How to Measure Earmuff Volume Regarding the Occlusion Effect?

I have tried reading up on the occlusion effect lately, and one especially good paper I have found about it:

http://www.protectear.com/wp-content/uploads/2010/10/earlog19.pdf



However, when I measured the physical volumes of the largest ear protector I have (and know about), the Peltor X5A, I found that the free inside volume, the volume not occupied by foam inside the muff (yellow space in my drawing under), was only about 100cm^3.

When I measured the outer volume, that means the volume of the empty inside space + the foam + the outer plastic shell (yellow+grey space+black lines in the drawing), I found it to be about 400cm^3.



Because the paper says that an "occluded volume" of about 300cm^3, I wonder witch one of my measurements are what people mean when they talk about "occluded volume". In short, is the foam to be included in the volume measurement or only free space/air?

I have seen this term "occluded volume" be used also in other papers, but does anyone know how it is measured correctly?

 

Did you ever figure this one out, @K.A.?

 

@ajc, unfortunately not yet. I ended up sending an email directly to on of the authors I found mentioned in one of the papers about this, but haven't received a follow up answer.

https://www.researchgate.net/figure...and-2-calculated-as-the-occluded_fig1_5923418

Summary from conversation:

Me:
In your publication it says;
The volume given for the earmuffs is the load volume, which is not necessarily the same as the internal volume of the earmuff itself.
But what is the definition of "load volume", how do we measure this on a specific earmuff, e.g. Peltor X5A, which is the biggest mainstream earmuff?
By my own measurements, X5A has 100cm^3 of empty space (air) inside, but also about 300cm^3 of foam and rubberlike dampening material, but what is then the "load volume"?

Author:
The difference between the internal volume and the load volume is that the pinna will fill up part of the volume inside the ear mull, thus lowering the air volume that is loading the opening of the ear canal. One way to measure it is to fill the earmuff with water, place a ear (an artificial preferable) in the earmuff, and then measure the remaining water volume.

But it didn't really answer the question all the way, so I wrote back:

I do understand now by this explanation the difference of the loading volume and internal volume.
One thing however that it still a bit unclear to me/us, and that is whether the sound proofing foam inside the earmuffs are to be included or excluded when measuring the "internal volume"? Some earmuffs have quite big enclosures but are almost totally filled with foam, while others have more air inside and foam only glued to the outer shell/enclosure.

PS: In your published paper figure 3 shoes that a volume of 300cm^3 will have a low occlusion effect, but is this 300cm^3 on each ear or 150cm^3 on each side (right and left ear) totalling 300 when added?

I haven't gotten an answer back on this yet...