The Sphere is all about entertainment. The entertainment incorporates numerous special effects, including infrasonics and haptics, to create 4D environments. In this case, “D” doesn’t refer to a physical dimension; it refers to additional sensory inputs beyond audio and visual.
This FAQ reviews the use of moving magnet linear motors and class D drivers and amplifiers to deliver the infrasonic and haptic effects.
The Sphere has 18,000 seats, of which 10,000 are outfitted with haptic and infrasonic technologies. The haptic technology is augmented with 2,500 audio channels provided by 718 quad-output audio amplifiers.
The haptic system is called Mover, and it lets audience members feel sound by vibrating the seats enabling them to feel the sound through bone conduction that stimulates the inner ear and generates perceivable sounds and sensations.
The system uses a high-efficiency moving magnet linear motor that can deliver significant power and highly controlled maximum sound pressure levels (SPL). Moving magnet drivers consist of multiple co-packaged permanent magnets placed between two electromagnet coils. The permanent magnet assembly can move while the coils are stationary. An external class D amplifier drives the coils to maintain system efficiency and minimize heating. This approach is especially beneficial for low-frequency infrasonic movements, where large forces are needed to produce sustained sound and vibrations. A mover is a shaker-type transducer and requires 100 W to deliver up to 900 N (200 lb) of force (Figure 1).
A mover is available in direct drive and inertial drive models. Direct drive Movers attach to a surface like a floor or, in the case of the Sphere, the bottom of a seat. These Movers excite the surface with ultrasound energy and can create an offset of ±15 mm. In addition to vibrating, it can move sharply to create the sensation of falling or jumping off a ledge. Mover is available with a subharmonic generator that reproduces ultra-low frequencies down to 5 Hz. For example, four direct drive Movers in parallel can vibrate and shake a platform with 4 people using 100 W at 5 Hz to simulate riding a vehicle down the road.
The piston rod drive in the direct drive models is replaced with four holes in inertial drive Movers. These Movers are also attached to a surface like the bottom of a seat. In this case, the ultra-low frequency sounds from the Mover excite the surface and deliver sensations to the person in the seat. Inertial drive Movers can’t deliver any offset movement like that produced with direct drive models.
Class D audio
In the Sphere, the Movers are augmented with 2,500 audio channels provided by 718 quad-output class D Quattrocanali audio amplifiers. These 1U high amplifiers are available in models rated from 1,200 to 9,600 W of audio power (Figure 2). These digital signal processors (DSP) controlled amplifiers include power factor correction and have an input voltage range of 90 to 240 Vac. Their smart rails management (SRM) technology uses real-time voltage tracking to minimize the differences between the voltages on the output rails and improve overall efficiency.
Quattrocanali technology highlights:
- Texas Instruments C6000 multicore DSP.
- Dual 24-bit at 48 kHz tandem AD/DA converter architecture.
- Input/output independent parametric equalizers on each channel, plus raised cosine, infinite impulse response (IIR), and custom output finite impulse response (FIR) filters.
- Up to 100 ms delay for time alignment of channels.
- Active dampening control and cable compensation for effects of the added resistance due to varying cable lengths. By entering the length and diameter of the cable, the amplifier automatically compensates to ensure the same power is delivered to each speaker.
- The TruePower limiter modulates the gain by tracking the impedance curve, allowing control of the real output power, and reducing the temperature of the speaker voice coils.
- AES67 digital audio networking is available on some models. AES67 is the industry standard for the transport of high-performance audio (at least a 44.1 kHz sampling frequency, at least 16-bit resolution, and latency of less than 10 ms) over IP networks.
Haptics and infrasonics are important technologies used to deliver an immersive 4D experience at the Sphere in Las Vegas. Those technologies augment the immersive audio and visual systems in the Sphere. And they rely on class D power conversion to deliver high-efficiency solutions.