Originally Posted by bossobass
It's a tradeoff.
There's no doubt that the floor (and ceiling and walls) physically react to the ULF pressure waves. Consider that the subs are dual-opposed, so that they don't in any way jump up and down. Consider also that they are in corners, where the structural integrity of the floor is highest (as opposed to the middle of the floor where the most deflection would occur). Then, consider that the room is on a 2"x10" @ 10" OC structure, supported in the center by a sandwiched quad-LVL beam and the entire floor system is 24'X27'…
Then that pressure wave is moving the entire floor system all by itself, thus, the tactile feel.
OTOH, concrete construction has up to 20 times less transmission loss. Here's a case in point. A while back I put in a pretty decent HT for a friend in her basement, which I had completely remodeled some years ago, so I already had the scaled drawings and construction details. 2 of the walls are concrete with studs, insulation, sheetrock and panelling over them. The floor is also a poured slab. The room is close to 2900 cubes with a 4' doorway that's open to the rest of the basement floor, an approx additional 5800 cubes.
I put a small dual-opposed 15" sub signal shaping through a Marchand Bassis and powered by an American Audio big iron amp. I set the Bassis according to the close mic and standard room gain profile, then measured the room before any tweaks, smoothing EQ or level cal.
I saved that measurement and have overlaid it onto a graph that has various subs I've built in various configs in various placements, all in my HT space:
Using the same sig shaping boost pattern I use in my own room, she gets +10dB more return in single digits than I do.
Now, that can be overcome with multiples, but if you look at the original measurement, that single digit peak was 103dBSPL. With a single 2X15" sub.
So, that's the tradeoff. IMHO, the ultimate coup is to build your HT in a basement, but on a suspended wood frame floor. That way you get the benefit of far less TL with the tactile effect.
The above post shows the impact of transmission loss compared to a suspended wood floor versus concrete construction.
We've always known that the construction materials that encase your HT room does have an impact on db in your room. Where you have lossy construction, you will get less gain as compared to dense material like concrete or brick. The current ULF score methodology does not currently consider the construction of your HT walls and floor. So I'm going to take a shot on how this might be integrated in:
Currently, to calculate your ULF score we need two variables: Room Size and Subs. Trying to keep this simple, we could add 1 more variable; # of concrete/brick surfaces. From the post above, it looks as though from 10-20hz, there is an avg of 6db gain compared to the single raven. The HT owner has 3 surfaces that are concrete (2 walls and floor). Generally speaking and being conservative, what if we say for every concrete surface of your room, we add 2db to your room output. Let's take some examples on how this might change the current scoring:
Using the log calculation, for every 2db gain, we would multiply the number of SIs for HT by a certain factor:
1 concrete wall = 1.26
2 = 1.58
3 = 2.00
4 = 2.51
5 = 3.16
6 = 3.98
JapanDave's HT is all concrete; walls, floor, and ceiling
6 concrete walls = a factor of 3.98
3.98 * 23.5SI = 93.6 SI
2900cf / 93.6 = ULF Score of 31
GP 1/8 space estimate = 134.6db @ 10hz
MK's HT has 4 concrete surfaces (3 walls, floor)
4 concrete walls = a factor of 2.51
2.51 * 12 SI = 30.1 SI
1510cf / 30.1 = ULF Score of 50.1
GP 1/8 space estimate = 124.8@10hz
I have 3 concrete surfaces (2 walls, floor)
3 concrete walls = a factor of 2
2 * 4.4 SI = 8.8 SI
1900cf / 8.8 = ULF Score of 216.4 (upgrading me to 5 star)
GP 1/8 space estimate = 114.1@10hz
Basshead has 1 (?) surface; concrete floor
1 concrete wall = a factor of 1.26
1.26 * 3.6 SI = 4.5 SI
2400cf / 4.5 = ULF score of 529 (remains 4.5 star)
GP 1/8 space estimate = 116.9@16hz
Based on the above examples, it seems reasonable. The only way to see how well it works is to go through more member examples.
Check your score based on the new methodology above...does it make sense compared to what you've measured?
Depending on the feedback will determine if this is instituted or not.