Alpine 5-Channel AMP Review - 12 Volt Tuning

New Section !!From Editors Of Auto Sound & SecurityAlpine's latest five-channel offering will power a smaller, clean system or form the base of a larger scheme, and gets bonus points for delivering more power than it states. Todd Ramsey rides the pine.

There is a reason why Alpine is, hands-down, one of the most recognized and respected names in car audio: consistent quality. With its recent foray into the extreme high-end with the F#1 Status line, we were curious to see if a plain old, complete system amp would stoke our interest anymore.

Enter the MRP-F320 five-channel, an all-in-one powerplant meant to drive an entire system with conservative power (four channels and a fifth, more powerful, path to drive a sub). Simple on-board features suggest this amp is targeted at simple systems that thrive on moderate power and don't require insane amounts of signal processing.

On The BenchThe MRP-F320 is rated at 40Wx4; 120Wx1 RMS and you can bridge four-channel mode to pump out 100Wx2; 120Wx1. For our testing, we ran it at 4-ohm stereo for each of the five-channel measurements. We used the on-board fixed filter high-pass function to our 6.5-in. components and loaded a sub (@ 4-ohms) on the fifth channel via the on-board low-pass filter. We fed it a full 4.55 volts of signal input even though it's rated to accept only four. It turns out that it can even take a bit more before clipping.

The MRP-F320 hit its rated RMS 4-ohm power with absolutely no problem, even exceeding by almost 10 watts on the four channels and more than 20 watts on the sub channel. These measurements were taken with minimum measured supply voltage of 13.85. Not to take anything away from the amp's performance, but these very slight increases (and in other cases, decreases) however, are virtually inaudible under real-world conditions.

As usual, we like to note that although the MRP-F320 amplifier is rated to play 2-ohm stereo loads, our measurements and testing reflect what we feel provides long-term reliability and minimal installation problems.

Efficiency, Accuracy And FlexibilityIn terms of efficiency, the Alpine was about average. At full power into 4 ohms stereo, the highest measured current draw was 21.2a at a measured minimum supply voltage of 13.85. This rates about 62 percent. And although Alpine doesn't list an idle current measurement on the spec sheet, we found it was a minimal .5amps (500mA for those of you who've forgotten metrics).

Filter accuracy on the crossovers and bass boost was very good. Frequencies for both HP filters-fixed at 80Hz, 18dB/octave-were just about perfect. Since they were fixed at 80Hz, there wasn't any fine-tuning adjustment (if we had, for example, a smaller front or rear speaker arrangement to filter). The HP is simply switched on or off.

In off mode, those channels function full-range. The LP filter on the MRP-F320 amp is variable between 50-200Hz at 12dB/octave and can't be switched off, a good thing since you won't want to run a subwoofer full-range anyway. And more credit to Alpine for silk-screening accurate numbers around the rotary control corresponding to the 50-200Hz range.

The bass boost circuit almost made its rated spec. Claiming 8dB of boost fixed at 50Hz, we measured it just shy at 6.5dB. It is indeed, however, fixed at 50Hz. At any rate, we're not big fans of bass boost. Good installers should be able to get the same results with the correct enclosure and placement.

This amp is an easy install. It has a 30a on-board fuse, meaning you'll need to add a fuse at the battery for protection (Alpine suggests an additional 30a fuse). All power and speaker connectors sit on one side of the amp, while RCA, high-level inputs and various adjustments are located opposite. Installing a four-channel RCA signal cable allows fading between front and rear channels while the subwoofer stays non-faded. This is a nice, but often overlooked, feature. The trade-off of missing a dedicated sub channel RCA input is that you can't independently control the sub level if your head unit has a "sub pre-out" feature.

Finally, considering it has five channels, the MRP-F320 requires very little space for installation. It measures 10.8(L) x 9(W) x 2.25(H) in., which means it will fit under most front seats and nearly every trunk location, while still leaving room for Rollerblades and golf clubs. The manual suggests trunk mounting to allow the amp to breathe. We ran it hard at 4 ohms and found it only generated moderate heat. Give it 4 volts of input, set gains at minimum, run all five channels at 4 ohms and you'll likely never have heating problems.

