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Product Review
 

Krix Seismix 3 Mk2 Subwoofer

January, 2005

Ed Mullen

 

Specifications:

● 10" Driver

● 80 Watt Amplifier

● Dimensions: 17.25" H x 14.25" W x
    16.25" D

● Weight: 40 Pounds

● MSRP: $975 - $1,375 Depending on
    Finish; Black, Beech, Jarah

 

www.krix.com.au

 

USA Distributor: Compass Xpress/Full Discount Wholesalers; Shawn McLoughlin, Manager; shawn@fullcompass.com; www.fullcompass.com

Introduction

Founded in 1974, Krix is a loudspeaker manufacturer located in South Australia. They have a successful line of speakers for consumers and also for commercial theater installation.

The Seismix 3 Mk2 is the smallest of three subwoofers offered by Krix, and is designed for small to medium size rooms. MSRP ranges from $975 to $1,375 depending on the finish, which includes vinyl as well as wood veneers.

The Design

The MDF cabinet interior is neatly lined with polyfill, and does not contain any bracing. The exterior of the review unit is nicely finished in a real beech veneer on five sides, with the rear panel finished in a satin black.

The grille frame is made from lightweight wood, and is attached to the cabinet with a plastic pin ball/socket arrangement. The speaker cut-out is irregularly shaped, to reduce the potential for resonances. The close knit fabric is stretched tightly over the frame and secured with adhesive. A “Krix Loudspeakers” metal nameplate is located on the grille at the bottom center.

There are four large doughnut-shaped soft rubber feet mounted on the bottom of the cabinet. The rubber feet worked well on carpeted and hard surfaces alike, with no buzzing, vibrating, or wandering. This is a high quality floor interface solution.

The Seismix 3 Mk2 is a bass reflex design, and the woofer and vent are both front firing. The plastic vent is flared at both ends, with an inner diameter of 4" and an outer flare diameter of 5”. There is also a wooden dowel mounted inside the cabinet which extends partially up the vent. This dowel prevents small objects which are placed into the vent from falling completely inside the subwoofer cabinet, which would then necessitate removal of the woofer for retrieval.

The 10” woofer is secured with four T-15 head wood screws and features a synthetic rubber surround, impregnated pulp cone with inverted dust cap, a shallow stamped steel basket, soldered amp leads, and a double stacked magnet structure. I would estimate the woofer weighs about 7 pounds.

Amplifier Description

Features:

- 80 Watts Continuous, 200 Watts Program
- On/Off Power Switch
- Auto-On (15 minute delay before shut-off)
- Low Level L/R RCA Inputs (gold plated)
- Input Sensitivity Switch (9mV on “Hi” and 320 mV
     on “Lo”)
- Low Pass Filter (22-120 Hz, continuously variable,
     no disable switch)
- High Pass Filter (22 Hz non-user adjustable)
- Gain/Volume
- Phase Control (0/180 switch)
- Overload Clipping Protection (with indicator light)
- Fuse (1 amp) Protection
- Detachable Power Cord


The control layout is logical, and the rotary knobs move smoothly with a slightly heavy feel. I was pleased to note a beefy toroid power transformer. In my opinion, toroidal transformers are better than standard (El, EL, etc.) laminated transformers due to their inherent phase cancellation of noise and radiation products. I also noted two 6800 uF capacitors. There is no heat sink, and the amp got hot during the ground plane session, but stayed reasonably cool during normal use. The detachable power cord is heavy duty and grounded.

I liked the amplifier overload protection circuit. It softly ramps down the subwoofer output when the amp is driven into an overload or clipping situation. I was only able to engage the overload protection circuit during the ground plane session, and never during normal use.

The Hi/Lo input gain switch is a nice feature for when your subwoofer pre-out signal is weak. The Hi setting allows the amp to be driven to full power with only 9 mV of input.

Even with the input sensitivity switch set to Hi, the auto-on circuit was a bit hard to initialize, requiring a boost in system volume. There is a 15 minute no-signal delay before the amp shuts back off.

Ground Plane Objective Testing and Measurements

All objective tests were conducted using ground plane methods with the microphone facing the woofer and vent, at a distance of 2 meters from the acoustic center of the enclosure. Control settings: low pass filter set to high, gain switch set to Hi, and phase control set to 0 degrees.

Frequency Response: A short-duration (about 1.5 seconds), digitally synthesized logarithmic sine sweep was used to evaluate the frequency response of the subwoofer. The Seismix 3 Mk2 frequency response measured
± 3 dB from 38 Hz -127 Hz, and was characterized by a plateau in 50 Hz - 70 Hz region with a falling response above and below those points.

