Fundamentals of Isolating Suspensions
In Sidebar 1, I explained, graphically, how the resonant frequencies of a solid structure relate to its modal activity when stimulated by vibrations. It is apparent that, regardless of which method of rigid coupling, damping, or a combination thereof is used to minimize the negative impact of vibration on a platform, stand, or component, the best one can achieve through these means alone is a reduction in amplitude approximating the ideal rigid body line. To further reduce the impact of vibration, we must isolate any rigid structure from outside…
On a number of occasions we have commented on the effects of an amplifier's output impedance on a system's performance. A high output impedance—such as is found in many tube amplifiers—will interact with the loudspeaker's impedance in a way which directly affects the combination's frequency response. The Cary CAD-805, for example, has a lower output impedance than most tube amplifiers, and should be less prone to such interaction. Some months back—before the CAD-805 arrived—I investigated this phenomenon in conjunction with measurements for a forthcoming review of the Melos 400 monoblock…
A letter in response appeared in April 1994 (Vol.17 No.4): Thomas J. Norton's "Questions of Impedance Interaction" in January (p.109) showed that a ghostly echo of a loudspeaker's impedance modulus can be imposed on its frequency response by virtue of an amplifier's source impedance acting as the top limb of a potential divider. Mr. Norton illustrated the effect with some specific graphics, but the data can be usefully generalized by means of a simple rule arising from the ohmic arithmetic.
Assuming a worst-case situation of very large impedance undulations, with, for instance,…
Although Kentucky loudspeaker manufacturer Thiel has produced some standmounted models for home-theater use, all of their serious music speakers have been floorstanders. Enter the PCS: even though styled to match every Thiel speaker since the groundbreaking CS5 of 1989, the 19"-high PCS sits on a stand, not the floor. All the PCS's drive-units are made in-house by Thiel, and the heart of the speaker is the coaxial tweeter-midrange unit, similar to that used in the Thiel CS2.3. As Brian Damkroger discussed this unit at length in his January 1999 review of the '2.3 , I will refer you to…
But there still wasn't any deep bass, nor was there the "rounded" quality to the upper bass that I had found appealing with the Mirage MRM-1, reviewed elsewhere in this issue. On the 1/3-octave warble tones on Test CD 3, the speaker really didn't want to "give" any lower than the 63Hz band in-room, and was producing some doubling at lower frequencies. The end result was a rather "gruff" quality to the Thiel's low registers. This surprised me, given the efforts Jim Thiel makes to minimize distortion in his woofers. Part of the problem seems to be "chuffing" coming from the shallow port.…
Sidebar 1: Specifications Description: Three-way, stand-mounted, reflex-loaded loudspeaker. Drive-units (all anodized aluminum): 1" (25mm) dome tweeter coaxially mounted in 4" (76mm) cone midrange; 6.5" (165mm) cone woofer. Bandwidth: 55Hz-23kHz, -3dB. Frequency response: 57Hz-18kHz, ±2dB. Phase response: ±10 degrees, minimum. Sensitivity: 87dB/2.83V/m. Impedance: 4 ohms nominal, 3.3 ohms minimum. Recommended power: 50-200W.
Dimensions: 19" (483mm) H by 7.25" (185mm) W by 11.5" (292mm) D. Weight: 30 lbs (13.6kg) each.
Serial numbers of units reviewed: 367, 368.
Finishes:…
Sidebar 2: Associated Equipment Office System
Digital source: Meridian 500 CD transport, Panasonic A-120 CD/DVD player, Musical Fidelity X-24K 24/96 D/A processor.
Amplification: Yamaha @PET RP-U100 desktop receiver.
Cables: Canare interconnects, AudioQuest CV-4 and Symo loudspeaker cables.
Accessories: Pentium MMX 166MHz with Digital Audio Labs CardDeluxe soundcard connected to D/A via 75 ohm S/PDIF link, running Windows 98, WinAmp 2.5, and CoolEdit 2000.
Home system
Digital source: Mark Levinson No.31.5 CD transport and No.30.6 D/A processor, connected with…
Sidebar 3: Measurements To judge from his speaker designs---all of which feature generally low impedances---Jim Thiel has no sympathy for amplifier designers. While not as demanding as some Thiel speakers, the PCS's impedance magnitude (fig.1) hovers between 4 and 6 ohms over most of the band, and drops to 3 ohms in the lower midrange. Note also the punishing combination of 4 ohms magnitude and 55 degrees capacitive phase angle at 120Hz. This is a speaker that needs to be driven by an amplifier rated into 2 ohms to give of its best. But at least that amplifier doesn't have to be very…
In the vertical plane, the PCS's dispersion pattern (fig.5) indicates that it is very important not to sit with your ears above the tweeter, as a deep suckout appears around 700Hz (presumably where the woofer crosses over to the coaxial unit) even as little as 5 degrees above that axis. High stands will be better than low ones. The spatially averaged in-room response (fig.6) ties in pretty well with my auditioning comment: a basically flat balance with restricted bass extension and perhaps a little too much energy in the region covered by the coaxial unit.
Fig.5 Thiel PCS, vertical…
That's right, that's no typo; the name of this speaker is the Thiel CS.5—not 1.5, not 8.5, just point five. The CS.5 is the smallest of Thiel's floorstanding CS (Coherent Source) loudspeaker family, and is likely to remain so—a name like CS.125, for example, is a bit unwieldy. If you're familiar with the rest of Thiel's CS line, then you can imagine what the CS.5 looks like: it resembles the other CS speakers, except it's smaller (footnote 1). And, being a typical smartypants 'ender (as in "high-ender"), I bet you think you know 'zactly how these sound, too, don't you? Well? I thought so.…
