Sound dampened through an object

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In summary, for a sound with an intensity of 1x10^-6 W/M2 passing through an object with a rating of 25dB, the resulting sound intensity would be approximately 1.58x10^-9 W/M2. This is a reduction of about 35dB from the original intensity.
  • #1
dbag123
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Homework Statement
Intensity of sound in a room is 1x10^-6 W/M^2. Object is rated at 25dB. What is the intensity of sound after passing through the object assuming the sound does not go around the object.
Relevant Equations
i=10lg(i/i0)dB
1x10^-6 W/M2 is 60 dB

The sound goes through both mediums --> 25dB *2 = 50dB lost

Therefore the dound after object is 60dB-50dB = 10dB and converting to intensity it is 1x10-11W/M2
is that it?
 
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  • #2
The phrase "Object is rated at 25 dB" does not mean anything to me.

The most obvious interpretation would be that sound passing through the object is diminished by a factor of 25 db. Given the previous problem that you had posed, it seems very likely that this is the intended interpretation.
 
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  • #3
dbag123 said:
Homework Statement: Intensity of sound in a room is 1x10^-6 W/M^2. Object is rated at 25dB. What is the intensity of sound after passing through the object assuming the sound does not go around the object.
Homework Equations: i=10lg(i/i0)dB

1x10^-6 W/M2 is 60 dB
You missed a sign in your 60dB calculation... :smile:

Also, dB need to be referenced to something (your "i0" in your equation). Are you supposed to use 1W or 1mW for the reference power? If 1mW, then the usual notation is dBm to make it explicit that you are calculating the "power above 1mW".
 
  • #4
diminished is the word yes
 
  • #5
berkeman said:
You missed a sign in your 60dB calculation... :smile:

Also, dB need to be referenced to something (your "i0" in your equation). Are you supposed to use 1W or 1mW for the reference power? If 1mW, then the usual notation is dBm to make it explicit that you are calculating the "power above 1mW".
reference is 10-12
or 1mw
 
  • #6
dbag123 said:
reference is 10-12
or 1mw
Really? That's kind of weird, but if you are given that for i0, then your +60dB number is correct for the starting power.
 
  • #7
dbag123 said:
1x10^-6 W/M2 is 60 dB
60 dB is a dimensionless ratio. It cannot be equal to something with units.
 
  • #8
jbriggs444 said:
60 dB is a dimensionless ratio. It cannot be equal to something with units.
1x10-6 is the intensity of 60db is what it refers to
 
  • #9
dbag123 said:
1x10-6 is the intensity of 60db is what it refers to
Both "10-6" and "60 db" are dimensionless numbers. They are not intensities of anything.
 
  • #10
jbriggs444 said:
Both "10-6" and "60 db" are dimensionless numbers. They are not intensities of anything.
what about now 1x10-6 W/m2
 
  • #11
dbag123 said:
what about now 1x10-6 W/m2
That is an intensity. It is not a pure number. You can see that because it has units attached: W/m2.

You can express intensity ratios as pure numbers. You cannot express intensities as pure numbers.

Edit: apologies to both @berkeman and @dbag123 for repeating Berkeman's point more belligerently than necessary.
 
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  • #12
righty. so sound of 60dB is then dampened when it travels through the object. the question is by how much?
once? or twice?
if its twice due to the sound passing through 2 mediums then why is the object not "rated" at 50dB?
 
  • #13
dbag123 said:
righty. so sound of 60dB is then dampened when it travels through the object. the question is by how much?
once? or twice?
if its twice due to the sound passing through 2 mediums then why is the object not "rated" at 50dB?
See the response in #2.

You are the one who has assumed that the attenuation takes place at the interfaces to the object rather than within the object.
 
  • #14
so the ratio by which the object dampens is 102.5 or by 316.2 times
 
  • #15
dbag123 said:
so the ratio by which the object dampens is 102.5 or by 316.2 times
sound after object 0,189dB that is an oddly small number
 
  • #16
but is it right?
 
  • #17
dbag123 said:
sound after object 0,189dB that is an oddly small number
How did you arrive at 0,189 dB?

I am guessing that you took the original power intensity expressed on a scale where 10-6W/m2 is expressed as 60 dB, divided the 60 dB by a factor of 316.2 and arrived at 0.189 dB.
 
  • #18
(1/316.2)*60dB
 
  • #19
jbriggs444 said:
How did you arrive at 0,189 dB?
dbag123 said:
(1/316.2)*60dB
You can divide an intensity by a ratio and get an intensity.
You cannot divide the log of an intensity ratio by a ratio and get the log of an intensity ratio.
 
  • #20
i see. so how would i apply the fact that i know that the sound is dampened to 1/316.2 th of what it is?
 
  • #21
dbag123 said:
i see. so how would i apply the fact that i know that the sound is dampened to 1/316.2 th of what it is?
Divide the intensity (given in the problem statement) by the intensity ratio (which you just calculated).
 
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  • #22
35dB is what i get out
 
  • #23
60-25 is 35 makes sense
 
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  • #24
thank you very much again
 
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Related to Sound dampened through an object

What is sound dampening?

Sound dampening is the process of reducing or suppressing sound waves in order to decrease the volume or intensity of sound. It involves using materials or techniques that absorb, reflect, or block sound waves.

How does sound dampening work?

Sound dampening works by using materials that absorb or block sound waves. These materials can include foam, rubber, or other soft materials that absorb sound energy. Sound can also be reflected or deflected by hard surfaces, such as walls or barriers.

What are some common materials used for sound dampening?

Some common materials used for sound dampening include acoustic foam, rubber mats, fiberglass insulation, and mass-loaded vinyl. These materials are chosen for their ability to absorb or reflect sound waves and reduce noise levels.

Can sound be completely dampened through an object?

No, it is not possible to completely dampen sound through an object. Sound waves can still travel through materials, but their intensity can be reduced significantly through the use of sound dampening techniques and materials.

What are some practical applications of sound dampening?

Sound dampening is commonly used in buildings and homes to reduce noise levels from outside sources, such as traffic or loud neighbors. It is also used in recording studios, theaters, and other performance spaces to improve sound quality and reduce echo or reverberation. Additionally, sound dampening can be used in industrial settings to protect workers from loud machinery or equipment noise.

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