Subwoofers in Cinemas - The Problem No One Discusses

It’s the movie watching problem no-one wants to talk about, but someone needs to address. What is that problem? Subwoofers in Cinemas. And why are subwoofers a problem? Seat to seat volume variance. Let’s take a look at this problem and how to solve it. 

Some years ago, I had the privilege, as part of a group from the Audio Engineering Society, of visiting NBC Universal Studios – Studio Post. Not only was the tour a lot of fun, but we met with the crew that was mixing feature motion pictures in the Dolby Theater. They are an amazing group of people, and they gave us a demo of their latest 3d audio mix. We were all blown away. 

Can I say something personal here? My first job out of college was working at Harrison in Nashville, doing engineering design on mixing console components and accessories. I worked with Dave Harrison and other outstanding technical people. The first Audio Engineering Society trade show I visited was with Harrison, and for that show I answered questions about the film console. It was fun to see two Harrison mixing consoles on the Studio Post tour.  

One of the problems discussed was the problem with subwoofers not delivering consistent volume to each seat. Here is where the laws of physics come into play.  Subwoofer waves are very long. A 100 Hz signal is approximately 11.2 feet (3.4 m) long. A 30 Hz signal is approximately 37.5 ft (11.4 m) long. This makes 3d sound positioning in the theater practically impossible for subwoofer sounds. To compound the issue, and to fill the space, cinemas install multiple subwoofers. Some cinemas have one subwoofer for every 25,000 cubic feet (5,666 cubic meters) of theater volume. In a very large theater with a high ceiling, that can turn into many subwoofers. 

What does this mean for patrons? Well, the subwoofer waveforms will naturally meet throughout the theater. When they meet, the waves mix together, increasing or decreasing the volume at that location. If you are sitting in a seat where the mix occurs, the volume for a special effect may be too loud, or too soft. This certainly takes away from the movie experience. 

What is the solution? The solution is to inject the subwoofer audio directly into each viewer’s hearing channel. What am I talking about? Each of us has more than one hearing channel. The first and most obvious channel is through the ears. This is the channel that cinemas currently use. The second, and less obvious channel, is delivering audio through bone conduction.   

Using the bone conduction channel, the theater can directly inject the subwoofer signal into each seat. Not only does this approach eliminate seat-to-seat variance, it also gives the patrons some feel of the special effects. Theme parks and military simulators have been using this hearing channel for many years with great success.   

The Clark Synthesis TST329 Gold and TST429 Platinum Transducers are perfect for this application. Problem eliminated!  Better movie experience!  More satisfied customers!