I linked this thread in popalock's build after Bosso posted some interesting information that related to the discussion that formed here. I still stand by what was said by myself and Bosso, that at VLF sound behaviour remains as sound waves no different than LF, MF, and HF, except that in the typical home environment the wavelengths are so long they become no modal and entirely constructive, yielding increased SPL as frequencies decrease. The increase is proportional to the lossyness of the reflective boudaries, however. As a result of my post, LTD02 posted the below.
Originally Posted by LTD02
it is not according to drs. rienstra and hirschberg who are at one of the most prestigious technical universities in europe. one is a physics and math professor, the other is a physics and fluid/gas dynamics professor.
see sections 2.2.3. on compactness and 4.1 on plane waves (read through to the first footnote, about one page) where it is discussed how below the critical frequency, air, which is normally a compressible fluid, behaves as an incompressible fluid and pressure is pretty much uniformly increasing and decreasing everywhere at the same time.
if you'd like to discuss it some more, revive the other discussion thread.
Thanks for your post LTD02. Previously in this thread we were told that the increased SPL as frequency decreases (relative to the anechoic response) was a result of Pressure Vessel Gain (PVG), then from a huge Hemholtz Resonator in the room, the sympathetic resonances. And now the above.
I've read the noted sections in the provided link and fail to see anything in there that changes my opinion of how sound works. Perhaps you could clarify LTD02.
In Section 2.2.3 the authors discuss "Compactness". What I get out of this section is that as wavelength becomes proportionally large, the Hemholtz number (He) becomes much less than 1 and the fluid can be treated
as an incompressible fluid in the compact region. The section goes on to call it an acoustic field with waves.
In Section 4.1 on Plane Waves, the section describes wave behavious in a infinitely long pipes for the purposes of duct acoustics, and goes on to say that the acoustics may be approximated by that of an incompressible fluid.
I feel that these first and foremost don't offer support to the idea of PVG and also they are not applicable.
I hope raising up this thread was a good idea