Decibels

How to solve a decibel equation. 

Decibels are one of the most confusing units of measurement that we use. It’s not like other measurements in that it stays the same every time. It’s not a set size or distance . The thing you must understand is that a Decibel is a relationship between  two values of power.

Generally the numbers that are being compared are of a vastly different magnitude.

Think of human hearing. You can hear your finger brush a paper as well as a gunshot. To compare the sounds to one another would be like comparing the softest audible sound (0.000000000001 watt/m2) to a sound that will actually cause pain in your ear (1 watt/m2).

The numbers are so far apart that we need a way to compare them that is easily understood. This is where Decibels come in.

If a sound is 10 times more powerful (10dB) than the original sound  it sounds twice as loud. If we only double the power (3dB),  the change might not even be noticeable.

Decibels are a generally a ratio between units of power, intensity or amplitude. 

If the decibel is positive then the unit is increasing. 3dB means twice as big.

6dB = 2 x 2 = 4X the original

9dB = 2 x 2 x 2= 8X the original

20dB = 10 x 10= 100X the original

30dB = 10 x 10 x 10= 1000X the original

 

Positive and Negative Decibel Conversion Table

Ultrasound decibel conversion chart for physics. Positive and Negative decibels.

 

Example 1. If Intensity or Amplitude has a factor of 4 = how many decibels? 

Answer: 4 x or 2 x 2 = 6dB

Example 2. A reduction of intensity to 1/2 its original value is what in dB?

Answer: – 3dB

Example 3. -10dB means that the intensity is reduced to what portion of its original power?

Answer: 1/10

 

Ultrasound decibel practice exam

Congratulations - you have completed Ultrasound decibel practice exam.You scored %%SCORE%% out of %%TOTAL%%.Your performance has been rated as %%RATING%%
Your answers are highlighted below.
Question 1
For every 3dB the intensity will what?
A
Double
B
Increase 4x
C
Halve
D
Increase 10^2
Question 2
A reduction of intensity to 1/2 its original value is what in dB?
A
-6
B
6
C
3
D
-3
Question 3
Negative decibels show that the intensity is what?
A
Increasing
B
Stays the same
C
Decreasing
D
Halved
Question 4
A reduction of intensity to 1/8 its original value is what in dB?
A
3
B
6
C
9
D
-9
Question 5
For every 10dB the intensity will what?
A
Decrease 10x
B
Increase 100x
C
Increase by 1/2
D
Increase tenfold
Question 6
Positive decibels show that the intensity is what?
A
Stays the same
B
Increasing
C
Halved
D
Decreasing
Question 7
If the starting intensity is greater than the ending intensity then the gain in dB is what?
A
- 3dB
B
Negative
C
3dB
D
Positive
Question 8
If the final intensity is greater than the original intensity then the gain in dB is what?
A
- 3dB
B
Negative
C
3dB
D
Positive
Question 9
-20dB means that the intensity is reduced to what portion of its original power?
A
1/10
B
1/100
C
-10x
D
10x
Question 10
10dB means that the intensity is increased by what compared to the original power?
A
-10x
B
10x
C
1/100
D
1/10
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I am the founder and lead Instructor here at ExamRefresh.com. I strive to help those that are entering the field of Ultrasound to be the best that they can be. Ultrasound is my passion.

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Comments

  1. HI Mr Franco i will love to take classroom class to prepare ARDMS HOW CAN I FIND OUT WHERE TO CONNECT WITH YOU, I AM LIKE YOU Ultrasound is my passion, i had the chance to practice out the US for more than 12 years, now i am back, i need to take the test, i had see your videos and i live it, hope you can help me.

    • I have been talking with a few people about the best way to do some classroom training. Maybe either an online webinar for each exam topic? Still not sure what is the best way. I am in washington state so if I did do classes it would be up in the northwest.

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