Ariel2

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The Ariel

By Lynn Olson

Ariel Tweaks and Bug-Fixes

Easy Tweak: Fill the upper chamber of the Ariel (or the side chambers of the ME2) with fine, dry, "silver sand" or lead shot. If the base of the Ariel is large and heavy enough, the added weight will not make it top-heavy. (A hazard for those with small children and active pets.) Some people have built large bases for the Ariel out of marble, slate, or Corian; that should be both heavy and very inert.

It's desirable to have these heavy masses at the top and bottom of the cabinet; that way, mechanical vibrations within the cabinet structure are absorbed at both ends with a minimum of standing-wave reflection. (I haven't done this, but others have, and have reported good results.)

Extreme Tweak: One reader in Holland mentioned removing the rear plastic assembly from the tweeter and using the built-in tweeter sub-enclosure in the Ariel & ME2 to replace the tweeter's own integral baffle.

Those of you who have more mechanical aptitude than I can succeed in removing the rear plastic assembly; all I succeeding in doing was knocking sharp little chips off the ceramic magnet. If you go ahead and carefully remove the rear chamber, make absolutely sure the air-seal where the wires go into the rest of the enclosure is air-tight. Any air-leak at all between the woofers and the tweeter dome will result in very high distortion and eventual failure of the tweeter.

If you succeed in modifying the tweeter, resigning yourself to the loss of warranty, and making absolutely sure there are no air-leak into the tweeter chamber, yes, there will be a performance increase for the D2905/9000 or D2905/9300. By making the rear chamber of the tweeter about 20 times larger in volume, the free air resonance of the tweeter goes down (good), the minor bump around 1.5kHz is removed (good), and midrange distortion probably goes down as well (assuming the air seal for the tweeter chamber is very, very good).

If you want to get even more tweaky, you can drill three very small holes between the tweeter chamber and the outside of the cabinet; this acts as a pressure-relief, or resistive-vent, for the tweeter, and would lower distortion even more. I would suggest drilling three 2mm or 3mm holes (in a vertical line) on the Left side of the cabinet, about 4.5" back from the plane of the front baffle. (This is for the Right cabinet; for the Left cabinet, drill the holes on the right side.) No matter what you do, the tweeter chamber should be lightly filled with long-fiber wool or crimped-Fortrel filling material, the same as the straight section of the transmission line. You want to get even more fancy, use the same Deflex or felt damping pads used elsewhere to damp the rear panel directly behind the tweeter.

This tweak is a major hassle, and I haven't done it myself. For those of you who are adventurous, though, it would almost certainly improve the D2905/9000 or D2905/9300 significantly, and make the L4, R4, and C4 notch filter unnecessary.

Bug Fix #1: On close reading of North Creek's crossover assembly manual, there appears to be an error on connecting the 0.3mH inductor used in the tweeter circuit. In the assembly manual, the "hot" end of the inductor is incorrectly shown connected between R1 and R2. The correct connection is between C1 and R1, as shown in the Web schematic. As you folks probably already know, the Web page is the reference master, and supersedes everything in the PF articles, the "Soul of Sound" book, or the North Creek manuals. I expect this error will be resolved in the next press run of the manual.

Bug Fix #2: Out of the hundreds of people who have written me about their experiences with the Ariel or ME2, myabe five have mentioned problems with dull, boomy, or recessed sound. If this happens to you, check the following items:

The Ariels do not work in rooms with suspended ceilings ... they become very boomy and heavy-sounding. Of course, rooms with suspended ceilings have wretched acoustics anyway, which is why you never see them in performing spaces used by musicians. A very quick test of any room is the quality of speech ... when you first walk into a room and speak out loud, does your voice sound lively and natural, or is it dull and distant sounding? This tells you a lot about how a speaker will sound in that room. Rooms with low ceilings (8 feet or less) can also be difficult for transmission-line speakers, which energize the room boundaries.
For a "difficult" room, the ME2 is probably the best choice ... one of the charms of a minimonitor is they work in almost any acoustical space, a genuine advantage in an unpredictable hi-fi show environment. Yes, there is less bass, but what's there is less room-dependent
If you must use a transistor amp, and are not happy with the sound you're getting with Ariels, try increasing the C1 tweeter cap to no more than 7 uF. This increases the "Q" of the tweeter crossover and adds a bit more overlap between the midbass and the tweeter, raising the level in the 3.5kHz region. This makes the sound more "forward" and aggressive - but it also diminishes the sensation of depth. I regret to say that many high-end transistor amps just don't sound good with the Ariels; if the transistor amp has banks of power transistors, electrolytics the size of beer cans, and complex floating bias schemes, it probably won't sound good on the Ariels. The Ariels are intended for simple, moderate-power amps, which in the transistor world is 60 watts or less.
Did you remember to bi-wire the crossover going all the way back to the output terminals of the amplifier? This may seem like a small detail, but using a single speaker wire for both the tweeter and midbass sections results in a flat and undynamic sound. (This happened to me until I took my own advice and went back to the recommended bi-wire configuration!)
With bi-wire, of course, you are free to select different types of wire for the tweeter and midbass sections. I would particularly avoid stranded wire for the tweeter; microscopic corrosion can subtly increase distortion, impairing resolution of fine detail. Good alternatives to stranded wires are: flat (Nordost, Goertz), solid-core (Kimber), or Litz (Cardas, Nirvana). The "SuperCables Cook Book" by Allen Wright has terrific-sounding wires you can make yourself; this is advertised in Glass Audio or Sound Practices magazines.
Are the crossover parts the recommended ones, or simply what was available from the vendor? The Hovland film-and-foil capacitors are the best choice, along with Ohmite, Mills, or Caddock precision wire-wound resistors. I also recommend 10 or 12 gauge air-core inductors, even for the tweeter inductor. It may seem counter-intuitive, but as the tweeter inductor gets larger, the tweeter crossover becomes more effective at very low frequencies, greatly improving the clarity of the treble range.
Some folks are allergic to external crossovers; this is unfortunate, since capacitors are quite microphonic, acting both as electrostatic speakers and low-quality condensor microphones. You can't do much about the emission of sound (except consider oil-filled caps in metal cans), but you can isolate them from the heavy vibration of the enclosure by using an external (non-metallic) enclosure.
Is the lining material on the interior cabinet walls the recommended 3/8" 85% to 100% wool felt? If other materials (like foam) are used, the sound will be adversely affected.
For filling the straight part of the transmission line, never use fiberglass. Drop in small handfuls of cleaned and carded wool (best), or Fortrel or Dacron fiberfill. The filling should be very loose and fluffy; don't compress the filling material or try to pack it tightly.
Did you "cut corners" and not use the recommended large radii on the cabinet corners? I know the large radii are a hassle, but they make a big difference!

If none of these fixes work, the most drastic solution is to adopt a "minimal" crossover for the Ariel, consisting of a single 2 to 3uF capacitor for the tweeter, and a single 10 to 16 ohm resistor across the tweeter terminals. No crossover at all for the Vifa midbass drivers. Some listeners prefer the more "raw" presentation of the minimal crossover; the choice is yours!

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mercoledì 02 luglio 2014

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