The lost art of tuning fork testing has been found again in this DigiCare tutorial on the vital techniques for measuring human hearing and amplification performance.

By Dr. Max S. Chartrand,  PhD

Introduction

Once upon a time, hearing professionals had no electroacoustic audiometers, real ear probe tubes, or electronic soundfield. As in all fields where technological metamorphosis followed practice, hearing health professionals---whether diagnosing or treating hearing loss---had to rely upon quick, qualitative methodology. "Cone of light" otoscopy has given way to impedance tympanometry. Live voice has given way to recorded voice calibrated soundfield, manual screwdrivers to digital ones. Tuning fork audiometry has given way to the electroacoustic audiometer.

Weber, a qualitative test for conductive loss, could be performed utilizing the bone conduction oscillator of the audiometer. Rinne, a qualitative test for sensorineural impairment, was simply forgotten. So, too, the Schwabach and Bing. Since these tests have come and gone, there have been found other uses for tuning forks, developed by the author and his colleagues over the years, which can be utilized in delivery of new hearing instruments and in trouble shooting of patient complaints.

In truth, tuning forks can still serve a valuable purpose in dispensing practice. They add another dimension to hearing and hearing aid assessment that is often left out of today's regimen. They inspire confidence in patients seeking resolution of difficult to describe fitting complaints. They provide addition tools of measurement and a quick test methodology to enhance dispensing effective. It is my hope that this brief tutorial and accompanying professional education coursework will bring back a vital and exciting tool into dispensing practice. And with it, a return of creativity, imagination and resourcefulness in the art and science of hearing instrument dispensing.

Tuning Fork Basics

Your tuning fork set should ideally comprise the following frequencies:

• 256Hz
• 512Hz
• 1024Hz
• 2048Hz
• 4096Hz

Construction of the fork should be thick aluminum or stainless steel able to produce vibratory signals of at 50-60dB, with the longest possible sustained tone. Sound is produced by striking one prong of the tuning fork against the thick area of the handle of another tuning fork. It is imperative that the hand holding the fork that is being struck be far enough down the handle of the tuning fork so as not to dampen its vibration potential.

Practice striking the tuning forks, striving for uniform and solid vibration. Hold the prongs in-line with each other to reinforce their signal. You'll quickly find that when the prongs are lined up, the sound pressure virtually doubles (summation). When you point them to one side or the other, the signal is significantly reduced. Gripping by fingertips only, turn the fork prongs in different directions, and notice the increase and reduction of sound pressure. It is important that you become intimately familiar with this concept, for there will be reasons you will be moving the angle or direction of the forks from time to time. Also, you'll need to be ever conscious of lining up the prongs when taking quantitative tests, such as determining user VC setting for balancing binaural fittings, etc.

Following are individual characteristics of each tuning fork:

• 256Hz- Is a low tone that requires tremendous striking force to produce an audible air conduction signal. In fact, 256Hz will require energy many times greater than 512Hz just to produce the same sound pressure. The difference between the sound pressure of 256Hz and 4096Hz is a difference in the thousands of times! Hence, using this fork for air conduction purposes is not very successful. It's best use is for Weber, which given strictly in bone conduction mode.
• 512Hz- Is the most common fork used for the Weber, Schwabach, Rinne and Bing tests. It is also good for spectral adjustment for balance between two hearing aids. In this case, 512Hz is used to balance the low frequency region of amplification.
• 1024Hz- Often referred to as the "fulcrum" of speech energy, or that point where the balance between the sound pressure of speech vowels (1KHz and below) and the clarity of speech consonants (above 1KhZ) is about centered. 1024Hz also is that frequency that most approximates with the Speech Reception Test (SRT) score. So, philosophically speaking, if you were stranded on a desert island full of hearing impaired individuals, and you could only take one measurement tool with you, this would be the fork to take! Use this test also for balancing VC settings in binaural cases, and for determining impedence-integrity of the amplified system on a patient's ear. This fork is also the second half of the set needed for Weber, Schwabach, Rinne and Bing tests (512Hz being the other half of the set for these tests).
• 2048Hz- This fork vibrates near the center spectrum of the 2nd format of speech (in the English language), making this a valuable tool for ascertaining aided sensitivity at varying distances (described below). This particular fork often helps you ascertain improvements in aided versus unaided soundfield in precipitous high frequency cases. Generally, this fork provides the highest frequency for your tuning fork testing regimen.
• 4096Hz- Use this particular fork with judgment and with good reason. It represents the approximate center frequency of the 3rd format of the consonants in the English language. Many severe high frequency losses will not hear this fork even in aided position, because of cochlear "dead spots" or because amplification cannot overcome the degree of loss at this frequency. Also, its vibrating time is short, usually no more than 5 or 6 seconds. Its use should be restricted for demonstrating aided soundfield only, using methodology patterned after the Schwabach (described below).

