Audiology is in its infancy in Ghana, West Africa. There is much progress that has been made by the first audiology graduates in Ghana. To my knowledge, all the graduates have audiology-related jobs throughout Ghana. Two of our former students are now pursuing PhDs at universities in Canada. Another audiologist, working at a teaching hospital in northern Ghana has just submitted a manuscript to the American Academy of Audiology (peer-reviewed journal) that was accepted for publication just this week. The title is “Inter-regional newborn hearing screening via tele-health in Ghana.” Graham Amponsah Ameyaw is first author. This is pioneering work that has been ongoing in Ghana since 2014. I could not be more pleased with these young audiologists as they forge new paths to providing hearing healthcare to their fellow Ghanaians.

I have just finished a case that dealt with possible hearing loss due to exposure to gunfire. It was an unusual case in that the hearing loss that followed exposure to gunfire did not manifest itself in the high frequencies as would be expected, but rather at 500 and 1000 Hertz. There was not a preponderance of evidence to support a causal effect of the gunfire. The case settled out of court. There is a lot to be said about gathering evidence to build a case; it must be accurate, current, thorough, and adequate. One issue in this case that bears repeating is that whenever an audiologist takes an intake history, or makes chart entries, or records audiometric and related data, or writes a report–those items are medico-legal documents subject to subpoena. Best practice is to make the entries as clear and legible as possible so that if the audiologist is called upon as a witness or another audiologist is to review and deliver an opinion to the court, that there will be adequate information to form such an opinion. Finally, practicing clinical audiologists must always consider that their priority is to the safety and wellbeing of their patients. If an audiologist is being asked to provide services for which he or she is not qualified, and/or for which he or she does not have practical experience, a referral to another qualified colleague is the appropriate course of action. Failing to do so is an obvious injustice to the patient/client and a violation of the professional code of ethics.

There is mounting evidence that chemicals, asphyxiants and some heavy metals can affect hearing. Workers in many industries around the globe are exposed daily to chemicals that are ototoxic. Some research reveals that there is a synergistic effect when workers are exposed to chemicals and noise. This is an area of interest to me and I feel strongly that this issue needs to be addressed in workers compensation cases. Audiologists should be among those who are educating attorneys and others in related professions about the dangers of chemicals, asphyxiants and heavy metals when combined with exposure to noise.

I have recently retired from my faculty position in audiology at Utah State University and am now focussing my time consulting on cases involving worker’s compensation where hearing loss is an issue.

My mailing address is:

Forensic Audiology Consulting Services, LLC

1876 South Alondra Drive

Washington, Utah 84780

Cell: (435) 512-0898

Several cases that I have recently taken involve plaintiffs working in petrochemical plants. These are individuals that have spent 30-40 years exposed to loud levels of noise. Each case is unique and requires attention to detail in order to better understand the impact of the hearing loss acquired over years.

I would be interested to know what questions others  have about hearing, hearing loss, medical audiology, forensic audiology, balance disorders, noise and hearing conservation. I would like to address those questions as a public service in this blog. If you have a question, please submit it to john@forensicaudiology.com.

John

Audiology is the study of hearing and balance. Audiologists are allied health care providers who evaluate individuals whose primary complaints are hearing or balance related. This is a relatively new field which explains why there might be some confusion as to what audiologists do. I have had three inquiries recently that asked for my forensic services in evaluating recorded tapes for possible tampering. As interesting as that might be, it really does not fall into the scope of practice of audiologists, rather an audio technician or engineer should be consulted. Hopefully this helps clarify the issue.

I just returned from a meeting at the American Speech-Language and Hearing Association in Rockville, MD. I sit on the coordinating committee and serve as the editor of  Special Interest Group 8. This group focuses on public health issues relating to hearing and balance. Below is  a list of the current areas of focus:

• Noise and hearing conservation
• Acoustic measurement and standards
• Environmental studies and policy
• Legislation pertaining to public, educational, and occupational accessibility and accommodations for those with hearing and balance problems
• Forensic (investigative) audiology
• Emergent issues related to high risk variables such as ototoxins, infectious disease, acoustic (neuro-otologic) trauma, and domestic abuse/violence.
• Innovations in teleaudiology

We are looking for input regarding areas that are timely and of importance. What would you like to see addressed by this committee?  Our goal is to disseminate information to the public and to professionals.

