Noise reduction questions

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Re: Noise reduction questions

Post by RadulescuPaul »

It seems like a bit complicated if I think about it.
Let's say you would want to ask the total sound level in a room with different wall structures, doors , windows of you know the external noise.
You have the attached formula.
Lm is external noise
Si is the surface of different separating elements like walls , windows etc.
Ri is the insulation coefficient of each element
A is absorption area of the enclosure

I think you could add the hole in the wall as a 0 dB Ri and take the surface into account.
I don't know about another way to do it but I can research a bit
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Re: Noise reduction questions

Post by johnb »

funkface42 wrote: Wed Dec 09, 2020 5:42 pm First, I am very happy to have Mr. John Brandt's forum, he has provided a lot of knowledge and inspiration for me :ugeek:

But I have a question,
Does anyone know how to calculate the reduction of soundproof value of a soundproof wall construction, due to a hole in the wall.
I've read from a book or heard from a lecture on youtube, but I forgot where.. :roll:

hopefully my question is not against the rules on this forum

Thanks :P
Page 353 of Architectural Acoustics by Marshall Long gives the equations and examples.
"Sound Propagation through Multiple Partitions
When two reverberant rooms are separated by a partition consisting of two separate components,
such as a wall with a window in it, each having a different transmission loss, a
composite transmission loss may be calculated based on Eqs. 10.4 and 10.6
Using this expression, it soon becomes clear that the component having the lowest
transmission loss will control the process. It is much like having a bucket full of water with
several holes in it. The largest hole (lowest transmission loss) controls the rate at which water
flows out. Let us take, for example, the case where a 3' x 4' (915 mm x 1220 mm) window
having a 25 dB transmission loss occupies part of a 20' x 8' (6.1 m x 2.4 m) gypboard
and stud wall having a transmission loss of 45 dB. The composite transmission loss may be
{formula} = 35.5 dB
Thus, although the window has a much smaller area than the wall, it significantly reduces
the overall transmission loss of the composite structure.
Composite Transmission Loss with Leaks
An even more dramatic example of a reduction in composite transmission loss is that produced
by a zero transmission loss path such as an opening under a door. Using a 3' 6'8" (0.9 m × 2 m) solid core door having a transmission loss of 30 dB and a 1/2” (13 mm) high
opening under the door with a transmission loss of zero dB (at high frequencies), we obtain
an overall loss of = 21.4 dB
In this case, 8 dB, more sound energy comes through the slot under the door than through
the remainder of the door. Figure 10.2 shows the effects leaks on the overall transmission
loss of a structure. The relative area of the leak when compared with the overall area of
the partition determines the composite transmission loss of the structure in the diffuse field
This is a book you MUST have if you are going to do this kind of work. ;) It's linked on my resources page.
All the best!
John H. Brandt
Recording Studio, Performance Hall, & Architectural Acoustics Consultants
"Twenty Thousand Dollars worth of Snap-On Tools doesn't make you a Professional Diesel Mechanic"
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