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The distortion curves in figs.3 and 4 show a rising distortion at higher frequencies but a reasonable performance, particularly up to 10kHz. The triode distortion in fig.4 is actually slightly higher than that for tetrode operation, though the differences are not huge. The THD+noise waveform is shown in fig.5. The triode result (shown here) is marginally worse than the tetrode. As MF conjectured, it is heavily low-order, but it is mainly third- rather than second-order. There are also unmistakable higher harmonics present. The 2 ohm result (not shown) transitions to a dominant third harmonic…
A plot showing the output spectrum resulting from a 50Hz input is shown in fig.6 (the power level was 99.4W into 4 ohms). The artifacts are relatively high (-47.4dB or about 0.4% at 100Hz, and -36.7dB or about 1.5% at 150Hz). A similar spectral plot in fig.7 shows the IM at the output resulting from a 19+20kHz input at 70.3W into 4 ohms (the highest output possible with this signal prior to visible clipping). The 1kHz IM distortion here is relatively high (46.2dB or 0.5% at 1kHz, and -36dB or about 1.5% at 18kHz). The corresponding spectral responses in the triode mode, and also into our…
Okay, what does a turntable look like? Take your time—I'll wait. Dum de dum de dum dum dum... Oh, you're tired of this game already?
I never thought much about what a turntable looked like until I got Immedia's RPM2 in for review. After all, there are a lot of high-end turntables out there, from the venerable Linn Sondek LP12 to VPI's TNT, and few of them look like one another. Right?
Well, maybe they do, at that. Because I took one look at the Immedia and thought, Where's the rest of it? And simultaneously, This is a high-end turntable? Then I tried to pick it up. I thought it…
In fact, the two parts of the bearing proper, as well as the spindle and the platter, must all be machined at the same time. Most bearings are simple devices, consisting of a spindle and a cup—or some variation on that theme. The RPM's bearing has two cups, one of which is attached to the platter and fits down over the bearing well, rotating around it. This outer cup contains a downthrust spindle that fits into the bearing well inside the inner cup. The bearing well has a wedge-shaped bottom, into which is fitted a steel ball. A sapphire disc sits atop the ball, acting as the bearing. The…
Sidebar 1: Specifications
Description: Belt-drive turntable with outboard motor controller.
Dimensions: 19" W by 6" H by 15" D. Weight: 65 lbs.
Serial number of unit reviewed: None found.
Price: $4995 with acrylic motor mount, $5995 with aluminum motor mount (1997); not currently available (2005). Approximate number of dealers: 10.
Manufacturer: Immedia, 1101 Eighth Street, Suite 210, Berkeley, CA 94710. Tel: (510) 559-2050. Fax: (510) 559-1855. Web: www.immediasound.com.
Sidebar 2: Associated Equipment
LP Playback: Linn LP12 with Naim Armageddon Power Supply, Naim ARO tonearm, van den Hul Frog cartridge; VPI TNT Mk.III with Immedia RPM-2 arm, Lyra Clavis D cartridge.
Preamplifiers: Conrad-Johnson Premier Fourteen linestage, Premier Fifteen phono section; Ayre K-1.
Power Amplifiers: Krell FPB 600, VTL MB750 monoblocks.
Loudspeakers: Aerial 10T, EgglestonWorks Andra.
Cables: Kimber KCAG interconnects, Kimber Black Pearl speaker cables.
Accessories: Audio Power Industries Power Wedge 112; MIT Z-series power cables; Highwire Audio Power Wrap…
This series of articles was initially written (in slightly different form), as a paper presented at the 103rd Audio Engineering Society Convention, New York, September 1997. The preprint, "Loudspeakers: What Measurements Can Tell Us—And What They Can't Tell Us!," AES Preprint 4608, is available from the AES, 60 East 42nd Street, Room 2520, New York, NY 10165-0075. The AES internet site, offers a secure transaction page for credit-card orders.
What's the point of measuring the performance of an audio component if what owners do is listen to it? Of the 20 or so regularly published…
Subjective loudspeaker performance is thus a multidimensional phenomenon. However, to make objective measurements that are both meaningful and practicable involves a subjective choice about what parameter to plot against one, or at most two, other parameters. All other parameters have then to be held constant. If you plot, say, a loudspeaker's sound-pressure level against frequency for a given input voltage, the result is the typical amplitude or "frequency" response. But this measured response will only be valid on the chosen axis in an anechoic chamber at the chosen sound-pressure level at…
Voltage Sensitivity
A loudspeaker's sensitivity appears to be universally confused with its efficiency. Efficiency is strictly defined [6, 7] as how much acoustic power the loudspeaker puts out for how much electrical power it is being driven with. If you feed a loudspeaker with 100 electrical watts, how many acoustic watts of sound does it produce? The answer is "not many," a typical moving-coil loudspeaker being about 1% efficient.
A loudspeaker's sensitivity appears to be universally confused with its efficiency. Efficiency is strictly defined [6, 7] as how much acoustic power the loudspeaker puts out for how much electrical power it is being driven with. If you feed a loudspeaker with 100 electrical watts, how many acoustic watts of sound does it produce? The answer is "not many," a typical moving-coil loudspeaker being about 1% efficient.
Efficiency, or more correctly sensitivity, is usually expressed in the form of a sound-pressure level produced by a speaker at a specific distance, 1m…
In 1990 Ronald Aarts of Philips [9] carried out a study of the effect of loudspeaker response on perceived loudness. He concluded that weighting the spectral balance with the popular noise A-weighting curve gave limited correlation with subjective loudness, instead calculating the loudness in phons based on critical-band analysis (ISO932B). Critical-band analyzers not being easy to come by, at Stereophile, I feed the loudspeaker with 20kHz-bandwidth noise at a standard level, capture the output waveform with the DRA Labs MLSSA system used in its storage-oscilloscope mode [10], and apply B-…