On Elephants and Listening Trials...

By Bryan Geyer

On Elephants in the Room...
Two of the most notable absurdities in home audio share a common fault: They’re grossly oversized and/or overweight for any normally dimensioned residential living room. You’d really have to live in Hearst Castle in order to claim that the use of these components is sensible or appropriate. I’m talking about (a) those monster (100 pounds apiece) power amplifiers that cost $5k-$10k ea., and (b) those towering pairs of planar electrostatic loudspeakers that cost a bundle—despite their poor efficiency, inconsistent performance (always subject to numerous ambient variables), and comparatively (to dynamic/magnetic drivers) crummy reliability.

It’s very likely that the era of the 100 pound power amplifiers is now ending, and that all such boat anchors will eventually become obscure relics. Future hi-end speaker systems just won’t be built that way. The old concept wherein one big power amplifier is used to feed a passive crossover network that’s in series with all drivers is truly archaic. The modern trend is to use active line-level crossovers that feed multiple power amplifiers. Those bandpass amplifiers can then directly drive the separate segments of a multi-driver speaker system, and do so with precise accuracy, better damping, and fully independent gain control. This method presents vital convenience and flexibility advantages, since each amplifier’s response can then be optimized as needed to assist in attaining a desired room response (EQ) profile. The use of one big power amplifier/channel was a natural and practical solution that fit the past, but new size and integration breakthroughs have now made it preferable to consider this multi-amplifier alternative. Top quality hi-end systems will embrace this concept. In many cases, it’s likely that some of these bandpass power amplifiers will be fully integrated with their designated driver, and buried inside the speaker enclosure. In those instances, compact class D power amplifiers will become the preferred tool, just as with the self-powered subwoofers that are so popular today.

Big planar panel electrostatic loudspeakers (see photo) will soon become extinct unless there’s substantial design improvement. In general, the existing electrostatic means for implementing planar propagation is just too “buggy” to sustain consistent, reliable performance. Such speakers are sensitive to variations in ambient temperature, humidity, and altitude (moon phase too?). They’re  easily damaged, inefficient, and vulnerable when pushed to sustain high sound pressure levels. They’re also costly to make, ship, and sell. Robust redesign seems essential. It’s possible that new materials (such as graphene) might spur this progression. Regardless, dynamic/magnetic loudspeaker design has steadily evolved, and the focused propagation advantage that’s attributed to planar speakers seems less distinctive now than in prior decades. Barring a dramatic upgrade, I see a dim future for those big electrostatic panels that resemble room divider screens; they’re looking obsolescent. That said, the large planar model 10e ESL from Sanders Sound Systems looks exceptional. It’s an elegant “no compromise” product (price with designated Magtech Stereo amp ~ $22.5k) that’s aimed to satisfy the pride of its creator and the respect of the ultra-niche market that it serves. This looks to be a fine example at what’s possible when good engineering meets a targeted (lots of listening space + gobs of money) consumer. That’s a convergence that I’ve never experienced, but maybe it fits your profile.

And On Listening Trials…

If you want to conduct a listening trial face-off between your regular power amplifier and another amp that’s on loan from a friend or dealer, do make certain that you compare the two amplifiers fairly, under identical test conditions. Of course, that means using the same cable connections, same loudspeakers, same room setup, and the same listening seat, but don’t automatically use the same position on your master volume attenuator. Be aware that the internal voltage gain of various power amplifiers will routinely vary by design; they commonly range between ~ +23dB and +29dB. You can research differences in gain by checking the respective amplifiers’ specifications; they’re generally printed on the last page of the related instruction booklet, as well as appearing on makers’ websites. One can easily compensate for a gain difference by adjusting the main volume attenuator to assure that the sound pressure level (SPL) at the listening position is precisely equal for all amplifiers under test.* The incoming source signal’s amplitude range is normally sufficient to accommodate any adjustment of the attenuator that might be needed to set an accurate SPL match at any desired listening level.

To accurately monitor the SPL matching, use a basic SPL meter (https://www.bhphotovideo.com/c/product/1149079-REG/nady_dsm_1x_digital_spl_meter.html), and position it (mounted on a tripod, or on a lighting or microphone stand) at the listening site. Use a fixed frequency sine wave source as the test signal; something between ~ 400 Hz and ~ 800 Hz is generally best. Match carefully! A difference of as little as ± 0.5 dB in SPL could unfairly bias your judgment, and the loudest output will always win, regardless of any other aural distinction that might seem evident.

Given modern solid-state power amplifier design, and assuming that such amplifiers are not driven into clipping, and that their sound pressure levels are accurately matched, you will probably conclude that there’s zero audible difference between the contending products. This expectation does not apply if the on-loan amplifier is an appealing new component that you’ve recently considered buying. In that instance, the on-loan amplifier will always sound spectacularly superior; it will “blow away” the old amp.

BG (September 2019)

*If your master stereo volume attenuator has calibrated stepped detents you might find it difficult to achieve a setting that yields a precise SPL match. In that event, check the rear panel of both power amplifiers. Many amps include a pair of rotary potentiometers, installed at the input stage, to facilitate balance adjustment of the incoming left/right stereo source signals. You can use these pots as supplementary volume controls to trim the SPL output in small increments that are finer than a stepped attenuator might resolve. Just remember to return these pots to their previous positions (generally full up) when your testing trial is finished.