Signal to Noise:Head Units - Marcus Fitzhugh

- How Things Work / DIY Section -

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For automotive usage, CDs are obsolete. CDs were an improvement over cassettes. Just as cassettes were better than 8-tracks, and 8-tracks over 45-RPM turntables (yes, there was a time when cars had turntables). Now, music stored on flash memory is an improvement over CDs. Why? CDs are bulky, skip, degrade in quality over time, and only hold about 70 minutes worth of music. Compare that to a head unit that reads solid state (flash) memory. Solid state memory is small, never skips, takes much longer to degrade (and when it does, can be easily copied and replaced), and has a storage capacity that cannot be compared to CDs.

The Alpine iDA-X305 is a good example of a head unit that reads solid state memory. Aside from an AM/FM radio, the X305 is designed to read digital files directly from an iPod or iPhone through a USB cable. In addition to reading an iPod or iPhone, it can both control and charge them. The Alpine will also allow you to make calls though the iPhone or any Bluetooth connected phone, but phone calls are an unrelated side benefit. If a buyer doesn't have an iPod or iPhone, the Alpine can read MP3, WMA, or AAC files from a USB powered drive. In addition to iPods, iPhones, and USB drives, a head unit like the X305 will also talk to the iRiver Clix, Creative Zen, or Toshiba Gigabeat through the USB connection.

For USB drives, I prefer solid state technology. Solid state drives (SSD) have several advantages over magnetic hard drives. The advantages stem from the SSD not having any moving parts. A traditional drive has a drive motor that's used to spin magnetic platters and at least one read/write head. The storage on a solid state drive is handled by flash memory chips. SSD's use less power, have faster data access, and are not impacted by jarring roads. If you're confused as to how to tell the difference, a thumb drive is a solid state drive. If you're shopping for a larger drive, just ask for a USB powered SSD.

An inexpensive 16GB flash drive (under $20) will hold over 150 hours worth of MP3 music. 64GB flash drives will hold over 600 hours. Those with a very large music collection can use a USB powered external hard drive. 500GB drives cost about $130. Using an MP3 format, music recorded at 64 Kbps to 128 Kbps delivers quality similar to audio CDs. Using 192 Kbps (50% better than CD quality), a drive can hold 750 hours per 100 GB.

At this point, you may have been swayed toward an AM/FM digital music manager that can interface with your phone and play music for over 5 months before having to repeat a song. However, you may have some other questions. Things like - Can it be installed by the average stereo guy? Don't companies like Mercedes-Benz and Porsche use fiber optic cables? Will my dashboard light up with "malfunction" messages? Won't I lose my multifunction steering wheel controls? Isn't Bose incompatible with aftermarket head units?

The answers to those questions are - Yes. I've seen "a" fiber cable. No. No. A $20 Bose interface will correct that.

Some people feel replacing the factory head unit on a Mercedes-Benz requires major work. Some stereo installers have told customers, "We'll have to rewire the whole car." Stereo installers may say this because they get paid by the job. On the other hand, some of them may not be very familiar with this task. I looked into this and the head unit can be changed by someone with the same tools you'd use to change any car radio.

Having access to a W208 CLK, I used that as a sample. The only fiber optics connection from a non-COMAND (no navigation) head unit is to the CD changer. Since the CD changer is obsolete, the fiber won't be a problem. Unplugging the fiber cable and leaving it detached does not cause any errors. Cars that are not equipped with a trunk mounted CD changer may already have the cable sitting around unplugged.

Retaining the steering wheel controls is straightforward. A company called PAC Audio makes interfaces for this. To use an Alpine head unit in a W208 CLK, a PAC SWI-CAN2 and a PAC SWI-JACK are needed. This same combination works with head units from JVC, Clarion, and Kenwood. For the same price, PAC makes other interfaces that work with head units from Sony, Eclipse, and Pioneer.

Installation is straightforward. The input side of the PAC SWI-CAN2 plugs into the Mercedes-Benz factory wiring harness. The output side plugs into the PAC SWI-JACK. The output side of the PAC SWI-JACK plugs into the Alpine head unit. Here's the conceptual basis for how this works: The PAC SWI-CAN2 reads the output signal of the Mercedes-Benz steering wheel controls and converts it to a universal signal. The PAC SWI-JACK converts the universal signal from the SWI-CAN2 to a format that is understood by the Alpine head unit.

The process of making an aftermarket head unit Bose compatible is simple. The theory behind how it works is a little more complex, but we'll cover both. Why anyone would want to use Bose amps and speakers is a matter of personal preference, but we'll delve into that as well.

First, the implementation. PAC audio sells a converter box called an OEM2. The audio output from the head unit goes into the OEM2. The output of the OEM2 is the Bose input. A wiring harness adapter is used so that everything plugs directly into the Mercedes-Benz wiring harness. Yes, it's that simple. The same plug and play routine works for Porsche. If you don't care why it works or why anyone would want to use Bose equipment, you can stop reading here.

How this works takes a little more thought. The input signal for a Bose amplifier is different from most "standard" car amplifiers. Like many high-end / professional audio equipment manufacturers, Bose uses a balanced, differential signal interconnection. Most aftermarket audio systems use an unbalanced connection. The PAC converter box reads the unbalanced input and produces balanced output.

As for why someone would use Bose equipment, it's a personal choice. Some appreciate the Bose active equalization. The active equalization is tailored for specific car models and is designed for the speakers in that car. The equalization curve for the specific car is programmed into either the amp or the head unit - it varies by manufacturer.

Other the other hand, some people hate Bose. Some haters feel the marketing department at Bose is better than their audio R&D department. They feel the marketing group makes wildly exaggerated claims about their mundane products. Outside of that very loud minority, the remaining ninety-five percent of the populous think it sounds pretty good. I'm not saying the minority is wrong, just that most people don't care. If you're a true audio fanatic, one who's verbose, bombastic, and determined to get your point across, I'm a ninety-five percenter. To me, music is just mindless entertainment while I'm driving.

Many people who dislike Bose refer to a quote from Stereophile Magazine where a reviewer wrote a Bose system was "unexceptional and unlikely to appeal to perfectionists with a developed taste in precise imaging, detail, and timbre, and that these shortcomings were an excessive price to pay for the improvement in impact and ambiance generated by the large proportion of reflected sound [to on-axis sound]." The same author also wrote "the system produced a more realistic resemblance of natural ambiance than any other speaker system." Two things. First, I can't tell whether he liked it or not. One minute he says it's unexceptional, and the next he says it's the most realistic thing to pass through speakers. Second, this Stereophile article is over 30 years old. Bose equipment has improved.

For me, this says it in a nutshell: Ferrari, Maserati, Mercedes-Benz, and Porsche all use Bose equipment in their optional high end audio packages. Call me a lemming, but if it's good enough for them, it's good enough for me.

Those with other preferences can eliminate the Bose system and use any amps and speakers they choose. The same applies to the head unit. Alpine is not the only manufacturer who has elected to move away from CDs. If you prefer another vendor, there's a good chance that vendor has head units that will read USB attached solid state memory.

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