Film-Tech Forum ARCHIVE: Screens

This is topic Screens - Sound Transmission in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=005098

Posted by Andrew Lee (Member # 1330) on 07-16-2003, 08:14 AM:

It has come to my attention lately that there is no set standard for the measurement of sound transmission (frequency fall-off) through screen materials. Currently, samples of screen material are placed in front of a boxed in horn, a microphone placed in front of the screen, and a frequency sweep of 20 - 20K Hz is then generated and recorded. The results are then graphed as a function of dB loss over frequency and compared to no screen material at all. These tests are completed by individual labs, and sometimes speaker manufacturers, but to my knowledge, never the same way.

Some aspects of these tests bother me as there are no known standards for: size of test sample, microphone placement, and screen to horn distance. These tests can be easily optimized to suit the marketing needs of the company or individual involved. I and a few others would like to investigate test set-ups and possible submit a proposal to SMPTE and others for application to become a future standard.

As most of you are the experts in the field, your input would be most valuable. I am especially interested in coming up with a speaker to screen distance or range for consideration. Is there a nominal distance? Is there a distance specified by speaker manufacturers? What's the closest and farthest distance you have seen in an installation? Thank you all in advance for your feedback.

Posted by Gordon McLeod (Member # 33) on 07-16-2003, 08:34 AM:

The farthest back I have seen is what Sonics does about 2.5 feet the closest was on stage accompany where it was virtually touching the sheet
The consensous had always been as close as you can get it to prevent reflection off the back of the sheet

Posted by John Pytlak (Member # 331) on 07-16-2003, 09:00 AM:

The ISO has been working on a standard for measuring screen reflectance and sound attenuation. It is "Item of Work" 173, ISO/CD 8396. Contact Carl Girod at SMPTE (ISO/TC36 Secretariat) for the latest status and to contribute to the drafting of the standard:

http://www.smpte.org/engineering_committees/

Posted by Andrew Lee (Member # 1330) on 07-16-2003, 09:42 AM:

Something that is also in the back of mind which could be the result of all this is quite simply optimized specifications published by the screen and/or speaker manufacturers. Designers and installers would then simply work to those specifications and hopefully provide a better quality presentation.

Posted by Gordon McLeod (Member # 33) on 07-16-2003, 08:08 PM:

Only problem I could see is if a brand X screen was replaed at a later date with brand Y and it had peculiar characteristics I can't see a theatre agreeing to remount speackers or new frame