Oct 21, 2004 4:32 PM, By Barry Cleveland

HIGH-RESOLUTION ACTIVE STUDIO MONITORS

Mackie has been, and remains, one of the primary players in the project studio revolution. Its 8-bus analog recording console is arguably the standard by which other small consoles are judged, and the company’s new Digital 8-Bus console promises to be a strong contender in the burgeoning digital mixer market. In addition to mixers, Mackie has also produced the UltraMix automation system, the FR Series of power amplifiers and the new HUI controller for Pro Tools. However, an active studio monitor is one product that most people probably didn’t expect Mackie to make. Retailing at $1,498 a pair, the Mackie HR824 High-Resolution Active Studio Monitor carries on the company tradition of offering products loaded with professional and often innovative features at a reasonable price.

Mackie spent a lot of time and money developing the HR824. Specialists were brought in to augment the design team and very expensive new test equipment was purchased, such as an Ometron VPI4000 FFT analyzer. Mackie’s goal was to create active monitors with an exceptionally flat frequency response, which would be flexible enough to operate optimally in any reasonable listening environment. To achieve this, the developers went back to square one and took a fresh look at all of the components involved.

NOW FOR SOMETHING COMPLETELY DIFFERENT
Perhaps the one thing that most distinguishes the HR824 from other monitors is how it handles the waves emanating from the rear of the woofer cone. Instead of using a port to extend low-frequency response, the HR824 employs a 6x12-inch passive radiator made out of a composite honeycomb material. This “mass-loaded flat piston” is mounted on the inside rear of the cabinet and radiates nondirectional bass energy, complementing the woofer. As far as I know, Mackie is the only manufacturer that has employed a passive radiator in a professional monitor design. The woofer itself has an 8.75-inch die-cast magnesium frame, a massive oversized magnet structure and a mineral-filled polypropylene cone. The other end of the frequency range is handled by a 1-inch high-frequency driver with a viscous edge-damped aluminum-alloy dome and a ferrofluid-cooled voice coil. The driver is physically aligned with the woofer and works with a huge, nonresonant, zinc exponential waveguide, which precisely controls high-frequency dispersion. Each speaker is individually calibrated by hand under lab conditions before being shipped.

Cabinets are made of 3/4-inch MDF wood with a 1-inch-thick MDF front panel featuring radiused edges to reduce diffraction. An internal “H” brace contributes to rigidity, and internal reflections are absorbed by a foam-filled acoustic damping material. The integral power amplifiers and other electrical components are mounted on a large metal chassis, which is partially recessed into the cabinet. The external side of the chassis contains the HR824’s various controls and very helpful graphic representations of their functions. Audio inputs and the IEC power cord socket are located on the bottom of the chassis, exiting down, allowing the speakers to be flush-mounted against a wall without crimping any cables. Audio is input via balanced XLR or 1/4-inch TRS connectors, which also accommodate unbalanced TS plugs. The jacks are wired pin 2/tip hot and connected in parallel so they can be used for daisy-chaining to other speakers or amplifiers. Input sensitivity is adjusted from off to normal (+4 dBu) using a pot on the rear panel. Internal shielding reduces noise from outside sources.

The HR824 employs Mackie’s FR (Fast Recovery) amps. The low-frequency amplifier is rated at 150 watts into a 4-ohm load. The high-frequency amplifier is rated 100W into a 6-ohm load. Both amps operate at <0.035% THD, with a signal-to-noise ratio of >102 dB (referenced to 100W into 6 ohms). A modified 24dB/octave Linkwitz-Riley crossover operates at 1.8 kHz. The HR824s also feature overload and thermal protection. If the OL indicator on the front panel lights for an extended period, then a very audible limiter automatically reduces input level. If they become too hot, then a thermal protect circuit switches the amplifiers to standby mode until they cool.

On the rear panel are four three-position switches: acoustic space, low frequency, high frequency and power mode. The acoustic space switch adjusts the HR824’s bass response to compensate for room placement. The whole-space (normal) position is recommended when the speakers are free-standing; the half-space setting cuts –2 dB at 100 Hz to compensate for nearby placement against a wall; and the quarter-space position cuts –4 dB at 100 Hz to compensate for corner placement. The low-frequency switch inserts a steep roll-off at 37 Hz (normal), 47 Hz or 80 Hz. The latter is used to simulate the limited low-frequency response curve of some small near-field speakers. The high-frequency switch boosts or cuts 2 dB at 10 kHz to compensate for slightly bright or dull mixes. The power mode switch works with the power switch on the front panel. In its off position, the power amplifiers are placed in standby mode; in the on position, the front panel switch controls power on/off; and in the auto-on mode, the amps turn off automatically when there is no signal present (-45 dBu minimum) for five minutes and back on once the signal returns. When the speakers are powered up, there is a four-second delay while the power supply and circuitry stabilize.

LISTEN TO THIS
Mackie asserts that the HR824s are “smooth from 39 to 20k Hz (±1.5 dB),” and our tests corroborated the claim. This is no mean feat for monitors this size and at this price. Though they may lack some of the openness and depth of field that I have experienced using much more expensive active monitors, there can be no question about their frequency response. You may or may not like what they have to say, but they speak the truth. They also have a wide off-axis listening range due to the high-frequency dispersion of the waveguide. Nevertheless, I invariably got the best results while sitting in close in a classic triangle relationship to them.

