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Spall's Home Theater - Basement Build - Page 2

post #31 of 50
Thread Starter 
Ted, since you're here chiming in anyway, maybe I can save John another one of my emails.

If I'm planning on doing a decoupled ceiling. Is there a reasonable way to engineer what mgkdragn is talking about above and keep isolation intact?

Could I install clips to the floor between joists, double 5/8" w/ GG on hat there and then connect that "higher ceiling" to the rest of the ceiling with more double drywall? Almost creating an inverted soffit above the screen?
post #32 of 50
Quote:
I want to make sure I understand your position 100% correctly.

Here's how you can fully understand my position ... It is your room, it is not my room. My job is to tell you the pros and cons of doing (whatever it is) vs some other way, so you can make an informed choice in such matters. It is very easy to pull an "oh oops" and many of those oh oops will be expensive to fix (usually more than my fee) or provide a lifetime a negative karma in your room. And, yes. above the screen but aimed down toward the seating positions.

Now...there is another advantage to that. The difference in distance between the ears in the first row to the speaker and the ears in the second row to the speaker is reduced. Because that difference is less, the difference in SPL between row one and row two is also reduced ... that is a good thing.
post #33 of 50
Quote:
Originally Posted by Dennis Erskine View Post

Now...there is another advantage to that. The difference in distance between the ears in the first row to the speaker and the ears in the second row to the speaker is reduced. Because that difference is less, the difference in SPL between row one and row two is also reduced ... that is a good thing.


Can this be corrected by adjusting the channel-specific level balance in one's AVR? Most go up to +/-15 dB or so, don't they?

Also, if the center channel is "closer" to the audience, wouldn't it also be closer than the front L/R speakers, so they would have to be adjusted also?
post #34 of 50
Thread Starter 
Quote:
Originally Posted by Dennis Erskine View Post

My job is to tell you the pros and cons of doing (whatever it is) vs some other way, so you can make an informed choice in such matters.

In case it doesn't translate well in text, I truly do appreciate it.
post #35 of 50
Quote:


Can this be corrected by adjusting the channel-specific level balance in one's AVR? Most go up to +/-15 dB or so, don't they?

No, that would adjust the volume at the speaker. What you want to do is minimize the the difference in SPL between each row of seats. To do that, you need to reduce the difference in distance between the speaker and each row, and/or, move the speakers further away from the seating area (approx 6dB decrease with each doubling of distance). For example, the difference in direct sound between rows at 5' and 10' would be 6dB, between 10' and 15' would be ~4dB but between 15' and 20' would be 2dB. (Direct sound intensity decreases inversely with the square of the distance, or I = 1/d**2 )

Thus minimizing the difference in distance from the speakers and/or increasing the distance from the speakers will minimize row to row variances in SPL. This comes significantly into play where the back row of seats is very close to the back wall (rear surround speakers) or you place seats too close to side walls (side surrounds). You now have the effects field completely overwhelming the L/C/R at the expense of intelligibility, clarity, focus, and sound stage width/depth.
post #36 of 50
Thread Starter 
Dennis, does that mean that above is actually better than behind? (assuming the speaker can't move further back)
post #37 of 50
That depends on a long list of factors. When all weighted together, behind generally wins with above coming in second.
post #38 of 50
Thread Starter 
It seems unlikely that I'll be able to mount a speaker above the screen. So, if I decide to go with an AT screen, what is the reality in terms of picture hit?

I've seen references to loss of brightness, potential moire issues, etc.

Also, if I switch to AT, I'm really considering CIH. Deciding on a not-AT screen originally was my main reason for skipping CIH. I've been reading through the CIH threads, but are there any gotchas I should be sure to be aware of if I go that route?

Thanks..
post #39 of 50
The biggest reality of going to an AT screen is the reality that someone, somewhere, at some point is going to try and scare you into not doing it. There's your reality.

Here are some other realities:
1. Loss of light reflected back into the seats from the screen. True fact. You can measure the difference between 22 ft lamberts but you cannot tell the difference between 22ft Lamberts and 20 ft lamberts.

2. Loss of image quality. Nuts. If you are outside the range where visual acuity doesn't allow you to resolve the holes in the screen, you are also outside the range of human visual acuity actually seeing any loss of picture quality (I suppose if someone can hear the difference between bzillion dollar speaker wire and lamp cord, I suppose they could also see a pion with their naked eye.)

3. Moire. Yup. Was a problem once. Not a problem any more.

Let's see now. If human visual acuity isn't going to let you see the difference between an AT and non-AT screen, but your hearing will hear all the problems with a non-AT screen, do you really have a choice?
post #40 of 50
Quote:
Originally Posted by Spall View Post

Also, if I switch to AT, I'm really considering CIH. Deciding on a not-AT screen originally was my main reason for skipping CIH.

