NOTE: For three days in March, Your Humble Content Marketing Manager at CEDIA attended the training session called “Home Theater Boot Camp” at the association’s HQ in Indianapolis. Here’s a summation of Day Three. (The entry for Day One
is here, and here's Day Two
Jeff Gardner – musician, soundman, recording archivist, and current executive director of ESPA – is the guest speaker this Saturday morning. Since Gardner lives in Indy, instructor Ken Erdmann has turned over the sonic section of the training to this particular subject matter expert.
“If you want the commercial theater experience,” notes Gardner in his remarks, “bring in a crying baby and throw some gum on the floor.”
Nope, what an integrator is trying to recreate is the maker’s intention: a true “reference” experience – or as close as one can manage given a client’s budget. What were the cinematographer, sound engineer, producer, director, and effects guys all after?
Gardner’s explaining how low-powered amps can blow speakers: When an amp pushed to its limits can only drive a speaker to reproduce a portion of a wave, the wave becomes flat. That square wave means the components of a speaker aren’t moving smoothly – they’re being pushed all the way out and pulled all the way in rapidly. That movement creates heat, and goodbye, driver. 9:30 a.m.
80 Hz is the magic number when it comes to subwoofer crossovers. Remember that.
After showing the group an actual speaker with cutaways to reveal the components, Gardner’s talking about speaker efficiencies — the amount of wattage to pump more dB (twice the power for every increment of three) — and the level of background noise. The class, ever curious, is downloading various dB measurement amps and real-time analyzers to their smart phones. Dialogue in a standard room needs to be around 68 dB in the case of the conference room we’re in, or 10 dB above persistent background noise. 10:30 a.m.
Speaker placement: “Toe in the left and rights to anchor the image, ensure line of sight if needed by placing the center speaker above the screen if it can’t live behind it, place the surrounds in a 5.1 system just behind and two feet above the sweet spot” – Gardner’s got tons of best-practice tips.
“In one double-blind study I read, both pros and regular folks preferred a set of $200 speakers over a pair valued at eight grand,” notes Gardner. Design is everything. 11:15 a.m.
We’re talking subwoofers: where to put them so they’re not cancelling one another out, and how and when to decouple them from a floor with a simple absorbent platform so all the energy isn’t transferred into the basement or crawl space. 11:30 a.m.
Remember: Impedance loads are vastly different when speakers are in series as opposed to a parallel setup. 1 p.m.
After lunch, it’s time to learn about sound isolation and room acoustics. A low E note played on an electric bass has a wavelength of around 27 feet, which is one reason the garage band next door is audible – if muddy. (Sound can be airborne and structure-borne – but you knew that, right?) 1:15 p.m.
We’re learning about sound absorption versus sound diffusion, and the various ways sound is reflected and dispersed. Erdmann weighs in with a story about a Dutch concert hall – after hundreds of years, the place was given a thorough cleaning, and the elimination of several centuries of dust changed the acoustics dramatically.
Next up, reverb time – “RT60” represents the length of time it takes for an initial sound to drop by 60 dB. 1:45 p.m.
Gardner, having worked in professional recording studios, describes the ultimate de-coupling procedure: Among other techniques, the performance area is literally on a separate slab from the booth. The recording engineer needs to hear the performance through the monitors and the monitors alone; any noise from the band corrupts the process. 2:00 p.m.
You don’t know it, but you’re an echo-locating genius: Reflected sound gives you information. Knowing how that sound reflects in a room, killing ring and flutter, ensuring that a structure isn’t so “mathematically related” that sound bounces back in upon itself (cubes are especially awful) – these are all key to proper calibration. 2:15 p.m.
“The first question you ask: How many seats do you want in this theater? If it’s two, talk ‘em into three,” says Gardner. You don’t want the sweet spot to be between two armrests in the middle of the room! 2:30 p.m.
The tools of calibration are being set up – pro-model analyzers and SPL (dB) meters, along with the right mics to read a room. The best theaters have a low noise floor – since an 85 dB dynamic range is what we’re after, a span of 20 to 105 dB provides an upper end that’s not uncomfortable – or injurious. 3:00 p.m.
Pink noise is run through the system. Measurements are taken. The AVR we’re using is advanced enough to assist with the setup – it adds delay where needed. We’re moving the subwoofers about. 3:30 p.m.
Ladies and gentlemen, please enjoy the modern Star Trek reboot in 4K on an OLED display complete with 3D immersive sound. Now let’s watch it projected on the screen …
Pardon the vulgarity, but: Damn.