Page 7 of the SDA SRS 1.2TL owner’s manual states:
“The SRS is equipped with two sets of inputs to facilitate bi-amplification or bi-wiring….This enables the system to achieve greater dynamic range with lower distortion.”
Page 4 of the 1990 SDA SRS brochure states:
“For even greater dynamic range and lower distortion, the SRS loudspeakers may be connected for Bi-Amplification using the two sets of inputs provided on each loudspeaker. No electronic crossover is necessary. By permitting different amplifiers to reproduce the high and low frequencies separately, the SRS loudspeakers achieve their greatest sonic potential.”
I’m certainly interested in having my SRSs achieve their greatest sonic potential! I like my SDA SRS 1.2TLs because they are capable of producing a life-size sound stage, accurate stereo imaging, and clarity that is comparable to what I hear in a live jazz concert.
Reference Equipment Configuration:
Denon DCD-1650AR CD Player (modified with higher grade analog op amps and master clock)
Adcom GFP-750 preamp
Two Adcom GFA-5802 power amplifiers
One 1-meter pair of Monster Z200i RCA interconnect cables (cd/preamp)
Two 1-meter pairs of Monster Z200i RCA interconnect cables (preamp/power amps)
Two 10-foot pairs of Monster Z3 speaker cable with medium gold spade connectors.
Polk Audio SDA SRS 1.2TL Speakers with upgraded crossover components and Cardas CCGR-S binding posts.
The GFP-750 preamp has two sets of RCA output jacks to facilitate bi-amping, therefore no Y-adapters were required.
My listening preferences are well-recorded instrumental and vocal jazz records and CDs.
Reference Recordings (CDs):
1. “Time Out”, Dave Brubeck Quartet, Track 3-“Take Five”.
2. “Chameleon”, Herbie Hancock, Track 1-“Chameleon”.
3. “The Very Best Of George Howard”, George Howard, Track 1-“Love Will Follow”, Track 5-“Diane’s Blues”.
4. “Kind Of Blue”, Miles Davis, Track 1-“So What”.
Listening notes were made with respect to sound quality, sound stage dimensions, and image placement within the soundstage. Diagrams were drawn of the relative locations of instruments within the soundstage. Four Tiptoes aluminum isolation cones were used under each power amp.
Prior to this experiment in bi-amplification, I tried bi-wiring with the GFA-5802 amp and bi-amping with two GFA-5500 amps. The details of those experiments are detailed Here.
First, I wanted to make sure that I had a reasonably matched pair of GFA-5802 amplifiers. Test tones and musical selections were played through each amplifier and sound level measurements were taken to verify that no obvious differences in gain and sonic characteristics existed. To my ears, there was no audible difference between the two amplifiers.
My evaluation began after an hour of warmup with the amplifiers in a horizontally bi-amped configuration. The speakers are not designed for vertical bi-amping, although I am aware that some SRS owners successfully use this configuration by tying the grounds of the two amplifiers together. Listening notes were made with the system in single amp mode first and then in bi-amped mode. Sketches of the placement of instruments within the soundstage were made in both single mode and bi-amped mode. The average SPL of the music during the listening session was 92 dB. I was seated 17 feet back from the plane of the speakers. The 1.2TLs were spaced 6 feet - 8 inches apart and 11 inches from the rear wall.
Due to the good results I heard with the bi-amped GFA-5500 configuration, I had high expectations for the bi-amped GFA-5802 configuration. Regrettably, those expectations were not realized. Whereas I heard more dynamics, clarity, and fullness of sound with the bi-amped GFA-5500 configuration compared to the single amped GFA-5500 configuration, I heard the opposite with the bi-amped GFA-5802 configuration. The bi-amped GFA-5802 configuration sounded worse in every respect.
The dimensions of the soundstage and the relative positions of instruments within the soundstage remained the same when going from single amped to bi-amped GFA-5802 configuration. I experienced some sonic degradation when I went to a bi-amped GFA-5802 configuration: there was a noticeable loss of sonic detail, dynamics, clarity, and particularly bass articulation and impact. Some examples:
1. Paul Desmond’s alto saxophone solo on “Take Five” has a light airy quality that is noticeably diminished in the bi-amped configuration. The notes of the acoustic bass become less distinct. Dave Brubeck’s piano notes lose some of their sparkle and take on a slightly “glazed over” quality.
2. “Diane’s Blues” is a study in contrast and dynamics. The hard slamming bass lines contrast sharply with George Howard’s soprano saxophone notes swirling and floating above them. In bi-amped mode, the bass loses some of its kick and the saxophone loses some of its sweetness and clarity.
3. On “So What”, John Coltrane’s tenor sax and Cannonball Adderly’s alto sax lose some clarity. The acoustic bass lines become less articulate and boarderline “muddy”. The drum kit high hat loses some “shimmer” and “air”. There is less of the “metallic” sound of the wooden drumstick striking the metal cymbals.
Sometimes bi-amping produces very audible improvements (as in the case of the GFA-5500). Sometimes it produces no audible effects at all or it produces audibly inferior results (as in the case of the GFA-5802). When I emailed Adcom customer service about my interest in bi-amping with two GFA-5802s, their reply stated that I would probably notice little, if any, sonic improvement. Their view is that the higher you go up in amplifier power, the less beneficial bi-amping becomes. I am sure the design of the speaker has a lot to do with it also. Theil does not offer a bi-wire/bi-amp option with their loudspeakers because they believe a high quality single amp configuration provides the best and most coherent sonic presentation. John Dunlavy (formerly of Dunlavy Audio Labs) personally told me that, even though DAL offers bi-wire/bi-amp capability with their speakers, they do it for marketing reasons rather than their belief in any sonic benefits. In Dunlavy Audio Labs’ listening room at their corporate headquarters, none of the speakers were set up in a bi-wire/bi-amp configuration. Mr. Dunlavy said he personally didn’t believe in bi-wiring/bi-amping because when you double the amount of cables and double the amount of amplifiers, you are doubling the amount of distortion and other non-linearities that cables and amplifiers introduce into the audio path.
With regard to Polk’s statement that: “For even greater dynamic range and lower distortion, the SRS loudspeakers may be connected for Bi-Amplification using the two sets of inputs provided on each loudspeaker.” I found that this was true for one pair of identical 200 watt amplifiers and not true for a pair of the same company’s flagship 300 watt 2-channel amplifier. Assuming that the vast majority of audio enthusiasts do not use high-powered amplifiers, Polk’s advice to bi-amplify the SRS series speakers was useful and appropriate. However, my results lead me to think that I might achieve more audible improvements with moving to a higher powered single amp, like the Bryston 14B-ST (500 watts) rather than bi-amping.
I am interested in learning about the bi-amplification experiences other SRS owners have had with other amplifers, other SRS series speakers, and other bi-amp configurations (vertical vs. horizontal).