Acoustics forum, edition II: How new formats affect your audio planning
The next edition of the Cinema Acoustics Support Q & A Forum is now complete. These are questions we have received from experienced designers of cinemas that will illuminate issues for those involved in other ways with the presentation of movies (and other content) to the public. This edition is focused on some of the new technologies and renovations making their way into the cinema exhibition world.
With the introduction of new cinema sound technology such as Dolby Atmos and Barco Auro 3D, are there adjustments that need to be made to an auditorium’s acoustics?
Briefly and hopefully doing proper justice to the concept of both mentioned manufacturers, these new sound systems expand the concept of total envelopment of the moviegoer into the multi-dimensional realm of the director and sound designer’s intent. Loudspeakers are positioned in new locations above and behind the listeners and more channels are added at the front of the auditorium through which specific effects emanate from locations that convey the illusion that the listener is actually physically inside the scene they are viewing.
Fortunately, acoustics of the cinema auditorium are already largely developed to address the nuances of supporting complete listener envelopment. That is, if the auditorium is designed to have an efficient sound-absorbing ceiling, abundant sound-absorptive wall treatments and acoustical insulation on the wall behind the screen. As has been the case with traditional Left–Center–Right, Surround Left–Surround Right, Sub-bass channel arrays, the room should be designed to effectively stay out of the way of the sound coming from the loudspeakers.
Are adjustments necessary to an auditorium’s acoustics when alternative content, such as opera/ballet/classical, sports, gaming, wrestling, UFC or concerts, are brought into the space made much easier with the migration of the cinemas into digital video?
This question was posed to me a couple of years ago (actually six years ago—my, how time flies!) by Variety magazine for an article they were doing around the rock band U2 simulcasting some of their concerts into digital cinemas.
Actually, most multi-screen auditorium complexes are already designed to accommodate the aural needs of just about any alternative event. Cinema sound systems are capable of a wider dynamic (frequency) range than any classical composition or sporting event or even rock concert. As you know if you’ve followed this column space over the years, the only limitation where “sound bleed” or excessive sound transmission may occur is in the extended low frequencies, and that’s usually not due to insufficient demising walls between houses. If, as I like to characterize it, we are “rolling a lot of boulders” with the sub-bass loudspeakers, it will start to get noticed in adjacent auditoriums if the sustained sound levels exceed 90-100 dB sound pressure level (dB re: 20 µPa), particularly if a very quiet moment is occurring in the adjacent house. In 25 years of measuring sound levels of nearly every occurrence of low-frequency sound in the common world, I have yet to encounter sub-bass sound levels that exceed what occurs in cinema auditoriums.
Do motion-enhanced seats (sometimes called the fourth dimension of cinematic presentation) introduce any particular concerns acoustically?
Actually, yes, be somewhat concerned. Any transducer mounted to a seat or motor functioning to induce movement in individual seats or rows of seats becomes a concern because we are leaving the airborne realm of sound transmission and entering the world of structure-borne sound transmission. While the concern is probably moot for a single-floor cinema in a standalone building on-grade with no neighbors on the lower floor, this is occurring less and less often in multi-use developments.
Structure-borne sound transmission can be very challenging to control, because you can’t simply stuff some insulation into the cavity below the risers or mount the studs on neoprene pads. Structure-borne isolation typically requires fully decoupled masses of drywall ceilings or even completely floated floors, and costs for such elements can be quite steep, especially if being considered after the fact. The most efficient approach usually involves keeping the vibratory source as distant as practical from the quiet area on the floor below. A good rule of thumb to remember is minimum two full structural bays should occur between an auditorium equipped with 4D equipment and a quiet space on the floor below.
What design considerations are considered in renovating auditoriums for food service?
As strange as it may sound (sorry), thinking of “quiet food” is one of the most important considerations associated with expanding a patron’s food-service options. Nothing distracts from a suspenseful or tender moment more in a dark cinema than a metal fork clinking on a porcelain plate, especially if you have one of those folks behind you that aren’t satisfied that their steak was sawed completely through unless they have cut through half of the plate’s thickness.
That basic thought process aside, attention to the physical path being created in the renovation from kitchens and food-prep areas into the auditorium seating areas should be focused on keeping kitchen noise in the kitchen. Doors are typically freely swinging (non-latching), so avoid creating a line of sight between any seated patron and the kitchen doors. Kitchens should have efficiently sound-absorbing yet cleanable ceilings. That allows the noise build-up in typically acoustically lively kitchens to be kept in the reasonable realm. A swinging door stops very little sound transmission.
Considerations that don’t usually get properly vetted in food-service renovations are those items of equipment that clean dishes, transport compressed air, or freeze/refrigerate perishable food. Many times, space limitations locate these items of equipment under an auditorium’s risers or on an auditorium wall. Any item of equipment that induces pressure on a volume or flow of air, water or refrigerant should not be mounted on a wall common with an auditorium. Put storage shelves on auditorium walls. They’re usually fairly quiet.
Finally, I need to mention that I am corporately residing in new digs. The former company I co-owned was acquired by a multi-discipline engineering firm. I am now the president of a new venture, Acoustical Design Kubicki, Consultants in Acoustics. I welcome your feedback and correspondence at email@example.com, 913-400-3694.
Until we meet again, keep those questions coming!