I'm helping a friend, and the only tool I have is Soundflow.

His space is tiny, and the depth of insulation can't excess 150mm.

So I played with Soundflow, and designed the most simple MSM system :

12,5mm plasterboard
Basic insulation material
12,5mm plasterboard

My question is quite simple, can I trust Soundflow?

I used this software for his absorption coefficient, and the prediction were great. It really helped me solved problems in my room. What about insulation? Is there a better software? I'm reading more about insulation atm

Ok for anyone curious

I compared a design from IR 761 doc (page 331/370) TL-93-263.


And that same design with Soundflow


Results here (left Soundflow, right IR-761)





STC measured by IR-761 = STC-58. STC predicted by Soundflow = STC 54


Will do more tests later

Anyone can explain why, for the same density, do I have two different STC results?

140 mm of brickwall (1800kg/m3) = 252,00kg/m2 STC = 47
220 mm of Plasterboard (1150kg/m3) = 253,09 kg/m2 STC = 44

STL is the same though (mass law)

I've been an acoustic consultant in the UK for around 10 years, can't say I've heard of Soundflow over here. The main software for transmission loss prediction that most people would use is Insul, this has got a decent amount of published results and research behind it. It's generally within 2 to 3 dB of the result though you do need to be a little big careful with bespoke constructions. For a simple lightweight construction like you've attached it'll do the job easily.

You can get a 30 day trial, just search Marshall Day Insul.

Othetwise, if you looking at simple lightweight constructions like you appear to be doing, I would just search for the British Gypsum Partition Selector, or the White Book. This has tonnes of tested partitions which will have sound reduction indices test within a laboratory.

Good luck!
Chris @ ParkerJones Acoustics

Different materials, different critical frequencies.

Chris, Avare, thank you!

Materials with a density of 1800kg/m3 are light-weight where you come from?

Yes, these types of walls are known as lightweight walls.... heavy density but only thin layers of it, say, 4 layers of 12.5mm, compared to a thick 140 to 215mm blockwork wall!

Soundflow overestimates soundproofing when the Rw values go up (I have compared it with several lab tests).

What happens usually is that you get approximate results at low frequencies
but when it comes to mid and high frequencies the results are completely different. SoundFlow gives me much HIGHER results.

SoundFlow has several limitations which should be considered:

The current software version does not support glued or laminated layers, metal studs and similar constructions or flanking effects.

With respect to plates, the current software version is also limited to the theory of thin plates which allows considering structures with a thickness of up to 3 to 4 wavelengths in practice.

The numerical models used in SoundFlow assume that surface elements are large compared to the wavelength of interest. Although SoundFlow accounts for some finite-size effects such as the increased effective surface area due to edge diffraction effects, the prediction accuracy for small surface elements will depend strongly on the properties of the material and the shape of the sample.

In terms of Bass Traps, you cannot predict accurately membrane Bass Traps with it

It cannot model restricted acoustical membranes. Membranes (foils) are infinite in size. Low frequency band absorbers can be done by perforated panels.