Audioholics On Location #3: Axiom Audio

Axiom Audio is a company that needs little introduction since they are so well branded among the well- informed home theater crowd passionate about purchasing products that live up to their reputation - with none of the BS often found in high end audio. You won't find a product that they offer without full disclosure of its performance metrics which are measured in a controlled, precision method that dates back to the ground-breaking research done by Dr Floyd Toole, Axiom's own Ian Colquhoun and others at Canada's premier industrial research facility, the NRC (National Research Council) in Ottawa. Axiom Audio focuses itself on the science of audio and NOT the science fiction so readily espoused by many of their competitors. (You know the type: wishing to sell you the latest and greatest audio tweak or technobabble about how their speakers require hundreds of hours of break-in before an accurate assessment of their performance characteristics can be made).

We've had the good fortune of visiting our friends at Axiom Audio every summer to get the scoop on their new products under development. This year's On Location visit, however, had a slightly different focus - namely, Axiom Audio's commitment to research and development. Given the latest additions to Axiom's arsenal of test, measurement and production facilities, it's fair to say few companies in this industry are so well equipped in their efforts to design more accurate products and push the limits of the performance envelope.

During our last two consecutive visits ( On Location Tour #1 and On Location Tour #2 ), Ian drilled us with the NRC gospel of loudspeaker design, stressing that if a loudspeaker doesn't measure up, in terms of the family of curves discussed in the editorial below, it likely will not succeed in accurately reproducing music in normal listening rooms. Axiom can now carry out, in house, just the sort of research many other companies would have to tap the world-class measurement facilities at the NRC to accomplish.

Editorial Note on NRC Metrics and Design Criteria
According to NRC research, an important goal in loudspeaker design is that the end product be able to measure with both a flat on-axis response and with an even but constantly declining (or tilting) off-axis response. Ian is a firm believer in the family of curves (established by the NRC) to predict subjective and identify objective loudspeaker performance, which relates to:

• On-axis frequency response - direct sound; first sound to arrive at the listener's ears

• Listening Window - response average drawn from a +-15 degrees vertical, and +-30 deg horizontal region directly in front of loudspeakers

• Early Reflections - first axial reflections from room boundaries

• Sound power (sometimes referred to as "total radiated sound power") is measured in watts, though when referenced to 10, can then be expressed in dB's. It's a metric that represents the total amount of sound that radiates from a loudspeaker, in every direction. It's useful when you consider the typically un-anechoic acoustical character of a typical home listening space.

NRC practice is to first measure a loudspeaker's on-axis response, then rotate the system in 24, 15° increments horizontally, for a full 360° assessment. The procedure is then repeated, this time rotating the system vertically, once again, in 24, 15° increments for a full 360° assessment.

From all these measurements, an average is generated and from the resulting data, the sound power curve is produced. If needed, polar response & the directivity index (DI) can also be derived from the data.

Axiom Audio Anechoic Chamber & Test Facility

Free Field: [is] an isotropic, homogeneous, sound field free from bounding surfaces. Free wave (free progressive wave): [is] a sound wave propagated in a free field. A free wave can only be approximated in practice.
From: Acoustical Measurements, Leo L. Beranek © 1988

Measurements are, of course, an essential part of the loudspeaker design process. Certain stages of that process require measurement data which exclude, to the greatest practical degree possible, any undesireable curve-muddling acoustical artifacts. dB SPL amplitude response curves resulting from the measurement of a free wave propagating in a free field is the theoretical ideal, which as Beranek points out in his book can only be approximated in practice. The anechoic (literally, "without echo") chamber and tower measurements are two very effective means of approximating the theoretical ideal, especially when used in tandem, as does Axiom.

Last year Ian Colquhoun informed us he would be constructing a replica of the NRC Anechoic Chamber found in Ottawa . And that's exactly what he did - a duplicate chamber, built by the same company (Eckel Industries of Canada ( http://www.eckel.ca/ )) that assembled the original. The NRC crew would feel right at home.

