Acoustic terms

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sg400

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Does anyone here know the relationship between Transmission Loss (TL) and the Sound Transmission Class (STC)? Is it mathematical or empirical?
 
sg400 said:
Does anyone here know the relationship between Transmission Loss (TL) and the Sound Transmission Class (STC)? Is it mathematical or empirical?
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I thought mathematical and empirical went hand in hand.

Maybe you mean to ask if it is theoretically calculated or empirically found?

Either way, I'm not sure, but maybe the question makes more sense now.

Looking forward to the answer.
 
Trying to help...

According to the information I've been able to gather in the last three minutes:

It appears that:
Sound transmission loss (TL) is a laboratory measure of a barrier's ability to reduce the flow of sound energy through it. It is the ratio of the sound energy striking one surface of the barrier to the energy radiated from the opposite surface, and it ignores diffracted sound that bends around the top or ends of a free-standing barrier. The primary determinants of TL are mass (lb/sq. ft.) and leaks (air paths through the barrier). Essentially any barrier material with a mass of at least 4 pounds per square foot that is also free of leaks will function well as an outdoor, free-standing noise barrier. TL is measured by ASTM E-90 which utilizes a sealed opening fitted with the test panel. Its relevance to an outdoor, free-standing barrier is minor.


Sound transmission class (STC) is a rating number derived from TL readings at 16 different frequencies, in accordance with ASTM E-90 and ASTM E-413. It is a laboratory measurement in a sealed opening taken in such a way that there is no diffracted sound reaching the receiver. Plywall has been tested per ASTM E-90 and E-413, resulting in a Sound Transmission Class of 38.
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-- From http://www.frtw.com/products/noise/pw_tech_acoustical.html

After reading this, it appears empirical, since lab work is done.

Boring stuff after this point.
Hypothetically, if you gave me some untested (eg random or theoretical) TL readings for 16 different frequencies, I could pump out a calculation based on that information. This STC would definitely be theoretical. If I took an actual measurement of TL and then derived the STC via equations and actual data, then the TL would be empirical but the STC would be theoretical.

But, if the website is correct: (STC)"...laboratory measurement in a sealed opening..." Then, since they are doing measurements with instruments, then it is empirical.

I think I almost confused myself. I think the mystery is in the definitions of theoretical and empirical. ;)

Another way to look at it:
A) A circle with radius x.
B) Using radius x, calculate the circumference of the circle. This is not empirical since no measurements were done.
C) Using tools and a whole lot of patience, measure the circumference of the circle. Empirical.

B and C could be the same result. If the input is right (A), I don't see a need to measure (C), when you can just use the equation(B).

So I guess you asked a loaded question. The relationship between TL and STC is not fixed at either theoretical or empirical.

(Now of course, since I have no experience with these two things, I could be completely wrong. Someone let me know if this doesn't jive.)
 
Thanks D. I guess that after all that what I really wanted to know was the relationship between the two numbers. It seems to be direct,meaning the hight the STC the higher the transmission loss (TL) at a given frequency. Does that sound right? Some books seem to us the two values interchangably and I wanted to be sure .
 
Thanks D. I guess that after all that what I really wanted to know was the relationship between the two numbers. It seems to be direct,meaning the higher the STC the higher the transmission loss (TL) at a given frequency. Does that sound right? Some books seem to us the two values interchangably and I wanted to be sure .
 
sg400 said:
Thanks D. I guess that after all that what I really wanted to know was the relationship between the two numbers. It seems to be direct,meaning the hight the STC the higher the transmission loss (TL) at a given frequency.
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GENERAL SOUND ISOLATION CRITERIA
LOCATION USE MINIMUM STC
Light duty warehouse (70 dB)
Executive offices 50 dB 20
Normal offices 55 dB 15
General offices 60 dB 10
Shop offices 65 dB 5
Light manufacturing (80 dB)
Executive offices 30
Normal offices 25
General office area 20
Shop office 15
Medium manufacturing (90 dB)
Executive offices 40
Normal offices 35
General office area 30
Shop office 25
Heavy manufacturing (100 dB)
Executive offices 50
Normal offices 45
General office area 40
Shop office 35



STC VALUE OF STANDARD COMPONENTS
MATERIAL STC
3/16" TEMPERED GLASS 25
1/4" LAMINATED GLASS 35
1/4"LAMINATED GLASS - SPACED 2" - 3/16" GLASS 45
1/2" INSULATED GLASS 32
HOLLOW CORE DOOR 25
SOLID CORE DOOR 35
3/16" HARDBOARD WALL PANEL 25
5/8" GYPSUM WALL PANEL 35
SOUND SILENCER WALL PANEL 45
Roof deck with mineral tile ceiling 35
SINGLE SHEET 18 GAUGE STEEL 30
SINGLE SHEET .O25 ALUMINUM 19
SINGLE SHEET PLYWOOD 1/4" 22
SINGLE SHEET LEAD 1/16" 34

From http://www.nationalpartitions.com/engineering/sound.html
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"...The amount of incident sound that a barrier transmits can be described by its sound Transmission Loss (TL)."
"...It should be noted that there are other ratings used to express a material's sound transmission characteristics. One rating in common use is the Sound Transmission Class (STC). STC is a single-number rating derived by fitting a reference rating curve to the TL values measured for the one-third octave frequency bands between 125 Hz and 4000 Hz. The reference rating curve is fitted to the TL values such that the sum of deficiencies (TL values less than the reference rating curve), does not exceed 32 dB, and no single deficiency is greater than 8 dB. The STC value is the TL value of the reference contour at 500 Hz. The disadvantage to using the STC rating scheme is that it is designed to rate noise reductions in frequencies of normal speech and office areas, and not for the lower frequencies of highway traffic noise. For frequencies of traffic noise, the STC is typically 5 to 10 dB(A) greater than the TL and, thus, should only be used as rough guide."

From http://www.fhwa.dot.gov/environment/noise/3.htm
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So, according to that last site, it seems we have the answer. Roughly, the STC is 5 to 10 dB higher than the TL.

The .gov site appears to be easier to understand. They also have pictures!!
 
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