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Hafler TRM8 Trans•Nova, August 1998

Oct 21, 2004 2:57 PM, By Barry Cleveland

REFERENCE MONITORS

David Hafler began making power amplifiers in 1954 and founded the company that bears his name in the mid-’70s. In 1987, Hafler Professional was acquired by the Rockford Corporation—of Rockford Fosgate car audio fame—which had previously acquired a decades-old speaker manufacturing company, now called Rockford Acoustic Designs (RAD). Engineers from both Hafler and RAD collaborated on the new Hafler TRM8 Trans•Nova Reference Monitors.

At first glance, the TRM8s are rather conventional-looking, but a closer examination reveals some interesting features. For example, to properly synchronize the delivery of high and low frequencies, the upper section of the cabinet is stepped, positioning the tweeter slightly behind the front plane of the woofer. Additionally, the tweeter is mounted on a large waveguide, or axis-symmetrical horn, which helps to focus high-frequency dispersion both on- and off-axis. The cabinet itself is made of low-resonance 3/4-inch MDF, lined with damping material, and features a rear-firing bass “Exoport.” It has a black semi-gloss finish and includes a rubber pad that can be attached to the underside of the cabinet to control unwanted vibrations.

The TRM8’s power switch is conveniently located on the front of the cabinet, as are two LEDs, one for each amplifier. Audio connectors, the IEC power cord receptacle and 16 DIP switches are located on the rear panel. According to the manual, unbalanced connections are to be made via an RCA jack, with the (DIP) input switch set to the RCA unbalanced position, while balanced connections are to be made via a dual-function 1/4-inch TRS/XLR jack, with the input switch set to the XLR or 1/4-inch balanced position. However, the manual then goes on to say that unbalanced 1/4-inch TRS and unbalanced XLR connections may also be made via the dual-function jack, which is a little confusing. (However, that said, the manual is generally excellent and includes lots of information about every aspect of the TRM8s.) The remaining 15 DIP switches are used to select input sensitivity (+4 dB, +1 dB, -2 dB, -5 dB, -8 dB and -11 dB) to mute either or both of the amplifiers and to supply four levels of bass shelving (40 to 200 Hz) and four levels of treble shelving (3 to 20 kHz), ± 4 dB in 2dB intervals.

INSIDE
The TRM8s are bi-amped, with 150- and 75-watt amplifiers powering the woofer and tweeter, respectively. Both amps utilize the proprietary Trans•Nova (TRANSconductance NO-dal Voltage Amplifier) circuit—common to power amplifiers made by both Hafler and Rockford Fosgate—a design topology that uses just three stages instead of the usual five or more. The Trans•Nova circuit significantly shortens the signal path through the amplifier, which allows audio to pass at low voltages and produces less coloration, extended bandwidth and higher linearity.

The input stage operates at ±17 volts, functioning pretty much like a Class-A preamp, while the secondary stage supplies about 20 dB of full-voltage gain to the output stage. The output stage utilizes fully floating dual power supplies with MOSFET devices and is configured into a “trans-impedance” stage, resulting in short loop-negative feedback and a slew rate of 100V/µs. DIAMOND (Dynamically Invariant AMplification Optimized Nodal Drive), another proprietary circuit, produces five times the current headroom of previous Trans•Nova amps, greatly reducing high-frequency distortion.

A fixed fourth-order Linkwitz-Riley active crossover with adjustable high- and low-frequency shelving operates at 2.5 kHz, and a subsonic filter eliminates all frequencies below 30 Hz with a 12dB/octave slope. Components in the amplifier and crossover are surface-mounted on double-sided glass-epoxy PC boards.

The TRM8’s high frequencies are handled by a 1-inch hemispherical silk-dome tweeter cooled with Ferrofluid. A “Phase Lens” and the previously mentioned waveguide improve off-axis response and phase coherence, resulting in a more open sound. Low frequencies are handled by a proprietary 8-inch die-cast basket woofer with a 20-mil, mica-filled polypropylene cone and a 38-ounce vented and shielded magnet assembly. An extended-collar flat spider is used to reduce harmonic distortion, and the woofer’s 1.5-inch voice coil is wound on a black-anodized aluminum former for maximum heat dissipation.

WHAT I HEARD
I evaluated the TRM8s by using them to mix some instrumental pieces, listening back to mixes done on familiar monitors and listening to a variety of CDs. The CDs ranged from orchestral works to electronic music to African pop, with the Mix Reference Disc CD tossed in for good measure. The TRM8s handled them all easily and even reproduced test tones up to 20 kHz (which I felt more than heard). Hafler claims an upper frequency response of ±2 dB at 21 kHz, and it’s not hard to believe.