I used the HR824s while mixing a project by composer and slide-guitarist extraordinaire Carl Weingarten, whose music has been described as “world music with a science-fiction edge.” Weingarten combines guitars, bass, acoustic percussion, sequenced samples, ambient sounds, cello, sax and other instruments in complex, layered mixes. The HR824s performed admirably, allowing us to distinguish very fine shades of tonal color and to establish subtle timbral and harmonic relationships between sounds. When the mixes were played on other monitors, including some that cost more than twice as much, they translated very well. I also listened to quite a few CDs using the HR824s. I chose four particular CDs for my most concentrated listening because they each presented a different sort of challenge: Jon Hassell’s City: Works of Fiction, Led Zeppelin III, Charles Mingus’ Epitaph and Cloud Chamber’s Dark Matter.

I chose the Hassell recording because of its extremely high and low frequencies, its use of sophisticated effects and the density of the mixes. The HR824s handled the ultralow bass remarkably well, considering their size, while the mids and highs were tightly focused, and the stereo image well defined. The production values on this recording are very high, so no significant problems were apparent.

Led Zeppelin III was chosen because it is a classic analog rock recording embodying all of the technical limitations of its era. The HR824s revealed lots of tape hiss, bleed-through, distortion and even Mellotron wobble. Of course, they also revealed the innovative panning, double-tracking, and reverb and echo effects that distinguish this as one of the most influential rock recordings ever made.

Epitaph is a work for “jazz orchestra,” recorded live in 1990, long after Mingus’ death. The orchestra comprised 31 instruments, including six trumpets, six trombones, eight saxes, contrabass clarinet, vibes, two bassists, etc. It was recorded in orchestral fashion, with one overhead stereo mic pair and spot mics on the various sections, and it displays all of the strengths and weaknesses commonly found in such recordings. The HR824s revealed the flaws but allowed each instrument to “breathe” in its own space. The overall imaging was extraordinarily clear and detailed.

Dark Matter is a CD by Cloud Chamber, an improvisational quintet comprising fretless bass, cello, cymbalom, percussion and (me on) guitar. I chose it because I mixed it using much more expensive monitors, and I wanted to see how those mixes would fare on the HR824s. I am happy to report that they translated very well, and that there was really not a lot of difference between the two. The same problems were evident (such as a very slightly distorted cymbalom part on one piece) but so were the more subtle details (such as slight auto-panning effects, complex reverb tails) and the overall clarity and spaciousness.

If you are in the market for a pair of compact active monitors and you are not afraid of the truth, then do yourself a favor and give the Mackie HR824s a critical listen.

Mackie, www.mackie.com.

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Lab Analysis of the Mackie Monitors
By Mike Klasco

Physical Characteristics
The Mackie HR824 monitor’s cabinet is solid, with 3/4-inch MDF sides and back covered with vinyl laminate. Internally, an H brace between the front and rear baffles further increases rigidity. The front baffle is 1-inch-thick MDF. No grille is provided, but a screen is integrated into the tweeter waveguide. The enclosure is stuffed with two blocks of open-cell foam. The drivers are recess-mounted flush into the baffle with an integrated die-cast tweeter waveguide/woofer trim ring. The front baffle of the enclosure has a “waveguide” profile, which provides some pattern control above 3 kHz and lessens “spill” onto the mixing board and adjacent surfaces. A large 6x12-inch honeycomb passive radiator is mounted on the rear baffle.

The woofer features a rubber surround and curvilinear polycone. It has a bucking magnet to reduce stray flux and appears to be similar to a Vifa or Seas model used in another popular studio monitor. The flat spider provides more linearity than a cupped spider. The frame is cast (does not drain magnetic flux from the motor structure) and the motor structure (pole piece) is vented, which helps keep the voice coil cool and reduces power compression.

The aluminum-dome tweeter with rubber compliance is a popular Seas model. The magnetic structure is ferrite and, like the woofer, has a bucking magnet to reduce stray flux. The voice coil is ferrofluid-cooled.

Line-level input is via balanced XLR and 1/4-inch phone connectors; an input limiter reduces the chance of overdriving the system. Discrete amplifiers drive the woofer and tweeter separately, and equalization further linearizes frequency response. A rubber vibration isolator is positioned between the amplifier section and the cabinet, and a “low hum field” toroidal transformer is used in the power supply.

Acoustic Characteristics
The Mackie monitors’ measurements were outstanding. Frequency response was the flattest we have measured so far, varying only ±1.5 dB from 100 to 20k Hz. In Mackie’s ads, the company boasts that every unit is “hand-tweaked” for flattest response. From the (coherent) impulse response, it would seem that the woofer and tweeter are in the same acoustic plane.

The distortion measurement, taken at 90 dB at 1 meter, is quite respectable and measures well under 1% from 100 Hz upward. In the midrange, the THD+N is less than 0.5%, and the second and third harmonics are significantly lower. Spectral contamination is also very good, typically 50 dB down from the signal tones.

The print advertisements for the HR824 make much of the direct-coupled servo loop between amplifier and speaker, from which one might infer that the HR824 features a distortion-reduction accelerometer feedback system. A look at the distortion measurement curves does not confirm this hypothesis; the distortion curves show a well-behaved characteristic but still have a conventional rise in distortion with deepening bass. Direct observation (yes, we looked inside) found only a two-wire connection to the woofer, not an accelerometer scheme. So we can assume that some sort of motional feedback/negative output impedance “servo loop” is used. The ad mentions “motional parameters,” a partial confirmation of the latter assumption.

Negative output impedance and motional feedback bass speaker systems do have tangible benefits including improved settling time. (Does anyone remember the Ace Bass hi-fi speakers from Europe in the late 1970s or more recently the Yamaha YST stuff?) The HR824’s settling time is quite good for a long voice coil woofer used with a passive radiator.

The elliptical passive radiator has an unusual double-spider configuration that may help control the passive radiator mass. This may be as important to good system settling time as the amplifier’s negative output impedance.