SEPT, 2023

Speakers, Transducers, and Coils, Oh My!

The inHarmony Meditation Furniture is equipped with devices known as tactile transducers. The term "tactile" derives from Latin and means "perceptible by the sense of touch." A transducer serves to convert one form of energy into another. In the case of the inHarmony tactile transducers, they transform electrical audio signals into physical, acoustical, or vibrational energy. Transducers frequently convert a physical energy form (such as temperature, light, sound, motion, or pressure) into a corresponding electrical signal, which can be measured or employed in various ways, like reading water or pressure gauges, activating motion-sensitive lights, or operating badge readers to unlock doors. Electric guitar pickups are also a type of transducer, changing the vibrations of metal strings above a magnet into an electrical signal for amplification.

While various types of transducers exist, this blog will focus primarily on electro-acoustical or electro-mechanical transducers. The most familiar examples of these are audio loudspeakers, microphones, and the tactile transducers found in all inHarmony technology.

Did you know that most microphones essentially function as speakers in reverse?

Speakers, tactile transducers, and microphones all share a common foundation, relying on Faraday's Law of Induction, formulated by Michael Faraday in 1831. Working in conjunction with other greats such as Maxwell, Henry, Lenz, and Gauss, Faraday discovered that when electricity flows through a conductor (such as a wire), it generates a magnetic field around the wire, directly proportional to the current's strength. Conversely, if you move a conductor through an existing magnetic field, it induces electricity in the wire in direct relation to the magnetic field's strength and the speed of movement—a process called induction.

During my tenure as an MRI engineer, I vividly recall our experiments with coils of copper wire that we connected to light bulbs. We would sit inside the MRI machine, nothing happened when we remained still, but as soon as we started moving the coil back and forth, the bulb illuminated. Astonishing! The motion of the coil through the potent magnetic field induced electricity in the wire, causing the bulb to light up. This same principle underlies the operation of badge readers. Your ID badge contains a chip with a single function: transmitting its unique ID number when activated. Paired with this chip is a coil connected to the chip's power inputs. The wall-mounted badge reader generates a static magnetic field approximately the size of a basketball. When you move your badge through this magnetic field, it induces a current in the tiny coil inside, powering the chip, which then transmits its code for the computer to decide whether to unlock the door.

As an MR engineer, I also always carried a handheld Gauss meter. Magnet field strength is measured in units known as Gauss, named after the German mathematician and physicist Carl Gauss. You can hold the meter near a wire or magnet to measure the amount of Gauss present. For example, if I laid out 25 feet of wire in a circle, connected it to a light bulb and a battery, and lit the bulb, I would read a small amount of magnetism along the wire (around 5 milliGauss or .005 Gauss). Although it's only a small amount at any given point, there are many millimeters in 25 feet of wire. If the wire is coiled instead of laid out straight, all the magnetism is concentrated in one place and it behaves like a single strong magnetic signal (hundreds of Gauss) that can be utilized for various purposes.

In reality, an MRI machine is essentially one giant coil of wire with enough turns and electrical current to generate a powerful magnetic field suitable for imaging human anatomy through magnetic resonance (15,000 Gauss for 1.5T systems or 30,000 Gauss for 3.0T systems). To put this in perspective, the Earth's magnetic field that affects a compass measures only about half of one Gauss.

In simple terms, a coil is a length of wire coiled in a circular or cylindrical shape, rather than laid out straight. Here is what a coil designed for a speaker, called a voice coil, looks like:

Speaking of speakers, let's delve further into the subject. This legendary "Wall of Sound" by The Grateful Dead was the largest and loudest PA system ever taken on tour in both outdoor and indoor arenas. It nearly bankrupted the band due to the logistical challenges of having 2 systems leapfrogging each other, city to city, due to setup time, but those who experienced it live claimed there was nothing like it. Fidelity and volume were the core objectives, featuring approximately 600 JBL speakers and 48 600-watt McIntosh MC2300 amps, delivering a staggering 30,000 Watts.

Now, let's break down how a typical speaker works. Please refer to the speaker diagram below as you read through the explanation.

