Oct 21, 2004 2:33 PM, By David Ogilvy

ACTIVE NEAR-FIELD STUDIO MONITOR

Monitors with internal amplifiers offer the luxury of bringing a fairly compact and familiar playback system to every studio in your engineering travels. The surge of 5.1 mixes has also created a higher demand for self-powered speakers. To fill this need, Fostex has manufactured an amplified version of the NF-1: the NF-1A. The design is as different as it is efficient.

A NEW LOOK
When I lifted one of the 25-pound monitors out of its box, I was surprised not by the weight but by the woofer’s truly unique appearance. I’ve never seen a speaker look anything like this: The cone does not have the usual uniform crater appearance but is mountainous, with symmetry in the form of a five-pointed star. In addition, the edge of the woofer diaphragm has a novel design that is intended to eliminate unwanted anti-resonance through UDR (Up-Down Roll) construction. Upon looking at the woofer edge, I realize that UDR means that the woofer won’t just move in and out, but that it may actually twist a bit as it moves with the sound. The elastic UDR edge may also extend the life of the cone while minimizing resonances returning to the cone from the entire enclosure.

There are two diffractive reflectors inside each cabinet to minimize internal standing waves. These reflectors are about 6 inches in diameter and they, too, are pentagonal. Another unique detail is the fact that banana fibers are used in the combination of materials for the woofer, thus the off-yellow color. Fostex chose banana fibers because they are longer than other potentially usable fibers and have a higher level of bonding strength when combined with the base pulp (wood) used to make the diaphragm. The tweeter diaphragm is urethane-film laminated over cloth, touting a frequency range of as much as 40 kHz. The tweeter and woofer each receive 60W through bi-amplification.

CONNECTIONS AND CONTROLS
The back panel allows for connection via 1/4-inch phone jack (-10dBV unbalanced input) or 3-pin XLR (+4dBu balanced input, with pin 2 hot). Two level control pots and three switches are recessed for adjustment with a small screwdriver. The recessed design prevents inadvertent changes, although at times I felt these controls were too inaccessible. One level control is for tweeter SPL and is continuously adjustable from -3 to +3 dB with a detent at zero. The other potentiometer is for overall power output and is also continuous in its travel (not stepped). This presented the only major drawback for me: Without a stepped level control, it is extremely difficult to exactly match left vs. right speaker volumes, especially with the pots as small as they are. Yes, I could set this output at maximum on both the left and the right speakers (more watts equal cleaner sound), but then I end up keeping my mixer output well below unity gain to avoid getting blasted.

The switches for varying the speakers’ EQ give us fewer choices than the potentiometers, but make left-to-right matching more uniform. An on/off hi-mid attenuator drops the 1 to 5kHz range down by 3 dB, centered at 3 kHz. The low-frequency filter selector, with positions at -3 dB, 0 and +3 dB, affects the frequencies “around 60 Hz.” The high-frequency filter switch adjusts the frequencies “around 10 kHz” up or down by 3 dB. The legends on the back panel are complete in the details of the functions of the controls and jacks, including three frequency response charts pertaining to the EQ switches. Half of the back is covered with the heat sink, which did not get overly hot after leaving the speakers powered up for a week of initial listening.

THE SOUND
I set up the speakers about five feet apart, with the tweeters at ear level. After sending a balanced pair of cables to the XLR inputs, I listened to a variety of music, checking for differences in DAT mixes that I’ve worked on. The EQ controls on the NF-1As were left flat for these early impressions.

The sound of these monitors is pleasing and natural in the upper frequencies. The NF-1As don’t make the listener jump up shouting, “Everything sounds so much better through these!” This is as it should be; one does not want to mix with a speaker that is overly bright or makes the mix sound better than it might on a majority of systems. One needs to be able to hear details in the sound, and the versatility of the EQ controls allow tailoring these monitors to suit specific needs.

The bass is quite impressive for this sized enclosure. Small speakers often overcompensate for their lack of bass with a design that allows the cabinet to resonate at about 50 Hz, pumping the resonating frequency out in an ugly way. The NF-1As steer clear of that common flaw. The bass sound is wonderful, and it’s amazing how well they play back 808s and other low-frequency elements from hip hop recordings. The kick didn’t pummel me over, and I enjoy the full roundness and uncolored strength of the five-string bass and 808: clear and deep. I never needed to use the +3 setting on the low-frequency EQ (although it could come in handy to check for the effect of a potentially speaker-damaging mix, as most listeners tend to turn up the bass on their car systems).

While familiar mixes translated quite well through the NF-1As, there is still a hint of difference in the realm of the upper mids. I heard side sticks and clave clicks at slightly higher than the level I gave them during the mix, although this was a subtle difference. A tiny bit of hiss also emanates from the speakers when no music plays. However, the NF-1As provide enough clarity and depth to reveal the true textures of various reverbs and effects. The imaging was excellent, especially while listening to an analog recording of a New Hampshire thunderstorm, in which I could hear each raindrop fall in specific locations.

After using these monitors with all the EQ settings flat for a couple of long days of overdubbing, I didn’t experience an unusual amount of ear fatigue. Listeners at the session remarked that the NF-1As didn’t sound “near-field,” which meant that they enjoyed the detail and frequency response, even when standing back a bit. My most common complaint about near-field speakers is that the band, while standing at various distances around the control room, does not hear the details that the engineer in the sweet spot hears. The frequency dispersion of this monitor is respectable and maintains an even tone throughout the room.

