John Sayers' Recording Studio Design Forum Archive

Hi everyone!, It's my first post here in more than ten years...that's a loooong time. I have a question that remains unanswered, after a some research, i thought maybe someone here could have the answer. My apologies if this has already been covered before. Here it goes. When i compare the results of a pourous material ( say 3" of Roxul Safe'n sound) using the online porous absorber calculator ( and entering all the material parameters) and the published absorption value from the manufacturer spec sheet, the results don't match. There are substantial differences mainly in the low end region. That raise the question: Who's right? The calculator or the manufacturer?

any hints welcome
regards

The Calculator/Predictor has various Models. Also try different angles of incidence. Around 70 degrees may show results closer to the measured and 'optimistic' ones.

also, bear in mind, the manufacturer is using tests based on certain industry standards - thickness, air temp, backing, humidity, etc so the results are measured to that/those specs. how that translates into performance in a given situation: best guess using a model, or empirical testing to optimize. so the published specs are just that, and they should reference the standard their testing to which usually includes fire safety, health warnings, temperature insulation, acoustics, etc etc so check their spec sheet. likely to find acoustics testing is limited down to 125hz and 1 or 2 mounting options.

Dan and gulfo thank for the answer.

DanDan wrote:The Calculator/Predictor has various Models. Also try different angles of incidence. Around 70 degrees may show results closer to the measured and 'optimistic' ones.

When you say "measured" are you talking about in practice or in the labs?

Which is the best for predicting real world outcomes?

Measured in the Labs. I also think 70 degress is quite representative quite a bit of the real world incidence.
Lab tests are typically done to standards which are not optimised to represent our use. They typically don't include an airgap. The area of tested absorber is typically contiguous, omitting the effect of multiple exposed edges in our word. Finally we avail of the vast magnification of corner placement. Labs stay away from corners.

The models used in the online predictor are from Lab Testing afaik.

Over time one gets to see manufacturers claims, studio build results ongoing, etc. etc. One gets an averaged sense.
I would trust the predictor to select the optimum GFR for the varous thicknesses. But also remember the 'drumhead' damped membrane effect of corner staddling rigid fibre.
And the lack of it with fluffy deep traps.