PET absorbers for low frequency?

[ripmixburn]

I'm in contact with a company who produces panels made from PET (Polyethylene Terephthalate, not domesticated animals). They send me their performance data for a 15mm (0.59 inch) thick panel… Does the low frequency absorption seem unusually high to you too or am I misreading it?

 

[abdo123]

the density is really huge, this might not be something you could hang on a wall. keep that in mind.

 

[Sancus]

0.56 absorption coefficient at 100hz for a 0.59" panel? Um, I really really doubt it. That is comparable to like 3" rockwool. This would be some majorly magic material unless there is some kind of unmentioned installation requirement. The density is ~50% higher than the densest rockwool but there's no way that accounts for a 6x performance improvement at 100hz.

 

[ripmixburn]

I think this might be for a ceiling (cloud) installation but wouldn’t that be measured in Sabins?

 

[abdo123]

I think this might be for a ceiling (cloud) installation but wouldn’t that be measured in Sabins?

It says installation type E-200, perhaps it’s worth checking what that means?

 

[youngho]

It says installation type E-200, perhaps it’s worth checking what that means?

It means mounted in front of a sealed air cavity 200 mm in depth. Not likely for most people's use.

 

[Sancus]

It means mounted in front of a sealed air cavity 200 mm in depth. Not likely for most people's use.

Ohhh that makes a big difference yeah

 

[ripmixburn]

Here’s a PET bass trap for sale in the UK that claims some absorption down to 50 Hz "due to its 150mm depth and innovative design with multiple gaps at the rear".

 

[DonH56]

If they are what I think, these type of absorbers are often called "membrane" absorbers. I have a few papers on them, always thought I might try to build a few but never had the time. Essentially, if it is what I am thinking, they create a panel with lots of little "holes" that act as resonators (absorbers) at specific frequencies. That allows high absorption without a thick panel, and also allows them to be designed to target specific frequencies and/or have a range of holes to cover a broad bandwidth. There are some commercial versions but I do not recall the companies -- seems like Stillpoints (the company making the isolation feet) makes some? The others I have seen are by professional (not consumer) oriented companies, I think...

 

[Saponetto]

Perhaps it's one of my many mistaken thoughts, but I always meant the room as a bigger replica of the volume within a speaker box.
If I am able to add acoustic wool in a box simulating it's bigger by increasing the time needed to the sound to reach the box inner reaches, I can apply the same principle in my room.
At the end of the day, if canceling resonances is -so- difficult, just getting the stationary waves moved away (delayed) from my listening point is for me a good result.

 

[abdo123]

If they are what I think, these type of absorbers are often called "membrane" absorbers. I have a few papers on them, always thought I might try to build a few but never had the time. Essentially, if it is what I am thinking, they create a panel with lots of little "holes" that act as resonators (absorbers) at specific frequencies. That allows high absorption without a thick panel, and also allows them to be designed to target specific frequencies and/or have a range of holes to cover a broad bandwidth. There are some commercial versions but I do not recall the companies -- seems like Stillpoints (the company making the isolation feet) makes some? The others I have seen are by professional (not consumer) oriented companies, I think...

I don’t think so, these absorbers claim a very broad range of absorption.

 

[pozz]

I'm in contact with a company who produces panels made from PET (Polyethylene Terephthalate, not domesticated animals). They send me their performance data for a 15mm (0.59 inch) thick panel… Does the low frequency absorption seem unusually high to you too or am I misreading it?

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It's mounting type E, which means tested with an airgap, and the number after the E is the airgap in millimeters. That combined with PET being plastic sheeting is why there are resonant peaks. The actual test report would have more description about the procedure and room, which would help you understand how to get similar results. If, for example, you mounted this directly to a wall, the absorptivity would drop significantly.

 

[Frgirard]

I'm in contact with a company who produces panels made from PET (Polyethylene Terephthalate, not domesticated animals). They send me their performance data for a 15mm (0.59 inch) thick panel… Does the low frequency absorption seem unusually high to you too or am I misreading it?

View attachment 183337
View attachment 183338

If They are measured in reverberant room, they have poor performances. Why nothing under 100 Hz?
If they are measured in impedance tube, this is revolutionary for 15 mm.
Use proven material such as Gik, Rpg, Caruso isobond, Basotect.

 

[dasdoing]

the density of the core is crazy. this would basicly be a sheet of pet, like the one used for a bottle. balsa wood!!! has lower density.
I would ask for the lab report. they wouln't fake it.

here is a calculator for a membrane absorber http://www.acousticmodelling.com/helmholtz.php

 

[dasdoing]

here is a piece of 30kg/m3 pet. I put the SPL meter to show that this is allready pretty rigid

 

[Frgirard]

Our living spaces are full of allergens. Glass or rock fibers avoid this problem.
BS Marketing.

 

[MCH]

I trust all materials allowed to be used in construction are safe if used properly (=important). That said, from the chemical point of view strictly, polyester would be a safer alternative over melamine formaldehyde foam or fibers glass/others.
As someone pointed out in other thread, at the end of the day you have all these already in air conducts etc in your home or office...

 

[Vict0r]

I chuckled at your "not domesticated animals" joke and instantly wondered what a cow in my office would do for room acoustics. I'm sure cows are pretty dense.

 

[Frgirard]

I chuckled at your "not domesticated animals" joke and instantly wondered what a cow in my office would do for room acoustics. I'm sure cows are pretty dense.

What is the gas flow resistivity of a cow? With and without horns.

 

[dasdoing]

Is it me or is post number 16 and add-bot?