Practice striking each tuning fork. Listen to each one at your ear and note the length of time they freely vibrate. The longest vibrating fork is usually 512Hz, next the 1025Hz, etc. Note the effects of a hair touching the fork while it is vibrating (slight damping, loss of vibrating time). Note the effects of holding the fork with your fingers touching the thick area of the fork (damping, slight change of pitch). Note the effects of turning the fork in different directions, and the effects of air movement when moving its physical location. Note the acoustic effects of nearby surfaces, and body baffle effects.

Practice counting seconds while you hear the tone: One-thousand, Two-thousand, Three-thousand, Four, etc:.time you tempo at 60 beats per minute. Synchronize with the second hand of a watch or clock. Practice these techniques until they become second nature to you, and you are comfortable with them.

Conventional Tuning Fork Tests

Next, you'll need to review the types of tuning fork tests, and how to instruct your patient. We will cover each conventional type of tuning fork test so that you are familiar with them. In practice the only two that will be of significant value in your armamentarium are the Weber and Schwabach tests. The others are simply variations on a theme, and may be used when needed.

Note the suggested dialogue and how to mark results on your audiometric form. Remember, that you are performing tests that require environmental sound control. They require the same sound level standards as for bone conduction testing (<45dBC), including an anechoic or non-reflective environment. In the section following the conventional tests, we will discuss non-conventional tests, which may not require the same level of sound control, and can be performed in more ordinary circumstances. The following tests are considered the "classic" tests and are named after their 19th century German originators. They comprise the standard pure-tone audiometric battery before the electronic audiometers were invented, and still remain the screening protocols for modern otologists.

Weber Test- This test is, by far, the most common and the most essential of the qualitative tuning fork battery of tests. As part of the middle assessment regimen, the author recommends use of the Weber in every comprehensive hearing evaluation. Its purpose is to ascertain the presence of unilateral conductive loss. You will use the 512Hz and 1024Hz forks for this test.

It is executed by first instructing the seated patient:

"I will now strike a tuning fork and place it's handle in the center of your forehead. Please, tell me in which ear you hear the tone the loudest. Do you understand?"

Then, you will strike the 512Hz fork to yield at least 50-60dBSPL of sound pressure (you may use a sound level meter to ascertain this level), and place directly between the frontal sinuses of the patient's forehead. After a few seconds, the patient should indicate in which ear they hear the tone the loudest. This should be the ear with the best bone conduction sensitivity at 500Hz.

Record the ear of choice with a "R" or "L" notation next to the test frequency (500Hz or 1000Hz). Repeat the same instructions and procedure using the 1024Hz fork and record response. If it is the same or they cannot distinguish in which ear they hear the tone the loudest, you may simply write in "R/L".

Now, since this is a test in ascertaining unilateral conductive loss, you may also refer to the results as "Weber Positive", meaning that the ear with the greatest air conduction loss is the ear in which the tone was heard the loudest, or "Weber Negative", indicating that the ear of response was the ear with the greatest air conduction loss.

Of course, you will have to have air conduction thresholds in front of you to determine whether the test was positive or negative. That is the reason that I suggest simply indicating which ear a particular frequency is heard the loudest, so that later one can ascertain whether the results were indeed positive or negative.

Rinne Test- We will not spend as much time on this test, but merely describe its use, as it is rarely needed in today's test battery. It's purpose is the opposite of the Weber in that it is a qualitative test to ascertain if the loss is sensorineural. Hence, a "Rinne Positive" indicates sensorineural loss, while a "Rinne Negative" points to the presence of at least some significant conductive loss.

You begin by instructing the patient that you'll be striking the fork and holding it out 3" from the ear. When they indicate that they no longer hear the tone, you will immediately place the unimpeded handle of the fork over the mastoid bone (behind the ear) to see if the sound reappears. If so, they exhibit at least some conductive component in their hearing status. If not, it is presumably a sensorineural and/or central loss. (Note: there is an entire discussion surrounding the finer points of this discussion, which is provided in the training course).

Bing Test- This test is another rarely used, but one with which every hearing health professional should be familiar. Again, it is a qualitative test, but this time to ascertain where there is a bilateral conductive component or not. It's positive/negative indications are confusing, because, though it is primarily a test for ascertaining conductive component, it is notated like the Rinne, which is primarily a test for sensorineural loss. Hence, a notation of "Bing Positive" means no conductive component evident (a normal ear is also a Bing Positive), whereas evidence of at least some conductive component is notated as a "Bing Negative". The test is administered by instructing the patient to,

"Tell me when you no longer hear the tone from this tuning fork. At that time I will apply slight pressure against your ear to close the canal, and at that time you will let me know if you hear the tone again."

