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AMPLIFIERS
Amplifier technology has come along way. New technologies, like Class D amplifiers, allow car audio manufacturers to create small, powerful amplifiers optimized for specific applications like subwoofers. At an MSRP of $300 dollars, the KAC-8151D is a fine example.
First Look
The KAC-8151D is an attractive, true single-channel Class D amplifier rated to deliver up to an impressive 500 watts into a 1-ohm speaker load (See Sidebar). As with most Class D amplifier designs, the KAC-8151D employs an "always on" 18 dB-per-octave low-pass crossover that’s continuously variable from 50 Hz to 200 Hz. Other standard features include speaker level inputs and low-level RCA inputs and output. What sets this amplifier apart from others in its price range is its remote bass boost control, dynamic "Expander", and "Infrasonic Filter" — impressive features for an amplifier in this price range.
A Closer Look
Many amplifiers offer ways to boost the bass output. Here, the KAC-8151D doesn’t disappoint. With the remote control installed, you have the ability at your fingertips to boost 90 Hz up to 12 dB in 3 dB steps. While the selectable remote is quick and easy to use, I believe a lower center frequency, around 50 Hz, would yield better results.
The KAC-8151D also includes a correctly named "Infrasonic Filter" (most often called a sub-sonic filter). This feature protects your system by preventing potentially damaging woofer excursion caused by extremely low frequencies (below 25 Hz). By blocking these low frequencies with its selectable 15 or 25 Hz, 18 dB-per-octave filter, this Infrasonic Filter drastically improves woofer reliability and amplifier efficiency.
The "Expander" switch is different and interesting. The owner’s manual claims that selecting the switch increases the dynamic range. Does it work? I played 30 seconds of a bass track and measured the average output and the max output with the switch in both positions. The results yielded an increase of around 1.5 dB of dynamic range with the switch engaged. Did I like the sound difference? The jury is still out on that one.
Installation
The installation of the KAC-8151D went smoothly. Its well-made cast heatsink incorporates mounting feet that are solid and well placed. The power and speaker connections are on one side of the amplifier, while the low-level signal and adjustments are on the opposite side. The connections and adjustments are well marked. The connector size is adequate for its application and 40-amp fuse size. The cool blue LED on top of the amplifier lets you know the amplifier is working properly.
The KAC-8151D was easy to operate with a small adjustment screwdriver. The gain control and crossover are easy to use. The adjustment switches required a small pick tool and a steady hand to select.
Manuals/Web Support
The owner’s manual covers general safety precautions, features, and basic installation with trouble shooting advice. Given the low impedance capability of this amplifier, the manual could be improved by offering more detailed descriptions on how to connect multi-woofers for low impedance operation. Unless you understand speaker wiring and impedance, this amplifier is best installed by your authorized Kenwood dealer.
Many consumers (myself included) do their research about product on the Web. With that in mind, I went onto Kenwood’s Web site (www.kenwoodusa.com) and, through normal navigation, was able to get an excellent amount of information about the amplifier. No manual for the KAC-8151D was available for download.
Sound Q & Performance
Weighing in at a mere 6.5 pounds, the KAC-8151D packs a lot of punch in its small chassis. The amplifier developed 269 watts into 4 ohms, 414 watts into 2 ohms, and 517 watts into 1 ohm. Even though the current draw (55.4 amps) measured at 1 ohm exceeded the on-board fuse rating, the 40-amp fuse should prove adequate under normal operation. Driving the amplifier into clipping at 1 ohm quickly blew the internal fuse.
Efficiency is where this amplifier really shines. Its Class D design was extremely efficient in the 4-ohm and 2-ohm mode nearly hitting 90 percent efficiency! At 1/3 power (a low efficiency point of an amplifier), the KAC-8151D averaged 73 percent efficiency in all modes of operation, maximizing its efficiency in the 2-ohm configuration. At 2 ohms, this amplifier really delivers the power, taking only small sips from your vehicle’s electrical system.
Summary
The Kenwood KAC-8151D is a very good subwoofer amplifier perfectly suited to drive a pair of 4-ohm subwoofers. With its cool remote bass boost feature and excellent efficiency, The KAC-8151D is the great choice for someone looking for a full-featured amplifier that’s easy on your vehicle’s electrical system as well as your pocket book.
Lies, Damn Lies, and Amplifier Power Ratings
Kenwood claims their amplifier will make 1000 watts max power. I couldn’t foresee a situation where this amplifier could make a useable 1000 watts (you know, less that 50 percent distortion, etc.). Don’t blame Kenwood — the KAC-8151D is a damn fine amplifier. Their marketing people are faced with a dilemma: if they don’t exaggerate their maximum power, uneducated consumers might not purchase their amps. That’s because someone else is already making these incredible claims.
Here’s a good rule of thumb: If the power spec doesn’t have criteria in which someone could independently prove the spec, its just market hype.
Kenwood Responds: Kenwood provides multiple power ratings so that consumers can compare apples to apples ratings with a variety of competitive products. Maximum Power is one such rating that is commonly used within the mobile entertainment industry, and is often displayed on various manufacturer’s amplifiers and subwoofers.
Additionally, Kenwood provides other industry-accepted power ratings, such as the power ratings you list in the Specifications section of your review of the KAC-8151D. In fact, even Kenwood in-dash stereos are rated "Full-Bandwidth Power" in addition to the more widely publicized Maximum Power.
By providing as many different types of power ratings as we do, Kenwood feels that we are giving our customers the information that will enable them to make the very best decisions when planning and purchasing a mobile entertainment system.
The Kenwood KAC-8151D On The Sonoda Scale
Strengths: Good power output, excellent efficiency into 4 and 2 ohms
Weakness: Much lower efficiency in 1-ohm operation
Weight Factor: 517 watts at 6.5 pounds
Best use: Two 4-ohm woofers and this amp will rock!
Performance Value:
****
Performance vs. Weight:
****
Power vs. Efficiency:
****
Manuals, Online Support:
**
Kenwood KAC-8151d Specs
Price & Contact: $300; 800-KENWOOD; www.kenwoodusa.com
Operating Voltage: 14.4 Volts (11-16 Volts allowable)
Power Output: Max Power 1000 Watts (not verified)
Rated Power: 200 watts into 4 ohms; 400 watts into 2 ohms; 500 watts into 1 ohm
Measured Power: 269 watts into 4 ohms; 414 watts into 2 ohms; 517 into 1 ohm
Current Draw @ Max Power: 21.7 amps @ 4 ohms; 36.4 amps @ 2 ohms; 55.4 amps @ 1 ohm
Amplifier Efficiency @ Max Power: 89% @ 4 ohms; 81% @ 2 ohms; 66% @ 1 ohm
Amplifier Efficiency @ 1/3 Power: 73% @ 4 ohms; 76% @ 2 ohms; 68% @ 1 ohm
Frequency Response: 5 Hz to 200 Hz +0, -3 dB
Low-pass Crossover: Variable 18 dB-per-octave from 50 Hz to 200 Hz
Bass Boost: 0, +6, +9, and +12 dB Boost at 90 Hz via remote control
Infrasonic Filter: Selectable 15 Hz or 25 Hz @ 18 dB-per-octave
Amplifier Weight: 6.5 Pounds (2.96 kg)
Amplifier Dimensions: 11-1/4 inches x 2-1/4 inches x 10-9/16 inches (285 millimeters x 57 millimeters x 268 millimeters)
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