  

After construction was complete, a comparative Axiom vs. NRC chamber performance assessment was made. As part of that comparison a mic correction curve was derived to ensure identical measurement performance. A photo of the chamber's associated test gear appears below left and on the right, peering into the chamber from the catwalk. More on correction or calibration curves in a moment.

  

Ian and Gene posing for a shot in the chamber with the Axiom M2 v2 "golden unit" (pictured left). Gene caught red handed attempting to steal the M2's from Ian (pictured right).

The platform seen in the left pic actually rotates a full 360 degrees. This allows for an easy and accurate way to do off axis measurements for plotting polar response curves of loudspeakers.

Flying subs!

In addition to the anechoic chamber, Axiom installed a 30.5m (100') outdoor tower, used mainly for subwoofer testing. Why hoist a sub that high up, then measure? At that height the deleterious effect of boundary reflections are minimized to the point where their influence on the final, measured dB spl curves is negligible. Essentially, by hoisting the sub 30.5m up in the air and firing its acoustic output upward into all that clean Canadian airspace, Axiom takes advantage of a nearly ideal, anechoic free-field measurement environment, courtesy of Mother Nature. The amplitude response curves acquired using this method (so long as the weather and other environmental factors cooperate) are so "clean" they can be used to build mic correction or calibration curves. In Axiom's case they are used in conjunction with the Anechoic chamber to produce measurements that by Ian's estimation allow for response curves accurate to a dB or so, down to 20 Hz. (Necessary as the chamber by itself is not anechoic down to 20 Hz). The end result from using the tower & chamber in tandem is that Axiom's engineers can test their products, in-house, with a high degree of confidence that the results are indeed an accurate, objective picture of a system's performance.

The photo above left shows the tower. You'll note at extreme left nothing less Gene (in the red shirt) keeping an eye on a nearby white van loaded with loudspeakers. Above right is (from left to right) Axiom's Alan Lofft, Uncle Tom manning the golf cart (used as a hoist to lift the device under test to the top of the tower) and Gene, casting a vigilant eye on the day's proceedings.

Anechoic chambers are also a superb resource where it comes to measuring various forms of distortion. The effects of a room's acoustical character coupled with an often less-than-desirable noise floor can all too easily conspire to produce inaccurate distortion measurements. Those same measurements, done in a reflection-free environment, using properly calibrated mics against the comparatively low noise floor typically exhibited by an anechoic chamber expectedly produce superior results.

Pictured above is an example of an ordinary Max dB spl & THD+N measurement comparing two manufacturer's products, selected at random for the occasion. The dark blue & green curves are, of course, the max dB spl amplitude response plots. The light blue & green curves are the THD+N curves.

The THD+N test was used as an example as it was easy to set up. However, its usefulness in practice is limited. Can you tell which sub sounded more distorted? One sub had a cabinet leak that was quite easy to hear when the sub was run in an anechoic chamber, but under ordinary listening conditions was inaudible. Can you tell which had the leak? Here's a hint, it's NOT the product with the higher measured distortion profile. There exist other better focused approaches to distortion measurements than are traditionally used in the industry and an Audioholics technical article focused on this topic is now a work in progress. Stay Tuned!

Axiom On Location #3: New Products

 

8 Channel Power Amplifier

It's been a long time coming but as you recall the mantra from the Heinz Ketchup commercial - " best things come to those who wait ", fits Axioms new "super amp" like a glove (and not the OJ Simpson type). Rather than embarking down the safe, yet dull, design path of classic linear A/B designs, Axiom once again decided to push the envelope of performance by going digital - just like they did a nearly two years ago with the EP500 and EP600 subwoofers.

Digital amps are growing in popularity for home theater today which only a few years ago were mostly limited to car audio amplifiers, subwoofer amps and low fidelity applications. As with all things, technological advancements allows for practical expansion of good ideas into the realm of infinite possibilities.

While there are several companies today offering digital or switching amplifier designs, only a handful of them are actually implementing them correctly for high fidelity applications.