You then strike the fork and place it's handle over the mastoid bone. The patient should indicate that they hear the tone at that point. If they do not, you may need to strike the fork with much greater force and place it again over the mastoid. When they indicate that the tone has stopped, you leave the fork in place and immediately close the tragus over the opening of the canal with your fingertip. If they hear the tone return upon closure of the external ear canal, it is supposed that their loss is either normal or sensorineural without conductive components on that ear. Conversely, if the tone does not return, that ear already has some form of occlusion and is notated as "Bing Negative". Be sure to indicate with "R" or "L" ear which ear is under test. Repeat procedure for the opposite ear.

Schwabach Test- Probably the most important tuning fork test in your armamentarium of tests is the Schwabach. Before the development of the modern audiometer, this was the common test for determining relative hearing thresholds of a given patient. While the results are much dependent upon the hearing acuity of the one performing the test, with practice it can sharpen one's testing skills overall, as well as serving as good screening procedure. Calibrating to one's own thresholds, and assuring reasonable sound level control of the test environment combined with experience and practice can make this a highly desirable skill.

The author feels strongly that dispensing professionals, in particular, need to use some form of the Schwabach in terms of frequency-specific soundfield, when a more scientific method (i.e., calibrated speaker system, etc.) is not available. You'll be using the following forks for this test: 512, 1024, 2048 & 4096.

The test begins with these instructions:

"I am going to strike a series of tuning forks to test your hearing sensitivity. I will hold each fork at your ear until you say that you no longer hear the tone. Then, I will place it at my own ear and count the seconds that the sound remains to be produced. Be sure that you stop hearing the tone completely before indicating it has stopped. Are you ready?"

You then begin with the 1024Hz fork, striking it with enough force to produce at least 60dBSPL of sound. Immediately place the prongs in line at 2" of the patient's ear. Let ring until they indicate they no longer hear the tone. At that point, quickly place the fork (in-line position) exactly 2" from our own ear and count the seconds that pass while you hear it (counting "one-thousand-two-thousand-three-thousand-four, etc.). Record the number of seconds that you heard it after they stopped hearing it as; "1024Hz- 6 seconds". Repeat procedure using the 2048 fork; then, the 4096 fork; repeating 1024 again; then, 512. Record results at each frequency as indicated above.

Note: As you will note further in this primer, you may use the above procedure for aided pure-tone soundfield to ascertain the "after picture" of a given amplification or programming strategy.

Now, let's say that you'd like to convert the above scores to an actual audiogram, to be marked with demarcation points and connected with lines in the customary manner. To do this requires a great deal of practice in determining "calibration" standards in a given test environment. There are two ways to do this:

1. Tone decay rate- This refers to the rate of loudness decay, or how fast a given fork loses vibratory energy (i.e., audible sound pressure at HL) over time. Each fork will be quite different. For instance, in the set we use at our practice we have determined that fork 1024Hz loses approximately 2.5 decibels per second. That would translate a notation of 1024Hz @12 seconds to about 35dB on the audiogram. 2048Hz decays much faster at about 5dB per second, in which a notation of 12 seconds would translate into an approximate audiometric threshold of 60dB. The long-lasting 512Hz fork decaying at the rate of 1.5dB per second would yield at 12 passing seconds an audiometric threshold of about 20dB. Likewise, the fast-as-a rabbit 4096Hz fork with a decay rate of 12dB per second would at a mere 6 seconds of passing time yield an approximate threshold of 72dBHL.
2. Loudness comparison- Much less scientific than the above, but a quick screening approach is to simply become so familiar with various sound pressure levels as to be able to subjectively compare them in audiometric terms. For instance, let's in your years of experience in testing you've attained a high degree of relative accuracy in determining sound levels, you would be able to, within a +/- 5dB be able to notate where a given sound level falls on the audiogram. Of course, in doing so, you would not be as concerned as to the passing seconds counted after the patient stopped hearing the tone as much as the estimated sound level at your ear at that given moment.

No foray into the Schwabach test would be complete without discussing the limitations encountered by the hearing threshold levels of the one performing the test. It is often and erroneously assumed that one must have normal hearing thresholds for this test to be valid. But, a more accurate depiction of this thesis is that one's aided hearing thresholds should be normal or near-normal. Hence, for one with corrected thresholds, it will require a great deal of practice and careful administration to assure accuracy in determining hearing threshold levels.

