Current Trends in Electronic Larynges
Article By: Brian Shute, Ph.D., CCC
Originally published in Advance for Speech-Language Pathologists & Audiologists, July 25, 1994.
Advancements in technology over the last decade have had considerable impact on the new generation of electronic voice aids. Known to many as the artificial larynx (AL), these machines provide functional voicing for an estimated 30,000-35,000 laryngectomees in the United States. Ranging in cost from $400 to $650, the electronic larynx is a useful communication device that the laryngectomee can use quickly. After a comparably short amount of practice and therapy time, the AL offers functional communication to the new laryngectomee and others who have lost function of their vocal folds.
For patients who cannot achieve functional esophageal or tracheo-esophageal punctured (TEP) speech, the AL remains an excellent option for alaryngeal speech communication. Even with functional esophageal or TEP speech, many laryngectomees find the AL a comforting option.
Speech with an AL is typically louder, faster and often more intelligible than esophageal production. Other then a device that simply emits a buzz tone, how does the electronic voice aid work, and what makes it different from the machines of yesteryear?
Overall the neck-type AL is an oscillator that generates a focused signal that penetrates the neck for voice. It is this penetrating tone or new voice that is articulated for communication. When a patient loses vocal function of the true larynx, the AL simply provides a tone replacement for speech. The signal from the AL moves through the neck and into the mouth and is used to produce the vowels and voiced consonants in speech.
While most users press the device on the neck for signal transfer, a minority of laryngectomees utilize an intraoral tube. This simple rubber cap and tube assembly delivers the signal directly in the mouth, thus eliminating the need for neck placement. Most neck-type AL devices can be changed easily for neck or intraoral applications.
The most common new generation of electronic voice aids are lighter and smaller and generate a tone that is termed, periodic or consistent. Actual tone production is accomplished by an electromagnetic plunger that repeatedly strikes a hard membrane or drum.
The hard membrane, located in the head of the machine and on the outer side, has contact with the patient’s neck. In order to create an oscillated signal, the device must automatically turn on and off so the plunger creates a cycle of repeatedly hitting the drum. Depending on the speed and force in which the plunger strikes the drum, variations in pitch and volume are controlled.
Rather than using the once bulky electronic parts to create an on-off cycle for oscillation, the new style machines use a silicone chip that serves as a timer. These timers are smaller than a penny and weigh less than a gram.
Typically these silicone timers use very little energy to operate, thus smaller, lighter and more efficient batteries can be used. One device utilizes surface-mount electronic components that are extremely light and small. The ability for artificial larynx manufacturers to reduce overall weight and size while maintaining good tone quality is largely the result of micro-electronics. Many patients are at an age where arthritis and muscle weakness is prevalent. Aside from age, the laryngectomy surgery itself may leave a patient with weakened upper extremity movement and limited range of motion on one or both sides. When considering these issues, it is not surprising that a light-weight device is easer to hold and operate. For the non-laryngectomee, having to communicate with a hefty machine is akin to writing with a heavily weighted pencil.
The use of space age materials also has improved the current type of machine. The incorporation of micro and silicone electronics give rise to a machine that is more durable and forgiving to shock damage.
Some manufacturers now are encasing electronic components in resilient material to resist shock and damage from water. New plastic materials and molding techniques offer devices that are easy to hold and manipulate.
Although not considered a neck-type device, one manufacturer has molded a tiny sound generator in an upper denture plate for limited voice production. Another device utilizes a lightweight titanium shroud to protect the components within and to dampen extraneous noise emitted from the body of the machine.
Controls on several devices now allow for easier operation. Small, low-friction micro-switches and dials are presently used on most models to easily adjust pitch and volume, replacing the trigger or large switches of old style machines. Pitch range can be adjusted quickly to approximate a male or female voice. Most controls are easily accessible on the external case and are user friendly.
Aside from pitch and volume controls, some models allow for limited pitch inflection. One manufacturer provides internal adjustments that alter tone decay – the variance of tone that automatically changes downward after the machine is initially turned on. Still other models offer a variable head that physically adjusts the distance between the plunger and drum. This feature provides limited fine tuning and, on one model, alters the softness of tone.
Power sources for AL devices also have changed. Once limited to disposable 9-volt radio batteries, mercury batteries or a heavy battery pack, the electronic voice aids of today offer rechargeable batteries for months of service. Some machines utilize high capacitance, barrel-type batteries while others can use 9-volt rechargeable batteries or alkaline batteries. One device can be used with household current or an electrical source from an automobile cigarette lighter.
Most AL devices today come with a charger that rejuvenates a rechargeable battery for many cycles of use. Various factors including volume/pitch settings, actual on-time and battery care essentially will determine the frequency of recharging. Typically these battery chargers will fully recharge a battery in 10-14 hours. Some units offer an automatic shutoff that reduces most problems with over-charging. Some charging units also vary in their ability to charge more than one battery at a time. This feature conveniently allows the patient to carry a fully-charged alternate battery. Like automobiles, the artificial larynges of today have become smaller, lighter, more efficient and user friendly. If we continue this trend into the future, we will likely encounter electronic devices that are more compact and energy efficient. They will possibly be implanted at the time of surgery and recharged monthly by way of a subcutaneous recharging coupler while the patient sleeps. They might utilize the existing musculature to control voice initiation and intonation.
Perhap such devices will harness the naturally existing electrical voltage of the body for operation. Devices in the future might allow for more normal sound production and vocal inflection, making it difficult to differentiate between normal and synthetic alaryngeal voice. With some amount of imagination, maybe the ultimate possibility will be observed: the need for an artificial larynx will be eliminated completely.
Updates:
Since 1994 when this article was first written, some manufacturers have developed devices that use digital electronics to create the oscillated signal. This does away with some of the analog adjustments (i.e., potentiometers) and allows for adjustment using a personal computer and/or by manually putting the device in an adjustment mode. Aspects of volume and pitch can then be pre-adjusted for a single button. For example, devices that have two activation buttons, one can be adjusted for a loud male voice while the other button can be used as a soft male whisper. Digital models may also reduce the number of electronic components on the circuit board and may be less expensive to manufacture. In terms of sound pressure levels and pitch, these devices are essentially the same as their analog counterparts.
Other technology has included the use of a sensor in relationship to the activation switch. The sensor electronically reacts to thumb pressure and alters the pitch after the device is activated. The result is an instrument that dynamically changes pitch during speech. This allows for more natural inflection and even singing.
11/2011
© Inland Speech Pathology, 2011