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  Axiom Environmental Chamber
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  Axiom's Contribution to A/V Standards
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  Distortion and Rumbling in Subs?

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Axiom Environmental Chamber Simulates Extreme Climates

One of the newer additions to Axiom’s testing regimen is a special temperature and humidity chamber that can duplicate sweltering tropical heat and humidity or dry, freezing conditions—basically, any weather that an Axiom loudspeaker or amplifier is likely to encounter during its travels and residence anywhere on planet Earth.

The chamber, pictured here with Axiom Electrical Engineer Tom Cumberland inside preparing to be roasted by the heat and humidity he used to endure in Miami, Fla., is a Tenney model TH65SPL. It’s big, measuring 54 x 54 x 72 inches, and can be set to any temperature from –20 degrees Celsius to +100 degrees C (that’s –4 degrees Fahrenheit to 212 degrees F, respectively), and from 20% to 98% relative humidity. Because of its generous size, the chamber can also be used to test our largest speakers and subwoofers, Axiom electronics or even to subdue a rebellious Axiom employee. – A.L.

News You Need to Know

Wondering if your old analog CRT TV set will go dark when the U.S. stops commercial analog TV broadcasts next February? Do you receive broadcasts on cable?

Your cable-TV box will still make the conversion from digital TV to analog signals and supply your old tube TV with audio and video that it can work with. The shut-down of analog TV broadcasting in February 2009 only affects TV viewers who receive their TV signals from an outdoor antenna or indoor rabbit ears and who continue to use an analog TV set. For them, the screen will go dark unless they purchase a digital-to-analog converter box using the $40 coupon the US government is supplying until the end of March 2009. The converter boxes are inexpensive, about $60 each; with the coupon, the expense is negligible. – A.L.

Axiom's Contribution to A/V Standards
by Alan Lofft

Axiom Audio has always been about science and engineering—the science of loudspeaker design and accurate music reproduction, based on careful anechoic chamber frequency-response measurements of prototype speakers backed up by double-blind listening comparisons in our Axiom listening room. Out of Axiom’s research, which evolved from the original standards of speaker measurement developed by Dr. Floyd Toole at the National Research Council Physics division in Ottawa, came a set of performance standards that all of Axiom’s speakers must meet.

Without standards of acoustical and electronic design, where would we be? Very likely in the land of conjecture, smoke and mirrors and casual opinions. The latter, of course, can be fun to read, and over the years have certainly fueled the content of some high-end magazines and web sites. But if a designer or manufacturer is serious about producing superior products, then real electrical and acoustic standards must be applied to measure real performance gains, and disregard those aspects of performance that can’t be detected or heard under realistic playback conditions.

When Axiom recruited Tom Cumberland, our electronics engineer, research and design engineer and resident "conehead," we got ourselves hitched to a serious engineer with impressive credentials dating back to his work with NASA and the US Dept. of Defense, followed by electronics he designed for Luxman, Infinity, JBL, Mark Levinson, Lexicon, McIntosh Labs, Niles, and Bang & Olufsen. Among his many accomplishments, Tom invented the concept of "multi-zone" home audio applications for Lux (he coined the term) and currently participates in a CEA multi-room A/V sub-committee because of his early years doing multi-room engineering for B & O.

Setting Standards
Tom sits on the audio standards committee (R3) of the Consumer Electronics Association (CEA) and co-chairs the Home Audio Board. His input and activities for the CEA and his work for Axiom demonstrate how a small entrepreneurial company can participate in global research and the development of specific standards of measurement for amplifiers, AV receivers and of course loudspeakers.

Why Are Standards Necessary?
The history of audio points to many companies playing fast and loose with the specifications and measurements of their products’ performance in order to gain a perceived performance advantage over a competitor. Most everyone has seen ads touting a "1,000-watt" AV receiver in which the power output of all channels is added together with no mention of a distortion specification. (It’s easy to triple the rated power output of an amplifier if you measure it at 10% distortion. This might not bother you in a portable boombox but in a hi-fi audio component, 10% distortion is very audible and fairly horrendous.)

Besides inflated claims of amplifier power output, it’s just as easy to claim that a loudspeaker has "frequency response down to 20 Hz" when in fact the speaker’s cone may move slightly at 20 Hz, but if the speaker’s real-world output at that frequency is –15 dB from its output at 100 Hz, you won’t hear the 20-Hz tone. That’s why standards of frequency response qualified by a dB specification are essential to accurately represent real performance in a loudspeaker or a subwoofer.