To understand some of the issues with Digital and Switching Amp designs, please refer to these articles:

Switching Amplifiers: The Technology and the Issues

Design Overview

The new Axiom Audio eight (8) channel (that's no typo) "digital" amplifier has many differences over others currently deployed in the industry besides the extra channel. The new Axiom multi-channel amplifier is a very high power design using the latest in semiconductor topology. The high clock of 500kHz makes the amplifier non-alias with the music signal applied. It uses a self oscillating Sigma Delta modulator with enhanced protection and safe shut down. The MOSFETs are the latest generation of high current - high speed switching N-channel devices with 16mOhms of Rdson and very low gate capacitance. The analog circuitry is extremely low noise design with four layer G4 boards using 2oz copper foil to ensure plenty of copper for grounding. Proper layout and grounding is imperative in high speed, and high power designs such as this one and the designer must not only obey classic analogue design guidelines but also consider EMI and RFI countermeasures typically employed by RF designers. This is where many manufacturers fall flat on their faces. Typically, they design amplifiers that dump tons of noise above the analogue filter causing AM reception degradation and possible induced contamination of system grounds which can have audible effects down the signal chain.

Another design deficiency commonly found in most digital amp designs is the lack of post filter feedback. There are two likely reasons why so many manufacturers fail to deliver in this imperatively important design aspect: lack of math skills and desire to use cookie cutter designs from IC manufacturers. Axiom Audio put a lot of thought into the post filter feedback of this amplifier which is a proprietary design of theirs. There are several reasons to employ post filter feedback such as improved amplifier stability, low output impedance and to linearize frequency response when driving reactive loads such as real world loudspeakers.

In order to deliver ultra high power and take full advantage of the high efficiency of Class D amplifier design, Axiom Audio employed one of the most robust power supplies I've ever seen in an amplifier. As you can see centered in the prototype amplifier (right pic), the 1500VA power transformer is huge. The total capacitance for the amplifier is a whopping 139,520uF at 100V - 105 degree C of which 7520uF is topical at the MOSFETs (there are other supply caps that would bring the total over 140,000). It's rare to find 100V power supply caps in a commercial power amp and even rarer to find ones rated to 105 degrees C. This is extremely costly for the manufacturer but a necessity to ensure enough margin for high voltage rails, and higher reliability while also minimizing ESR (effective series resistance). Axiom claims a Power Factor (PF) of 0.9 which means the supply can literally convert 90% of the power it sources from the wall into usable power. Most amps' power supplies have around a 70-75% Power Factor and traditional linear A/B amps efficiency run in the ballpark of around 40-50%. Add these two factors together and it makes it quite impossible for a classic linear A/B design to deliver anywhere near the full power capabilities from a 15A line to the speakers. In contrast, the new Axiom amp will nearly deliver all of the power from the wall outlet.

The rail voltage is +/- 90V unloaded (amps not driven but connected) with 120VAC on the primary. The primary is 120V/240V switchable 50Hz or 60Hz. The toroid transformer uses a core that minimizes 50Hz losses when used in 50Hz countries. Each toroid is wound exactly with the same number of turns. This is a significant achievement by the transformer designer as it allows the manufacturer to use one power supply for all countries thus reducing inventory costs, as well as industry approval certification costs.

Preliminary Power Tests

I had the folks at Axiom Audio run some preliminary power tests for me and they came up with the following unusual and extremely impressive results.

At first glance, these power measurements look unusual. Allow me to clarify. Firstly, these are CONTINUOUS unclipped power measurements taken on a 15A unregulated line. This is the first amplifier I've ever seen which can actually dump its entire power supply into one channel if called upon. This amp truly acts like an ideal voltage source doubling its power each time the load impedance is halved. With a single 1500VA transformer, highly robust power supply design, and ultra efficient amplifier topology, Axiom has managed to design an amplifier that could deliver nearly the full power from the wall outlet with minimal losses.

