Film-Tech Forum ARCHIVE: standard vs. micro perforations

This is topic standard vs. micro perforations in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jeff Else (Member # 4063) on 01-20-2010, 01:08 PM:

what is the difference in terms of the sonic performance of standard and micro-perf screens? is it signiificant?

Posted by Tony Bandiera Jr (Member # 2365) on 01-20-2010, 01:26 PM:

Jeff, So far I have not found any significant difference between the two, of course the microperf attenuates the HF a bit more. As a rough guess as I have never done A/B testing in the same room, I would guess the microperf has about 1-2dB attenuation at freqs above 4k.

I honestly feel that the behind the screen acoustic treatments have a much larger effect than the difference between standard and microperf screens.

Posted by Monte L Fullmer (Member # 2797) on 01-20-2010, 06:59 PM:

Microperfs are good for home cinemas where the screens are a lot smaller than the ones at your local cinema...and your speakers are smaller as well ...

Kinda annoying a bit when you're sitting close on a small screen that you hacked up from a screen that some cinema tossed out for a new one and you're paying attention to holes than the show itself...

-Monte

Posted by Steve Guttag (Member # 268) on 01-20-2010, 07:53 PM:

It really depends on the microperf...just like not all screens are alike, neither are the microperfs. I have dealt with some where the micros were more sound transmissive than the standard perfs!

See if the manufacturer will give you a specification for their normal and micro-perf.

Remember too, when working with digital images, micro-perfs are MORE likely to give you Morie distortion since the pixels will likely be on the order of the perforation distribution.

Steve

Posted by Eric Robinson (Member # 2966) on 01-21-2010, 12:08 AM:

Moire maybe
or is Morie a new type of distortion?

Posted by Joe Redifer (Member # 3) on 01-21-2010, 12:47 AM:

Moire is the evilness of a defined resolution.

http://en.wikipedia.org/wiki/Moir%C3%A9_pattern

Steve hs never been the best at spellin' so ignore the typo. [Smile]

Posted by Tim Asten (Member # 4051) on 01-21-2010, 08:43 PM:

I believe Harkness do (or used to do) two types of microperf - standard Microperf and Microperf Super. The former, as has already been said dulled the sound but gave better light efficiency and is better for close viewing, and the latter which had the same smaller holes but more tightly packed that gave better sound than even standard perf but not as good light wise. I heard Stage Accompany recommended Microperf Super as being best for their ribbon HF units.

Tim.

Posted by Pete Naples (Member # 761) on 01-22-2010, 08:24 AM:

I saw Moire patterns for the first time on a 2k digital install earlier this week. The screen came from Canada IIRC, and was standard perf.

Posted by Richard Hamilton (Member # 321) on 01-22-2010, 09:03 AM:

quote: Jeff Else
terms of the sonic performance

What are the "terms" and what is "sonic performance"?

Posted by Frank Angel (Member # 248) on 01-22-2010, 10:36 AM:

Thing is, whatever the attenuation of the micro-perfs, it will be uniform and given the ability to get decent performing 1/3rd octave eqs at reasonable prices these days, you can pretty much compensate for any rolloff the imposed screen barrier might create. And I agree with Tony, back reflections from the wall or whatever is behind the speakers and the screen can be more problematic than any HF attenuation that the screen might cause.

Posted by Steve Guttag (Member # 268) on 01-22-2010, 10:58 AM:

I have found that one compensates for such roll offs by boosting the driver (HF shelving or like filter), you tend to get a strained sound out of the compression driver. While yes, you can get an analyzer to say all is well...the actual sound tends to disagree.

Steve

Posted by Jeff Else (Member # 4063) on 01-22-2010, 04:36 PM:

According to the documentation harkness has provided me, there is significantly greater HF attenuation for their micro perf offering (they only offer one variety of micro perf unfortunately). I think I will stick to a standard perf so as not to stress my 802-8T's. Also I have a concern about the potential for a Moire effect. The screen is 20' wide, first row is about 10' back so the standard perfs are pretty much invisible anyhow...

Posted by Marco Giustini (Member # 4544) on 01-23-2010, 08:59 AM:

Steve

Interesting. So do you usually avoid using HF boost and do you use only 1/3 EQ or do you avoid boosting HF frequencies at all?

About moire, you can reduce or remove it by slightly defocusing the picture, the minimum amount needed to reduce the effect. Play a white screen to see the effect.
Nobody should defocus the picture of course, but I believe that moire is much more annoying, if severe. Defocusing slighgly should basically remove the black borders between pixels and not affect too much the overall picture.

Let's consider the upside: if you get moire you can be sure that the picture is well focused! [Smile]

Posted by Steve Guttag (Member # 268) on 01-23-2010, 10:59 AM:

No, I do tune for a flat response...but I've noted that those systems that don't inherently have good HF response can't be tuned to give it to them...they sound strained.

I don't defocus the image to reduce moire. I tend to try and use devices that inherently reduce it. For instance, I prefer Stewart screens. Their perforations are, sort of, hand done. As such, there is an inherent lack of uniformity that breaks up moire.

Also paying attention to the pixel density versus perforation density. Screen manufacturers can also rotate their perf pattern so it breaks it up a bit.

Steve

Posted by Marco Giustini (Member # 4544) on 01-23-2010, 01:59 PM:

Ok.

About defocusing, your solutions are the right ones, mine was just a sort of patch where nothing else is possibile - mainly because of costs, I reckon.

Has anyone ever tried "fabric" screens? Their perforations are not exactly holes but spaces between wires and they should outperform in sound transmission standard perforated screens, I guess.

Posted by Steve Guttag (Member # 268) on 01-23-2010, 02:50 PM:

There is a French manufacturer (Screen Concepts, maybe) that has a really good fabric screen. It attenuates no more than a typical speaker grill. Uniformity was nice and we lit it up with a Kinoton FP30E premiere (3-wing shutter) and a Christie CP2000-ZX...neither experiences moire patterns (I would have been real surprised if the film showed any [Wink]

).

The film, honestly did look better in that screening room...there is something about 3-wing shutters that just makes the image look that much better...particularly when you have the light.

The worse case Moire I've see are always micro-perf with an LCD projector where the pixel densities are similar to perf density. I always recommend standard cinema perfs for them to avoid that...while the Moire will be there...the tiger stripes are so wide that they don't really show as much...when they are fine and well defined, they are quite annoying and ANY vibration makes them move horribly.

Steve

Posted by Marco Giustini (Member # 4544) on 01-23-2010, 06:25 PM:

Interesting! Thank you Steve.

Posted by Alan Gouger (Member # 543) on 01-23-2010, 06:46 PM:

Steve if we are thinking of the same company that would be Screen Excellence. Their material is a Fabric/weave with a slight negative gain. They have a 4k material.
There is also a company in the US called SMX whos screens are based on the same material. Several of their screens are installed in post production houses.

Posted by Steve Guttag (Member # 268) on 01-23-2010, 11:04 PM:

Different company...this one is based in France. http://www.screenresearch.com/website/product_clearpix_fabrics.php

They are Screen Research. I didn't spec or install it but the results were pleasing just the same. I don't think it had that Stewart "pop" to it but again...it was very good and with the right light it was REALLY good. For film, we were at 16fL and for digital we were at 14fL.

Steve

Posted by Marco Giustini (Member # 4544) on 01-24-2010, 05:11 PM:

I have something similar to SMX in my Home Theater. Quite good, but do you know what actually is? Sun shade fabric, or how it's called. The thing you use for seats on the beach! [Smile]

Works nicely [Smile]