To recapitulate, I definitely enjoyed the sound of these speakers. (Yes, I wanted to keep them.) Flat response, clear bass and great imaging translated well to other speaker systems, and the extensive high-frequency response can be adjusted to your taste. I only wish that the level controls were stepped instead of continuously variable. In the past, Fostex has provided products that are affordable and reliable—a difficult combination. That tradition continues with the NF-1A, which at $899 each, offers an excellent alternative to other powered monitors.

Fostex, www.fostex.com.

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Lab Analysis: Fostex NF-1A Active Monitor
By John Schaffer and Rob Baum

Physical Characteristics
The Fostex NF-1A active monitor’s enclosure is a two-way, bass-reflex design with dual flared elliptical ports. The enclosure is made up of 7/8-inch-thick vinyl-covered MDF on the sides, while the black-painted baffle includes an additional 1/2-inch of thickness at the woofer. Transducers are recessed in the baffle and secured with wood screws. The interior sides and top of the cabinet are lined with 1/2-inch Fiberglas, while the back and bottom each include “hyperbolic paraboloid” deflectors to damp standing waves and any internal back waves reflecting inside the enclosure. The amplifier compartment is isolated from the rest of the enclosure by the 7/8-inch-thick MDF.

The visually impressive woofer design of this near-field monitor blends new and old technology: The hyperbolic paraboloid cone design, which Fostex labels HP, is based on well-established structural engineering principles. Harry Olson used these principles to design a similar complex-topology loudspeaker cone for the RCA LCA-1A studio monitor, and JVC also introduced a speaker system using a similar woofer cone in the 1970s. Today, to minimize weight but retain tensile strength, soft drink companies manufacture plastic bottles with hyperbolic paraboloid bases. The HP cone offers extended bandwidth (no puckering on the extreme low frequencies and reduced breakup on the high end) and the cone and surround allow this transducer to operate well past 5 kHz.

The foam surround is also well-thought-out. Fostex calls it a UDR (Up Down Roll) tangential edge, which comprises alternating up half-roll, down half-roll sectors, divided by a tangential wall. (Tangential crease or pleat surrounds have long been used on tweeter and compression driver diaphragms to minimize diaphragm rocking modes.) Other key features on this cast-aluminum frame woofer are double-stacked flat 33/4-inch-diameter spiders, a 11/2-inch-diameter aluminum bobbin voice coil assembly and a vented pole piece. The conventional ceramic-magnet motor structure is magnetically shielded by a bucking magnet and shielding can. Terminations are 0.205-inch and 0.110-inch male tabs.

The faceplate to the Fostex tweeter is a black cast-aluminum horn that loads the diaphragm by means of a wide dispersion waveguide. The 21mm soft dome is a “UFLC” (Urethane Film Laminated over Cloth) diaphragm, which is attached to a Kapton bobbin voice coil assembly. The conventional ceramic magnet motor structure is shielded with a bucking magnet. The T-yoke is topped off with a hemisphere of felt to absorb the backwave off of the diaphragm. Terminations are also 0.205-inch and 0.110-inch male tabs.

Powering the transducers are dual 60-watt amplifiers with a 6dB/octave minimum-phase active crossover at 5 kHz. The power supply includes an oval low-hum field transformer. Inputs can either be balanced (XLR) or unbalanced (1/4-inch). User controls include a continuously variable power input adjustment and a continuously variable tweeter level adjustment (±3 dB). Three-way switches modify LF and HF output (+3 dB, 0, -3 dB) and there is also a mid-frequency attenuator switch (-3 dB). For the measurements, all user controls were set to neutral or off.

Acoustical Characteristics
Measurements on this system were made using a SYSid test system, Earthworks M30 microphone and Lab 101 mic preamp. The speaker was supported on a K&M 21300B Crank It Up speaker stand. Our measurements showed that the frequency response of the Fostex NF-1A is not “flat,” despite its very low-distortion measurements. From 200 to 2k Hz, the on-axis response rises 3 dB, with a narrow band valley centered at 750 Hz. From 2 to 3 kHz, the response falls off 4 dB and then climbs 8 dB to around 7.5 kHz. After 7.5 kHz, the response falls off again by 4 dB up to 15 kHz. The 30° off-axis response follows that of the on-axis until 1 kHz, where it falls 3dB/octave to that of the on-axis. At 10 kHz, the off-axis response equals that of the on-axis and then falls off sharply after that.

The impulse response shows decent alignment in time between tweeter and woofer, but not perfect. The decay is damped, but not smooth.

Now the good news. Besides the cone technology, the major highlight of this monitor is its very low distortion. The Fostex NF-1A studio monitor is the lowest distortion speaker we have tested to date. Above 50 Hz, the THD is less than 1%, with most of the spectrum under 0.5%. The multitone spectral contamination test looks at the system’s intermodulation and cross-modulation products (“self-noise”). Once again, the spectral contamination is the lowest we have ever tested, with the noise floor being around 60 dB down from the input tones.

The Fostex NF-1A has likely been designed to emulate commodity loudspeakers used in portable combo systems and is probably best suited to producing a reasonable impression of what mixed material will sound like in the real world. But with the judicious use of a parametric equalizer, the NF-1A can put out both a flat response and superclean sound.