With about 90 million new vehicles shipped in 2019 (a number that will be down in 2020, for sure) and very conservatively assuming an average of four speakers in each vehicle comes to more than 350 million speakers. The future may see very different numbers - with the pandemic far less vehicles but each with far more speakers. This new math is about in ultra-near-field microarrays for each seat. Traditionally speaker selection and layout has been configured by the design team for the entire passenger compartment as a whole cohesive space, but the new trend is "personal audio arrays" designed for each individual seat.
The "Ultra-near-field" concept uses clusters of small full-range speakers configured and tuned as phased-arrays to direct sound to individual seats. If only one person is driving the vehicle, then the arrays will be optimized for immersive audio for the driver. When kids are in the back, they can watch and listen to cartoons while the adults in the front seats can get the news or talk on the hands-free speakerphone. Bass can be somewhat contained by the use of haptic drivers (bass shakers) in each seat driven by the relevant program material.
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Personalized sound zones inside the car have been previously attempted, but now speaker technology is allowing much more effective applications, combining clusters of small speakers with active noise cancelling (ANC) - a topic extensively covered in audioXpress
' June 2020 Market Update on Automotive Audio Solutions.
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In the next model years, we will see innovative mounting locations for new form-factor compact speakers in these microarrays including center dashboard, visor areas, A and B pillars (front windshield supports and door pillar behind the driver position). Also in the front and back of the headrests. These next-generation autosound speakers will likely be in the 2.5" range (at least in the horizontal axis) both to fit and to function in a full-range array.
And, active noise canceling (ANC) systems are expected to enable effective drive train, road, and wind noise reduction up to 500 Hz or even higher (using the headrest speakers for ANC). The micro-arrays and close coupling to the listeners, such as through headrests, enable practical ANC with far more viable results than using existing autosound design practices. Aside from smaller speakers, expect to see higher thermal power handling in these drivers than what you would expect. ANC requires continuous operation, resulting in the need to re-scale for voice coil overheating and power compression. So larger voice coil diameters, ferrofluids (even in full-range drivers) and other design techniques will keep transducer engineers busy adopting techniques learned in pro-sound as well as past solutions from autosound aftermarket designs.
Installation of factory engineered systems using high power, compact, full-range drivers in micro-arrays will be extensive, including in-door speakers with clearance for full window roll-down, and most intriguing, the center stage in-dash, the A and B pillars, and head rests.
By bringing speakers closer to the listeners, there are significant weight savings, and anyone involved in the automotive industry knows that all vehicles designs are subject to strict diets. Part of the solution that the automotive industry has migrated to include lightweight and streamlined wiring harnesses (often with aluminum conductors instead of copper) with multi-pin termination, fiber optics, and Class-D amplifiers. Neodymium magnets on speakers has also contributed, but the pressure is on to go further.
Compared to current state-of-the-art automotive systems, micro-array and headrest systems offer weight savings of more than 50%, while still delivering an immersive audiophile-quality listening experience. This is achieved using small drivers in lightweight enclosures, and DSP-powered beamforming to deliver acoustic pressure to precisely defined sweet spots. Adding smart haptics leveraging DSP and tactile perception, significant further gains can be realized by lowering subwoofer amp and speaker weight.
The next-generation autosound speaker micro-arrays has an impact on the transducers and their performance targets. While smaller speakers positioned near-field to each listener will enable personalized audio for each seat, with clean direct sound to each listener, they will also provide effective zonal ANC for reduction of road, tire, and wind noise to 500 Hz or higher. Yet, attempting this for extended freeway driving for hours will result in power compression to build up in typical mini-speakers.
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| Voice Coil featured the Prescient Audio TD-12 woofer in its Test Bench column, in August 2015 - now available online. |
ThinDriver Technology
These transducer design changes do not come from thin air. A pioneering effort, the ThinDriver has been in development since 2008, and the first working prototype, under the Prescient brand, was presented in 2010. The concept was named an International CES Innovations 2014 Design and Engineering Awards Honoree. Conceived of by Paul Niedermann with engineering support by speaker industry veteran Bob True, patents were applied for in 14 countries to protect the invention, granted in 2016, and more recently in 2019. The thin speakers can be made for anything from smartphones to laptops.
The first implementation was in 2016 with an autosound aftermarket 12" TD-12 woofer. The TD-12 had a physical mounting depth of only 2.25" to the bottom of the frame. The TD-12 had a stiff flat 12" cone that uses a carbon fiber surface sandwiched with a polyurethane composite formulation and a 9" diameter flat poly cotton spider. All this, driven by a 250-mm diameter (9.85") voice coil wound with flat copper-clad aluminum wire (CCAW) parallel wound.
The TD-12 was characterized by Vance Dickason, in the August 2015 edition of Voice Coil, but by the time the product was launched the remains of the autosound aftermarket evaporated. With 1000 W power handling and a retail price of $1,000, the autosound OEM business did not bat an eye.
Prescient faltered and Len Foxman, one of the investors, bought the assets and relaunched the company as Eagle Audio in Chicago, IL. For branding and marketing, the new-generation ThinDriver products will use the Trulli Audio name.
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The Trulli TD38S 2" (JAM5) micro-array speaker is a promising solution for automotive personal sound zones with ANC, due to its combination of high thermal power handling while maintaining a small footprint and shallow depth.
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For autosound near-field arrays (and quite a few other applications) the Trulli TD38S 2" ("JAM5") is impressive, with its combination of high thermal power handling while maintaining a small footprint and shallow depth. The topology is a flat diaphragm, by repositioning and expanding the voice coil to the juncture of the diaphragm periphery and the juncture of the surround. This 2" speaker boasts a 1.3" voice coil. This configuration also enables more spider corrugations so both huge gains in excursion and thermal power handling are practical.
Stacked (double) spiders further enable enhanced coil centering and distortion reduction. The TD-38S increases the volume velocity (pumping power = piston x excursion) through a square diaphragm for over 20% more piston area than a round speaker.
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This is the new-generation ThinDriver TD 200 woofer from Trulli Audio.
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Also in late stage development is the TD200. This is a 10" woofer with a 7" diameter voice coil with less than 3" depth (which includes clearance in front of the speaker for excursion). Ideal for in-wall subs, underfloor autosound, and truck mount (or even in the spare tire), and other applications.
Trulli is looking for development partners and licensees, and will soon be launching a consumer audio product. For further information, contact Len Foxman.
