than building one now the the price is down from what used to be $1500:)

    Flanagan Tests Neurophone 2014.png
    1 reply

    Reply 4 years ago on Introduction

    This device should have NEVER been priced so high from the very beginning. Anybody who's investigated the electrical components that actually comprise the Neurophone know it costs very little to make and put together (under $20) and yet this Flanagan guy marks it up 7,500%. No thanks. And no thanks to this $400 model. The price is still too high. Maybe $50 to under $100 would be acceptable if it's build quality was solid and they actually backed their product. Right now you pay huge bucks and cross your fingers you didn't get a dud that burnouts less than a year later from minimal use. These things should last forever if taken care of. I really hope someone or group cranks out a cheaper more reliable version like whats being done with the tDCS devices. $500 vs $90...that's what I'm talking about. :)


    6 years ago on Introduction

    What type of inputs can be used? I am thinking peizo or moving coil microphone, speaker


    If I'm not mistaken, the original patent shows the device ending with a tank circuit & the piezos in the circuit should be the tank circuit capacitor plates. This schematic looks wrong.