Perforated Screen?

ilkand

Active Member
Can anyone who actually has one or has seen one give me advice on perforated screens?
I saw and heard a Stewart the other day and it was very impressive. Cannot afford one though.
Was interested in cheaper alternatives. Harkness Hall?
Threads on here mention getting one, but don't mention what they are like.

Thanks for any help
Andy
 

ReTrO

Well-known Member
What projector do you have or will you be using?

There are image quality issues with lower resolution fixed panel porjetcors, moire effect.
 

ilkand

Active Member
Hi,
Its a 1024 x 768 DLP. 600:1 contrast. 1200 lumens. Not the best I know, but a nice picture I think. I would be buying a newer projector about christmas and keeping the screen.
I sit about 12' from the screen.

Cheers
Andy
 

ReTrO

Well-known Member
I'd suggest taking the projector along to test on a screen to see if you have any issues with it.

Cheaper options wise then I suggest a look at Vutec, typically available from the same dealers who offer Stewart screens.

Link on the fabric here:
http://www.vutec.com/vuteccatalog/screenfabricsandfinishes.pdf

Further info can be obtained from myself as UK distributor.
 

Peter Parker

Distinguished Member
Just to add to Richards good advice, there are some screens that are woven, and not perforated as such, so will not show the moire effect.

If you are DIY minded, and can make a fixed frame, then there are some woven DIY materials that may work for you. Dazien is a name that comes to mind, and Lycra is meant to be OK as well. I've not tried them myself, but I've read about them so thought it might be of interest to you.

There has been some threads over at avsforum covering this in detail, so that might be worth a look for more info.

IIRC, all that's needed to get the center volume back to matching the stereo fronts with the DIY material is an increase in the center channel volume at the amp. You might like to use a sound pressure meter to get them blanced equaly.

Another tip is that sometimes light can leak thtrough the screen and cause reflections of the speaker(s) that are behind them. You may need to lay some accoustically transparent black cloth such as speaker grill cloth between the speakers and screen.

This place seems to stock the speaker grill cloth at a reasonable price:

www.iplacoustics.co.uk

HTH

Gary.
 

ilkand

Active Member
I thought I'd try a DIY approach first, so got some Celtic Cloth from Dazian as per AVSForum. Have to say am somewhat disappointed. The image quality was ok, no moire, but the sound was muffled by the cloth, and putting the speakers behind the screen (with them on the wall where they normally live) seemed to increase bass and give it a hollow quality. All in all, pretty bad.
I know a proper perf screen would be better, but I think speakers underneath the screen would probably be best for me in my room.
Fun to experiment though.;)

Andy
 

Peter Parker

Distinguished Member
Did you try the speakers in the behind screen position without the screen? I just wonder what they sounded like, and if it was the position, and not the screen that caused the sound quality reduction.

Interesting result though, so thanks for letting us know the how you got on. :)

Gary.
 

ilkand

Active Member
It was definitely something to do with the screen being there. Perhaps it needed to be further foreward away from the speakers more, or perhaps it was the way I'd made the frame - too much wood. Not sure but it didn't work for me. Without the screen there the speakers are detailed and pretty clean. They are Kef thx ones.

Andy
 

Peter Parker

Distinguished Member
Thanks for the info.

Did you have a center brace in front of the speaker? That may have made a difference. There are some recommendations for distance between the speaker and screen (12ins?) as being too close can cause problems IIRC. I seem to remember reading something about it over at avs, so it might be worth another look to see what problems others had and how they remedied them.

I've read some people claiming so much for perforated screens, I do wonder how much better they are than having the speakers just underneath. I'm sure that with a visual image actualy playing, you're unlikely to notice the sound coming from behind the screen just because it's 18ins higher than when it was under it...

Gary.
 

ilkand

Active Member
I braced it in three parts, so each speaker had a third of the screen. I tried about 8" between speaker and screen as I had seen this distance recommended a few times, and it was easier when hanging it.
I find that speakers under the screen are good when people are speaking and your brain convinces itself the sound is from the person onscreen, but incidental music or explosions etc often sound wrong.
Do you find any problem from your setup? I notice you have your centre low to the ground rather than directly underneath the bottom of the screen. Is this for a reason?

Cheers,
Andy
 

Peter Parker

Distinguished Member
My center is only an inch or two under the screen:

http://www.g-lightfoot.pwp.blueyonder.co.uk/scans/ht/screen1.jpg

I couldn't get it any closer. :)

I don't have any problems that I'm aware of. I did once notice that when playing a movie without the projector on, (Matrix helecopter rescue scene) the imaging across the front soundfield sounded more accurate. You could easily trace the bullets as they went from the left of the screen across the middle to the right speaker.

With the projector running, the imaging seemed less clear. I can only put this down to the visual stimulus taking some processing away from the audio processing that was going on in the brain (well, my brain anyway. ;) ).

I also don't think that moving my center speaker up another 12 to 18 inches (if I had a perf screen) would make a lot of difference audibly, as I don't think that we can tell height movements that well from distance. With the above mentioned discovery and the visual clues you get, I think it's less likely to make a difference either. Given visual clues such as speaking, the brain ties in the video to the audio anyway, so I think for a perf screen to make a big difference, you'll have to be sitting very close, or have a poor center position for you speaker to start with.

IMHO of course. :)

Aestheticaly speaking though, I think having all your speakers hidden looks a lot better though.

Gary.
 

ilkand

Active Member
Oh ye, sorry. Been a while since I looked at your photos. Could have sworn it was lower:blush:
I fancy doing a setup like you so often see in Home Cinema Choice, with all 3 speakers below the screen and in a cabinet with speaker grille fabric doors. Think it looks quite professional, but I am sure this must bring many other problems too. It is the most common layout though. Perhaps professional installs all use some form of EQ.
 

Peter Parker

Distinguished Member
Funny you should menton equalisation - I believe Stewart perf screens come with an equaliser to help with the audio problems that putting the center speaker behind a screen can cause.

Gary.
 

ilkand

Active Member
Ye I know. One came up in the forums once. Strangely, I think they only sell one of them. As if you should only put the centre behind the screen and EQ it to match the left and right either side of the screen.
Its all money. :(
Have decided that a Prismasonic lens will be my next upgrade.

Andy
 

Peter Parker

Distinguished Member
I think that unless you've got a big (wide) screen, you may compromise stereo imaging by having the stereo pair behind the screen as well, as they'd possibly be too close.

I don't think you'd gain as much having the stereo pair behind, as they'd probably tie in less with on-screen action etc because it's variable in screen position etc. Idealy you'd need some speakers that would move around with the action. :)

Of course, I could be wrong. ;)

Gary.
 

Gordon @ Convergent AV

Distinguished Member
AVForums Sponsor
Gary: At the cinema and in the dubbing suite the speakers at front are all within the limits of the screen width. That is where they should be ideally. The problem arises that for correct seating and to be able to do this you need a really wide screen or to be sitting really close. Current projection technology (bar CRT) means this isn't such a great idea.

Of course even with CRT you have an issue if you want a really BIG screen....nothing is ever simple.

Gordon
 

Peter Parker

Distinguished Member
Hi Gordon,

Thanks for the info (is there anything you don't know about home cinema??). :)

So what you're saying, is that my theory of moving speakers was crap then? :D

Cheers,

Gary.
 

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