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A New Reference Listening Room for Consumer, Professional & Automotive Audio Research
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by
Dr. Sean Olive
Director of Acoustic Research
Harman International R&D Group
Overview
Harman Reference Listening Room:
Motivation for room
Description and features
Acoustical performance
Summary & Future Work
Motivation
Global Harman standard listening room for:
training & selecting listeners
product research & competitive benchmarking
cross-site testing and validation of listening test results
Why a standard listening room?
Listening tests can be replicated at multiple Harman sites while controlling important listening room nuisance variables
Benefits:
cross-site test validation, larger listener pool, greater flexibility in scheduling listening tests, study cultural-demographic differences in preference
Listening Room Nuisance Variables
Timbre
Preference
Distortion
Spatial
Influence
Dynamics
Main Features of Room
Quiet (low background noise)
Adjustable room acoustics
High quality calibrated playback system
Automated in-wall speaker mover
Automated control, collection & analysis of listening test data
Harman Reference Rooms
Northridge
Farmington Hills
Bridgend
Karlsbad
Shanghai
Room Dimensions
Rectangular shape (common & provides symmetrical distribution of reflections )
Supports 7.4 channels arranged in ITU-R circle
Large enough for 6 listeners
6.4 m (w)
2.9 m
7.32 m (l)
2.74 m (h)
Construction
Laminate floor
Foam Pad
1.9 m plywood
5 x10 cm wood studs on neoprene sleepers
Concrete Slab
1 layer of 1.9 cm plywood
3 layers of 1.59 gypsum board
5.08 x 25.4 cm wood stud
15.24 cm metal stud
1 layer of 1.27 cm gypsum board filled with fiber glass
1 layer of 1.27 cm gypsum
5 x 15.24 cm wood stud
1 layer of 1.9 cm plywood
3 layers of 1.6 cm gypsum board
9.2 cm metal stud filled with fiberglass
1 layer of 1.27 cm gypsum board
Acoustical Treatment
Removable wide-band absorptive and diffusive wall treatments to simulate variety of different acoustics
Removable area floor rug
First lateral sidewall reflections from front channels left untreated to encourage spaciousness, image widening
Front + rear wall reflections absorbed and diffused (< IACC)
RT60 Measurements
No absorption (bare room)
Seats/carpet only
Absorption Only
Seats/Carpet + Absorption (no diffusion)
Reference Setup (seats/carpet, absorption + diffusion
Reference Room RT60
Background Noise
Microphone Self-noise
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~ NC-15
Note: Measurements are flawed > 1 kHz and are being repeated due to self-noise of microphones
Playback System
Our requirements:
In-Room Loudspeaker Response
Each curve based on a spatial average over 6 seats with 48 ppo, 1/6-octave smoothed
Average of 7
Front L
Front R
Front C
Side L
Side R
Rear L
Rear R
AES-EBU
Firewire
Toslink
CAT-5
In-wall speaker mover
Allows multiple comparisons between three different in-wall / on-wall /near-wall / desktop speaker systems
Automated control via Harman Listening Test software
Loudspeaker Types For In-wall Tests
In-wall
Near-wall
Desktop
On-wall
Acoustically transparent curtain
Summary
New Harman Reference Room designed to control important loudspeaker-room variables for product testing & research
Allows validation and comparison of test results across multiple Harman sites
Main features:
Future work
Provide objective and subjective verification that all rooms are similar: perceptual confirmation using binaural room scanning, listener training, test results
Study perceptual effects of different acoustical effects on loudspeaker-room interactions, particularly how they influence performance of loudspeaker-room correction technologies