Thank you John. This series has shown me that I am even more clueless than I thought I was, about acoustics. Thankfully a listening or recording room doesn't need to be perfect. It just has to be good enough. : )
Thanks for great videos and talks John and Ron. What do you guys think about Helmut Fuchsˋ real life tests of VPRs and BKAs? To me the VPR topic seems quite well researched…
Seems that way. If they are tested properly in a laboratory capable of testing low frequency then we'd know. It's all speculation until we have valid data. They haven't been tested properly and that's all I know.
@@yellowledbutter There aren't any, I've looked. So in order to test to 25 Hz you need a laboratory of at least 2000 cubic meters. But it's not just the volume that's important. You need to know where the modes are at the low frequencies. So modal density can be described by the number of room modes in a given band, but it's not just the number of modes in that band. If all the modes are in a band or at the same frequency, you're not gaining anything. So you want to have those modes spread out at various portions of the band, and ideally, we'd like them to be almost uniformly distributed throughout the band.
@@JHBrandt not only you have the papers, you also have a detailed description of the experiments and results in Fuch's book about silencers and absorbers.
Here is an excerpt of Fuchs' book (translated with DeepL) that described the testing of the VPRs, I hope that information is helpful: However, the problems discussed in Chapter 2 make it necessary to first qualify the measurement room for frequencies below 125 Hz. Since it has been shown that the usual slanting of the opposite boundary surfaces and the installation of additional diffusors do not contribute significantly to the equalization of the sound field at low frequencies, the only solution is a suitable damping of the room modes, as described in detail in [17]. For the measurement of the absorption coefficient, 3 VPR modules with the dimensions 1.5x1.0x0.1 m each with 1 or 2.5 mm thick steel plates in closed frames in two lower corners of the 392 m3 reverberation chamber of the IBP have proved to be suitable to obtain well reproducible results at least up to 63 Hz (measured in thirds). Figure 5.15 shows the reverberation time of the damped reverberation room shown in Figure 5.14 without the sample in comparison to the room without the sample. The corresponding mean equivalent absorption area in Fig. 5.15 below shows that the damped room still easily meets the requirements of the standard if only the limit curve defined there is extrapolated horizontally up to 63 Hz.
Great video. Very deep insights. Thanks to John and Ron. I have a question with regards to diaphragmatic / membrane absorbers. At what sound pressure level would these begin to work and at what SPL would these stop working? In other words would these membrane even work at low SPL values, or do they only work at higher SPL's? Since these purely work on pressure, so at what SPL range would these be most efficient?
GREAT question! The BassMod diaphragmatic traps work at very low SPL. If there is sound, they resonate. The mass/inertia of the panel is extremely low. I'll interview Richard Lenz in the coming weeks. I'll ask him about that and many other things. Stay tuned! 😁
i dont get whats the big problem to get data reg the VPR`s? its just the polyester stuff + cold rolled steel plates. put the stuff in rons lab and voila.
Yes, please! Somebody pay to have it done. I spent about $30k getting testing done and shall probably spend another 30k. Do it. Then we will know if they work or not. From experience and data on how these things work... the VPR things probably don't work very well at all.
