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Bridging the Gap Between OEM and Aftermarket
by mikel7829 06-09-2009, 11:03 PM


By Chris Yato
Photography by Casey Thorson

JL Audio's success in car audio largely results from their continual drive to make products that are both innovative and in tune with the market. Although they have primarily manufactured subwoofers and amplifiers rather than source units, processors or electronics, JL Audio's product development team saw the increasing number of vehicles with fully integrated source units (which make installing an aftermarket source unit extremely challenging and costly) as an opportunity to create a new product.

From a sound-quality perspective, the biggest challenge of trying to integrate with recent OEM source units has been extracting a quality audio signal with flat frequency response to feed into aftermarket amplifiers and speakers. Car manufacturers have been quick to adopt audio systems with digital signal processing that allow their engineers to "optimize" the sound behind the scenes with equalization that cannot be adjusted or defeated. Although this may be great for the factory sound system with factory speakers, it quickly becomes a problem when trying to integrate aftermarket audio products and make them sound good. While some factory systems still have unequalized or mildly equalized audio outputs that may have acceptable sound quality when interfacing with aftermarket amps and speakers, many use quite drastic equalization curves to try to level out the poor frequency response of cheap factory speakers. JL Audio's CleanSweep CL441DSP is the first OEM audio interface on the market that addresses the issue of imbedded equalization in many of today's vehicles.

The most unique feature of the CL441SDP is its 32-bit SHARC DSP processor that allows it to automatically "unequalize" the uneven frequency response of the factory audio signal through four channels of 30-band equalization. Some may argue that it is possible to interface an aftermarket equalizer (with the use of a real time analyzer) and perform the same task, but the CL441DSP automatically flattens the frequency response to +/- 1 dB in approximately 20 seconds if you simply insert the calibration CD into the factory source unit, turn up the volume to 3/4 volume and press a button. I think it would be safe to bet that even the world's fastest audio tuner wouldn't be able to beat the CleanSweep unit. Each channel is independently equalized to deal with systems that have different equalization curves for front and rear outputs.

The "flattened" audio output is converted back to the analog domain and output in the form of 8-volt RMS pre-amp outputs. Just to clarify, the CleanSweep is designed to create an electrical signal output with "flat" frequency response, just as an aftermarket head unit would, not to make the tonal balance of an aftermarket audio system (what you hear) sound "flat." The input level setting of the CL441DSP is also fully automatic, so whether you feed it low-voltage pre-amp-level signal or high-power amplified speaker-level signal, it compensates automatically and provides an 8-volt RMS pre-amp output.

After installing a CleanSweep unit, there are two ways to operate the volume. The first option is with the factory volume knob/steering wheel controls, just as it came from the factory. While this may be the most user-intuitive way, some factory audio systems incorporate volume-dependent equalization curves, and the CL441DSP cannot fully compensate for factory equalization when the curves vary with volume. The good thing is that many volume-dependent equalizer effects can be minimized (through the factory radio settings) and the volume-dependent curves are usually variations in bass response from the baseline equalization curve. This means that the "flattened" response provided by the CleanSweep at 3/4 volume will be in the ballpark throughout most of the frequency response even at 1/4 or full volume.



For audiophiles who prefer sound quality over ergonomics, the CL441DSP comes with a master volume control, a simple rotary knob that is small enough to be installed in many easy-to-reach places. The use of the master volume control allows the CleanSweep to provide maximum signal-to-noise ratio and eliminates any effects that a volume-dependent equalization curve would have.

The thoughtful product development team also incorporated an auxiliary input on the CleanSweep to allow your iPod (or other audio source) to easily play through the system via line-level input, rather than poor-sounding FM modulators. Left and right input level potentiometers with clipping indicators allow the volume of the auxiliary source to be matched to the volume of the factory source unit. The CleanSweep controls the volume of the aux input and switches between the factory source unit and the auxiliary source through the master volume control, so it must be installed when incorporating an external audio source. A provided source indicator LED can be mounted and glows green with the factory source and red with the auxiliary source.

Many of today's OEM source units are data-bus controlled and do not have dedicated wires that signal when the unit is on or off. The CL441DSP features audio input signal-sensing circuitry to control the remote turn-on wire for the aftermarket amplifiers (and other products). One detail of the signal sensing on the CleanSweep that I like is that the unit turns off immediately when the ignition is switched off, while other units stay active for the duration of their turn-off delay, even after you've removed the keys and gotten out of the car, making me wonder if the unit is going to power down or not. Another nice detail is that the signal sense circuitry has an on/off switch that allows it to be turned off in the rare case that the OEM system features its own remote turn-on wire or if the user wants to have a switch to manually activate the CleanSweep.

The CL441DSP is designed to correct the response in systems that have four full-frequency outputs. Some vehicles only have one pair of full-range outputs available (with the others electronically crossed over by the factory amplifier), which may result in losing the ability to use the factory fader when adding a CleanSweep. In many vehicles, the frequency-divided signals can be summed back into a full-frequency signal with the use of a line output converter with summing capabilities. Complex multi-channel audio systems like the Mark Levinson systems in the newer Lexus models and the surround sound systems in the Acuras and Volvos are not prime candidates for the CleanSweep due to their multi-channel, divided-frequency outputs.

As with any aftermarket car audio product, the CleanSweep cannot single-handedly rid the world of bad-sounding stock systems, but it will likely be considered a "superhero" by installers who have been struggling to get great sound into these "evil" integrated source units. I applaud JL Audio for creating a product that is well engineered and smartly addresses a major problem facing the world of aftermarket car audio. I'm sure that this is the tip of the iceberg and they are already working on the next several generations of CleanSweep products. With the CL441DSP, JL Audio has definitely set a high standard for other OEM audio integration products to come.
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File Type: jpg 0602cae_clean_03_z.jpg (25.4 KB, 924 views)

Last edited by mikel7829; 06-10-2009 at 08:12 PM.
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