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Author Topic: standard vs. micro perforations Jeff Else Expert Film Handler Posts: 125 From: Detroit, MI, USA Registered: Nov 2006 posted 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?  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 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.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 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  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 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  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 01-21-2010 12:08 AM                     Moire maybe or is Morie a new type of distortion?  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 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.  |  IP: Logged Tim Asten Film Handler Posts: 98 From: Brighton, United Kingdom Registered: Nov 2006 posted 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.  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 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.  |  IP: Logged Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 01-22-2010 09:03 AM                     quote: Jeff Else terms of the sonic performance What are the "terms" and what is "sonic performance"?  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 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.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 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  |  IP: Logged Jeff Else Expert Film Handler Posts: 125 From: Detroit, MI, USA Registered: Nov 2006 posted 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...  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 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!  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 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  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 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.  |  IP: Logged

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