Thiel Owners

CS3.5 update

As you know, I've been investigating internal hookup wire this spring and summer. It's been quite a long and winding ride. Among the twists and turns has been learning how some wire configurations interface with other wire configurations - for better or worse. Backing up, I wasn't convinced I was sending a neutral signal to the 3.5s, especially with the equalizer in between the pre and power amp. I took a detour with Dick Hardesty's 'series-bypass' method where a wire (in this case) is added then removed from the feed stream. The result was that some 'upstream' cables just don't like driving a particular 'downstream' cable. I propose that just such a condition occurs when a speaker cable feeds an internal wiring harness. Mismatches abound. The bright side is that this test shone light on which cables are more tolerant of their downstream load, and those cables move higher on my interest list. I'll have some final results to report within a short while. Let's just say what many other commentators have said: excellence doesn't necessarily track price. Today I received a second batch of cable from Iconoclast, which interests me greatly.

I will reiterate what I reported recently. Belden's 4694A is a surprisingly good cable for short money ($30s) . It is sold as a 75 ohm digital coax for ultra high definition video with a 12GigaHertz rating. Indeed it shines in that digital role. But, it also shines very brightly as an analog interconnect. I invite anyone to compare it with whatever you're using, and please report your findings here.

Now, back to the 3.5. I settled on driving the 3.5s with that 4694A Belden digital S/P-DIF, plus StraightWire Rhapsody 3 analog interconnects and StraightWire Octave II speaker cables – single wired. The StraightWire cables hold up very well to competition and I have known them intimately for decades.

Now another tangent. A couple years ago, my first crossover experiments were on the CS2.2. Again, I know it very well, using it for listening and musician / mix / master evaluations for decades. I had reported that removing the crossover from the cabinet, optimizing the layout without the EMF of the woofer, and upgrading many critical components – all combined to produce substantial qualitative upgrade in performance. That 2.2 workhorse is back-burnered via for greater ease and lower expense of using the model 1 with its two-way configuration and shorter wire runs.

My report today regards the unexpectedly large improvement in the 3.5 by simply moving the crossover. No new parts, no new layout, still inside the cabinet. The move is from behind the woofer (very bad environment) to shock-mounted on the bottom of the cabinet.

Over the years, the consensus about the 3.5 (among other Jim Thiel designs) is that it gets 'confused' or 'compressed' when the volume gets high or the score complex. Fair enough. There also are reports of an over-analytic, electronic presentation. Fair enough. The equalizer contributes some of those attributes. But I am using a Jim Williams / Audio Upgrade replacement which rivals most amps that would be used with the 3.5.

The test uses signal from the Philips CD80 through the Benchmark stack with a vetted cable chain (with or without the EQ). That stock 3.5 and its mate with the XO on the bottom are side-by-side, both fed the same mono signal. The modified 3.5 takes on a more lively, vivid, sweeter musicality. Surprisingly so.

The differences got real in the measurements; there have been persistent anomalies in the frequency and phase measurements of the 3.5. Specifically there is a suck-out (15dB @ 80 to 100Hz) and the top octave droops nearly 10dB. The FuzzMeasure sweeps are taken near full scale – just under clipping. Nearfield single driver measurements are taken at far lower levels. They showed no such anomalies. I assumed the 'problems' were in the room. But no. The 'problems' vanish when the XO is moved to the bottom of the cabinet.

Flash back to the 1982 development of the CS3. This very issue was discussed in the hypothetical. We had noted how much purer the sound was before consolidating the XO into the cabinet. But the XO bottom mount was dismissed due to slightly higher labor cost. Hindsight sadly shows that decision to be significant. That 'behind the woofer' mounting persisted until the removable passive radiator in 1995s CS1.5. (The earlier passive in the CS2.2 was built into the baffle.) That particular 'electronic crunch' follows models with the XO close behind the woofer.

Short of all the labor and expense of a full-blown redesigned outboard crossover, there is a lot to gain by simply moving the XO. Very soon, I anticipate having some firm recommendations for hookup wire upgrade. Those wire and XO position modifications provide significant improvement that is accessible to the DIY owner.

That's fascinating information Tom. I look forward to your conclusions about hookup wire.

tomthiel

Thank you for your contributions and hard work here. Jim is smiling on this thread.

Happy Listening!

There are methods to adjust the resonance point of the crossover even when it is mounted internally. This adjustment can be done externally and improvement can be both seen and heard. Much like a string instrument. You cannot do this with so called isolation materials they deny energy transfer and store energy. TomD 

TomD - I interpret what you're saying as decoupling the crossover from its environment via optimal tuning, such as the various mass/stiffness springs tend to quiet themselves quickly. That can work, but requires ongoing vigilance since the stiffness of the xo panel changes (creeps) over time. I realize that you understand the equation in other terms - transfer of energy and mechanical grounding. I don't have my mind around that, although I believe you may be onto something - your results are good.

We both agree that the xo functions better out of the box, and we understand that distance from EMF and reduction of mechanical vibration are beneficial - much more so than might be intuitively obvious. When the XO is in the box there are many assaults: the air is in episodic resonance and fluctuating pressure; the cabinet walls, the crossover panel, and the components themselves all vibrate causing microphonics and motor-currents via motion in the EMF. All considered our best production results (in the old days) were to mount the panel tightly to the cabinet and all the components tightly to the panel. The wires hung in free air, generally away from each other. In practice we controlled buzzing and rattling and considered the job accomplished when quiet was attained.

I have tried a different approach with more satisfactory results (although less good than the outboard XO.) The new approach is to isolate the various resonances, which spreads them out to various frequencies and reduces their resonance magnitudes because each individual part has far less mass than the combined whole.

Each capacitor or resistor is mounted on blue tack or mortite, held in place via its lead wires. Coils are mounted via zip ties against rubber donut standoffs. The driver leads are more carefully routed away from coils and seated in gooey tape to the cabinet walls and routed radially to the driver, avoiding the central flux axis. 

The crossover is broken into individual panels for each driver, and those individual XO panels are separated from each other as far as possible and as far from the driver magnets as possible, and mounted via fiber bolts isolated from the cabinet wall via rubber stand-offs and from the XO panel via rubber standoffs. These changes would not be very expensive in new construction - they're a bit more of a hassle in retrofit, but still far less cost than swapping out components. This description is of a level 1 upgrade, probably including replacement of any and all electrolytic caps with ERSE-level PPs, and some or all resistors with Mills.