Space Theater Sound System

When planning began for the Space Theater’s new sound system, 3 considerations arose immediately: 1) noise & vibration control, 2) architectural acoustics and 3) the sound system technology itself.

1. Noise and Vibration Control

Isolation from noise sources inside and outside the theater such as traffic, fans, compressors, IMAX projector and the eventual Fulldome projector.

The IMAX projector is quite loud, and we wanted to reduce the amount of leakage from the projection booth into the theater. Unlike conventional booths, located in the rear of the theater and separated by glass, our projector is underneath the center section and moves up a 2 story elevator to the center of the theater. The large box in the middle of the upper set of seats is the location of the projector when in operation. The central position at the focal point inside a hemisphere causes the sound to be even louder.

It’s like the whisper dishes in the Science Center exhibit area!  The cube the projector operates in is made of concrete, and will be covered inside with new soundproofing material. Additionally, the front of the projector will have soundproofing installed in the form of a “bladder”, a flexible material which will seal between the projector and the concrete box when it is in the upper position.

We were surprised to find that much of the IMAX projector’s noise actually comes though the glass of the lens, and there may be little that can be done to reduce this. However the lens is being replaced in the upgrade and this is an unknown factor for now.

Our plans for the future include a Fulldome projector located in the central area called “the pit,” the location currently occupied by the Digistar, our existing digital star projector.  We want this projector to be as quiet as possible and plan to use external cooling, routing the heat exhaust though the air ducts located on the walls of the pit.

2. Architectural Acoustics

A major goal of acoustics is elimination of unwanted sound reflections and control of reverberation to produce a good listening environment. Extensive replacement of deteriorating fiberglass sound proofing material on the theaters interior walls was completed during the replacement of the dome structure. The reverb time was measured at less than 3 seconds, prior to the refurbishment process. We look forward to a reduced reverb time when we are finished.
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3. Sound System

Advancements in sound system technology since the original system was installed in 1973 enable a higher dynamic range and better quality reproduction, as well as ease of operation and maintenance. It was a testament to the designers that a system installed in 1973 continued daily operation with almost NO lost performances.

Sound Source

For 35 years we operated an analog sound system. The main sound source was a 35 mm magnetic tape machine called a Magnatec. The tape was in the same format as 35 mm film, with sprockets on the side. Once a mainstay of theater sound and commonly used in Hollywood mixing rooms, this system has been completely abandoned in modern production facilities for digital production.
The sound produced by the Magnatec was routed to a control panel custom designed for us by Pacific Recorders. Each sound source could be routed to a different amplifier and speaker location, and its level was controlled by a manual control. While extremely reliable, many components used in these devices are becoming difficult to find and repair. The crown DC 300 amplifiers we used are now obsolete.

The replacement for the sound source is a Digidesign Protools HD system. The heart of modern sound production and playback, and ubiquitous in recording studios, this hardware and software combination allows precise synchronization with film or video, and control over every possible parameter of the sound such as volume, equalization, panning and much more. The system is capable of playing a wide variety of digital formats, up to an extremely high level of quality. This was specified to ensure the system was future proof and expandable. While the fast pace of digital improvements my not allow the new sound system to last 35 years, we are satisfied that it will give many years of service, and contains the ability to add additional capability when required.

Unlike DVD s, theater sound is uncompressed, 48 kHz, 24 bit audio. Every individual track is completely separate, and not “matrixed” together.

New sound tracks will arrive on multiple CDs, and will be copied onto the computers hard drives. Old films that are not available in the new format will be converted to high resolution digital audio in the production facility and made available for playback in the theater. The sound track is synchronized with the film using SMPTE time code generated from a tachometer on the IMAX projector.
The production facility in the basement will function as a back up in case of problems with the main sound source.

AMPLIFIERS AND SPEAKERS

We elected to use the QSC Audio amplifiers and speaker system. We have used some of their components for several years already with no breakdowns.
However, their system is much more than just amplifiers and speakers. Each component contains built in digital signal processing that will replace the old racks of equipment such as equalizers, delays and crossovers. A self monitoring facility will make reports via email on the systems health. I will get detailed information on specific problems with the sound system.

This is a 3 way speaker cabinet. Two 15 inch speakers for the lows, one mid range and one high frequency driver divide up the sound spectrum and route the appropriate portion to the driver capable of handling it. It is 74″ high by 30″ wide and can deliver 1000 Watts.

dcs_sc-423_hi

QSC 3 way speaker cabinet ( QSC 424-8-F)

Below are shown two  of four subwoofers that will handle the low frequencies.

Each 30″ X 48″ cabinet can handle 1500 watts.

Add them all up, and that is a watt of power. (sorry)…

dcs_sb-5218_7218

The old speaker cabinets were up to 15 feet from the screen causing some diffusion of the sound though the metal dome skin.These speaker cabinets will be mounted directly on the dome on an ingenious trolley system designed by Spitz Inc,  that will allow us to raise and lower the cabinets with a built in winch.

This is all going in now, and we are so excited! We can’t wait to start hearing sound through this tremendous system!

 

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2 Responses

  1. What QSC amps are you using? and what processing
    are you using?

  2. Those speakers look really great, i would love to havet them in my living room.

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