On Alternator Whine, A Noise That Messes Up In-Car AUX Ports

A couple of weeks ago, we reviewed Griffin’s Noise-Reducing Audio Cable, a special auxiliary audio cable designed to fight “alternator whine,” a high-pitched sound that appears when certain iPod or iPhone accessories are connected to the auxiliary (AUX) input ports in certain cars. Since AUX ports should deliver optimal sound quality when properly connected to Apple’s devices—unlike comparatively noisy FM transmitters and cassette tape adapters—users should expect to have clean a connection as possible between iPod or iPhone and the car, without interference. Yet that’s not the case, at least with some accessories, and thus this particular sound joined an increasing list of potential in-car audio issues users have experienced, including:

* Perceptible hard drive whirring sounds in the headphone ports of certain, older iPods.
* Perceptible but quiet signaling beeps and bloops in the headphone and Dock Connector ports of certain iPods, apparently related to changing menus and perhaps the “clicker” features of some models.
* Loud screeching noises (known as TDMA interference) emitted wirelessly by original iPhones and iPhone 3Gs operating in EDGE mode, correlated with any use of the cell phone, EDGE data, or occasional status checks between the phones and nearby cell towers.
* Quieter, higher, pitched noises emitted wirelessly by iPhone 3Gs operating in 3G mode, correlated with cell phone and data use.
* A high-pitched “alternator whine” related to an electrical ground loop, which starts as a perceptible but quiet whistle and appears to change pitch when the vehicle accelerates.

In our review, we temporarily put aside the question of whether car makers or accessory makers were to blame for this noise. After testing our vehicle’s AUX port with a custom-built dual 47 k ohm, impedance-matched loading resistor cable, the answer turns out to be “accessory makers.” By using filters to remove the high sound frequencies the whine falls within, the Griffin cable solves a problem that various accessory makers appear to have created themselves with engineering that—depending on one’s perspective, and the specific company in question—is either sloppy, deliberately bad, or deliberately good.

In any case, the cost to affected users is $20, and the need to use a long, bulky cable with a big filtering box in the center.

Viewed most charitably, or under the “deliberately good engineering” theory, in-car accessory makers should make engineering decisions that optimize an iPod’s sound output for the maximum number of cars, thereby enabling most users to avoid additional costs and suffering from noticeably reduced audio quality for the sake of insuring compatibility with a small fraction of problem vehicles. A company might argue that a minority of users will hear alternator whine because the accessory has been built to produce clean sound in the majority of cars; the solution for the minority is an additional cable. Assuming that the cost of making the main accessory work better with all cars is relatively high, or the cost of increasing compatibility for all is to decrease the sound quality for the majority, this might just be acceptable.

Less charitably, alternator whine from a ground loop could signal sloppy engineering—something that could be fixed very easily by a small change to the accessory—or worse yet, that the manufacturer is deliberately creating a sound problem that its own parts are required to solve.

It’s bad enough having to pay through the nose for iPod and iPhone accessories as is; a Monster Cable-like system of separately-sold magical “noise-cleaning” cables and chargers for specific cars would be a complete nightmare.

Our belief is that alternator whine isn’t being created intentionally by accessory makers, any more than Apple wanted to create the TDMA noises that have made iPhones less than fun to use in many cars. But as we’ve suggested to accessory companies who design these in-car products, it’s time to do testing and engineering for the most popular car makes out there, with a focus on making the best possible sound for the largest group of users. We were told by one company that it had for years been experiencing ground loop issues with Toyota vehicles, a reason why our Toyota Highlander test vehicle exhibited the alternator noise that Griffin’s cable can remove. But Toyota is the world’s largest seller of cars, and currently commands 16% of U.S.