| Search AudioEnz | |
| Articles | |
|
Current
reviews |
|
| News | |
| Community | |
| Buying | |
| About AudioEnz | |
About AudioEnz |
Perforated projection screens
The Holey Grail of home theatre?
By Max Christoffersen
February 2001
To perf or not to perf? That is the question that home theatre projection enthusiasts may end up asking themselves as they approach the edge of the performance envelope of home theatre.
Perforated projection screens are designed with thousands of pin-head sized holes allowing the placement of speakers behind the screen (just as they are in the movie theatre). And as a result, some argue that perf screens provide the most accurate platform for the replay of the film soundtrack in the home.
Home theatre perforated screens have been available for some time but myths, misconceptions and misunderstanding abound as to the benefits and trade-offs typically associated with using a screen designed to let sound pass right through!
Technically, the small perforations allow sound to come through the screen providing an accurate, synergistic soundfield linked directly to the on-screen video action. The cohesive audio-video effect is intended, as the film soundtrack was produced, mastered and created using this exact speaker platform on the dubbing stage.
But as always, there is a catch. It sounds great on paper, but there are tradeoffs to the home theatre perf approach.
The first trade-off is that the very same perforations that allow sound to come through from the back of the screen, also allow light to go through from the front. The result? Potentially, a dim, washed-out picture.
The second trade-off is that putting a screen in front of a speaker creates unwanted behind-the-screen reflections and loss of high frequencies. The result? A loss of sound fidelity.
The loss of light and sound can have major deleterious effects, but how bad can it really be? There's only one way to find out! A real hands-on Perf-test was required!
A Da-Lite Da-Mat perforated screen was kindly supplied by Tasman Screens (Auckland) for this review. The basic objective of the test was two fold:
- Did the Da-Lite screen provide an acceptable video image? (How'd it look?)
- Did the Da-Lite screen provide acceptable sonic performance? (How'd it sound?)
The screen arrived rolled (well done Tasman!!) not folded, and the aluminium frame with Velcro screen attachments was easily constructed inside 3-4 minutes. But at 100" wide and 56" high it was too big for my viewing room - it quite literally didn't fit!
Fred Jonathan standing by the screen
So over to Fred Jonathan, long time film projectionist and a home theatre enthusiast with the equipment, room and experience to evaluate the overall screen performance.
The screen gain was 1.0 and the vinyl matt finish provided a smooth surface on which to project DVDs through a Sony 1251 CRT projector using RGB direct from a Sony DVD player.
The first images of Batman and Robin came to screen in a mid-morning viewing and If I was expecting a dim, dark picture with a centre channel sounding like the top had been knocked off, what I got was a bright image with a centre channel no longer imaging below the screen and nary a pin-hole in sight! So far, so good! It wasn't yet sonically matched, but it was working well enough to confirm there is something worthwhile in the Perf approach.
A scene from Batman and Robin on the perforated screen
But my first major concern had been answered emphatically: did it look good enough? Yes.
With familiar scenes on screen, the effect of the centre channel location genuinely surprised me. I had anticipated that I would be aware all the time of the centralised location of the centre channel, but what I got was something slightly different. I was aware of it not being off centre which meant I could relax and allow the movie to work its magic instead of the day-to-day distraction of detached voices coming from 'down there somewhere.'
Interestingly, some of the most tell-tale scenes that demonstrated why Perf works, involved action, not dialogue. In Aliens the trackers emit a low level 'beep-beep' (chapter 11) as Ripley and team walk through the derelict building. With the Perf screen the 'beep-beep' of the trackers was located rock hard centre screen. And with Batman and Robin the click of Bat-belt-packs and weapons in the opening scenes made for a convincing screen centred experience. Dialogue was located to the characters on screen and without exception, it worked with very specific imaging.
I also played live music DVDs. Would a 5.1 music concert also benefit from a centre (and mains) located behind the screen. Simple answer? Absolutely.
I was amazed by the overwhelming sense of cohesion from James Taylor Live at the Beacon. What is otherwise a fairly rudimentary solo performance become a riveting band performance as the instrumentation appeared to be located to the very stage they were all playing on. The need for some lift in the top end to compensate for the screen was there, but EQ added some sparkle and the overall musical-video effect was riveting.
Over four nights of intense viewing the jury was in early. For us, the perf experience worked because whatever problems others may have experienced, we simply didn't see. The benefits of superior sonic imaging outweighed the trade-offs.
Very occasionally, there was a scene that drew attention to the screen, but this was more a function of scan lines popping out of the image than the perforated holes creating moire effects. And when you consider this is an extreme perf screen at its size of 100" x 56"(!) that is quite some performance from the Da-Lite material.
The perf-holes from our seated position (15 feet) were not visible and the centre channel imaging compensated for the necessary use of EQ to bring the centre back to a matched performance with the left and right mains
Some basic Perf-conclusions can already be drawn:
A) Perf works. It can and does produce an extremely watchable large screen image.
B) The centre channel sound loss is minimal and can be compensated for with EQ and behind the screen damping (which is made even easier if the loss is accurately stated by the screen manufacturer).
C) Matched speakers along a line at centre screen, is far less distracting than speakers located beside or underneath the projection screen.
D) A high gain perf screen would be a winner!
We were both absorbed by the film and found ourselves relaxing easily into a new home theatre experience. We were both recognising the familiarity that this is the way it sounds at the theatre.
And this I think this is the key point. Film is a visual medium enhanced and complemented by sound. The screen is the primary focus and if the sound is also located to the same point of visual focus, the sense of synergy with sound and video emanating from the same place is profound. I now find voices and images that aren't located to the screen to be totally distracting and a barrier to believability.
The conclusion is easy to state: Perf works. And with careful matching of projector and speaker to screen, the overall cinematic results can be very satisfying.
Want to comment on this review? Click here for Feedback