Check out those references
How do you know that something you’ve installed does what it says on the tin? Well, in home cinema, you follow the standards. Anthony Grimani gets into the nitty-gritty of references.
Marketing materials often use the word ‘reference’ to claim a status of superiority for the product. But what does that really mean?
For a watch, what is the reference? The fact that it keeps absolutely perfect time, or that it has more bling than a dress worn at the Academy Awards? It’s really up to the buyer to choose.
For a home cinema AV system, what is the reference? Is it only the sense that it has superb sound and picture, or is it something more?
Well, the good news is that there are, in fact, demanding, absolute, and objective references, and the systems you are providing to your clients can be measured by how close they get to those references.
Ideally, the closer you are to meeting all the specifications in the standards, the closer you are to hearing the soundtrack and seeing the picture exactly as the film director intended it. That can make the difference between merely watching a movie and being fully immersed in the action and the characters.
You can even offer your clients a few different choices for systems and pricing based on how close they are to these immersive reference standards.
Let’s review the standards:
For Audio, these ubiquitous documents form the list of best practices: SMPTE202M, ISO2969, THX Cinema and Post Production studio specifications, CEDIA RP22, and several general guidelines by Dolby Laboratories. These specifications show the position of speakers relative to the main seating areas.
Generally, the front left and right speakers form a 45˚ subtended angle to the viewer, at a height about half way up the screen. The centre speaker is in the middle of the acoustically transparent screen, also halfway up. The side speakers are along the side walls, up about 15˚ from the audience ears. The back speakers are on the back wall, also about 15˚ up. The top channel speakers form two rows at the mid-point between the centre and front L/R speakers, and at locations that match the side speakers.
For more detail on all this, consult the aforementioned documents.
Sound Pressure Level (SPL) capacity is generally 105dB per front channel, 100dB per side or back channel, and 115dB for the subwoofers. It will take amplifiers and speakers that are big enough to achieve these SPLs, and some careful engineering will predict the results during the design and quoting phase. Again, much more detail is available in the standards documents.
Frequency response accuracy is important so as to maintain even weighting across the audible spectrum. There is a general practice to measure and calibrate results to follow the ISO2969 X-Curve; in fact, this generally matches the audible spectrum of high-quality speakers in a residential space, to which the THX Re-EQ curve has been applied.
In all cases, it will take careful selection of the speakers, engineering of the room acoustical properties, and diligent equalisation of the system in order to achieve accurate frequency response.
Level and time alignment between all the channels should be within 1dB, and within 1ms, or else the spatial character of the movie may be lost. The entire soundfield could be too front-heavy, or too far back in the room. This is a matter of careful calibration, but also of proper integration between all the speakers in the system.
Distortion should be kept at a minimum – below threshold of audibility in order to avoid distractions and listening fatigue. It can be hard to get all the distortion data from residential audio manufacturers, but you can always measure a sample, or ask for the data from their engineering department.
Speaker coverage and sound field evenness are a big topic in cinema sound, and so they should be in home cinema. It is common to see speakers with merely 40˚of total dispersion arc trying to cover an audience placed over a 60˚ arc. Your clients’ friends who are sitting away from the ‘captain’s seat’ may get a bad impression of your work, and there goes your reputation! You need to know the dispersion characteristics of all the speakers you are installing, and make sure they fully cover the entire audience area.
Room reflection decay times are also carefully specified and acoustical materials are selected so that sound reflections are on the ideal standards – not too live and not too dry. This takes some careful engineering and layout of the various absorbers, diffusers, and bass traps to get to the right numbers, but when you do achieve it all, the sound is just glorious and accurate.
Background noise should be kept close the threshold of audibility, and that corresponds to what is known as NC20 (Noise Criteria). That’s about 20dB SPL in the middle frequencies, and higher in the bass and treble regions, following human hearing threshold curves. If a room is noisy, the audience will not get the full impact of the dynamic range in movie soundtracks, may lose some of the surround effects, or may even miss a few lines of quiet dialog. All bad!
For video, the best documents to review are the SMPTE and DCI specifications, along with recommended practices from CEDIA RP23, THX, and Dolby. These specifications cover viewing angles, resolution, illumination, colourimetry and colour space, greyscale, contrast ratios, and much more.
Too much to cover here, but just know that you can merely put up a picture, or you can set up a picture that matches all the standards by which the director judged the visual personality of the motion picture. This visual character is now infinitely tunable by the director of photography and the colourist, so you need to match the professional conditions if you want the ideal experience. Some display systems can get there, and some just can’t.
In addition to the measurable engineering data I just covered, know also that there are a few ‘defacto’ subjective standards. Yes, there are a few very commonly used screening rooms around Hollywood that members of the Academy of Motion Picture Arts and Sciences use to view the nominees for best sound and best cinematography.
If you are building a sound mixing room, you’d better make sure that it has a flavour that matches the top screening rooms so that you get a chance at winning Oscars for best sound. And your custom integrators had better work on getting that experience out to your clients when they demand nothing but the best.
It’s not just about spending unlimited amounts on esoteric surround processors, power amplifiers, and speakers. It’s about picking the right equipment for the job, placing it precisely, and calibrating it all to meet all the exacting film industry standards.
Now, imagine presenting system options to your clients as a percentage of compliance to reference standards – say from 30% to 120% – this would help your customers in picking the grade of system, rather than getting lost in elusive and unprovable notions that this ‘higher-end’ proposal is better than that ‘base-level’ proposal.
You may even get around to selling more 100% perfect projects, at a higher budget level than you might have originally anticipated!
Chase Walton ([email protected]) contributed to this article.