Positive Feedback ISSUE 69
precision transducer engineering
Phoenix SG Active Loudspeakers
as reviewed by Michael Wechsberg
Those of you who read my recent article on cables in PF may know that I have become disenchanted with typical audio systems tangled in cables, and I stand ready to explore the world of powered loudspeakers that eliminate at least some of the cable mess. During the next few months I hope to try out several active speakers over a range of prices and types, and to write up what I learn for PF. First up is the PTE "Phoenix SG" from Precision Transducer Engineering in Orange, California. I heard this speaker at the recent T.H.E. Show Newport Beach and was quite impressed. PTE is probably best known for their $60,000, 420 pound, 5-foot tall Statement active loudspeaker that they have demonstrated at several audio shows over the past few years. This is probably one of the highest dB-capable speakers available for the consumer market. However, this year's demonstration at T.H.E. Show Newport Beach featured their smaller and more affordable stand-mounted Phoenix model. PTE recently completed a major upgrade to the Phoenix, a new version called the Phoenix SG, with an almost $4000 price increase (from $5700 to $9500—the original Phoenix is also still available). The most obvious change for the SG model is to the cabinet; it is about the same size, but now has a 1.5-inch thick front baffle, rounded edges to reduce diffraction effects, more substantial internal bracing and padding, and a more striking finish in padauk hardwood veneer. The new cabinet also features layers of dissimilar materials to reduce resonances, and an improved proprietary method for mounting the drivers to further isolate driver motion from the cabinet.
As you can see from the picture these speakers have a pretty large footprint for a stand-mounted design, but they are suitable for most medium to large rooms. Being powered speakers, all you need to complete a system is a source component such as a CD player, computer, or music server, but it must have a volume control. Otherwise, a line-stage (or preamp if you want to play LPs) is also required. Each speaker requires a power cord, but the only other wires necessary are interconnects from source to each speaker.
The Phoenix SG is a two-way design with three drivers arranged in an MTM configuration. The mid-woofers are 6.5-inch Peerless models with Nomex cones and half-roll rubber surrounds. Shorting rings and a long-throw voice coil are used for low distortion even at high SPL. These woofers are fast for a very dynamic response, and though small, PTE claims the low end extends to 32Hz. They achieve this with a reasonably large cabinet, dual port on the rear, and the use of equalization. Since the Phoenix is a powered speaker, PTE is able to use a multi-stage active equalizer in front of the amplifier. This allows them to smoothly compensate for the low frequency roll-off of the driver by boosting the drive voltage to the amplifier, while at the same time limiting the drive voltage at subsonic frequencies that could cause the driver to distort. This type of equalization is not possible using passive components after the amplifier as in conventional passive speakers.
The 1 inch dome tweeter is a classic design from Scanspeak, modified by PTE. It has a smooth response over the full spectrum from about the 1700Hz crossover to 22kHz. A double magnet system is included for high sensitivity, and the driver has an exceptionally long excursion plus ferrofluid cooling for high SPLs. The off-axis response is also quite uniform. The tweeter gets its own amplifier and its own equalizer that further smoothes out its response. On their web site, PTE shows a measured overall frequency response of +/- 2dB from 32Hz to 20kHz.
The Phoenix SG cabinets are works of art made by a fine cabinetmaker in Riverside, CA. They are finished in a nice padauk hardwood veneer, similar to cherry wood. The rectangular cabinets are 28 inches high, 12 inches wide, and 15 inches deep, and are made of 1 inch MDF except for the front baffle that is 1.5 inch thick MDF. Edges are rounded to reduce diffraction effects, and extensive internal bracing is employed to minimize resonances. The drivers themselves are vibration isolated from the cabinets using a proprietary material. Total weight is 75 lbs. per speaker. A good deal of that weight comes from the electronics contained within each cabinet.
A sturdy aluminum panel on the rear of each speaker is a mount for three 130W (RMS) amplifiers, one for each driver. These amplifiers each use several integrated circuit chip amplifiers. Audiophiles may cringe at the notion of using chip amplifiers, but there are several reasons why this is the right solution for these speakers. The chip amp used is the LM3886 is from Texas Instruments and has world-class specifications for low noise and distortion as well as reliability. The amplifiers operate in class AB mode so they are not digital amplifiers. PTE puts several devices in parallel to further improve the signal to noise ratio, and they operate the amplifiers conservatively. IC amplifiers are typically closely matched in performance, something that is vital in a bi-amplified system that requires matching not only between left and right channels, but between drivers in each channel as well. PTE uses 1% tolerance components at critical stages to further improve matching between amplifiers. Furthermore, the three amplifiers are all on the same multi-layer circuit board so that everything tracks with temperature as well. This attention to matching results in good phase tracking between speaker pairs, which maintains good imaging performance. The amplifier circuit board also contains the all analog electronic crossover and active equalizer for each driver. The crossover is a fifth order design to minimize interaction between the drivers, and the equalization is tailored to each driver using 1% tolerance parts and matched op-amps. The aluminum panel containing all this stuff gets pretty warm during use, but I'm told this is normal and that the thermal design for the electronics is fairly conservative. A power supply with a toroidal transformer sits at the bottom of each cabinet.
