Post by Michael Lawrence on Jul 18, 2018 17:56:28 GMT
Okay, answers from Ethan. He had to call me back because he was busy getting beaten at pinball by his wife.
Apparently no one knows exactly why having the FRK in the middle of the panels (or on both sides) is not as effective. Ethan notes that this has been being discussed by acoustics experts for over a decade and no one seems to be sure. His business partner had done some tests to confirm the loss of efficiency, but the reason is unknown at this point. There is a property of acoustic absorbers called tortuosity [wikipedia] that describes, literally, how 'tortured' the curves are inside the medium. The open-celled foam used for absorbers has permeable paths through it that slow down the air particle velocity via friction. FRK halfway through the panel would interrupt these cell paths and decrease the ability for air particles to move through the material and decrease the effectiveness. Ethan thinks that my guess (above) is "as good an explanation as any."
It is tempting to think of bass waves as being really long and the panel depth being small in comparison, but remember that regardless of the wavelength, the physical reality is that of the displacement of individual air particles. So if air can't move...air can't move.
With regards to density, there are differences but they are not major. Ethan directed me to some experiments he's done in the past, which you can read about here. Lots of data to look at.
I love seeing the metal frames. Pasim does indeed have a well-balanced room although he does have plenty of absorption in it. I'd go with the 70kg/m3 since it'll probably give you more low-end absorption where it's most needed. No one has problems with ringing at 500Hz.
hi to everyone, ans thanks again for your entries...
so, i finished the phase 1 of my treatment. Results are a bit disapointing...
sorry for my english...to illustrate my post, i join some pics (room pic and rew measurement)
my room in basement : 6.60mx3.60mx1.98/2.00m
concrete walls of big stone
what material i used : about 14semi rigid fiber glass basstraps , about 30kg/m3 of density and 20cm thick
2 basstraps with very low almost fluffy fiberglass about 26 cm thick
what i already had : 4 basstraps 75kg/m3. 2 of 16 cm thick and 2 of 8cm thick
2 broadband panels , rigid fiber glass 65kg/m3
my room has 3 mains locations :
1 : rear wall : listening/mixing point
2 : room center : recording with my band, vocal ans acoustic instruments
3 : back wall, drum location
what i ve done :
ceiling : almost 100%( maybe 90%) absorbed with 30kg/m3 semi rigid fiberglass, 10 cm thick, a few centimenters gap, not enough, i know, but my ceiling is so low that i couldn t do more.
room corners : 4 bass traps from floor to ceiling 30kg, 20 cm thick
drums location, ceiling : a 4 panels cloud above , same density, 10 cm thick and between 8 to 10 cm gap
rear wall behind the drums : all absorbing, differents kind of traps /
side walls about 6 bass traps on each side, placed on floor, sometimes ( when i could) to ceiling, located at the pressure point of my 52hz mode (sine wave and ears opened)
front wall : broadband panel behind monitors, 10 cm panels on side reflections points, 10 cm panel above the listening position with 10 cm gap, and 10 cm panel in the center with 20cm gap
(behind the mixing position, no wall but a kind a cupboard in which there is 2 water heater from the house, the cup board is composed of 4 slim wood doors)
where i could i placed rolled (almost fluffy) panels beetween ceiling and walls...
all the wood strips in the room, especially on the ceiling are only test, and are about to disappear...
regarding at my first measurements before the treatment, i can notice some improvements, especially with a 80z mode, but the 52hz mode (axial i think so) is so strong, when i play a sinewave, it s just incredible. all the traps on side walls have a gap from 15cm to 20 cm...
i m a bit desperate, i know i won t have a perfect sound in this room, butfor now, it still sounds boomy and dull...
what could i do to improve things, i need advices on what i could or couldn t expect.... i m a bit lost....i m opened to every idea
on pics you can see my room treated ans an example of a measure taken about the center mic facing the ceiling about 130 cm height
Hey pasim, thanks for sharing time... This measurement is taken in the center of the room’ and not at the mixing position... At the desk , that is not perfect at all but better... On tomorrow i will post without any smoothing...in france it s time to sleep, for a young daddy
What do you think about that dip in low mid area? Dip created by a mode or too much absoption?
Alright, well congrats on making the effort. I see you went with half the density I recommended so I'm not surprised to see you have some extra ringing in the bass. Even so, you took the measurements in the center of the room so your SPL is going to be jacked no matter how much treatment you have.
Like pasim mentioned, if you measure at your listening position, that low end hump will probably come down a lot. You still have options regarding speaker and listening positioning. Though you have literally rock walls, I bet your problem isn't as bad as it looks. Just take another measurement and, if that doesn't satisfy you, try to sit at 38% toward the front and I'll be shocked if you aren't better off.
I got your PM, but it's better for me to answer here.
You are correct that the real issue is gas flow resistance more than density, though the two seem to be related. The good news is both of those materials work just fine. For thinner panels less than two inches thick (5 cm) higher density is a little better. And once you get to 8-10 inches thick (20-25 cm) lower density is fine and less expansive. But they all work very well, especially if you make bass traps thick enough. So buy whatever costs less, and just avoid the really lightweight stuff unless you're able to make the panels 12 inches thick (30 cm) or more. Then the fluffy insulation is fine too.
Hexspa,this is the reason i finally chose 30kg...all my basstrap are about 8 inches, i thought it was enough for that density...
although i am a bit dispointed, i stay motivated and keep on looking for new ideas to improve this room...
Pasim, i did measurement again with no spl smoothing and 1/48 WF smoothing... here we go