Audiology vs. Audio Tech or Engineer

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.

Special Interest Group 8

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

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 antilogb(y) is the inverse function of the logarithm function logb(x).”

The formula is: Antilog of x is = 10x

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)

Traumatic Brain Injury Conference

I have been working for the past few months in organizing a conference entitled “Traumatic Brain Injury: The Silent Epidemic.” This will be hosted by the Department of Communicative Disorders and Deaf Education at Utah State University on March 27th at the Eccles Conference Center on campus. It will be an all day conference and will be presented by an interdisciplinary faculty of experts who will address issues relating to TBI from the viewpoint of speech language pathologists, audiologists, lawyers, veterans vocational rehabilitationists, neuropsychologists, physiatrists, first responders, and TBI victims.

For further information go to http://tbiconference.usu.edu.

Early registration (before March 14th) is $75 and $25 for university students. Lunch is included. Parking is free.

This is a very timely event. Proceeds will support the Utah State University Student Academy of Audiology international hearing healthcare humanitarian mission.