Originally Posted by bossobass
I wonder if you can tell the resonant frequency of my wood frame floor system in my HT space?
I don't think I'm able to find the resonant frequency of your floor by watching the frequency response of your subwoofers.
But there is definitively something at about 5 Hz which is also visible in the close mic measurement. Do you have a long corridor or something like this? When I open the door of my home theater room there appears a strong mode of the corridor < 10 Hz. And even in the closest mic measurements I could always identify the room modes.
You often stated that in your room it is a big difference when playing the single digits. In my room I could not hear/feel a difference at all when activating a high pass at 10 Hz. Maybe it is my lack of experience with the ULF. But is it possible that your resonance at 5 Hz amplifies the perception? Usually resonances have a big impact on perception. Just an idea...
As I've said in other threads on this subject, it doesn't take much movement underneath you to leap to a whole new experience in movie watching.
I agree! No earthquake like vibration is necessary to give a noticeable effect. The passive riser is such a difference to the concrete floor that I can barely describe it.
I also was involved in the discussion years back where some claimed that a resonance could cause a cancellation at that frequency, explaining Ricci's FR suckout around 10 Hz. I argued for proof because I'd never heard of that in anything I read on the subject. When a resonance is externally excited, the result is always a magnitude increase, never the opposite.
I think so, too. A very narrow "suck out" is commonly caused by cancellation. Room modes are the best example.
I can only imagine that something resonates with a phase shift and cancels the original signal. But this phase shift has to be 180° and I never found an evidence, either. I fact several types of absorbers work with resonances and none of them "sucks out energy" up to a notch.
What was the formula you used for calculating the weight to spring isolators?
There are several mathematical principle I used:
- F = k * X (Hooke's law
= m * g (force of gravity
- n springs in parallel behave like one spring with kall
= k / n. Or the other way around the force on one spring is F = Fall
- balance point of the riser is at about 75 % of its length (strongly depends on the specific riser and seats).
I made an Excel sheet with these principles and calculated the compression distance for different spring models (with their datasheets). So I could choose the right one for my riser.
The 3 springs in the front are nearly half as stiff as the 3 springs in the back. This is the result of the balance point, because the couch will be placed in the back.
Originally Posted by WereWolf84
@Nils, how loud do you need to run your setup in order for to feel your riser move?
I can feel it down to -25 dB relative to reference SPL. I used the dragon crash scene in "How to train your dragon". When I put the chair on the concrete floor I feel nothing even at reference SPL.