The rear of the speaker has both balanced XLR and single-ended RCA inputs, in addition to a power switch, an IEC jack for the power cord, and four small toggle switches. One toggle switch selects between the balanced and single-ended inputs. A second switch affects the low frequency response and has three positions. One position is labeled "free space" and applies the most boost. This is intended for speaker positions well out into the room. The "corner" position applies no boost, figuring that the room will tend to enhance the lows. The bottom switch position is labeled "near wall," and is intended for installations relatively close to the wall. This applies a moderate boost to the lows. The other two three-position switches affect the tweeter response. One either boosts or cuts the treble by 0.5dB while the other boosts or cuts by 1.5dB. Using different combinations of these two switches the user can alter the treble response by +/- 2dB in 0.5dB increments. These three switches operate as substitute tone controls, but with a limited range so things can't get crazy. The analog tonal shaping is implemented in front of each amplifier in conjunction with the equalization mentioned earlier. Unlike tone controls on a preamp or integrated amp, the user should set these to taste and leave them alone, rather than change them for each piece of music. I found them to be quite effective for their intended use. The speakers come with magnetically attached grilles, but I did not use them.
PTE's Mark Thoke delivered the Phoenix SG speakers to me and helped with initial setup. He provided a pair of single-post Sound Anchor stands, customized for these speakers. These stands are available through PTE at an additional cost, but there are other 24-inch tall stands that should work just as well. The stands come with spikes, but I opted to use rounded bolts as feet instead to save my wood floors. With the bolts I could adjust the tilt back and level of the speakers, plus easily move the speakers back and forth and apart. Using the supplied stands, the tweeter ended up about 39 inches off the floor, which is a reasonable ear height. After some experimentation I tilted the speaker back about 1/4 inch so the axis of the tweeter was firing slightly above my ears. With the tilt back and the tweeter level switches on the back of the speaker there is quite a bit of range to adjust the treble to taste.
I also experimented with toe-in and spacing. I started with the speakers toed in slightly towards the listening position, about 3 feet from the front wall and about 7 feet apart. After a couple of days of casual listening and experimenting while the speakers were breaking in (this pair was used during THE Show Newport so were already broken in) I ended up moving them a little further out from the wall and pointing them straight ahead. In this configuration the speakers really disappeared and I heard a nice broad and deep soundstage. At the end, the speakers were about 7.5 feet apart and 4.5 feet out from the front wall, and I left them this way for the remainder of the review period.
I also experimented with the various bass and treble switches. Since the speakers were pretty far out from the wall I tried the "Free Space" position. This provided the most bass I really enjoyed on a few cuts, but overall it was a little much bass in my room. I settled on the center "No boost" position. I played with the treble switches quite a bit while auditioning the speakers, but most of the time settled on a modest 0.5dB boost.
Except as noted below, I used equipment and cables from my reference system during the review. This included the E.A.R. 868 preamp and Acute 3 CD player with the Townshend Rock 7 Turntable and London Reference cartridge. Power cables and interconnects were all Kubala-Sosna. Everything was plugged into my newly acquired Wywires Power Broker AC distribution box.
The best one-word description of how the Phoenix SG speakers sound is "dynamic." Music likes to jump out of these speakers in a very lifelike manner with great coherency and pace. Although they like to be played loud, they even sound dynamic at low volume levels. They have great transient snap while handling subtle volume and tempo changes with aplomb. I enjoyed live music through these speakers more than anything else. They seem to honestly portray that extra electricity in the air during a live performance compared to a studio one. Room or hall sound is there if it makes it onto the recording. I'm sure this is due both to the quiet background provided by the built-in amplifiers, and the excellent bass response. Extended bass is one of the advantages of a powered speaker because of the use of active equalization in front of the amps. Much of the hall sound is carried in these low frequencies.
The Phoenix SG powered speakers have an extraordinary extended low frequency response for their size, and that response is also quite flat through the mid-bass region. The in-room bass I experienced with these speakers was the equal of my Marten Django XLs that have 3 woofers. The Martens have just a tad better bass definition and nuance but don't go any deeper. I was able to measure the in-room bass response of the Phoenix SG speakers using a test CD with 1/3-octave pink noise bands and my trusty old Radio Shack sound level meter. I performed these measurements only after I completed my listening tests. Except for a shallow null between 62 and 80Hz caused by room cancellation, the speakers were flat +/- 1.5dB from 200Hz down to 31Hz. This is with the bass adjustment switch set to the "no boost" position where I did most of my listening. With the switch in the "near wall" position (but without moving the speakers) the entire low end was boosted by between 1 and 3dB which helped to fill in the room null and extended the bottom end to about 25Hz (just 5dB down). With the switch in the "open air" position the low end was boosted another 3dB or so. The overall spectrum of the bass was not quite as flat in this position but the null between 60 and 80Hz was much shallower and the response at 25Hz was down only about 3dB. I liked this switch position for some recordings where I thought the added energy at 60 – 80Hz gave the music more impact and realism. On the other hand, the lifted low end was a bit overpowering and flabby on other recordings that had a prominent low end already. The bottom line is that these speakers have a remarkable low-end response that should satisfy almost all music listeners (home theater enthusiasts are probably the only ones who would crave a subwoofer). Although you can see the woofers moving quite a bit on low frequency blasts, they play very loud while remaining clean and controlled. The home user should experiment with the bass controls to determine what sounds best in their homes and suits their taste.
