Reviews of Attainable Hi-Fi & Home-Theater Equipment

Reviews of Attainable Hi-Fi & Home-Theater Equipment

Theory Audio Design is the latest venture by audio engineer Paul Hales. Hales was a prominent name in the 1980s and ’90s, with successful speaker lines marketed under his Hales Design Group brand. I remember lusting after the Transcendence Five, a three-way floorstanding speaker that offered beautiful, full-range sound. It featured a heavily built, sealed cabinet with a contoured front baffle for excellent soundstaging. After Hales Design Group, Hales became director of research and development for QSC Audio, a company well known for its commercial cinema systems. From there, he started Pro Audio Technology, which features professional-level home-theater speaker systems designed for the most demanding applications. To complement Pro Audio Technology, in 2018, Hales started Theory Audio Design, a company specializing in residential speaker systems that can be placed wherever flexibility is required.

I first became acquainted with Theory Audio Design when I reviewed the sb85 5.2.2 soundbar-based home-theater system ($12,300, all prices USD). This system features an audacious 75″-long wall-mountable enclosure housing the left, center, and right speakers of a home-theater system. Four additional sb25 speakers were provided for the surround left and right speakers and the height channels. I had a brief listen to the sb25 speakers, using them as the main channels in my stereo system, and their sound was compelling—compelling enough to warrant a review of their own.

Theory Audio Design

The sb25 ($850 each) is an on-wall speaker, but throughout my audition, I felt it competed well with comparably priced bookshelf speakers. It does require (mostly, see below) an ALC-1809 amplifier-controller ($3500) to really perform, which essentially transforms the setup into a powered speaker system. At a system price of $5200 for the ALC-1809 and a pair of sb25 speakers, it is a fascinating alternative to a conventional system consisting of an amplifier and separate speakers, the typical basis of a SoundStage! Access two-channel sound system.


The Theory sb25 is a satellite speaker measuring 9.5″W × 21.5″H × 3.8″D and weighing 23 pounds. From the front, it looks like a large bookshelf speaker, but with a depth of less than 4″, it is much shallower than most bookshelf speakers. The sb25 features a tweeter mounted above two bass-midrange drivers. The tweeter used in the sb25 is a 1.4″ advanced-polymer compression driver manufactured by a third-party company to Theory’s specifications. A compression driver operates differently than a conventional dome tweeter. With dome drivers, the surface of the dome radiates sound directly into your listening space. However, compression drivers contain a chamber with a vibrating diaphragm; the sound emanates through a hole in the chamber and then out into the listening space. When sound waves emanate from the compression driver, there needs to be a means of guiding the sound into the room—with speakers like Klipsch and some JBLs, compression drivers are coupled to rectangular, contoured horns to direct the sound. In the Theory speaker, however, the MDF baffle is concave down to the compression driver, shaped, according to Theory’s design, in a proprietary axisymmetric profile optimized for optimum off-axis performance.

In addition to the compression driver, there are two 5″ carbon-fiber bass-midrange drivers vertically oriented below the tweeter. There are two ports below these drivers to augment the bass response. The sb25 has a rated frequency response of 58Hz to 23kHz, with a maximum output of 117dB and a sensitivity specification of 94dB/1W/1m. The latter two specs would be eye-opening for a floorstanding speaker to be able to reach, let alone the sb25, at only 4″ deep!

Theory Audio Design

The Theory sb25 speakers are designed to work with the ALC-1809 ($3500). The compact ALC-1809 amplified loudspeaker controller measures 1.75″H × 17″W × 15″D and weighs 13 pounds. It’s hard to believe, but inside the chassis, there are nine class-D amplifier channels and a digital signal processor (DSP). A single ALC-1809 can be configured using any speaker layout combination from 2.0 (two speakers and no subwoofer) to a 7.2 or 5.2.2 Dolby Atmos configuration (consisting of five main home-theater channels, two subwoofers, and two height channels). A maximum of three subwoofers can be controlled with one ALC-1809.

The controller has eight balanced input connectors and comes with Euro-connector-to-XLR dongles. There are nine Euro-style speaker outputs, designated 0 to 8. The discrepancy of inputs to outputs can be explained by the duplication of the subwoofer channel—channels 0 and 1 are subwoofer channels and receive the same signal. The first three channels have a rated power output of 300W into 4 ohms, and the other six channels are rated at 100W into 4 ohms. To configure the ALC-1809, you need to use the PC-based Theory Automator software and upload the configuration to the controller through a USB connection.


