A high dynamic range can do wonders for an AV installation, but only if you actually implement the technology. Anthony Grimani explains.

There’s a lot of talk these days about dynamic range – whether it’s 24-bit audio or HDR video (e.g. Dolby Vision). Perhaps you’re wondering what dynamic range is all about, or how it affects your business.

Simply put, dynamic range is the difference between the brightest white and darkest black on screen, or between the loudest peak and softest detail a sound system can resolve.

Surprisingly, the factors that typically limit dynamic range for both video and audio are in the room and system design – not technology! That’s where your expertise in integrating the entire home cinema space comes into play.

The top end of dynamic range for video is determined by the projector’s light output. (Since we’re discussing upscale home cinema, TVs need not apply.) Current standards require 55-69cd/m² (16-20 foot-lambert) from the screen, which translates to about 2,000 calibrated lumens for a 355cm wide screen. This is fairly easy to achieve; however, 4K systems with larger screens and HDR may require more peak light output from the projector. Stay abreast of the latest developments.

The low end of video dynamic range is largely determined by the room. Yes, the projector needs to have high ANSI contrast – measured using a checkerboard pattern of white and dark squares. Full-on/off contrast using solid white and black fields isn’t useful, because poor optical engines or lenses leak light from bright to dark areas of the picture.

However, even the best projectors cannot overcome a bad room. Best case ANSI contrast in a dark room with dark tones is about 300-400:1. In a room with high light-coloured surfaces, ANSI contrast drops to around 40:1. With ambient light, the contrast drops to 20:1 or less…

Average rooms offer less dynamic range than can be achieved with 8-bit video – much less than the new 10-bit format.

You must ensure that your rooms offer the maximum dynamic range possible. Explain to your customers why rooms can’t be white; if the room absolutely must have light tones, consider judicious use of directional and dark screens. Caution is advised, because these screens usually have uniformity, viewing angle and colour shift issues. They are measurable and visible, resulting in a picture that is not believable.

Over in audio, the top end of dynamic range is determined by the sensitivity and power handling of the speakers, along with the voltage and current capability of the amplifiers. 105dB peaks per channel at the listening position are the target.

There are a number of SPL calculators online, but one shorthand trick is to factor in 7dB of loss from the 1W/1m sensitivity rating of a speaker for a 30m² room. (In a 60m² room, it’s another 3-4dB.) Thus, a speaker with sensitivity 89dB/1W/1m will hit 82dB at the main seat of a 30m² room. It will take about 200W to drive that speaker to 105dB at the listening position. Can it withstand that power level reliably?

The bottom end of audio dynamic range is determined by the noise floor of the room. It should be around 15-20dB, weighted on a scale like RC or NC that takes into account the sensitivity of hearing at various frequencies. A typical living space might be 30-40dB!

Any sonic details below that level are masked by the room. Noise comes from all kinds of sources, such as outdoor equipment, HVAC, plumbing, AV equipment and normal household activities. Special gear is required in order to measure noise floor accurately, but one quick evaluation is to use earplugs for a few seconds or minutes, then take them out and listen. It’s amazing how much more sensitive you’ll be to the noise around you. The earplug test is also a fun demonstration to do with clients!

People love to claim a need to move to 24-bit audio with 144dB of possible dynamic range. If peak listening levels at 110-120dB are considered loud, and a room has a noise floor of 40dB, that’s 80dB of dynamic range – well under the 96dB dynamic range of 16-bit audio; so what’s the point of going up to 24-bit audio resolution?

You need a noise floor at 20dB (NC) to fully benefit from all that the program material has to offer. The factors limiting dynamic range are the sound system and room, and that’s your department. Power requirements drop by half for every 3dB increase in speaker sensitivity, so use a speaker with higher sensitivity versus higher power handling.

There are few 25mm tweeters that can handle enough power for a 10m room without a horn. Low bass can overwhelm woofers in large rooms, so set the surround decoder bass management speaker configuration to ‘small’ and use subwoofers.

To counter high noise floor, a home cinema should be acoustically isolated from the rest of the house. The design and construction of isolated spaces is tricky, with expensive consequences if they’re done wrong. I would recommend consulting an acoustical engineer.

To sum things up, the difference between nice and cheap gear can all but vanish without adequate dynamic range. If you sell clients high-end gear, but don’t take steps to maximise dynamic range of the environment, it’s a little like stealing from them. Not really, but you get the idea!