Setup is also a breeze. Once we found 4 volts unclipped from our head unit, we just dialed in our low-pass crossover and went. If your source doesn't have a full 4 volts out, consider that the gain set in the middle position equals 1 volt of input and adjust accordingly. Better safe than sorry, amigos! The MRP-F320 comes with Alpine's usual fold out, multi-language manual. It's essentially a handy reference for competent installers, but if you need more explanation, consider having a pro install it.

The VerdictOverall, Alpine's MRP-F320 is a great, single chassis system amp that makes a great power plant for a single or dual pair of coaxials and a small, but powerful subwoofer. It installs and sets up easily, produces very little heat and draws light current (about 20amps, meaning you won't have to add caps or a bank of heavy golf cart batteries to keep it running strong).

It'll work fine with a stock, functional charging system. It won't satisfy every appetite for loud, as 50 watts (140 when talking subs) has it limits. But if you're looking for a solid front stage upgrade and subwoofer addition, or an amp to build a bigger system around, put this near the top of your list of potentials.

We then added a modest 5dB of gain overlap to account for the average levels of music. The measurements we come up with result from playing actual music, not test tones, bass discs, or sine waves. Here's what we got:

Directed Electronics Comp-X 12-Inch SubThe same folks that brought us Viper and Python continue to edge their way into the car audio domain. The Great Malpractitioner, Howard Doctor, took DEI's new Comp-X to the lab and finds a potent driver with a singular role.

After becoming a dominant force in the car alarm industry, it seemed natural for Directed Electronics to branch out into autosound. In the couple of years that its speakers and electronics have been on the market, they've made a real name for themselves for delivering excellent value. Brand new for 2001, the Comp-X 12-inch woofer is one of a series of new high-performance drivers aimed squarely at autosound competitors. The Comp-X series includes a 10-in. 5108 ($250), the 12-in. model 5128 ($325), and the 15-in. model 5158 ($375).

A Double StackBuilt on a strong cast-alloy, four-leg chassis with a black textured finish, the Comp-X fits into a standard 280mm (11-in.) mounting hole. Up front is a non-pressed paper cone, but it is the huge glazed paper dust cap that forms the actual radiating surface. Carried by a very wide gray foam edge and a pair of flat spiders, it bears a dramatic Comp-X logo. Deeper inside the Comp-X 12 is a large and heavy 65mm (2.6-inch) diameter voice coil. The coil has dual two-ohm windings with four layers each, wound on a glass-fiber composite bobbin, allowing convenient connection to two channels of a power amp, or as a single 1-ohm or single 4-ohm load.

The magnet system is a double stack of 180x90x20 ceramic rings, coupled with generously thick, chromed-steel parts. The bumped T-yoke includes a slightly extended pole for improved magnetic symmetry. This is dressed up with a handy rubber front gasket-and a not-so-handy rubber ring around the magnet, together with our favorite spring terminals and medium-gauge tinsel leads.

A Trade For More Musically Valuable TerrainBased on our lab measurements, particularly the high BL factor (16 Tesla-meters) and the high energy-bandwidth product (EBP) of 102, the ideal enclosure for the Comp-X is clearly a vented system. With a combination of a very large magnet (130 ounces) and a large voice coil, there is a tremendous amount of motor driving the Comp-X cone.

Our faithful Linear-X LEAP software suggested a vented box of 22 liters (0.8 cu. ft.), a very convenient size. But it also suggested a ludicrous 900mm (3-ft.) long port tube. We did some preliminary listening with more rational ports, testing the 22-liter system with a 600mm(24-inch) long port, 75 mm (3 in.) in diameter. This port seriously exceeds our guideline of no more than 5:1 length-to-width ratio for ports, but even allowing this compromise the sound proved too "dry" and lacked the output that we expect in the lower octave. Shortening the port tube to raise the tuning frequency of the enclosure proved to be both more convenient and satisfactory. The port change cost us 3dB of 30Hz output, in exchange for 3dB more output in the more musically valuable 50 to 70Hz region-a most welcome trade. In the revised system, the Comp-X was tight, yet powerful, with good deep bass extension.

