Voice Coil Parts & Production

Voice coils are essential elements in loudspeakers of all sorts. Thus, understanding how a voice coil works is essential for audio engineers and DIYers alike. The main parts the bobbin, the voice coil wire, and the collar. Mike Klasco and Steve Tatarunis of Menlo Scientific provide in-depth information about voice coils in the March 2012 issue of audioXpress magazine.

The parts of a voice coil (Source: Precision Econowind)

Klaso and Tatarunis write:

“The bobbin provides a rigid structure on which the voice coil wire can be wound and the collar can serve several purposes. It secures the coil lead-out wires, reinforces the bobbin, and provides a convenient material for diaphragm attachment … In some cases—headphone speakers, for example—a monolithic (self supporting no bobbin or collar) voice coil may be used. But this article will focus on the more commonly used bobbin, coil, and collar designs.

Loudspeaker voice coils are seldom considered critical elements that contribute to sound quality, and few technical papers have addressed this issue. But when designing a voice coil, the selection and application of materials can have profound effects upon sound quantity, quality, and power handling. The mechanical energy from the winding stack moves by transconduction through the bobbin and collar before reaching the diaphragm. Any non-linearities in this path are superimposed upon the response of the speaker. Intrinsic characteristics of materials such as internal damping and Young’s modulus create specific sonic signatures and contribute to the residual distortion spectrum of the transducer … In selecting a particular material, a coil winder makes important trade-offs on the winding process. Knowledge of these variables can ensure better, more cost-effective coils, avoid conflicts, and improve production yields. Torsional resonances, internal losses, and electrical conductivity of the bobbin materials are some of the factors effecting the distortion, sensitivity, and sound quality of the finished loudspeaker.”

A close-up view of both a good voice coil and a burned voice coil (Source: The Speaker Exchange)

You can read the entire article here. For subscription information, go to www.audioamateur.com.

audioXpress magazine, like Circuit Cellar, is an Elektor group publication.


Robot Nav with Acoustic Delay Triangulation

Building a robot is a rite of passage for electronics engineers. And thus this magazine has published dozens of robotics-related articles over the years.

In the March issue, we present a particularly informative article on the topic of robot navigation in particular. Larry Foltzer tackles the topic of robot positioning with acoustic delay triangulation. It’s more of a theoretical piece than a project article. But we’re confident you’ll find it intriguing and useful.

Here’s an excerpt from Foltzer’s article:

“I decided to explore what it takes, algorithmically speaking, to make a robot that is capable of discovering its position on a playing field and figuring out how to maneuver to another position within the defined field of play. Later on I will build a minimalist-like platform to test algorithms performance.

In the interest of hardware simplicity, my goal is to use as few sensors as possible. I will use ultrasonic sensors to determine range to ultrasonic beacons located at the corners of the playing field and wheel-rotation sensors to measure distance traversed, if wheel-rotation rate times time proves to be unreliable.

From a software point of view, the machine must be able to determine robot position on a defined playing field, determine robot position relative to the target’s position, determine robot orientation or heading, calculate robot course change to approach target position, and periodically update current position and distance to the target. Because of my familiarity with Microchip Technology’s 8-bit microcontrollers and instruction sets, the PIC16F627A is my choice for the microcontrollers (mostly because I have them in my inventory).

To this date, the four goals listed—in terms of algorithm development and code—are complete and are the main subjects of this article. Going forward, focus must now shift to the hardware side, including software integration to test beyond pure simulation.

A brief survey of ultrasonic ranging sensors indicates that most commercially available units have a range capability of 20’ or less. This is for a sensor type that detects the echo of its own emission. However, in this case, the robot’s sensor will not have to detect its own echoes, but will instead receive the response to its query from an addressable beacon that acts like an active mirror. For navigation purposes, these mirrors are located at three of the four corners of the playing field. By using active mirrors or beacons, received signal strength will be significantly greater than in the usual echo ranging situation. Further, the use of the active mirror approach to ranging should enable expansion of the effective width of the sensor’s beam to increase the sensor’s effective field of view, reducing cost and complexity.

Taking the former into account, I decided the size of the playing field will be 16’ on a side and subdivided into 3” squares forming an (S × S) = (64 × 64) = (26, 26) unit grid. I selected this size to simplify the binary arithmetic used in the calculations. For the purpose of illustration here, the target is considered to be at the center of the playing field, but it could very well be anywhere within the defined boundaries of the playing field.

Figure 1: Squarae playing field (Source: Larry Foltzer CC260)

Referring to Figure 1, the corners of the square playing field are labeled in clockwise order from A to D. Ultrasonic sonar transceiver beacons/active mirrors are placed at three of the corners of the playing field, at the corners marked A, B, and D.”

The issue in which this article appears will available here in the coming days.

DIY Audio Design with Tymkrs

With the growing popularity of embedded design kits and microcontroller-based platforms for rapid prototyping, it’s now easier and more affordable than ever for engineers, DIYers, musicians, audiophiles, and academics to customize electronics applications of their own. The March 2012 issue of audioXpress magazine will feature an interview with two DIYers—the duo behind Tymkrs.com—who do just that. “Atdiy” and “Whisker” provide details about Zombietech.tv, their design interests, and their recent projects. Here are some of their most interesting DIY designs:

  • SidCog Organ: Combine a programmable SID chip from the Commodore 64 and an old Hammond organ
  • Laser Audio Transmitter: Use a laser to transmit audio with a laser transmitter and a solar panel receiver
  • High-Impedance Preamplifier: A preamp designed with a JFET for loud and clean sound

Note: All photos courtesy of Tymkrs. The interview will appear in the March 2012  issue of audioXpress. audioXpress magazine (www.audioamateur.com), like Circuit Cellar, is an Elektor group publication.