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February 2005
Enjoy the Music.com Review MagazineThe Nearfield
Defining The Desktop
Article By Steven Stone

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Audio Desk / Nearfield

  Before I can begin to pick and choose the best components for a high-end two-channel desktop audio system I must define the physical parameters of a desktop environment. What does my desktop listening environment look like? Let us take an imaginary stroll around my neighborhood.

 

The World is Flat
My own computer desktop measures 30" by 74" by 7/8". It sits 29.5" off the floor on three matching Hon two-drawer metal file cabinets. Made of high-density MDF covered with Birch hardwood veneer, this table provides a stable and rigid surface for the basic components of my working world.

 

From a sonic point of view this desktop delivers a mixed set of attributes. On the positive side of the ledger, unlike a hollow core door, it takes a very high SPL level to excite any sympathetic resonances. My tabletop also offers a rigid surface for transducers, but it has a large expanse of hard surface to reflect mid and high frequencies that interfere with the primary information from speakers. The ideal surface would be both physically rigid and sonically absorbent. How can we achieve this?

 

That Felt Good
In the late 1970's John Dunlavy filed the first US patents for using thick felt around loudspeaker drivers to attenuate diffraction effects. As far as I know, his patents are still in effect. My Dunlavy SC-VI speakers use 1.5-inch thick felt around their midranges and tweeters. Thick industrial felt does an excellent job reducing high and mid frequencies reflections coming off hard surfaces. Since it works so well on speakers themselves, why not use it on a desktop as well? Google provided me with several likely sources of industrial felt. I settled on The Felt People. They delivered a 45" by 75" by 1" thick industrial felt pad for $33.50 plus $20.72 UPS shipping.

After cutting the piece to fit my desktop I was left with several good-sized scraps to use for another sonic purpose that I'll mention a little later. I now had a working surface that is still rigid, but sonically absorbent. If you regularly test incendiary devices at your desk, smoke, or have a penchant for devotive candles, I must warn you that standard industrial felt is not fire-resistant. It will catch fire if you place it in intimate contact with a flame. Even without a felt-covered desktop I strongly suggest you keep a working fire extinguisher in your office space in case your computer or monitor decides to self immolate.

Consider this a legally sanctioned warning INDUSTRIAL FELT IS FLAMMABLE -- USE EXTREME CAUTION AROUND FLAME AND HIGH TEMPERATURES. If you have any doubts about the pyrotechnic security of your desktop environment, do not use felt that has not been fireproofed. Fireproof felt is available by special order, but is far more expensive and due to the nature of retardant impregnation offers less sonic advantage than untreated felt.

 

Back To Your Desks
Most computer desktops are not placed in the middle of a room, but near walls or in office cubicles. Although a computer desktop listening environment by the nature of the nearfield paradigm will have far less problems from room interactions than a conventional two-channel system, walls can still cause sonic reflections that can interfere with primary transducer sources. Again some sort of sonic absorber or diffuser will reduce these negative effects.

My own desktop sits in front of a large 72" by 50" window, with the back of the desk about 2" from the window ledge. My left wall is 30" from the edge of my desk, and a large industrial-grade 60" high metal file cabinet resides 8" to the right side of my desk. The rear wall of my office is 118" from the back of my office chair. Given their distances, both the left and rear walls of office offer little in the way of negative sonic reflections, so they have not required any sonic treatments, but the front and right side of my desktop environment have needed some attention.

I use two 15" by 15" 2" thick foam sound absorbing panels from Markertek on either side of my 19" CRT color monitor to absorb early reflections from the back of any transducers on my desktop. I also use a triple-pleated Hunter Douglas window covering to reduce reflections from the window itself. A half-inch thick corkboard reduces problems from the side of the metal file cabinet to the right of my desktop.

 

Screening the Screen
Computer monitors present the most obvious and possibly sonically pernicious object in a high-end two-channel desktop listening environment. Not only can they introduce baffle effects, but even a flat profile LCD's front panel can serve as diffraction surface. Once more industrial felt can vastly reduce the negative sonic effects of a monitor in a desktop listening environment. I use two 15" by 24" felt panels on either side of my monitor to reduce early reflections. Depending on the location of the front edges of the speakers on my desk, I place the felt panels so when I sight down the front of the speakers I can't see any of the front of the monitor itself. If I can't see the monitor face, the monitor will no longer be an early reflection source. Velcro does a fine job of holding the felt in place.

Common sense, which is often in short supply on office environments, indicates that the industrial felt should be placed so it does not impede your monitor's ability to circulate cooling air properly or the monitor's working life will be reduced. In a worst case scenario felt could cause your monitor's internal temperatures to approach hazardous levels.

Note: Do not block the circulation vents on your monitor.

 

Little Boxes On The Hillside
The less stuff on your desktop, the fewer opportunities for objects to cause unwanted reflections that alter your soundstage. Obviously you'll have a computer monitor and keyboard as well as speakers. Anything else is optional. I place my monitor on a monitor stand that gives me a 15" by 19"by 6" space under the monitor for a preamp or integrated amplifier. That way all my desktop system's controls are within reach. My system's subwoofer goes under the desktop. Sometimes I place a Brightstar Audio base on top of the subwoofer so I have room for a basic amplifier.


Other inputs for my desktop system (besides a digital feed from my computer), include a CD transport, minidisk player, and D/A. They are located off to the extreme left side of my desktop. My turntable and phono preamp are in another room about 20 feet from my desktop. When I want to listen to an LP I just run a pair of RCA cables from my Vendetta preamp to a spare line level input on my desktop preamp.

Obviously a desktop environment imposes certain physical limitations on the size of the speakers in your system. Using anything bigger than a smallish bookshelf speaker creates both ergonomic and sonic problems. While a bigger t desktop allows larger maximum speaker, three-way floor-standing transducers will never find their way comfortably into a desktop environment. In a conventional room-based two-channel system the general rule of thumb is that you should use the largest speaker a room will properly support, but with a desktop system the trick is to use the smallest speaker that will still give you adequate dynamic impact and integration with your subwoofer. Even mid-sized bookshelf speakers can impose placement, diffraction, and driver geometry issues that can noticeably degrade their desktop performance. On a computer desktop you must remember that small is beautiful.

 

The Lay Of The Land
Now that you have a reasonable idea of the physical dimensions, materials, and physical absolutes of my computer desktop, you have a better idea of how it compares with your own desktop environment. I've tried to make my desktop as standard as possible, so that the sonic results have maximum universality. The primary sonic modifications to my desktop, including industrial grade felt and foam sound absorbers are readily available at modest cost.

Next month I'll begin to look at individual components in my desktop system and begin to establish some basic performance benchmarks. See you then.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     
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