IMPROVED – ATELIER DE SYNERGY ACOUSTIQUE
Workshop of Acoustic Synergy, “Pro Monitor” not to be confused with “Baby Monitor” nor “Standard Monitor”
Here are details and specs of my six clones of the wonderful French ASA Pro Monitors.
Same as OEM:
Soft dome: Dynaudio Esotec D260 textile
Mid bass: Dynaudio Esotec 17WLQ (17cm, 6.7 inch), 8 Ohm
Dynaudio used the same drivers in two of their classic, best loved, and most renown stand-mounts, the Audience 52 SE (not Audience 52) and Contour 1.3 Mk II. Both models maintain high resale value. Up to around 2008 the ASA P/M was John Marks favorite stand mount. Both the ASA and the clone weigh 65% more than Audience 52 SE and 25% more than Contour 1.3 Mk II. Alan Yun’s Silverline Audio Reference 17 employs the same drivers and is one of Martin DeWulf’s all-time most praised speakers in “Bound For Sound.”
All clone crossover component values match OEM, no changes. As described below, capacitor value tolerance outperforms OEM by huge margin.
Paper In Oil Capacitors
OEM crossover has two capacitors. One cap is in series with tweeter. The other cap has resistor in series and these two components parallel the mid bass. I replaced the OEM mylar or polypropylene caps with ultra-refined paper in oil type, value approximately $100/ea. I spent many hours searching for the most complementary caps for this application. Every single strength and positive attribute of the original ASA speakers suggested paper in oil would be an upgrade with no downside, and this is the case. Paper in oil enhanced every musically satisfying quality, with no down side. Anyone with knowledge of the qualities of paper in oil capacitors who heard the ASA Pro Monitor or who read of it’s presentation would agree such caps are ideal for this application.
I upgraded the OEM crossover with a Zobel/impedance EQ network described elsewhere and designed by an award winning speaker designer for this specific application. Even the cap in the Zobel network is paper in oil type. This network parallels the input and no part of it is in series with the signal.
Zobel/Impedance EQ Network
Above the bass range the OEM speaker has sum total one impedance peak, a large one centered at 2.2k Hz. Duke LeJeune of AudioKinesis designed a custom Impedance EQ network to flatten this peak.
Duke’s original Zobel network was on a small board and was easy to connect or disconnect in parallel with the speaker binding posts. In quick A-B test the Zobel network audibly improved performance with both SS and tube amp (Atma Sphere S30), more so the latter, with no downside. The clone crossover incorporates the Zobel network, with three components (coil, resistor, paper in oil capacitor) all in parallel with the input (no components in series with audio signal).
Duelund Resistor In Series with Tweeter
I replaced the OEM tweeter series resistor with Swiss Duelund temperature sensitive type. The harder the OEM tweeter is driven the hotter it gets, causing resistance to rise, which decreases the crossover pole frequency. The Duelund resistance value falls with rising temperature, canceling the tweeter’s effect to maintain a stable crossover pole frequency.
Litz Coil In Series with Mid Bass
Replaced standard OEM solid-core coil with fine Litz coil, same value. Litz coils have lower resistance and are known for a cleaner, more refined sound, with no down side.
Capacitor Values Matched To Second Decimal
The only caps that are not paper in oil are smallest value bypass caps (polypropylene) used to finely match every capacitor value to the second decimal. This was a painstaking chore that took many hours to perform, especially on six monitors.
Every Cap Tested for Preferred Polarity
Finally, regarding the capacitors, the most critical part of any passive crossover: I performed audio tests on every single cap for preferred polarity, even the smallest value caps for tolerance matching. Some of the world’s most costly caps come pre-marked for ideal audio polarity. I proved the test reliable by duplicating with 100% accuracy the same results, days or weeks later when the earlier preference was unknown. Again, another chore that took hours to perform.
Horizontally Centered Tweeter
The OEM tweeter is offset (mirror image cabinets), which makes space on the baffle for the port, and spreads/averages diffraction effects resulting from vertical cabinet edges flanking the tweeter.
I generally prefer extreme toe-in, with speakers “cross-firing” a few feet IFO centered listener for improved reverberant field. Such siting caused the ports to pump air on my face at high levels. One of the clones would be a Center Channel speaker, where a horizontally centered tweeter outperforms offset tweeter. Centering the tweeter required moving the port to the rear panel, which eliminated air pump on my face. Sale includes two plumber’s plugs to air tight seal the ports for siting near the front wall.
