Originally Posted by Dennis Erskine
Bad judgment and the Flu are extremely common as well. If you want to use fiberglass, go for it. It's your room, not mine, and I don't have to listen to the final result.
Hah! Well, I
am absolutely going to have sand in my stage, since that's going to be the final step of my testing and there's absolutely no way I'm going to remove it. Ever.
I'm wanting to do this tests, though, to have quantifiable information on why
you'd want to do that. Not just "it's a good idea" but "it's a good idea because these numbers show the notable difference"
And that's what I'm really trying to figure out now -- HOW do I actually test all this where I could get useful data?
Sound is vibrational energy. Not all vibrational energy is sound and therefore your presumption is false.
My presumptions are often false, so no surprise there! But I want to explore all of this some more.
First, if the vibrational energy in the solid substances surrounding the riser are not detected as sound, then do they even matter? It's a "tree crashing in the forest with nobody around deal" -- if the vibrations are such that I can't even detect them, then should that be something that we're trying to prevent since nobody will even know they are there?
What's the purpose of sand in the stage? Two reasons. One, you have the equal but opposite reaction issue and you therefore want the subwoofer *bonded* to something of significantly more mass than the subwoofer in order for it to perform at its best. Of course, if you're using an undersized, cheap, under performing subwoofer, what the hay.
Okay, to see if I'm understanding this -- the common problem with a subwoofer cabinet flexing is that that energy is "wasted" and thus not being used to push the sound waves. Therefore, you'll have reduced output which translates to reduced SPL. A subwoofer that does not move as much, will transmit more of its energy to the sound waves and thus be "louder". That suggests, then, that I could test that using an SPL meter or an RTA graph? That is, if I have the exact same output level on the sub and the exact same mic location, then I should expect to register a loss in DB when the sub moves from the floor to the empty stage, and then a subsequent rise in DB when the stage is filled with sand? Correct?
I'm very curious at how much mass is "enough". If we assume a 5x13 stage with 2x8s or 2x10s and dual layers of 3/4" OSB, then we're looking between 500 and 600 lbs empty. A typical 12" commercial sub appear to weight around or under 50 lbs. So we see a 10x ratio of mass of sub to stage in this case. Not enough?
Finally, when you say "bonded", do you mean physically attaching the sub to the stage? Or just the weight of the sub pressing down on the stage?
Two, you need to damp the vibrational energy to prevent it from being transferred throughout the structure of the home. The subwoofer should have all of its energy directed to moving air in the room, not moving the structure of your house.
So this is the case where the true test should likely be done outside of the theater. Is this a simple SPL test as well? That is, if I have a sub going at 100dB at 35Hz, then go through the house running an RTA test, then some notable fraction of the measured SPL at that frequency will be coming through the slab. I would expect to see a notable drop when the sub is placed on a sand-filled stage vs directly on the slab.
Just to be clear, I am not in any way suggesting that you are wrong about any of this. I tend to treat what you say about theater building as the "word of god".
But... I'm the type of guy that can't be TOLD something but needs to be SHOWN it. I haven't ever seen any quantifiable numbers that SHOW the differences between stage types and so I want to gather those. That requires that I run the right tests in the right ways or I'm just wasting my time.