Axiom at the Cutting Edge of Standards
While all these credentials sound impressive, what sort of influence does Axiom’s Tom Cumberland have on setting audio standards?

With Tom sitting on the R3 board as a voting member, Axiom helped set global standards adopted by the IEC (International Electro-technical Commission) and other technical organizations on loudspeaker measurement, amplifier testing, and defining multi-room wiring. For example, one of the issues currently facing the board is establishing real amplifier measurement standards for the Federal Trade Commission (FTC). How many channels do you measure? Five? Seven? Do you apply the same measurement standards used for the front channels to the surround channels and measure all channels at full power output? "Probably not," says Tom, "because it’s not realistic to expect the surround channels would have to deliver the same high power output as the front left, center and front right. If not, then what weighting do you give to each channel?"

When the new standards are in place, then a manufacturer who claims he has a "3,000-watt" Home Theater in a Box or subwoofer will have to prove such outlandish claims or withdraw them. (Long-term AudioFile readers will know the example is impossible because you can’t draw that much power from a domestic wall socket).

Another standard being developed by the speaker output working group is the all-too-common "20 to 20,000 Hz" frequency response, which is essentially unqualified. The unqualified 20 to 20,000 Hz will be replaced by frequency response specifications qualified by + or - dB, and any claims about high SPL (Sound Pressure Levels) will have to be measured with a new set of standards.

New Standards for Grounding
Tom Cumberland also chairs the Voltage, Impedance and Grounding of Consumer Audio Devices committee. In the past, only standards of voltage and impedance were specified - there have been no standards for grounding, which explains why ground-loops/hum are such a pervasive problem in consumer audio/video. So the new grounding standards should help eliminate ground loop hum which all of us have experienced at one time or another when interconnecting audio and video gear.

Tom is also pushing to limit the source output impedance of components between 60 and 100 ohms. Currently some components have output impedances as high as 1 kOhm (1,000 ohms) which can trigger interconnection anomalies. And his participation on the audio board is to encourage the industry to understand that HD is not just about video; the HD experience is greatly enhanced by high-definition multi-channel audio, as any Axiom home theater system owner can attest. Next on the list - educating consumers about why 128-kbps music downloads are not only uncool - they're un-hi-fi. At Axiom, we feel that's just plain wrong . . .

Q. I have noticed that depending on the music played, the volume setting on my new EP350 v3 subwoofer must be adjusted to avoid distortion and rumbling. Is this normal? I have not positioned the EP350 properly yet.

No complaints – just wondering.

I'm using Axiom M60 v2 tower speakers, a Quad stereo pre-amp and separate power amplifier. My settings are: EP350's high-level inputs; 60-Hz crossover and volume set to 3:00 o’clock. -- Eric

A. You will find that the deep bass content will vary considerably from one recording to the next. Some CDs I own have poorly recorded bass or virtually none at all, so I have to increase the subwoofer volume level to hear what little bass is present on the recording. Others have way too much bass and I have to lower my subwoofer level to get a natural balance.

You will also find that the EP350 may sometimes reproduce some sub-sonic rumbles that are on the original recording but were not audible to the recording or mastering engineer because their monitor speakers didn't have deep enough bass response to reproduce it. For example, typical annoying deep bass such as the sound of the blower on pipe-organ recordings, air-exchange rumble from poorly isolated air-conditioning systems in recording halls and studios, subway sounds on recordings done in large cities where the studio, church, or concert hall isn't well isolated, footfalls on the stage in live opera recordings, etc.

You will need to adjust the subwoofer level in any of these situations. Fortunately they're fairly rare, except for the wide differences in bass content from one disc to the next.

There is a tendency at first to run your subwoofer volume too loud, so that you can hear its effects. You shouldn't "hear" the sub's contributions as such. The sub should just fill in the lower octaves, add a powerful sense of bass instruments when present, and remain sonically unobtrusive. Try turning down the sub level somewhat. Your EP350 may also be located in a "null" where there is a lot of bass cancellation so you've turned the volume up too high to compensate; or it may be the opposite. If the sub is in a spot where there is a lot of bass emphasis--a standing wave--it may seem boomy at one or two frequencies. I think when you find the ideal spot, you shouldn't have to adjust it so often.

Keep in mind too that all turntables generate some rumble and that a subwoofer may make it all too audible depending on the quality of the turntable and the frequency of its rumble component. In the era of vinyl and stereo, many preamps were equipped with a handy switchable rumble filter that rolled off deep bass below 30 Hz or a bit below to prevent power-wasting pumping of the woofers from turntable rumble. LPs with ripple warps may also contribute to pumping of the woofer.