Meeting Topic: Distributed Mode and Balanced Mode Transducers
Moderator Name: Dan Mortensen
Speaker Name: Marcelo Vercelli, Tim Whitwell, Tectonic Audio Labs
Meeting Location: Woodinville, WA USA
The PNW Section of the AES held the final meeting of 2017 on Tuesday, December 5, 2017 at the facilities of Tectonics Audio Labs in Woodinville, Washington, where we met for a tour and presentation on bending wave technology as used in audio transducer and system designs. There were roughly 35 attendees, of whom 19 were AES members. Section Chair Dan Mortensen started the evening off with a round-robin introduction of the attendees, followed by announcements concerning future meetings.
Dave Firestone of Tectonics Audio Labs introduced our presenters for the evening. Marcelo Vercelli is the CTO of Tectonic Audio Labs and owner of Chameleon Labs LLC. Marcelo has been designing and manufacturing professional loudspeaker systems since 1988. He founded two companies focused in the professional audio market segment and has been awarded five U.S. patents in the area of transducer technology and loudspeaker acoustics. For the last five years he collaborated on development of bending wave technologies and associated audio system designs, including Distributed Mode Loudspeakers (DMLs) and Balanced Mode Radiators (BMRs), while serving as CTO for Tectonic Audio Labs. He has experience in the areas of product development, industrial and mechanical design, acoustic and electronic engineering as well as manufacturing engineering.
Tim Whitwell, is VP, Engineering at Tectonic Audio Labs. During a 20+ year career in the loudspeaker industry Tim has designed a wide range of award winning BMR and DML transducers and systems for Hi-Fi, home theatre, professional audio, TV and compact portable sector. He specializes in DML and BMR technologies and the simulation of transducers and electro-acoustic systems. Tim is the cited inventor on a number of patents in the fields of acoustics, transducer design and haptic feedback technology.
Vercelli and Whitwell began by describing the development of the technology of Distributed Mode Loudspeakers, which began with research intended to find ways to reduce the noise in the cockpits of combat jet aircraft in the UK. Initial experiments wound up having the opposite effect, producing more noise. That suggested another use, and the company NXT was formed to develop the technology. NXT eventually became HiWave Audio, which was acquired by FLAT Audio Technologies. Tectonics Audio Labs is a privately held company providing speaker panels and OEM drivers for use in other products.
Distributed mode panels differ from traditional "pistonic" speakers in important ways. In a traditional design, the moving element of the speaker - cone or compression driver is functioning in a more or less "pistonic" fashion - it is "pushing air" as a single element, and great attention is paid in design to avoid any bending modes within the surface of the piston, as those will work against the goal of uniform movement. As the name suggests, Distributed Mode speakers are "all about the modes", with the goal being to have multiple modes across the panel, and to distribute those bending modes uniformly across the audio band being produced. Carefully designing the geometry, boundary conditions, locations of exciters and material properties of a panel radiator yields a diffuse sound field in which the directivity is no longer coupled to the size of the device.
Defining the edge conditions of the radiators - figuring out where to mount the panels to the structure - involves observation of where the modal lines in a panel under design concentrate, as these will be the points of minimal movement. Most of the design process involves exhaustive Finite Element Analysis of the behavior of the panels, including the effect of different shapes (including some 3-dimensional shapes for OEM products). The panels used in the Tectonics Labs PL-11 and PL12 speakers consist of carbon fiber skin sandwiching a honeycomb material. Current panels are designed to cross over to a ribbon speaker at 5 KHz, and to a subwoofer at around 100 Hz. One distinct advantage mentioned was that this means there is no crossover within the vocal range. Also, panels can be used alone (without sub or ribbon) as efficient ceiling mount speakers.
In addition to the DML panel, the Balanced Mode Radiator (BMR) speaker, smaller more traditionally shaped drivers which combine distributed mode operation with pistonic action were described. These allow a compact design to rely on pistonic motion for lower frequencies while using the distributed mode concept for higher frequencies.
Following the presentation, the chairs were cleared from the room so that attendees could walk the room listening to the pair of PL-11 speakers hung in the space. The space was the workshop for Tectonics Audio Labs, a hard-walled space with concrete floor, making a good space to demonstrate the ability of the panels to produce good level without exciting the reverberant modes of a difficult room. After that demonstration, the group split to rotate through two additional demonstrations in two different workspaces.
Written By: Dave Tosti-Lane, PNW AES At-Large Committee member