The lows were tight, solid and well-defined, while the highs were very focused and transparent, even while listening fairly far off-axis. In critical listening sessions, the Haflers revealed a slight unevenness in the lower mids on two of the CDs (Feelings by David Byrne and Space Groove by Projekct Two), though this was not as obvious on other speakers.

The speakers’ internal Trans•Nova bi-amplification provided a blend of gutsy punch with transparency. And with the TRM8’s stated peak SPL output in the 123dB range (thankfully unverified by this writer), these monitors are loud enough to fill nearly any listening space (or at least provide a huge margin of headroom to reproduce transients cleanly, while packing a mighty wallop on the LF side).

Mixes done on the TRM8s translated well to other monitors and vice versa, with the midrange staying in proper balance, which is, after all, the most meaningful test. At $1,990 a pair (or $995 each), I highly recommend that anyone looking for quality studio near-fields give the Hafler TRM8s an audition.

On- (top trace) and off-axis. (bottom trace) frequency response

Hafler Professional, www.hafler.com.



Lab Analysis: Hafler TRM8 Monitors
By Jack Hidley

Impulse response

Physical Characteristics
The TRM8 has a fairly conventional cabinet design. The cabinet is a rectangular box with a 3/4-inch step in the front baffle around the woofer, designed to put the woofer and tweeter acoustic centers into alignment. The cabinet has a 3/8-inch radius to soften the look. The panels are constructed of 3/4-inch MDF, except the baffle around the woofer, which has a double layer of MDF. The rear panel in the cabinet is inset several inches to house the power amplifier, and there is a slot-shaped rear port near the top of the cabinet. The cabinet is rigid and inert. The exterior finish is a lightly textured black paint. There are no provisions for a grille. The woofer and tweeter are flush-mounted into the baffle. There are indicator LEDs for each amp and a power switch mounted in the tweeter faceplate on the baffle.

The woofer appears to be a polypropylene Vifa model. The cone has curved sides and attaches to the frame with an inverted rubber surround. The voice coil leads are dressed tangentially to the cone, allowing very high excursions before they strike the cone. The woofer has a bucking magnet, but no magnetic shielding. The frame is cast-aluminum, which, in addition to the bucking magnet, will reduce the stray magnetic field somewhat. The motor structure (pole piece) has a large 19mm vent, which should help keep the voice coil cool and reduce power compression. The voice coil overhangs the top plate by at least 6 mm, allowing high linear excursion.

The soft-dome tweeter appears to be a Vifa model. The tweeter has a one-piece dome/suspension of a treated fabric. The voice coil former is aluminum, and the voice coil is underhung for low distortion. Ferrofluid is used to increase power handling and improve sound quality. The magnetic structure is not shielded. The dome is protected by a custom faceplate, which mounts on the tweeter with a fine wire mesh. The latter has a small dispersion-enhancing disc placed in its center.

The TRM8 has separate amplifiers for each driver. The two amplifiers share the same toroidial transformer and are built on the same PC board. Each amplifier has its own filter capacitors and rectifier circuitry to reduce the probability that one amp’s output will modulate the other. Discrete circuitry is used for both amp output stages. The chassis and heatsinks are both part of one very large extrusion, similar to the construction technique used in high-end auto-sound amplifiers. The chassis is mounted to the cabinet with long screws and rubber grommets for vibration isolation. The rear panel has a single XLR/TRS combo balanced input, an RCA unbalanced input, a socket for an IEC power cord and a row of DIP switches. The DIP switches can be used to select inputs, adjust the sensitivity of the speaker, adjust the high/low-frequency shelving or mute either driver.

THD+N ∆; 2nd m and 3rd q harmonic distortion

Acoustic Characteristics
As shown in Fig. 1, the TRM8’s on-axis frequency response is quite flat out to 4 kHz, with a slight roll-off above this to -4 dB at 20 kHz. There is a 3dB dip in the response at 5 kHz due to a reflection from the stepped baffle. Judging from the 30∞ off-axis response shown on the lower trace in Fig. 1, the speaker behaves like most 8-inch two-ways. The upper range of the woofer (800 to 2.5k Hz) starts to roll off mildly, the low range of the tweeter (2.5 to 4.5 kHz) has no attenuation and the high range of the tweeter rolls off considerably. This indicates that the TRM8 will give its best performance in near-field applications with little acoustic absorption.

The impulse response is quite good, as evidenced by Fig. 2. There is very little energy after the first 0.5 ms. The speaker has a high degree of time alignment due to the step in the baffle and choice of crossover design.

Spectral contamination measurement

At 90 dB SPL and above 1,500 Hz, the THD+N is low, below 0.3% over most of the range. Between 50 and 1,500 Hz, the THD+N is moderate, remaining below 1%. Distortion performance is shown in Fig. 3.

The spectral contamination levels (indicated in Fig. 4) are 40 to 45dB down from the signal tones, which is an average performance.

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