With the ALC-1809 acting as a power amplifier, I used the RCA output from my NuPrime IDA-16 integrated amplifier, with the NuPrime acting as a preamp in this configuration. I used RCA-to-XLR cables to connect to the ALC-1809 XLR dongles. One thing I feared was introducing noise or hum from combining unbalanced RCA outputs from my integrated amp to the balanced inputs of the controller. However, the setup was quiet. The other issue in my setup is with the speaker outputs from the ALC-1809. These are Euro connectors that only accept bare wire. Since my speaker cables are terminated with banana plugs, I had to remove them and insert the bare ends into the Euro connectors. For my source, I streamed music from my NAS to a Raspberry Pi single-board computer running Volumio2 music player software.

Theory Audio Design

The sb25 speakers were initially placed at the front of my room where I normally put my on-wall speakers—the speakers were 12′ from my listening seat and around 8′ apart. I placed them on 2′-high wooden stands and toed them toward my listening seat to achieve the best performance. I ended up with the sb25 speakers 1′ in front of the wall, 7′ apart, and 11′ from my listening seat. This put each tweeter right at ear height.

The next part of the setup involved the Theory Automator PC software. In this software application, you input the number of speakers and subwoofers, their locations, the speaker distances relative to your listening seat, and their proximity to corners. Once these parameters are entered, the software calculates the ideal crossovers (if you're using subwoofers), delays, and equalization. Once the software finishes its calculations, the settings are uploaded via a USB connection from your computer to the ALC-1809.

Theory Audio Design

Theory is constantly tweaking the software, and they send out updates periodically. When you update the ALC-1809 amp-controller with the latest software update, you get the benefit of better sound. Hales likened this to the Tesla automobile, which can be updated over-the-air to tweak its performance. During the time I had the Theory system, the software was updated once, with the sb25 speakers at v1.3.

Music listening

My first reaction while listening to the sb25s was one of shock—these speakers were remarkably dynamic, which really drew me into the music. Instruments like drums had a realistic snap that made them sound as if I was hearing the music live. For example, “Company,” from Patricia Barber’s Modern Cool album (16-bit/44.1kHz FLAC, Premonition Records), features a terrific Mark Walker drum solo that starts at around the 2:45 mark. As he hit the various toms and cymbals in his kit, the sb25 speakers reproduced the sound effortlessly. Each beat sounded crisp and tight, with nothing slowing it down.

Tonally, the Theory sb25 speakers were neutral throughout most of their range, except for a slight emphasis in the high frequencies. The upper registers weren’t too prominent, though. The highs were very revealing of source material. For example, when listening to “Take the A Train” from Casey Abrams’s Put A Spell On You (24/192 AIFF, Chesky), I could hear more of the texture of Jacob Scesney’s saxophone through the high-resolution track compared to the 16-bit/44.1kHz version. The background was also quieter through the high-resolution track. This album was recorded in a decommissioned church, and I could really hear the large acoustic space through these speakers.

Theory Audio Design

Imaging was another strong suit of the Theory sb25 speakers. When listening to Abrams’s rendition of the Creedence Clearwater Revival song “Have You Ever Seen the Rain?,” Taylor Tesler’s guitar is far left, with Abrams’s voice firmly in the middle of the soundstage. Abrams’s bass comes in mid-song, on the right side of the soundstage. With the Theory speakers, the bass wasn’t fully to the right; it sounded as though it was a foot or so to the left of the right speaker. When I switched back to Barber’s “Company” track, Walker’s drums spanned the space between the sb25 speakers. If I closed my eyes, I could picture where the snare drum, each cymbal, and tom were located.

In terms of bass response, the Theory sb25s were comparable to a typical set of large bookshelf speakers. By this, I mean they have enough bass for most music. For the jazz music I prefer, I was perfectly happy without a subwoofer. On Put a Spell On You, I could hear the depth of Abrams’s bass and I didn’t feel like I was missing anything. The sb25s’ bass response was tight—it didn’t plod along in the background. When Abrams plucked his bass strings, I could hear each note distinctly.

Theory Audio Design

With the Theory ALC-1809, you can easily add a Theory sub12 or sub15 to fill out the bottom end. I had a sub15 on hand to try this out. Incidentally, the ALC-1809 uses the 300W Channel 1 output for the LFE channel and bridges two channels each for the front left and right for a total of 300W apiece. When set up in this fashion, a track like “Temple Caves” from Mickey Hart’s Planet Drum (16/44.1 FLAC, Universal) filled my room with deep, guttural bass. The blend with the sb25s was seamless, with no indication of where the crossover was occurring. Unless you have a very large room, a single sub15 should be sufficient for most people.

