While the law passed in California's legislature doesn't actually prescribe the noise-makers for hybrids yet, it's expected that the committee will be looking for ways to add noisiness to hybrid and electric vehicles, reports the AP. Aside from developing some proprietary technology, however, the already-developed and tested systems available from Lotus Engineering and Eberspacher GmbH appear to be the best solutions on the market.
Lotus' Safe & Sound technology uses a combination of speakers, microphones and advanced processing to deliver a quiet cabin ride while also ensuring the people outside the car can hear it coming by simulating a brawnier combustion engine's sound. The Eberspacher system is a great deal simpler than the Lotus unit, but features the same basic technology, plus an in-exhaust speaker that can actually be used to silence the car almost entirely, in addition to modulating the exhaust note to make it more noticeable or more pleasing, including tuning a hybrid to sound like a V8.
Not everything is in the clear for the measure, however. The governor, Arnold Schwarzenegger, still has to sign the bill, and though there are 300,000 of the cars in the state and it's a public safety issue, he has yet to comment on his stance.