A secondary consideration is "calibrating by ear" which requires allowing for one's aided threshold at each frequency. In this case, where you stop hearing the tone, you would add your own pure-tone threshold figure.

Unconventional Tuning Fork Tests

There are several approaches to the use of tuning forks and tuning fork handles that have been introduced to the hearing professionals by the author over the years. The author feels that tuning forks can serve as essential, time-saving and confidence building tools in training and counseling hearing aid patients, as well as for quick test purposes. Below, we will describe each method, but will have to provide detailed analysis of each in another forum, usually in the training courses.

Establishing Balance in Binaural Fittings- One of the most challenging tasks upon delivery of new, modified or reprogrammed hearing instruments is in helping the patient establish a perfect balance in the VC settings (which, indirectly, represent in situ use-gain levels). The procedure for accomplishing the task is fairly simple, but the principles need a bit of explanation.

At this point, I refer the reader to my published articles titled "In Vigorous Defense of Volume Control" (The Hearing Professional, May-June, 2001) and "Another Elephant in the Living Room: To VC or Not to VC?" (Hearing Review, March 2003). These treatises will explain both the underlying principles and methodology in establishing VC levels, both of which topics are beyond the scope of this tutorial. In any event, the most important elements to remember are: 1) that the patient should set the VC levels to their own voice first, before setting to anyone else's voice, and 2) that their hearing thresholds will not remain stable throughout the day or even from day to day, and therefore, they need learn the rudiments of making minute VC adjustments from time to time.

Having said the above, we are ready to discuss using tuning forks in establishing a balance between the two instruments. You will begin by establishing that point where the patient's own voice is comfortable, not too bright or an echo (set too loud) or dull or occluded (set too low). Once that has been determined, you instruct the patient as follows:

"I am about to strike a tuning fork and then hold it directly in front of you. I'd like you to tell me if the loudness of the tone is the same on both sides, or if it is louder in one ear than the other. Please, hold your head still while making this determination."

Then, you will strike 512Hz and hold the fork so that the prongs are directly inline pointing toward the middle of the patient's forehead---holding the fork approximately 30" in front of them. A slight movement to right or left will throw off the validity of your test considerably. If they indicate they hear it louder in the left than the right, you will want to turn the left side VC down slightly, and repeat the procedure until the tone is identical in both ears. Remember, that in most cases they will be hearing two tones: an overtone at 1024Hz, which will last possibly only a couple of seconds, and the fundamental 512Hz tone, which can last up to one minute. It is easy for the patient to "jump the gun" and respond to the summated fundamental/overtone combined burst at the beginning, before the tone has had a chance to settle down. For that reason it is imperative that you ask them to listen to the tone for a few seconds before determining which ear the tone is heard the loudest. The objective is provide a balanced setting that evokes either "it sounds the same on both ears" OR "I can't tell which ear is the loudest". Either response indicates a balance.

Next, utilize the 1024Hz tuning fork in the same manner. This fork, remember, represents the "fulcrum" of speech energy, so is the most important. If, in the final analysis, you must choose between balancing for 512Hz or for 1024Hz, 1024Hz in the one to choose.

Another note on this technique: The reason you turn the VC down on the side that is loudest is because in most cases the VC set in a quiet setting often exceeds the use-gain that is most appropriate for all-around listening. Therefore, if the choice is between turning the loudest side down or the softest side up, the choice of default is always in turning down the side with the greatest gain sensation. When using complex sounds, such as speech, however, this rule may not hold.

Tuning Fork Handle Clicks- Tuning fork handles make excellent mid-range clicks that can be used for several purposes. Before we talk about some of those purposes, however, we need to cover procedure. The 512Hz and 1024Hz tuning forks provide a good pair for the purpose of producing a click that can be heard by even the most severe of losses in various amplification settings.

We begin by grasping the fork prongs themselves, leaving only the handles exposed, and by lightly rapping the handles together in about half-second clicks (two clicks per second). With arms extended, so as not to involve reflection from one's body, we usually instruct the patient to close their eyes, and begin a series of clicks starting at their right side and gradually moving to the left side. The patient is instructed to point precisely toward the clicks using the same hand at all times.

As you sweep past with steady clicks, the patient should move (point) in synchrony with those movements. At some point you will want to establish a "midline", which essentially involves both (right and left) hemispheres of the brain equally. Often, in cases of asymmetrical or unilateral hearing loss, you'll not be able to establish a midline. In binaural and transcranial fittings, though, finding or training for a midline is a major objective. Following is a review of where tuning fork handle clicks provide particularly useful information:

• Ear Training for Localization: After using the tuning fork tones of 512Hz and 1024Hz to establish a spectral balance as well as loudness summation balance, and VC position has been determined, you will want to perform an ear training exercise to help restore "localization" and "spatial mapping" abilities. The clicks are instead used for "ear training" to help the patient re-establish the central auditory ability to localize sound.