Although Hales didn’t recommend it, another thing I tried was using the Theory sb25s directly connected to my NuPrime IDA-16 integrated amplifier without the Theory ALC-1809. Tonally and dynamically, the sb25 speakers sounded more laid back in this configuration. When I revisited Barber’s “Company” track, the drums didn’t have the impact they had with the ALC-1809. The bass response was lacking as well, and there wasn’t as much of the bottom end as there was with the amplifier-controller. The stellar imaging was still present, though. I wouldn’t totally dismiss the idea of using the sb25s without the ALC-1809, but it definitely takes the speakers to another level of performance.

Theory Audio Design

Trying the Theory sb25s powered from my NuPrime IDA-16 got me thinking about a final configuration that I wanted to try—connecting the speakers directly to my Anthem MRX 720 receiver and using Anthem Room Correction to correct the response. In this configuration, I also used my usual subwoofer, the Paradigm Servo-15 V2, to fill in the bottom end. I was very surprised how good this sounded. The blend of the subwoofer and the sb25 speakers was particularly good. When listening to Abrams’s “Have You Ever Seen the Rain?” cover, Tesler’s guitar was particularly notable, having a warm, rich tone. The imaging was excellent as well, with precise placement of instruments. Ultimately, the speakers combined with the ALC-1809 were more dynamic and slightly more transparent, but the Theory sb25 speakers with good room correction can sound superb, a testament to the great design by Theory.


I had the PSB PWM2 on-wall speakers available to compare to the Theory sb25s. The PWM2 retails for $1500 each and has a driver array consisting of a 1″ titanium-dome tweeter with two 3″ carbon-fiber midrange drivers on either side of the tweeter, and two 4″ carbon-fiber woofers. The PWM2 is much taller, at 36″ high, and narrower, at 6.5″ wide. The depth, 3.38″, is similar to the sb25’s.

For this comparison, both sets of speakers were set up against my front wall, on either side of my 92″ home-theater screen. The PSB PWM2s were run directly through my Anthem MRX 720 receiver, with the room-correction processing off. The Theory sb25s were connected to the Zone 2 output using the Anthem receiver. The output levels were matched to get the same volume from each set of speakers. Having the speakers connected in this way, I was able to rapidly switch between the two sets of speakers and listen for differences.

I had a difficult time finding differences between the PSB PWM2s and the Theory sb25s. At the bottom end, their bass responses were comparable, with both extending as low as a large bookshelf speaker. Getting this type of performance from speakers less than 4″ deep is remarkable. Tonally, I found the PWM2s slightly laid-back—less detailed and warmer—than the more revealing sb25s. While listening to “September in the Rain” from the Roy Hargrove Big Band album Emergence (16/44.1 FLAC, EmArcy), I found that Hargrove’s (muted) trumpet sounded more detailed through the Theory sb25s. In the latter half of the song, when Hargrove sings, his voice was slightly richer through the PWM2s.

I’d be hard pressed to say which model is better, and choosing between the two would come down to your own preferences. The laid-back PSB PWM2s were more forgiving and might work better in lively rooms, as well as with less sophisticated electronics, which can sometimes sound harsh. The Theory sb25s did emphasize these characteristics, but on the other hand, they allowed me to hear every minute detail in my music.


The Theory sb25 is a fantastic sounding speaker that shattered a few myths for me, including for instance, the belief that a smallish speaker primarily designed for on-wall use can’t play loudly and can’t produce decent bass response. A pair of sb25s can play loudly and effortlessly, and the ones I tested produced enough bass extension that a subwoofer wasn’t mandatory for me.

Theory Audio Design

Although the Theory sb25 is designed to be part of a home-theater system, this stereo-only review of the system proved to me that anyone with space constraints need not miss out on the high-end-audio experience. If you have a smaller listening space, or even if you have a huge room and prefer an unobtrusive audio system, I urge you to give the Theory sb25-based system an audition. I’m quite confident that you’ll come away as impressed as I was.

. . . Vince Hanada

Associated Equipment

  • Receiver: Anthem MRX 720.
  • Integrated amplifier: NuPrime IDA-16.
  • Speakers: Definitive Technology BP8060ST, PSB PWM2.
  • Sources: Raspberry Pi with Volumio2 music player software.
  • Cables: Analysis Plus Blue Oval in-wall speaker cable, Analysis Plus Super Sub interconnects.

Theory Audio Design sb25 Loudspeakers
System Price: $5200 (including the ALC-1809 amplifier-controller).
Warranty: Five years on speakers, three years on amplifier-controller.

Theory Audio Design, LLC
25741 Atlantic Ocean Drive, Suite B,
Lake Forest, California
92630 USA
Phone: (949) 245-0505