Adding dB can be a challenge because dB, particularly when dealing with the world of acoustics, is based on the formula dB = 10 log₁₀ (R), where (R) is a ratio between two powers or two pressures.

It is important to note that dB IL (intensity level) and dB SPL (sound pressure level) are equivalent, i.e., 20 dB IL ~ 20 dB SPL. It is only the reference values and units that differ. The reference for dB SPL is: .00002 Pascals (20 µPa) or .00002 Newtons/M² (20µ Nt/m²); whereas the reference for sound intensity or power is 1 x 10^-12 Watts/m² or 1 x 10^-16 Watts/cm².

The following two formulae help us solve for dB:

dB SPL = 20 log₁₀ (Po/Pr) where Po is the pressure being measured and Pr is the reference pressure.

dB IL is 10 log₁₀ (Io/Ir) where Io is the power or intensity measured and Ir is the power/intensity reference.

Let’s say that I have two sources; one is 10 dB and the other is 15 dB and I want to know how many dB will result if the two sources are combined. Because the dB is not linear we know that adding of these two values will not result in a total of 25 dB, but rather in some lesser value.

The easy approach is to use a table or chart. Why go the easy route when we can figure it out for ourselves? It is important to understand the reasoning and the mechanism (procedure) behind the resultant dB value.

We have to break down the two sound sources into their basic components. By this I mean that we need to work backwards from what we know.

We know that 15 dB = 10 log₁₀ (an unknown ratio we will call R); so how do we find out what (R) is? Well, I’m glad you asked J

We have to follow this formula:

dB = 10 log₁₀ (R) can also be written (R) = antilog₁₀ * (dB/10)

Note that we are dividing both sides of the equation by 10 in order to solve for (R).  Before we go any further, let’s define antilog.

According to Wikipedia (http://en.wikipedia.org/wiki/Antilog#Antilogarithms ) “the antilogarithm function antilog_b(y) is the inverse function of the logarithm function log_b(x).”

The formula is: Antilog of x is = 10^x

Example:

We  know that the log₁₀ of 100 is 2  which can also be written 10² or 10 x 10  all of which equal 100.  The exponent of 100 is 2; therefore a log and an exponent are the same thing; the antilog of 2 (also known as x in the formula above) is 10² or 100.

Now we are getting somewhere. So, R is some unknown ratio of two powers or pressures. We need to know the R for 10 dB and the R for 15 dB. Using our handy dandy formula we are going to solve for both ratios.

(R) = antilog₁₀ (dB/10)

(R) = antilog₁₀ (1.5)

(R) = 31.62

To prove this let’s plug in our familiar formula for calculating dB

dB = 10 log₁₀ (31.62)

dB = 10 * 1.49 (rounded off is 1.5)

dB = 15

So all we need to do now is figure out the ratio that results in 10 dB.

(R) = antilog (10dB/10)

(R) = antilog of 1

(R) = 10 (you already knew this because the log of 10 is 1!)

All we have left to do is add the two ratios to come up with a new ratio and plug it into our trusty dB formula and voila you have zee new value which is zee sum of zee original two sources.

dB = 10 log₁₀ (R)

dB = 10 log₁₀ (10+31.62)

dB = 10 log₁₀ (41.62)

dB = 10 x 1.62

dB = 16.2

Conclusion: When you add 15 dB and 10 dB together you get 16.2 dB.

Wait a minute here—the formula for pressure is dB SPL = 20 log₁₀ (R), but I said earlier that 20 dB IL ~ 20 dB SPL. So how can this approach work?

Let’s plug in some numbers and see what happens.

dB SPL = 20 log₁₀ (R) and can also be written (R) = antilog₁₀ (15 dB/20), therefore:

(R) = antilog₁₀ 0.75

(R) = 5.62

dB SPL = 20 log₁₀ (5.62)

dB SPL = 20 * 0.749

dB SPL = 14.98 (rounded to the nearest decibel is 15!)

So whether you are using dB IL or dB SPL you still come up with the same answer. Remember we are dealing with ratios and that intensity is proportional to pressure squared and pressured squared is equal to the square root of intensity.

(I ∝ P²) or (P²∝√I)