Originally Posted by Mark Seaton
A diaphragmatic bass trap works in exactly this manner. A tuned bass trap is in essence a ported box with the right amount of internal stuffing and flow resistance. How is this not the sort of behavior described?
It hasn't been described at all. There's just the statement, standing by itself. Doesn't a sounding board act in exactly the opposite manner?
I don't think anyone has asserted this to be the only way we can see deviations from an ideally sealed chamber. Lossy or resonant boundaries will all deviate from an ideally sealed space or a set of confining boundaries. Once again, a definition of multiple boundaries each having various real-world characteristics does make for a model that applies over a wider bandwidth, but that doesn't invalidate the fact that rigid enough boundaries converge at some low frequency to the same function as a confined space less than 1/2 wavelength in dimension. That's all I've seen argued.
So, you (and everyone) agree with this:
Originally Posted by MBentz
Sympathetic vibrations below the modal region should always cause suckouts - conservation of energy would be violated otherwise.
I'm looking for a yes or no, not an answer with a bunch of 'ifs', like 'if the wall is properly damped', etc. How can a floor cause a suck out at its resonant frequency if the sound from the sub is pressurizing the entire room at the speed of light or whatever the heck you're discussing at this point?
This feels like we're all agreeing that the temperature is the same and the humidity has increased, but you're arguing that there's no more water vapor in the air.
Is there some revolutionary, or at least different, model, quantification or perspectivce which you feel better predicts the behavior many have documented at VLF in their rooms?
Of course there is an alternative explanation. It's in no way revolutionary and it doesn't require a constant evolution of new explanations when it's questioned. All room influences across the subwoofer bandwidth result from reflections, transmission losses and resonances.
Just because everyone is saying something this week doesn't make worth more than the price it cost to say it in a forum, and to be honest, the humidity/water vapor remark with the confused icon is typical of other's responses and not something I expect from you.
Take the "sealed room" aspect. Conventional wisdom has been that the more sealed the room, the more pronounced the pressure pot effect. Cool, so if I open a window and a couple of doors, the effect will be lessened. Nope, it actually increased. The data is explained away as 'opening a door or a window turns the room into the interior of a bandpass sub'. Later, the explanation changes to some nonsense about the pressure moving so fast that it can't escape the room through an open window.
Conventional wisdom says that a subwoofer pressurizes a room below the 1/2 wavelength-is-greater-than-longest-dimension frequency. So, I open some doors, but that somehow doesn't change the longest dimension of the room or the transfer function of the room.
Since the longest dimension of the room turns the sub/room relationship into a pressure pot, it won't matter where in the room you place the sub. Again, measurements prove otherwise but that's acceptable.
The so-called modal frequency doesn't correlate with room gain in any measurement I've seen, but that deters no one in the pressure pot camp.
Since we have the pressure in the room increasing and decreasing everywhere at once at 5x the speed of sound because the air is now water, we have every boundary vibrating in sympathy and if one of those boundaries is vibrating at its resonant frequency, that will always cause a suck out because of the law of conservation of energy.
And, never mind that all floors, all ceilings and all walls are of exactly the same construction for half a century, there is suddenly a huge variable in the damping of those boundaries. Josh's "suck out" at 12.5 Hz is said to be caused by the floor sympathetically vibrating at its resonant frequency. But, when he adds 3 subs, the suck out is halved and the center frequency of the suck out shifts, yet the floor vibrating story still holds.
Sorry, but I'm not buying that everyone is in agreement with this stuff.Edited by bossobass - 8/17/12 at 7:13am