As you can read in my All Channels Driven (ACD) Amplifier Article , I am not a fan of the traditional ACD test most publications use when measuring amplifier. Luckily the industry is starting to catch on by developing a more practical, real world test scenario for multi-channel amplifiers. The new CEA ruling suggests testing 1 channel at full power with all other channels being driven to 1/8th the rated power. Hence the power measurements in the last tabulated row above titled "7 (CEA Industry Rating)". As you can see, the Axiom amp has plenty of juice to deliver continuous high power to any given channel if called upon while still keeping up with the demand of supplying all of the other channels power. Under this test condition, I would consider 90% rated power delivery to the channel under test to be an excellent achievement when all other channels are driven to 1/8th power. Axiom blew this notion out of the water by being able to deliver full rated power to the channel under test for 8 and 4 ohm loads. It is likely this amp will set a benchmark in our new amplifier measurement standard (coming soon) as well as for all of their competition to follow suite.

Look on the back of most power amplifiers sold direct to consumers and you will find no safety or regulatory markings. I've always felt a little uneasy about this, especially when dealing with ultra high power amplifiers. Axiom Audio put my concerns at rest as they've informed me their new 8CH amp will in fact carry CSA US-C for North America and CE for global approval. This is a costly process, but ensures the amplifier will meet all of the regulatory safety standards that help protect consumers from fire hazards under scenarios such as power spikes/surges or overload conditions. It also usually serves as a sanity check for the manufacturer that their design is safe to operate by consumers. This is just another example of good design measure the engineers at Axiom Audio have undertaken.

The Mr. Freeze of Amplifiers?

What's the best thing about a digital amp? Aside from its ultra high efficiency and ability to deliver more real world power, they usually run extremely cool which is a paramount concern when packing equipment into tight moderately ventilated spaces such as equipment racks. Tom Cumberland - Chief Designer - managed to persuade me to place my hand right on the power supply and chassis while the amp was fired up and playing full scale into 7 speakers. Normally this would certainly earn the participant the Darwin of the Year award if it were a traditional linear amp, but instead I was safe from scorching my skin as this amp maintained a moderate lukewarm temperature, certainly NOT nearly hot enough to leave that fresh tanning bed smell of cooked human flesh. The amp runs cool, it's super-duper powerful and best of all it comes in a moderately sized chassis (4" H x 17.5" D x 16.5" D) weighing in at a very manageable 50lbs. Retail cost will be between $3,500 to $4,000 with an expected availability by early 2007. We are looking forward to getting our hands on a sample for review. Rest assured I'll be back to report on this new multi-channel amplifier marvel.

Axiom Audio Vassallo Series Loudspeakers

Axiom has taken their existing product line up a notch by putting the C in "Custom". Not only are they offering real wood veneer finishes, but they will actually custom build to your specifications in four weeks or less. Supply them with a sample, and they have the ability to match your existing wood finish. They will even send you wood sample swatches if you so request to ensure you are getting the right finish for your application.

We took a tour of their new facility set up specifically to handle the custom finishing of their Vassallo series products.

  

The clean room (or so I refer to it as) is where Axiom techs apply, and polish the Vassallo products.

 

Fit and finish of the Vassallo products are top notch. Notice the shine on the EP600. It was hard to capture a pic without my reflection getting in the way. Notice the custom feet on the EP600. With Vassallo, you get a choice of custom finish, grill color and accessories - now that's what I call custom!

Closing Comments

Visiting the folks at Axiom each summer is one of the highlights of my job. They are truly a great group of people who are as passionate as any true Audioholic is about great audio without the snake oil. Time and again, Axiom Audio has demonstrated an unswerving ability to buck industry trends in favor of pushing the envelope of performance by pursuing bleeding-edge technologies and setting the pace for the rest of the industry to catch up. We have high hopes for their new super multi-channel amplifier. We are pleased to see Axiom take the necessary steps in creating an even more robust testing facility to objectively quantify acoustical performance in loudspeakers. We look forward to seeing them develop new and exciting loudspeaker products to compete in the upper end market segment traditionally only found in high-end retailers. With their talented design staff and research capabilities, this is certainly within their realm. It is a natural and logical progression for their roadmap of success while living true to their heritage and passion of what it is to be an Audioholic.

Additional Pictures and Sights

    

Me feeding Bambi (left pic) before she became the main course
of our meal that night (just kidding, really)

Living proof of evolution (left pic Alan Lofft and distant ancestor??) My wife and I considering a career change (right pic)