Every speaker consists of three fundamental components: a powerful permanent magnet, a voice coil (where the speaker wires connect), and a paper cone (the visible part of the speaker that moves back and forth, also known as a diaphragm or membrane).

If you hold a copper coil in your hand and place it against a strong permanent magnet (such as one from your refrigerator), it will fall to the floor. Copper is non-magnetic and won't stick to the magnet. In the image above, the copper voice coil is represented by the purple wire leading to the "input voltage signal" connection point. This coil is wrapped around a cylinder that slides over the central North Pole of the primary permanent magnet. The voice coil is physically attached to the paper cone of the speaker and is free to move forward and backward.

As you begin playing music through the speaker, represented by the sine wave signal labeled "Input Voltage Signal," electricity flows through the coil, precisely following the input signal. While copper itself isn't magnetic, Faraday's principle tells us that electricity flowing through a wire generates a magnetic field. By concentrating this magnetic field in a coil, we transform the non-magnetic copper coil into a continuously changing, dynamic magnetic field. This field corresponds precisely to the input signal, displaying changes in polarity, amplitude, and frequency. A simplified representation of this process would resemble the diagram here, where the yellow arrows represent the electric current from the music, and the pink/purple lines indicate the dynamic magnetic fields generated in perfect alignment with the current.

“Once in a while you get shown the light, in the strangest of places if you look at it right.”

Grateful Dead - Scarlet Begonias

So, we no longer have a non-magnetic copper coil paired with a permanent magnet; instead, we have a dynamic interplay between one powerful permanent magnet and one coil that "dances" in perfect synchronization with the magnetic field it creates. The coil's movements—its "dance"—are determined by the electrical signal flowing through the speaker wire. Since this “dancing” coil is directly attached to the paper cone it too begins the exact “dance” generating sound pressure waves that vibrate your eardrums exactly. Imagine an elastic band glued to the vibrating paper cone stretched across the room and affixed to your eardrum (essentially what is happening in the invisible air). The air molecules already present right at your eardrum “dance” identically to the speaker cone since they are physically attached to each other through the air. That’s the essence of how speakers function!

Now that you understand speakers, let's draw a parallel to inHarmony's transducers. As Craig Goldberg, Co-Founder of inHarmony, aptly puts it, "in our meditation furniture we have what is called a tactile transducer, a fancy word for half of a speaker. In essence, removing the paper cone from a speaker leaves you with a tactile transducer.”

However, it's essential to note that the tactile transducers used in inHarmony devices are custom-designed and engineered from the ground up for the inHarmony Meditation Cushion, the inHarmony Practitioner, and the inHarmony Sound Lounge. These tactile transducers are more sophisticated. Tactile transducers generally use thicker wire with more turns in their voice coils and powerful neodymium magnets to induce vibrations in a metal magnetic body, transmitting those vibrations throughout the chassis and anything to which they are mounted (whether the inHarmony Meditation Cushion, inHarmony Practitioner, or inHarmony Sound Lounge). Here is a photo of an inHarmony transducer.

Like speakers, these tactile transducers vibrate precisely in response to the input musical signal, as dictated by the laws of physics. As the heart of the system, these tactile transducers boast superior quality, design, and physical construction. Their electrical specifications for power, frequency, and impedance far exceed the necessary levels to deliver a "best in class" experience. To borrow an old slogan, these transducers take a “lickin” and keep on “tickin”. They are exceptionally robust pieces of hardware that maintain their performance over time.

VAT (Vibroacoustic Therapy) is as powerful a tool as you allow it to be, and I discover its potential more each day. Let me leave you with one of The Grateful Dead's most iconic lines from their song "Scarlet Begonias": "once in a while you get shown the light, in the strangest of places if you look at it right." This song is also known to many younger listeners, as it was covered by Sublime on their first album.

Ultimately, it's all about perspective, and the shift required is often smaller than you might imagine. Beauty is everywhere, awareness is everything , like the grasshopper at your feet. Don’t you hear him? Pay attention, notice what’s significant, and listen!

I can be reached on the telegram user and affiliate chats as well as through email at [email protected] if you have any questions or comments or ideas for future blogs.

Rock on people! 

Link to Spotify Playlist

John Hill, Affiliate at inHarmony Interactive