We spent an entertaining Saturday experimenting with other enclosure types, including a small sixth-order bandpass system, but none of them approached the performance of our 22-liter vented system. After listening to several variants, our listening panel judged the 20-liter (.7 cu. ft.) configuration (with 280mm/11 in. long; 75mm/ 3-in. diameter port) to be the best sounding system. Even this dramatically shorter port still involved some juggling and the addition of a 90-degree pipe elbow to make it fit into the small enclosure.

The data sheet that comes with the Comp-X recommends two small, sealed systems, something we evaluated briefly and dismissed. Every manufacturer wants its drivers to work in every kind and size of enclosure, but the reality is that this driver is totally dedicated to vented systems and truly dismal when sealed. Perhaps the sealed box suggestion is intended for SPL competitors to keep cone motion to a minimum, but news flash: cone motion equals bass output.

Although not outrageous, the voice coil's inductance is 3.3 milliHenries, enough to prematurely trip the protection circuits of some power amps. The answer is to use an amp with very serious power supply, a factor that banishes most of the swap meet brands. The high inductance kept impedance well above the 1-ohm (both 2-ohm coils in parallel) that we expected, presenting a minimum of 2.5 ohms from 20 to 100Hz.

Distortion was about average at moderate listening levels, but rose rapidly as input power increased, reaching our six percent limit at 220 watts RMS. This represents the end of the driver's linear operating range, but additional power tests at 300 and 400 watts proved that the Comp-X still had some thermal capacity in reserve. We drew the line at 400 watts as the driver whimpered in distress and gross distortion. The factory data sheet indicates power ratings of 400, 700 and 1,100 watts, but at anything above 220 watts the sound quality deteriorates rapidly.

Gives A Good MassageSonically, the Comp-X 12 is fast and fluent. In our lab listening, it had plenty of output down to about 40 Hz, while in-car testing showed it went below 20Hz before fading fast. We experimented with our sweepable crossover and found 75Hz the ideal crossover frequency. This point is a little lower than we typically use, but not by much, and when worked in an 18dB-per-octave slope it allowed the Comp-X to almost "disappear." In unfiltered measurements, the Comp-X exhibited the normal high-frequency roll-off above 100Hz characteristic of heavy cones and high-inductance voice coils.

Starting with our orchestral tests, its performance was a pleasant surprise. Bass was very tight and well-defined, with plenty of authority on the kettledrum and bass. The low end of the piano test tracks did not expose any odd coloration or weaknesses, and it passed the 1812 cannon test with flying colors.

Moving on to more popular material, we gave it some of our toughest tracks to deal with, and in return it gave us a pretty good kidney massage. Annie Lennox's "Why" was warm and full, yet not fat at all. Paul Hardcastle's "Smooth Groove," always reliable for sound quality tests, showed the Comp-X to be capable of some subtlety and tact, while Thievery Corporation's "Focus On Sight" was built upon a rock-solid foundation of granite.

We used the fancy bass guitar line in Elvis Costello's "Everyday I Write The Book" for evaluating the subwoofer's integration with the main system, since the bass line runs all over the place around the crossover frequency. It passed this test with flying colors, integrating very well. With our most critical listening completed, we fed it some techno and turned it up to see how it behaved with a bass-heavy program and brutal output levels. Given the high 1-watt sensitivity of the Comp-X 12, it was no surprise that it generated a healthy 126dB in our test car, although sounded appreciably better when we kept levels down to a less abusive 118dB.

Thus Spake Judge HowardThe Comp-X 12-inch is a specialized driver with very specific enclosure requirements, positioned at the far end of the scale from generic replacement woofers. The benefit of this narrow design approach is that the Comp-X delivers a known and repeatable sound quality and quantity in every installation - namely excellent low bass from a small enclosure and stunning output levels. It doesn't seem to matter what Directed Electronics puts its hands to; it always turns out well.

Having tried to escape the car audio industry several times, only to be dragged back by bloodhounds, Howard Doctor's endearing writing style is a product of engineering prowess tempered by dry wit and legendary cider consumption.