And now he shows up in a video of the Cine Tech Geek [CinemaCon 2014 – X-Curve Update with Barry Ferrel of QSC] making a point that may be surprising to people:
Good Speakers – so the engineer doesn’t get trapped trying to EQ badly designed speakers (or a badly designed room, one presumes)
Placed Behind Screen – the sound is transmitted (hopefully) through little holes in a membrane stretched tight as a drum from speakers (hopefully) built into a wall that is not to distant from said screen
Subtract the function of sound in air – if you’re thinking inverse-square, you are right… play with the numbers at Inverse Square Law for Sound
Something like the X-Curve appears on the RTA as a ‘result’, not a target – give or take a few dB, and with variations in the size of the room, which was requirement to allow for in Ioan Allen’s (of Dolby) original X-Curve paper and in the SMPTE 202M
James Gardiner makes the point that SMPTE is working on this topic, which is an understatement. A lot of hype has been spilt on the need for the emerging immersive sound techniques to find a common distribution package, but now that the difficult Film To File transition has largely taken place, many more engineers are spending a great deal of time reviewing the basics, going through specifications and recommended practices that evolved but now appear contradictory or merely confusing, and not to be forgotten, how are settled techniques in the analog world different in the digital world.
Examples of this fundamental research is showing up in hundreds of pages of documents generated while recently testing various rooms around the world, or testing dozens of algorithms of pink noise samples or developing techniques to find what a screen really is doing in the room, or figuring the best methods of consistently measuring luminance or audio in an auditorium. None of this is public since committee work is private until published, but it is easily obtained when one joins SMPTE and participates in the various working groups.
There are nuances in what Barry says here that could be the subject of 10 slides each, examples being how the ear can discern and ‘deal with’ reflections that microphones can’t account for, or how different frequencies in the transitions between speakers of an array will act different enough that they need to be measured properly, or how EQing to correct speakers (or the room) will make the ear ‘wince’…OK, he didn’t say wince… but using graphic EQs in the recording business came and went surprisingly quickly, before their digital transition in fact, and that lesson should have gotten to the exhibition world back then. We’re talking the late-70’s.
The desired point of this article is that there is a lot to know and do to make rooms consistently good, and keeping them that way. Putting time into SMPTE committee-work is an excellent way to pay-forward on the benefits received.
The side point is to make common certain information, such as the requirement to use FFT when setting up or monitoring components of your system. Testing for the level of a single tone is better than not testing at all, but doing real FFT work to find the THD in a component or your system is truly giving relevant and usable information.