projection screen will vibrate?

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need a quick help here on a setup topic,
still working on my HT room for the new house.

If i suspend a projection screen in front of a wall of subwoofers, will it vibrate?

lets say the situation here is :

front wall = 9'high by 20' long
10 18" are distributed evenly on this front wall
and the screen would be in suspension or fixed at 2-4 feet in front of this wall

i have difficulty understanding how the subs waves will react toward the screen ..since it is very thin

my guess is that it will grab the same motion as the air particles have, but with different impedance thus quite a bit less

what effect will it have on the sound from the sub ?

what if i could make it very solid
( glued on a solid back/frame ..maybe carbonsandwich)


let me know ...need to finish concrete dimensions for the flooring, and the distance to the screen tells me where i need to put the 1' step for the second row of seats ...so it is different if i put he screen 3-4 feet from the wall than ON the wall :)

thanks again folks for sharing your knowledge!
 
If you have the subs set up and running, a very non-scientific test would be to place a hand on the wall/ceiling at the distance you want to hang the screen - whatever you feel there is probably what would be transferred to the screen if it is fastened directly to the surface. As far as what the actual visual effect would be, if any, you'd have to wait and see. I have a gut feeling the wall vibrations will affect the screen more than the air (more dense).

I think a good way to suspend the screen would be from metal hooks with short rubber bunjee cords - they should absorb a great deal of any vibration that is present.
 
ok

first as mentionned...this is for my next house that i will build this year ..so no i do not have the setup to test it

then, all of the walls will be made of :
2"foam / 8" reinforced concrete/ 2" foam
floor will be concrete slab
and ceiling will be poured in place concrete slab + concrete joists + foam isolation ..
so i do not believe that those subs will rock the walls
enough to transmit vibrations

then, as i mentionned, the screen will be HANG in front of th wall, thus not touching it no ceiling no floor...

what i am interested here in,
is to know what will be the result of the moving air particles form the wound wave when they meet the screen fabric ... and what will it result in
on the screen side and on the accoustic side

thanks neway! :)
 
ok

so it will vibrate
grr ...

shino : do you know what is the ratio of surface to holes on those screens? the problem with those usually,
is that you loose a big chunk of brightness, and with current home projectors, brightness is not something you want to give up ( lcd )

i'll have to look into that now then ...
probably 10 times as expensive as regular screens ..
 
diyAudio Member
Joined 2004
JinMTVT said:
ok

so it will vibrate
grr ...

shino : do you know what is the ratio of surface to holes on those screens? the problem with those usually,
is that you loose a big chunk of brightness, and with current home projectors, brightness is not something you want to give up ( lcd )

i'll have to look into that now then ...
probably 10 times as expensive as regular screens ..


Depends who's material you go with but on average the open area of a perforated or open weave screen is 5-12%. The best is from Screen Research with their Clearpix2 material. You can stick fullrange speakers behind that material and in blind test I bet you'd have a hard time telling the difference. Problem is its stupidly expensive.

For a cheaper alternative, thats around 90% of the performance, look at the 'Center Stage' material/screen from

http://www.seymourav.com/

Chris at Seymour is a top bloke and will sort you out with a good screen for sensible money.

The open area screens, because they allow air to pass, are ideal for reducing the pressure buildup that subs placed behind the material would produce. The material itself will still resonate but this is only detectable by touch and certainly doesn't affect the image.
 
OK i will look into that more ..

just for ref ..

"bloke" ??? explain the use of that word please
to a french canadian that seriously misses some real English classes ( not the usa/canada poor english )


Then i still need to determine if my goal of trying to work out with distributed front sub to produce some planar wave effect is correct or not.

At wich frequency does room modes start to be real problems?
my accoustical master handbook tells me that
between 100hz and 500hz the room modes are predominent, but i am not sure of what is hapenning below 100hz, wich is where those sub will be doing their magic work :)
 
diyAudio Member
Joined 2004
Originally posted by JinMTVT OK i will look into that more ..

just for ref ..

"bloke" ??? explain the use of that word please
to a french canadian that seriously misses some real English classes ( not the usa/canada poor english )

:)

Its slang for man, male... you get the idea. Not sure where it came from but it seems to be used a fair bit here in Northern England.

Certainly more disturbing was when we had some relatives up from Norfolk and I was telling them about how hard a day I'd had and mentioned the phrase "I was absolutely buggered". Which of course means something entirely different depending on where you come from. :D

At wich frequency does room modes start to be real problems?
my accoustical master handbook tells me that
between 100hz and 500hz the room modes are predominent, but i am not sure of what is hapenning below 100hz, wich is where those sub will be doing their magic work :)

Its room dimension dependant but I'd say the real meat is from around 40hz upto 300-400Khz.
 
JinMTVT said:
ok

so it will vibrate
grr ...

shino : do you know what is the ratio of surface to holes on those screens? the problem with those usually,
is that you loose a big chunk of brightness, and with current home projectors, brightness is not something you want to give up ( lcd )

i'll have to look into that now then ...
probably 10 times as expensive as regular screens ..


The point in which my 106" 16:9 screen's 'flapping' becomes visible at 15 feet (pink noise measured at 15 feet) is 114 db. Beyond the level most subs will operate.

Brightness doesn't seem to be that much of an issue with modern DLP or LCD projectors. - contrast and color purity does.
 
ok thanks for the sharing :)

there will be 2 rows ..front rows will be within 10-12feet
and second row will be adjustable at 14-16

screen diago will be between 100 and 115

and believe me that i will have no difficulty getting 115db
from of any sub frequency u like from this setup

still debating in my head if i want to go with a planar wave type of sub setup, or only put the IB subs on both sides and or bottom of screen on the front wall ..

i have a 12"concrete wall up front
that will have a 2' depth recess in the back of it,
that leads to a 4' high 2' wide opening directly into the garage that is 25'by25'
all in concrete :)
this shall be very fun to play with!
 
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