Стенд:
Fig. 1 shows a block diagram of the audio system used in this work. The main components (text boxes) are interlinked by various types of cables5 (arrows). The amplifier was plugged directly into a grounded wall outlet. The server and DAC were plugged into a Tice Audio6 Microblock power conditioner (which provides an isolation transformer to prevent ground loops, plus surge suppression to protect the components).
The music (media) server was a Bryston BDP-1 Digital Player.7 This fed a 1.5-m Straight-Wire8 Infolink digital interconnect through an AES/EBU XLR connector. The digital feed went to a Berkeley Audio Design9 Alpha DAC Series 2. This DAC has two isolated buffered pairs of ana- log outputs10 —single-ended RCA and balanced XLR—that were always active and fed the two interconnects that were compared in the listening trials: (A) a Straight-Wire Virtu- oso higher-end (retail price ∼$500 for 0.5 m) 0.5 m–long balanced XLR-to-XLR cable with polytetrafluoroethylene insulation and (B) a Monster-Cable11 Interlink 400 entry- level (retail price ∼$50 for 2 m) 2 m–long RCA-to-RCA cable with polyethylene insulation. They were both contin- uously connected to a class-A solid-state Spectral DMA- 250S Studio Universal Amplifier,12 which has balanced and single-ended switch-selectable inputs. This arrange- ment avoids the need to disconnect and reconnect intercon- nects during trials and avoids intervening external switch boxes and additional cables and circuit paths, which might compromise fidelity.
The signal levels for the two configurations were ex- actly matched within ± 0.0045 dB (using an AC-voltage measurement at the speaker terminals). The amplifier’s own noise levels were equal within ± 0.004 mV (mea- sured using the same instrumentation as for the ca- ble noise as described below); by comparison the noise difference between cables was a hundred times greater (∼1 mV).
The amplifier’s output was bi-wired to a pair of 2-way- monitor ProAc Response D2 loudspeakers14 through 3 m– long Straight-Wire Maestro II speaker cables. These cables were terminated with optimized RC networks (R = 18 in series with C = 3.3 nF at the tweeter terminals and R = 18 in series with C = 5 nF at the woofer terminals) to suppress reflections back toward the amplifier. The speakers were mounted on Target15 HJ20/T stands with lead-filled columns and with spikes on the top and bottom plates to suppress recoil.
Speaker distances (from front centers) were 1.88 m to the back wall, 1.69 m to the side walls, and spaced 2.08 m left to right. The room has a 56-m2 area with a 1.37 aspect ratio and 2.7-m ceiling height. The back wall was lined with 1.22 m–tall air-spaced rock-wool panels (average thickness of 245 mm) fronted by Roomtune16 reflective/absorptive aluminum-sheet/glass-wool panels and louvres of wooden strips. The floor is covered with very dense and thick nylon carpeting atop thick padding with a double layer of carpet- ing (total thickness of ∼40 mm) over 2 m2 areas where the first reflections from the floor occur. As a result the room has well-controlled acoustical characteristics: at the listen- ing position the 60 dB reverberation decay time is RT60 = 0.30 s with a negligible reverberant intensity IR—providing for a relatively unadulterated direct sound (acoustical mea- surements are described below). A photograph of the audio system is provided in Fig. 1 of [24].
In the hope that some audible difference will be detected, the cables in the two configurations were chosen to be as different as possible. With its much shorter length, bal- anced (versus single-ended) topology, and faster dielectric the higher-end cable A can be expected to have a more de- tailed and accurate sound. The question was whether inter- changing these interconnects would produce a recognizable and memorable timbral change that would be discernable in blind listening tests.
Выводы:
High-end audio is a subject that is shrouded in contro- versy. Aside from loudspeakers, consumers exhibit varying degrees of skepticism as to what affects sonic performance. The most contentious ingredient in the chain is the inter- connection between components, which concerns both the topology (balanced versus single-ended) and the character- istics of the cable itself. This work shows that two system configurations differing only by the interconnect pathway are audibly discernable even by average listeners with no special experience in music or audio. To the author’s knowl- edge this may represent the smallest change in an audio sys- tem proven to be discernable through IRB-approved blind listening tests.
The success of these experiments depended first on as- sembling an audio system with sufficient fidelity to avoid masking the minute differences being auditioned. Secondly the approach to designing blind listening tests was scru- tinized to see what might improve sensitivity. An EMP listening protocol was developed because preliminary ex- perimentation along with other published observations [22, 23] indicated that it would be more likely to form a robust and detailed impression of an HEA system’s sound quality compared to an SSC method.
This work did not conduct an exhaustive determination of all possible physical causes of sonic differences in intercon- nects. For example time-domain effects such as reflections were not studied because a balanced cable requires a dif- ferential amplifier and extra cable (both adding their own noise and distortions) before an oscilloscope. However the electrical measurements conducted here indicate that noise levels may be one determining factor of sonic performance. The measurements also show that characteristics such as resistance and frequency response, which na ̈ıve consumers may focus on, are irrelevant for distinguishing HEA inter- connect cables.
A worthwhile future extension of this work would be to develop high-performance instrumentation that can cleanly switch between two single-ended interconnects. This will allow assessing sonic differences arising from cables’ trans- mission characteristics that are unrelated to topology and also facilitate the study of time-domain effects.
[свернуть]
Социальные закладки