Description: Solid-state monoblock power amplifier. Rated power: 160W into 8 ohms, 300W into 4 ohms. Current capability: 40A continuous, 60A peak. Frequency response: 7Hzצ100kHz, +0/–3dB. Voltage gain: 26.5dB. Input impedance 75k ohms.
Dimensions: 19" W by 8¾" H by 19" D. Weight: 78½ lbs.
Price: $6000/pair (1986); no longer available (2006).
Manufacturer: Threshold Corp., Sacramento CA 95815 (1986); Threshold Audio, Inc. PO Box 41736, Houston, TX 77241. Tel: (713) 466-1411. Fax: (713) 856-0278. Web: www.threshold-audio.com.
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Sidebar: Specifications
Bill Firebaugh's first product, the outrageous-looking Well-Tempered (tone) Arm, established him as one of audio's most innovative designers. At the 1985 Winter CES, he showed a prototype companion product—the Well-Tempered Turntable—and was producing production units by January 1987. He discusses here the WTT's unusual design features. (Readers should note that, since we have not yet tested the new turntable, this interview is not to be interpreted as an endorsement of the product.)
Holt: Bill, what prompted you to get into the turntable business?
Firebaugh: Well, after I had…
I don't know if I could assign a magnitude to the improvement, but you can sure see it when you're making flutter tests. And you can hear it. A friend of mine who has a home-built, very massive turntable like a Micro Seiki, uses a very stiff belt with it, made out of rubber-impregnated Kevlar. He tried flipping it over and he told me he very definitely notices a difference. He always uses it twisted now.
It was while I was experimenting with belts that I discovered something amazing. The belt goes slower than the pulley. And it's not because the belt is slipping, it's more like it's…
Holt: Because the motor normally would have a tendency to cog. It is a hysteresis synchronous type, isn't it?
Firebaugh: Yes, it is. So I asked myself, "What would happen if I just put a certain kind of grease in there?" I happened to have some saltwater wheelbearing grease, which is quite heavy and doesn't get runny when it gets hot. And I squirted that in there, and gosh, that worked great. I mean, it made a difference you could really hear.
Holt: Doesn't it creep up the sides when it's spinning?
Firebaugh: Well, I had to experiment a lot with the viscosity of that…
The problem with using an oscilloscope was that, while it showed me that I had problems with resonances, it didn't tell me much about where those resonances were. So I bought a computer with a Fast Fourier Transform program, and all of a sudden I could see all those sidebands.
Holt: What you see is essentially all the release of the stored energy.
Firebaugh: Yes. An impulse contains all frequencies, and its duration is so short in comparison with the time it takes for the system to release the energy from the pulse that it stores, that all you read is the system's response. That'…
The speaker review in the July 1996 issue of the German audio magazine Stereoplay didn't hold back the praise. "Absolut Spitzenklasse III Referenz" was their overall rating, which I guess translates to "You'd better hear this, buddy," in American English. So when MBL of America's Marc Lawrence called to find out if I wanted to review the subject of that review, the MBL 111, I didn't need to be asked twice.
Radialstrahler
The 111 is a serious attempt at producing a true omnidirectional speaker, radiating the same sound balance in every lateral direction. This has significant…
When you hear this work live, the spatial presentation reinforces the enveloping tonal ambiguity. The spatial smearing of lesser speakers would interfere with the effectiveness of Holst's almost fetishistic scoring. By contrast, the combination of superb tonal accuracy and secure spatial accuracy offered by the MBLs allows the listener to appreciate the experience in a manner similar to the live event: Themes and accompanying figures restlessly shift in space as they move from one choir of instruments to another, but the listener can clearly hear what is happening and, more important, why.…
Sidebar 1: Specifications
Description: Four-way, omnidirectional, floorstanding loudspeaker with bandpass-loaded woofer. Drive-units: 24-segment carbon-fiber omnidirectional bending-mode tweeter; 12-segment carbon-fiber omnidirectional bending-mode upper-midrange unit; 5" (130mm) plastic-cone lower-midrange unit with conical diffusor; 12" (300mm) woofer in a separate bandpass enclosure. Crossover frequencies: 130Hz, 670Hz, 3.5kHz. Frequency range: 20Hz–40kHz. Sensitivity: 80dB/W/m. Nominal impedance: 4 ohms. Maximum power handling: 300W. Maximum spl: 106dB (conditions not specified).
…
Sidebar 2: System Context
My dedicated listening room measures around 19' by 16.5', with a 9' 3" ceiling broken up by 9" pine logs. The room is carpeted, and there are patches of Sonex foam on the ceiling to damp primary reflections of the sound. The other wall has RPG Abffusors behind the listening seat to absorb and diffuse what would otherwise be early rear-wall reflections of the sound that might blur the stereo imaging precision. Tube Traps are used in the room corners to even out the room's bass resonances, the result being a relatively uniform reverberation time of around 200ms…
Sidebar 3: Measurements
The MBL's impedance measurement (fig.1) was made with an Audio Precision System One. Although it reaches a minimum value of 4 ohms at 12kHz, the magnitude stays above 6 ohms for most of the upper midrange and treble. It does drop to 5 ohms or below in the upper- and midbass, which means using a good amplifier capable of sourcing current. Note the combination of lowish impedance (around 5 ohms) and large, capacitive phase angle (45° or so) in a narrow region around 36Hz. This will tax the partnering amplifier and might explain why the speaker's low-frequency…