Peak Dynamic Output: This test measures how loud the subwoofer can play across its pass band with a short-duration signal representative of typical music and movie transients. Frequency response sweeps were conducted at progressively louder (2 dB increment) levels until dynamic compression was noted. The purple curve represents the maximum uncompressed dynamic output of the Seismix 3 Mk2, with 103 dB at 60 Hz, and 91 dB at 30 Hz. Minor dynamic compression was noted below 40 Hz on the next higher curve (gold).

Power Compression: This test measures how loud the subwoofer can play across its pass band with a longer duration signal. A sustained signal (like the avalanche scene in the movie Triple X) can create excessive heat in the voice coil, thus reducing the output capability of the subwoofer.

Power compression was evaluated with a slow (about 30 seconds) reverse sine sweep from 100 Hz - 20 Hz. Sweeps were conducted at progressively louder (2 dB increments) levels until power compression was observed. The Seismix 3 Mk2 held fairly steady up to the green curve, with a maximum of 98 dB at 60 Hz, and 87 dB available at 30 Hz. The next two higher curves (purple and gold) showed more severe (3-4 dB) power compression in the 30 Hz - 40 Hz bandwidth, and the test was subsequently terminated.

Total Harmonic Distortion (THD): Harmonic distortion occurs when multiples of the fundamental signal are produced due to non-linear driver behavior. A subwoofer with low THD will sound clean and distinct, especially at the deepest frequencies. THD was evaluated with steady (5-10 seconds) sine waves, and was limited to 10% unless otherwise noted.

Distortion-limited output was low in the 20 Hz - 25 Hz region, partially due to the high-pass filter engaging at/near 22 Hz. In the 32 Hz - 80 Hz area, the Seismix 3 Mk2 posted more impressive numbers, and the sophisticated amp limiter did a good job of holding distortion to 6% or less.

Frequency SPL THD
     
20 Hz 64.6 dB 10-12% fluctuating
22 Hz 68.1 dB 10-12% fluctuating
25 Hz 75.8 dB 10.6%
32 Hz 93.6 dB 6.1% amp limited
40 Hz 98.6 dB 4.9% amp limited
50 Hz 102.6 dB 4.6% amp limited
63 Hz 104.2 dB 2.5% amp limited
80 Hz 103.8 dB 1.7% amp limited

Bandwidth Linearity: Developed by Tom Nousaine, bandwidth linearity is calculated by dividing the average distortion limited SPL by the maximum distortion limited SPL, and expressing the result as a percentage. A score of 100% means the subwoofer exhibits perfect output linearity across a given bandwidth.

Bandwidth Average SPL Bandwidth Linearity
     
20-80 Hz 88.9 dB 85%
22-80 Hz 92.4 dB 89%
25-80 Hz 96.5 dB 93%

Phase Response and Group Delay: This test measures the amount of phase shift which occurs across the pass band. A minimal phase shift means that all the bass frequencies will be perceived as time coherent. A sufficiently large and abrupt phase shift may cause the perception of time smearing at the affected frequencies. Group delay is used to quantify this phenomenon, and was calculated for select musical note frequencies. The approximate audibility thresholds are based on extrapolations (John Murphy) of existing group delay audibility studies. Group delay from the Krix remained below the approximate audibility thresholds at all significant musical bass frequencies.

Musical Note/Frequency Group Delay Approx. Audibility Threshold
     
F2 / 87 Hz 3 ms 15 ms
G1 / 49 Hz 13 ms 25 ms
C1 / 33 Hz 22 ms 35 ms
A0 / 27 Hz 26 ms 42 ms
E0 / 21 Hz 32 ms 50 ms

Enclosure Tuning Frequency: A phase wrap was noted at 30 Hz, indicating the tuning frequency of the enclosure. This was also verified with a close-mic sweep of the woofer.

Impulse Response and Spectral Decay: The impulse response (black line) shows transient overshoot and system ringing for about 50 ms. Spectral decay was evaluated to the –35 dB mark, relative to the test volume. This test floor was still well above ambient noise levels, ensuring the decay plot was not contaminated. Several minor system resonances were noted in the 50 Hz - 140 Hz region. The largest resonance dropped below the test floor after about 250 ms.

In-Room Frequency Response

To simulate a typical user set-up, the Seismix 3 Mk2 was placed in the front left corner of my 2,000 ft3 home theater room. For digital bass management, all speakers were set to small with a crossover of 80 Hz. The in-room FR sweeps were processed through the pre/pro with only the main speakers and the subwoofer operating. Setting the phase to 0 degrees provided the best results. The in-room FR was measured at three popular listening positions, all about 12 feet from the subwoofer. The three curves were then combined to create an average response curve.