Turning now to the midrange, I typically listen to a wide variety of vocal music to form my opinions, and supplement that with various piano recordings to look for specific problems in the midrange. The Phoenix SG speakers sounded terrific on every single one of my test recordings, including male and female vocals, solo piano, and ensemble recordings with piano and other instruments. The sound through the midrange was smooth and warm reflecting the source components. No peakiness, resonant humps, or other anomalies to be found. Each voice had its own unique character, and they sounded like real people singing. The crossover region was seamless as far as I could tell. As I added in more complex music the speakers did a good job of separating out individual musical threads. The music remained clean and detailed even as the complexity and volume level went up. I think the use of separate amplifiers for the mid and high drivers really helped make separation of musical threads a strong point for these speakers.
The high end of the Phoenix SGs is consonant with the midrange. It is clean, very extended, and smooth. All the sounds in the upper midrange and highs handled by the tweeter came across with clarity and definition and instruments sounded real. I did find myself fiddling with the tweeter adjustment switches, and with tilt of the speakers to try to gain more air and transparency. This worked for some recordings and not for others. Although the PTE-modified Scanspeak tweeter is a good one, this is one area where audiophiles might look for more. The tweeter did its job well and did not call attention to itself, which is something I can't say for some other speakers, including some quite a bit more expensive than the PTEs.
I know one of the areas that motivated PTE to improve the Phoenix model, and that led to the new SG design, was to improve imaging. I would have to judge the effort to be successful. The SGs provided a wide and solidly defined soundstage with good center fill, best appreciated on large-scale orchestral works. Images remained fixed within the sound stage. The speakers did an especially good job on live concerts portraying the interplay between players and their stage movements realistically. I did find images could be moved forward or back a bit by adjusting the tweeter level switches.
I experimented briefly with the stock power cords and some different interconnects. PTE does not believe power cords will make much of a difference in the sound of their speakers. In fact, the speakers sound fine with the stock power cords. I did find the highs to be a bit harsher with the stock cords. Reducing the tweeter level a bit mitigated this, but not completely. Bass continued to go very low with great power, but was not as well defined. If you spend $9500 for these speakers, it would probably be a good idea to invest at least a few hundred dollars more on some upgraded power cords.
The same is true for interconnects. I tried a couple of different lower cost single-ended interconnects with the SGs. The speakers were not especially sensitive to this change either and continued to work well. But the sound was a notch less involving and the highs especially less transparent. The speakers are good enough that you will be rewarded if you invest in better wires.
I find remarkable the level of performance PTE has achieved by combining relatively unremarkable components in a smart way. The speaker drivers do not use any exotic new materials often cited in advertisements by other manufacturers. The cabinets are not made from special space-age materials, nor do they have any flamboyant contoured shapes favored by others. The electronics inside the cabinets use conventional solid-state devices available for years, and I'm told there are few, if any, exotic passive devices either. Amplifiers use old-style class AB architecture, not class D, E, F or G, and the equalization and filtering is all analog. Even the wire inside the speaker is nothing more than twisted, stranded copper wire (which they keep short). I believe the Phoenix SG is a good demonstration of the possible for an active powered loudspeaker. There is tremendous potential in developing an integrated loudspeaker system where the electronic and electromechanical components are designed to be matched closely with each other, and where speaker cables that mostly degrade the sound are minimized. Of course it doesn't hurt that the principals at PTE have more than 20 years of speaker design experience and have great ears and musical taste. They have gotten all the basics right and have paid attention to numerous subtle factors that spell the difference between merely good speakers and great ones.
Assessed as a speaker alone in the $9500/pair price range, I would rank the Phoenix SG to be very competitive with some of the best-known names in the marketplace. It's a very involving speaker with terrific bass extension, definition and dynamics, and a smooth midrange and high-end response, and they play loud without distress. When you consider each speaker also includes 390 W of power amplification and no speaker cables are required, the Phoenix SG is a screaming bargain. Construction quality equals the best out there and craftsmen who care make it in the USA.
The Phoenix SG is not for audio enthusiasts who want to tinker and squeeze the last bit of realism out of their systems, although the tweeter and bass switches on the back panel do allow some adjustment for different musical tastes. But if you just want a system you can sit down with, listen and enjoy, then you should put the PTE Phoenix SG on your short list to audition. Mark Wechsberg
PTE Phoenix SG Active Loudspeakers