Do it! (keeping with the tradition of heartily endorsing anything I'm doing)

One thing to consider is whether you'll be implementing CIH using the "poor man's" approach (zoom), or a lens. My choice is using zoom (PT-AX4000). Then there's masking - personally, I'm not going to worry about masking until after I have everything else working properly. You'll also want to research projector mounting distance and height carefully, since there are additional variables being introduced into the equation (a lens if you go that route, or finding a mouting distance and vertical offset that works for both 16:9 and 2.35:1 zooms).
post #41 of 50
Thread Starter 
Quote:
Originally Posted by Dennis Erskine View Post

If human visual acuity isn't going to let you see the difference between an AT and non-AT screen, but your hearing will hear all the problems with a non-AT screen, do you really have a choice?

Well, I'm a bit more open to the idea than before. So now I need to examine how I can tweak my room design to account for that.

I also need to start getting a better understanding of CIH and lenses, et al. I like the 1-2 punch of fixing my center channel sound issue and going wide. If I keep the screen height the same, I think I end up with about with ~125" wide for scope. That seems to be about 82% of the room width. Close enough, or rein it in?

Also.. is there an easy to follow rule of thumb for throw with a CIH setup. I've read through the CIH faq thread, but I'm a bit confused still. For example, if I have a 54"H 16:9 screen, do I treat a 54"H 2.35 screen the same for throw distance?
post #42 of 50
Thread Starter 
I was reading through Dennis' "What I'd do differently next time" thread..

One of the gotchas there is:

Quote:
Originally Posted by Dennis Erskine View Post

Screen too big for the room. Screen widths should never be more than 80% of the room width. Keep the screen at least 3' off the floor (if not more) and don't mount it within inches of the ceiling. Big is not always better.

Because of my room size, trying to follow this to the letter is problematic. As I posted above, I'm considering going scope (along with the move to an AT screen). My screen wall will be confined to 153"W x 84"H.

So.. I could do a 120"W scope screen, but not without being about 26" off the ground and butted up pretty close to the ceiling. Say I were to leave 6" before the screen starts and try to hit 36" from the floor.. that would leave me with roughly a 99"W screen. It obviously keeps getting smaller from there if 6" is too close. In my minds eye that seems really small on the screen wall, but I realize the instinct is to go as big as possible.

Any opinions on this?
post #43 of 50
I wouldn't worry too much about the space above and below. I've seen screens right up against the ceiling (like mine!) and many have them much closer than 36" from the floor, with 26" or so being the lowest I've seen (mine is 27").

If you're able to apply some sort of anti-reflection treatment to your ceiling (triple black velvet or telescope flocking, or can paint it flat black, then you'll be in good shape.

But I agree that 99" width seems too narrow for a good screen.
post #44 of 50
Quote:
Originally Posted by Spall View Post

It seems unlikely that I'll be able to mount a speaker above the screen. So, if I decide to go with an AT screen, what is the reality in terms of picture hit?

I've seen references to loss of brightness, potential moire issues, etc.

Also, if I switch to AT, I'm really considering CIH. Deciding on a not-AT screen originally was my main reason for skipping CIH. I've been reading through the CIH threads, but are there any gotchas I should be sure to be aware of if I go that route?

Thanks..

Spall, when I first started out with my build it was my intention to do the speakers on the sides and center (bottom) flanked around a fixed screen. I was convinced this was the best way to go for not only audio optimization but also for video. Indeed, a local shop I was getting an estimate from refused to even do AT screen installs. In the end, after much research and endless hours on this forum, I decided to go AT as well as CIH. I have zero and I mean zero regrets going this route. Not only did I get a bigger screen (with the speakers behind) but having the sound come from the screen is much more important to me than I realized. I don't feel like I've compromised on the audio or the video at all. In fact, I'm blown away by the whole set-up.

One thing, however, that I did not know with CIH is that a lot of movies are not 2.35 so often you get the white space on the left and right sides. And a few will result in minimal bleed onto the frame.

As far as having the speakers so close up against the back row, I've got a similar set-up as well due to room limitations. Suggest going with dipoles instead of direct firing since the row is so close to the speakers.

Good luck!
post #45 of 50
Thread Starter 
Thanks for the encouragement, Queen..

I'm really leaning in this direction.. I just need to figure out an appropriate screen size for my room.

I can change the room dimensions.. that bathroom on the drawing doesn't exist.. it was just planned.. but I can scrap it and gain feet. Or.. if the screen ends up being smaller, the seats will most likely move forward.
post #46 of 50
Thread Starter 
Hmm.. just occurred to me: If I go larger than say 104"W I'm probably going to have to add a door in that 4' deep room in front of the theater to access behind the screen. I won't have enough room to wiggle around the screen/frame to get back there.

I'm not opposed to doing that.. but it's something I'd need to plan for especially for trying to isolate the room.
post #47 of 50
Well, do I give you the answer or let you worry about the additional expense and loss of sound isolation? Hum .....

Look at the manufacturer's frame, mounting, and fabric installation process. If you ponder it long enough, you'll find it will be very easy to remove either screen or the fabric to gain access to behind the screen wall ... both those times in 5 years that you'll really need to.
post #48 of 50
Thread Starter 
Dennis,

I see your point.

One could almost infer that you're saying 120" would be fine. :P
post #49 of 50
It's just a whole bunch easier to remove the screen than to build a doorway.
post #50 of 50
Thread Starter 
Well, again, thank you.

That had not occurred to me.
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