As expected, room gain helped to considerably shore up the low end, with the Krix holding flat to 30 Hz, and meeting its rated deep extension of –6 dB at 22 Hz. At each in-room test location, the Seismix 3 Mk2 showed a pronounced peak in the FR at 60 Hz - 65 Hz (blue line). Considering the shape of the ground plane FR (which also peaks in the 60 Hz - 65 Hz region), this was expected. Setting the low-pass filter to the lowest setting helped some (green line), but didn’t completely eliminate the response peak.

The 60 Hz - 65 Hz peak tended to dominate the acoustic signature, creating a chesty and congested sound on music. I normally avoid using a parametric equalizer to tweak review subwoofers, but in this case, it was necessary. After 10 minutes of running in-room sweeps and adjusting two bands on the Rane PE-17, I achieved an in-room FR of 25 Hz - 100 Hz
± 2.5 dB (purple line). Now the Krix came alive, with a natural and balanced bass presentation.

Movies

I played several action-oriented DVDs, evaluating the Krix for dynamic impact, sustained output capability, indications of audible distress, and deep extension. My overall subjective home theater ratings for the Seismix 3 Mk2 are provided in the table below.

Evaluation Criteria Rating (1-5)
   
Dynamic Impact 3.0
Sustained Output 2.0
Audible Distress 2.5
Deep Extension 2.5

I selected the Hellboy DVD for a more detailed demo. To set the playback level, I increased the master volume until the Krix exhibited some minor distortion and dynamic compression artifacts, and then I backed off 2 dB. I measured SPL peaks at the listening position with a sound meter set to C-weighted fast. The Krix performed well on most bassy passages in Hellboy, displaying good dynamics and decent extension to about 25 Hz. It missed some of the visceral infrasonics on the ice prison space scene, though. I noticed some power compression on the extended (25 second) fiery blast scene, where the Krix failed to break 100 dB at the 1:38:50 climax. After a cool down period, I replayed the last 5 seconds of that scene, and the Seismix 3 Mk2 recovered nicely, punching out a solid 104 dB peak at 1:38:50.

Hellboy Scene Time Stamp Peak SPL
     
Portal Opening 0:06:03 104 dB
Ice Prison In Space 0:06:35 98-102 dB
Hellboy Drops Dumbbell 0:24:08 103 dB
Monster Underwater 0:56:10 104 dB
Removes Tomb Cover 1:26:20 104 dB
Pendulum Swings By 1:31:08-12 104-105 dB
Fiery Blast 1:38:29-53 100-104 dB
Portal Lock Opens 1:44:06 102-103 dB

Music

With the parametric equalizer in the loop, I evaluating the Krix on several music selections for pitch, definition, coherence, balance, and overhang. My overall subjective music ratings for the Seismix 3 Mk2 are provided in the table below. Also provided below are some listening notes from a few CDs.

Evaluation Criteria Rating (1-5)
   
Pitch 3.5
Definition 3.5
Coherence 3.0
Balance 4.0
Overhang 3.0

1) Gladiator soundtrack - Hans Zimmer, Decca Records, 2000. The Seismix 3 Mk2 showed decent focus and separation on the deep, throbbing bass hits at the 6 minute mark of Barbarian Horde.

2) Time Out - The Dave Brubeck Quartet, Columbia Records/CBS, 1959 (1997 Direct Digital Remaster). The Krix did a credible job conveying the delicate timbre of the acoustic bass featured in "Three To Get Ready".

3) Kamkiriad - Donald Fagan, Reprise Records, 1993. The Krix occasionally lost a bit of focus and coherence on the deepest electric bass notes in “Springtime”, but otherwise performed well, providing good foundation to the soundstage.

4) Everything Must Go - Steely Dan, Reprise Records High Resolution DVD-A, 2003. “Godwhacker” opens with a well recorded bass kick drum, and the Krix displayed good impact with just a touch of overhang.

5) Flight Of The Cosmic Hippo - Bela Fleck & The Flecktones, Warner Brothers Records, 1991. The Seismix 3 Mk2 displayed decent pitch and definition on the fretless sliding bass of the title track.

Conclusions

While the Seismix 3 Mk2 is a little expensive for the performance it delivers, I liked the handsome looks, real beech veneer, quality amp, sophisticated limiter, and the well engineered floor interface. A parametric equalizer will help owners achieve the best sound quality from this subwoofer, particularly for music applications. In my mid-size room, the Seismix 3 Mk2 displayed decent dynamics and sufficient extension for most home theater applications.



- Ed Mullen -

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