Audio-Visual Core Facility
The Auditory-Visual (AV) Core Facility is ideal for research on spatial effects of auditory and visual sound sources on children's speech perception and comprehension, with special emphasis on the listening needs in children with hearing loss. The AV Core Facility includes:
AV Booth: a large sound booth with precise experimental control over sound and visual stimuli
Control Room: equipped with computers, amplifiers and other peripherals with cabling into and out of the booth via two holes in the front wall of the booth (the holes include conductive fill material)
Waiting Room for the parents/guardians and other family members of children participating as human subjects. This waiting room is used for consent procedures with the human subject and family, and is used for technical meetings by hospital personnel during other times
Office space for core personnel
AV Booth Construction
The AV booth (ETS-Lindgren) uses a single wall and ceiling sound isolation (AS-A506) with 6" thick wall panels (16 gauge steel outer skin, 1" gypsum wall, 5" acoustic installation and 22 gauge perforated inner skin). The AV booth floor is composed of an acoustically isolated floor system (4" thick, AS-R304E) with vibration isolation rails and nylon floor carpet. The internal dimensions of the AV booth are 19' by 17' with a height of 9'. An acoustically treated ventilation system, with ports into and out of the booth, is mounted on the external roof of the AV booth with silencers and duct collars connected to the HVAC system of the hospital.
An entrance door into the booth leads out from the control room. A ramp extends into the control room to accommodate the 7" step size into the interior of the AV booth. To provide additional sound absorption within the booth, Fire Flex melamine acoustic absorption wedges with a 4" thickness (Tecnifoam) are mounted on each wall and the ceiling. The acoustic reverberation time of the AV booth does not exceed 0.024 s at octave frequencies between 250 and 4000 Hz, and does not exceed 0.161 s at 125 Hz. An additional pair of bass traps is located at the corners of the AV booth to provide more attenuation at 125 Hz and lower frequencies.
Within the AV booth, lengths of steel tubing (Schedule 40 pipe) of circular cross-section with a 1" diameter are mounted onto the framing of the booth walls and ceiling (at a distance of 6" from the wall or 2" from the installed foam on the wall surface). These steel rails are installed on each wall horizontally with respect to the floor at a height of 48" and 96". An additional series of rails are installed in a rectangular configuration on the ceiling. These rails are covered by an acoustical foam cover along their lengths to minimize sound scattering. The rails provide a mounting point for speakers, microphones, televisions, cameras, and any other equipment being utilized in the space. The steel tubing may optionally be extended into more interior points of the booth.
Control Room Features
A control room outside the booth is setup with a second-generation Apple Mac Pro workstation. The workstation is equipped with an 8-core 3.0 GHz intel processor, 64GB of RAM, a Dual AMD FirePro D700 GPU, and a 1TB PCIe-based flash storage system. Video is handled directly by the Mac Pro, which is capable of delivering 6 simultaneous streams of 1080p video over HDMI, which is sufficient to generate separate video on 6 different HD television screens that can be used within the booth. The workstation connects to an equipment rack driving 28 channels of audio. The head of the audio rack is an RME MADIFace, a 196 channel input/output (I/O) USB3 audio interface. The RME passes a MADI signal to an Orion32 Antelope multi-channel array of analog-to-digital/digital-to-anolog (AD/DA) converters. An output analog signal is then passed from the Orion32 to an input in one of seven four-channel power amplifiers (model Art SLA4). From each amplifier output, a length of 10 gauge speaker wire enters the AV booth through one of two 3" square holes connecting to a series of aluminum trays lining the interior of the booth with banana binding post plates as exit points at locations within the booth.
The control room also includes an Apple iMac computer as well as a networked RAID storage array to store audio-visual files for use in experiments. The iMac is connected via USB to a Logitech PTZ Pro camera installed in the AV booth. This camera is used for both documentation and monitoring of the subject within the booth, with a live feed being broadcast to a waiting room on the other side of the control room for the convenience of parents/guardians and any family members. Additionally, the iMac is connected to a 3D printer (model MakerGear FDM) that is used to fabricate special-purpose adapters needed for the AV Core Facility or an individual experiment. For example, the 3D printer was used to make a mounting piece in a head-mounted gyroscope used in human-subject testing. Both Mac computers are equipped with professional audio and video editing software (Logic Pro Studio and Final Cut Pro) that is available to prepare experimental stimuli and analyze recordings after data are collected.
Controlling Sound within the AV Booth
A set of 25 6" Elipson Planet M spherical 2-way loudspeakers are available for mounting at any rail point in the booth. Each loudspeaker has a two-way coaxial driver with a 4" mid-bass, paper cone and damping process, and a 0.7" silk dome tweeter. The nominal audio bandwidth of each loudspeaker extends from 20 Hz to 20 kHz, although the response is attenuated below 200 Hz. The spherical external form factor of each loudspeaker helps control for directionality effects of sound, although the directionality index of each speaker is controlled for within the measurement software. The speakers use a custom designed, 3D printed nylon adapter to connect to a tool-less 1.5" ball joint system (model RAM). These adapters allow for the flexible mounting of loudspeakers, HD displays, or other peripherals on any of the rails within the AV booth. The aluminum trays are also equipped with four two-channel HDMI wall plates. These plates carry 1080p video signal to up to five 42" 1080p flat screen televisions (Vizio), or a 1080p projector (BenQ). The televisions can mount either on the rails inside the booth or attach to floor stands. The projector hangs from the ceiling and projects onto a 3.5 meter by 2.5 meter acoustically transparent vinyl screen.
A set of either two or four sub-woofers (Swarm model, AudioKinesis) are located at corners within the AV booth to generate sound below about 250 Hz so as to equalize the low-frequency spectrum at the location at which the listener is seated within the booth. A matched power amplifier is provided by the manufacturer (AudioKinesis) with cabling back to the outputs DA converters on the Orion32 Antelope.
Using custom room simulation, data collection, and video production software, the level of presented speech, background noise, localization, and artificial reverberation levels may be adjusted depending on the specific learning task used within the human-subject test protocol.
The laboratory also provides calibration equipment including multiple measurement microphones, and a KEMAR artificial head/torso that are available for use in all Boys Town National Research Hospital laboratories. Probe-microphone systems for recording and analysis of stimuli in the ear canal are available. Specialized software is available for implementing psychoacoustic paradigms, measuring acoustic stimuli, and analyzing data. There also is access to probe microphone/hearing-aid analysis systems, audiometers, tympanometers, and programmable/digital hearing aid systems.