AFMG Network Forum

Garry Hall · Member

I am currently evaluating the 30 day trial version. SoundFlow gives values for a 6mm glass + 100mm air + 8mm glass combination as Rw 33. This seems a bit low. I was expecting Rw 40 - 45.

Any suggestions?

Waldemar · Member

Do you have any mesurements? What are the paramters of the glass?
SoundFlow is calculating the Transmission Loss of an infinite large window.
If you have a window in a wall, there is higher loss in a distance from the window,
where the wall is effective also.
The test calculation for a 1 x 1 m² window gives 4 dB higher Loss.

Garry Hall · Member

I have labarotory data from a glass manufacturer. As an example 4mm float glass - Rw 31, 6mm Rw 32, 4mm +100mm air + 6mm Rw 46.

I personally think the values are slightly high for field assessment but possibly achieveble in a test facility. When I run SoundFlow I get the following results for Glass 68 ISO 354 (4m x 3m): 4mm Rw 30, 6mm Rw 31, 4mm + 100mm air + 6mm Rw 29.

The transmission Loss graph visually indicates a much larger tarnsmission loss than the calculated Rw in the Broadband Quantities. Changing the display to table form shows much higher transmission loss values in all 1/3 octave frequencies above 125Hz for the 2 sheets + 100mm air comapred to the 6mm glass.

Waldemar · Member

The Transmission Loss is increased for higher frequencies. But these numbers do not contribute much for the Rw value. The main problem here is, that we do not take the size of window in to account. The ISO size is only used to calculate the contribution due to the radiation impedance of the window in a 0-absorption hard wall (reverberation room).

We do not agree with the last statement. We have the same values in the table and in the graph. If you get other data, please send a screen shot to me personally please.(wrichert@afmg.eu)

Garry Hall · Member

Im may have not explained myself well. The graph and table values are in agreement for the 4mm glass + 100mm air + 6mm glass but the calculated broadband value of Rw 29 is not in agreement with the table and graph.

I have emailed you screen shot.

Tim · Member

Garry,
I've been talking with Viridian Glass (Australia) this morning about their published attenuation data. They have published data on various glass types - including freq. band values. You can see this here - http://www.viridianglass.com/Viridian%20Image%20Library/Knowledge/TechDirect/Sound.pdf
Viridian cannot tell me anything further about how this data was measured - apparently it has come out of Pilkington in Germany and this data is not publicly available.

Interestingly, I have created a structure (assuming 1.8x2.4m sample) in SoundFlow of 6mm Glass68 which provides Rw31, however a structure of 2x3mm Glass68 provides Rw35 - which is more what I'd expect to see from laminated glass.

Waldemar · Member

The broadband values like Rw are calculated from diffuse sound incidence.
To get the 1/3 oct values, which are taken for the Rw you have to select
“Diffuse Field” in “Direction of Incidence”.

Waldemar · Member

To use laminated glass, one has to use the "combinated" physical properties.
SoundFlow 1.0 cannot take laminated sheets into account.

Garry Hall · Member

Thanks Waldemar. The diffuse / angle of incidence option expains the different outcomes.

I am a bit surprised by the results between 4mm Glass 68 - Rw30 and the 4mm Glass 68 + 100mm air + 6mm Glass 68 - Rw29.

It appears from the results that for noise control it is better to have a single 4mm glass than go to the expense of double glazing with a 100mm air gap. The Rw+Ctr performance of the double glazed structure (Rw29, Rw +Ctr -6) is not as good as the single 4mm plate (Rw30, Rw + Ctr -3).

Waldemar · Member

Please kepp in mind, that the results in Soundflow are due to a special mathematical model. For this double glass pane the resonance of the air space between the glass panels dominate the mid range Transmission Loss. For higher frequencies there is a significant higher loss. In the mathematical model there is no influence of the size of the window nor of the specific construction of the frame. So, take the numbers of the result as estimation only. They are most applicable for comparisons, where you want to evaluate changes in the structures. Then you can see the tendency to higher Loss or to lower Loss.

ranti tassia · Member

Hi, I wanna ask about the transmission loss calculation. I'm using ISO 12354 Calculation. As you've said, the results in Soundflow are due to a special mathematical model, Could you tell me hows the software's work? what kind of mathematical model used on this software? I want to know the mathematical model to support my final project. Thank you.