In this case, the patient is seated directly in front of the professional, instructed to close their eyes, and asked to follow the clicks from side to side and to otherwise point to where the clicks are coming from.

Starting at a point just to the right of the right ear, you will click the handles together steadily as you move to the left side. Patient should be pointing directly at the tuning fork handles as you move. If they lag far behind, or do not arrive at the left side soon after you arrive there, you'll need to repeat the produced several times until they begin to stay with you.

In cases of cognitive overlay, you may need to explain instructions until they understand the volitional nature of this exercise. For this is indeed an "exercise", in this case, more than a "test" per se. You may need "sweep" across a number of times before they finally stay with you, and before they can truly establish midline. Once, this is achieved, you can then wait until the next rehab session to train again.

In addition to the above ear training exercise for localization, they should also be given aural rehab exercises that they can perform on their own at home.

Transcranial or Internal CROS Fittings

The principles and procedures described above will also apply to cases where there is an aided "dead ear" on one side and a good or better ear on the other. For a rudimentary knowledge of the Transcranial or Internal CROS fitting concept, I direct the student to my paper titled "Transcranial or Internal CROS Fittings: Evaluation and Validation Protocol" (The Hearing Journal, September, 1991). Currently, this is one of the few detailed explanations that define the protocols and principles of Transcranial.

But, suffice it to say here that there are various configurations of bilateral impairment where these principles may be applied, especially in cases of asymmetrical audiograms, where some of the amplified signal of a more deficient ear will resonate across the temporal bone to the better ear side. Often, this phenomena is overlooked in everyday dispensing practice, causing unintentional imbalance or disturbing over-amplification to the the better ear.

A point to keep in mind here is that when we involved the central auditory process (even indirectly by way of tactile information traveling the efferent pathway from the motor cortex) of both sides, we evoke: 1) binaural summation, 2) attention and squelch, and 3) spatial mapping. Our purpose in using tuning fork handle clicks in these cases is to assess the sensation of balance between the two ears, particularly when there is a "dead ear" that relies upon taction at the tympanic plexus of the TM as well as interaural attenuation contralaterally, and the almost purely auditory response of the better ear. In the trained ear, a non-tonal, discrete click provides an objective stimuli in determining optimal balance between the aided dead ear side and the unaided (or in Transcranial Bi-CROS cases, the lesser amplified side). Keep in mind that the response on the "dead ear" should not be flat. In fact, the best tactile/Transcranial aided configuration is a ñ12 slope at 40-45dB of use-gain. In other words, our objective is not to help the dead ear to "hear" through audition, but to utilize first the tactile benefits at the TM and secondly to enhance contralateral hearing in the better ear. The two stimuli together can create a binaural listening environment. Hence, there's no such beast as a "normal" single ear. Consequently, central auditory function is entirely dependent upon bilateral sensations, though in this case a portion of those sensations is based upon motor responses correlated (after training) with auditory sensory sensations.

In similar fashion as described in the foregoing, we instruct the patient as follows:

"Now, I'm going to click these tuning fork handles together as I move from side to side. With your eyes closed, please listen to these clicks until you, and point toward the sound of the clicks. Try to stay with me as I move from side to side."

You will then start by clicking just 12" from the good (or better) ear side until they point directly at the clicks. Then, stopping the clicks momentarily, move about 12" from the aided dead ear side. Click the handles together until they point directly at the sound of the clicks. If they cannot distinguish the click as coming from the dead ear side, or if the clicks seem to come from a position between the two ears, you will need to sharpen the signal on the dead by increasing gain over-all, or by increasing gain in the 1-2Hz range. If your frequency response is already set within the recommended frequency response (-12dB per octave), it may simply be a matter of turning up the VC on the dead ear side. Repeat procedure until patient can distinguish the clicks as coming from the dead ear.

Next, you'll want to sweep from to side, instructing the patient as needed. When you are finally able to stop in the center region, establishing a midline, their brain will apparently have developed the ability to integrate the tactile signal of the dead ear with the auditory signal of the good or better ear. The objective here is to sweep across enough times, their finger following you well, to help establish a relative the appropriate VC setting. There are yet other, more complex, principles in this concept, which go far beyond the scope of this tutorial.

Conclusion:

Other tests, which are taught in the seminar using tuning forks, but not included here, include:

• Aided Tone Decay Test
• Spectral Balance Test
• Testing for Mic Input Sensitivity