Recently David Johnson (Hoyts Australia) has been installing a new type of laser light source made by Walter Voigt in Switzerland and is reporting excellent results. Whilst these lasers have the downside of using conventional forward scan with it's vulnerable solar cell arrangement, they do offer similar crosstalk and frequency response performance (with narrow slit lenses) to a reverse scan system, plus much higher audio output level without the need for that noisy little Dolby pre-amplifier.

They also appear to have negigible fall off in light output level over time, unlike the troublesome visible red LEDs.

Anyone else tried these devices and if so what has been your experience?

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We have been supplying and installing Mr Voight's lasers for some time now. These are not the same as the Raytheon unit on Ernemman projectors, the Raytheon is a complete sound head really. The Audio Cine Laser is a drop-in replacement for the exciter lamp. Here's my experience of them.

You get loads of signal, in the odd case you get more signal than you know what to do with! I have had to mod a couple of Cat240's to reduce the input stage gain.

You get increased HF response, this is dues to the ACL slit being narrower than most optics, to describe the amount simply, if on a tungsten exciter the optic in question starts to roll of at 10KHz, you'll likely find it will now roll of at 12KHz. Less slit loss eq is required, so less noise and phase error.

Cross talk is reduced, on a head that had well within spec cross talk, it's now imeasurable using L-R film and a 'scope. This has a double benefit, particularly for Cinemecannica machines, in that you can afford to move the cell further away from the film, reducing the number of times you have to go and replace the cell!

The optics will last longer as we are not heating them up and cooling them down anymore. Less chance of it sucking in oil as it cools too.

Downsides. They can be an absolute pig to align. As the laser is outputing a slit, it follows that the laser and the slit mask in the optic MUST be in perfect alignment, otherwise the slit illumintaion is crap, and you can also get phase error. Getting this right is not as easy as it sounds, on some machines they just drop right in, notably Century, Westrex 7000 and of all things, Monee! Westrex 2002/3, can be trying, but the most awkward ACL alignment award has to go anything made by Phillips/Kinoton, because obviously you can't get at the thing to adjust it.
On newer Cinemec optics, the ACL clamps to the back of the optic tube, and once correctly aligned to the optic it works a treat.
The ACL seems to show up poor optics, so it's worth while checking very carefully the condition of the optic tube and reparing or replacing as required. I've stripped and cleaned out some very old Westrex tubes, which had been full of oil,but are now giving excellent service.

Steve

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I've only ever encountered microphonics on Westrex 7000 machines, and it was down to the rep-set isolating rubber being perished by oil contamination. But to be fair, I've had microphonic problems on Westrex 7000's with exciter lamps too.

Now compare this whiz-bang laser systemt to a conventional reverse scan reader (Kelmar or Component as examples though there are others). It is better or worse or the same...Please grade on ease of installation, stability, longivity and serviceability.

Steve

Have you noticed any noise modulation (under dialogue) with these lasers? This was the problem we had with the Japanese units. When you shine one of the Jap units onto a white surface you can see many small dots of light, rather than an even pool of light. This generates noise in the soundtrack. David Johnson tells me he has encountered no noise problems with the ACL units, which would suggest that Walter has overcome this problem.

Also have you noticed any drop off in light level since installing these devices.

I can't speak for the rest of the world, but here in the UK the ACL has a major factor in it's favour. Price. It comes in at about a third to a half of the cost of a CE reverse scan kit, and that is quite a significant amount of cash.

Ray, I can't say I have noticed any noise modulation. We did some system noise measurements with ACL, LED. The ACL is measurably noisier than the LED ( don't have the figures ). It wasn't much and certainly not audible. I seem to remember that early ACL's took some flak over this but the last time I saw Walter we chatted about that and he didn't seem to think it was a problem with his current product.

Ray,
Why don't you produce a little retro PCB that is quieter than Dolbys? You are after all the analog guru of theatre sound. I can't see it being that difficult to do......
Mark @ GTS

Mark we're mainly talking about retro fit to US made or designed projectors, the European makes do produce kits for their machines, but they are still seriously expensive compared to an ACL, and I can't really see Kinoton or Cinemec starting to make kits for Westar/Century, can you??! If money wasn't an issue then I'd opt for reverse scan almost every time. But in real life money is THE issue, and for some machines there are no reverse scan readers available. Fedi & Ross spring to mind.

To put things in perspective, the cost of a CE reverse scan to the customer is a little below £1000. The cost of an ACL can be around £350. To the theatre owner that's a heck of a difference.

The bottom line is that the ACL works well, and is cheaper than reverse scan (for us here in rip off Britain, at any rate).

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