The Dynaudio 17WLQ mid bass is designed for sealed or ported box. The audible difference is only moderate whether the ports are open or sealed.
Flared Port Ends
I replaced square port ends with large flared type, which reduces air speed, turbulence, and the resulting undesired qualities common to the OEM type.
Both OEM and clone have raised, beveled-corner baffle and rear panel, flush mounted tweeter, and mid bass flange overlaps the tweeter flange about .5? to minimize driver center spacing and “lobing” in the pass band (critical with ASA’s shallow crossover slope).
I knew it would be hard if not impossible to improve performance of ASA’s solid 1.25? thick Ovangkol tone wood panels for base, side, and top (tongue and groove construction). Solid tone wood for one pair ASA costs a small fortune.
In 2008 Stereophile Magazine described a new speaker panel laminate by two pro speaker designers in Europe. The laminate comprises classic old growth Baltic Birch plywood over plain old particle board. High end audio companies like Harbeth and music instrument cabinet builders still consider true old growth BB ply one of the best igid panel materials extant. Particle board is highly self-damped because it comprises glue with random shaped wood by-products. The two highest priorities for speaker panel material are rigidity and high damping factor.
I employed 3/4? BB ply over 3/4? particle board for 1.25? total, each panel separately laminated with several clamps for maximum adhesion, as opposed to laminating entire sheets with increased air voids. The lamination process offers constrained layer damping.
Comparing the requisite knuckle wrap on the panels, the clone top and base closely approximate the ASA. The ASA side panel resonated slightly less and at a higher frequency.
The clone baffle and rear panel comprise two laminated panels of 3/4? MDF for 1.25? total thickness (OEM was also MDF but IIRC a little thinner).
The clone comprises three different materials to spread and average resonance: MDF, particle board, and old growth Baltic Birch plywood. The clone matches or closely approximates OEM performance at about 1/5 the cost, and weighs almost as much.
I made high performance stands, a modification of the old classic “Stubby” DIY stands. Original Stubby comprised a threaded steel rod passing through a PVC pipe, with nuts torquing the pipe, a base/floor plate, and top/speaker plate.
My stands have two base plates and two top plates. The lowermost plate contacting the floor is 18? x 18? square (with four spikes) glued to a smaller square plate above, turned 90 degrees. Two top plates comprise a Delta-shaped speaker plate glued atop a smaller plate below. The Delta shape minimizes plate area to the speaker’s three spikes, thus minimizing plate resonance.
The vertical support is 5? square PVC fence post, much larger than Stubby’s PVC. You’d not know the vertical support is plastic if I did not disclose it, especially filled with sand. Filled with sand weight is about 40#. Weight is reasonable without sand. I will ship stands empty to be filled onsite by user. Painted black. The stands are extremely rigid and super well damped, IMO better than metal stands which tend to ring.
Direct A-B ASA vs. Clones
Three persons including a woman and two musicians participated in direct A-B test, OEM vs. clones. The consensus was the clone exceeded OEM performance with no down side. As one might surmise, the clones sound more refined, with finer detail resolution, the same pure listening enjoyment and satisfaction, and no increase in fatigue. Both speakers were similarly smooth, open, and dynamic.
Cabinets require primer and color coat because new stain and/or clear coat is too costly. Please mention color choice otherwise they will be black.
Mid Bass Above Tweeter
IMO both the OEM and clone benefit by MT (mid bass above tweeter) rather than ASA’s TM (tweeter above mid bass). Why? ASA has shallow crossover slopes. The shallower the slope, the deeper and wider is the range of driver overlap in the pass band, the greater is “lobing” (venetian blind effect), and the more does ideal driver time alignment benefit performance. Drivers are best time aligned with mid bass at ear level. Compared to TM, MT results in shorter speaker stands and the top cabinet panel is lower in elevation. Stability increases and audio performance improves for persons standing.
Optional Spikes and Threaded Inserts
I have three spikes, lock nuts, and threaded inserts per each monitor. Upon request I will cut holes for the threaded spikes after client selects TM or MT. No refund on cut cabinets because future buyer might prefer clean panels on both sides.