Acme Sound has long pursued a unique view on bass cabinet design, one that continues to stand out as much today as it did in 1998, when Bass Player named Acme’s unorthodox Low B-2 2x10 one of the 10 Most Important Gear Ideas of the Decade. The recognition was prescient, as one could argue that the Low B-2 marked the beginning of a new chapter in bass cabinet design that’s still flourishing. Rather than dark and thuddy vintage- style tone, many contemporary bass players want fidelity, big power handling, and balanced full-spectrum response, just like the Acme delivered way back when. Acme Sound owner and engineer Andy Lewis’ latest design, the “impulse compensated” 2x12 seen here, is as intriguing conceptually as its celebrated ancestor. The question, though, is whether the descendent sounds as good, too.
Obviously, this is an unorthodox cabinet. What’s with the weird speaker arrangement, you ask? Well, like most things, it all goes back to Issac Newton. Of his many useful insights, let’s focus on his Third Law of Motion: all forces exist in pairs, or ‘for every action, there is an equal and opposite reaction.’ When a speaker’s cone moves outward, or “excurses,” Newton’s Law tells us that it is only able to do so in tandem with an opposing force. In the case of a speaker cabinet, that opposing force is the cabinet itself. When an engineer designs a high-fidelity speaker cabinet, the elimination of this resonant vibration is a chief goal. The more energy that’s absorbed into the cabinet, the less available to produce an accurate representation of the incoming audio, because the absorption amount varies with frequency, thus coloring the sound.
To eliminate unwanted resonance, speaker cabinet designers have a few options. Arguably the best option is to mount speakers in a structure that’s rigid enough to withstand the peak force of an amplifier throughout the frequency range. The only rub to this plan is that in the case of a bass cabinet, which is required to produce high output at low frequencies with minimal distortion, the ideal structure would weigh hundreds of pounds. Another option is to damp the vibration of the cabinet externally. Sitting on it helps a little, as does stacking on a pile of lead ingots, but neither is a good practical solution. The most common solution, then, is to combine rigid cabinet materials with extensive physical and acoustic damping. Deconstruct the average bass cabinet and you’re likely to find stiff birch plywood throughout, with cross-bracing and bundles of soft insulation.
Suffice it to say, the typical solution works well enough. But for a real audiophile (or just a restless engineer), “good enough” isn’t good enough. Which brings us to the funky back-to-back speaker arrangement. Andy Lewis’ solution to Newton’s nagging problem is to place his cabinet’s two woofers back-to-back. The moving masses of the opposing speakers’ cones apply a net zero force to the cabinet assembly, reducing unwanted vibration. This so-called “impulse-compensated” design is not unprecedented—some high-end audiophile speakers utilize the configuration— but it’s nearly unheard of in a bass cabinet. A secondary benefit of the design is that each driver’s voice coil vent forces air on to the other’s, reducing heat build-up and thus increasing power handling and improving fidelity.
Dimensionally, the Acme 2x12 is sort of 4x10-ish in general girth, but its relatively light weight and large, well placed handles make it pretty portable. Its internal construction is excellent. The cabinetry is seven-ply 18mm plywood, well joined and internally stress-braced. Stress bracing puts tension on the cabinet’s interior walls, raising its resonant frequency. High-frequency resonance is more easily controlled using fiberglass damping insulation than low-frequency resonance. Given Lewis’ obsession with vibration control, the solidly bolted metal grilles are no surprise. Each uses bolts with threaded inserts in the baffle, secured with double-sided tape, and braced with screwed-in rubber standoffs. The Acme incorporates a 2nd-order crossover as a highpass filter for the tweeter. The woofers operate in full range. My only substantial criticism of the Acme’s materials is the durability of its spray-on covering. Over a month of light-duty gigging, the finish showed some damage, which wouldn’t be too bad if each ding and chip hadn’t revealed a bright white sub-coating beneath the black surface. [Acme responds: “We’re already looking at alternatives to the Duratex coating. Until then, we include free touch-up kits with every cabinet.”]
Beyond the exotic design, the Acme differentiates itself in other significant ways from many other cabs on the market. The Low B’s woofers have a fairly low sensitivity rating. A speaker’s sensitivity rating is a measure of the sound pressure level (SPL) it produces at a specified distance for a specified input signal. Usually measured in decibels, SPL is typically derived at a distance of 1 meter on axis with a speaker receiving a 1-watt signal. In layperson’s terms, sensitivity is a way of measuring how efficiently a speaker converts an amp’s output into sound, versus wasting it as heat. At 94.1dB SPL (1 watt/1 meter), the Acme requires more power to achieve comparable volume compared to many other bass cabs, which tend to have sensitivity specs in the 97dB–100dB range. This is not a bad thing, necessarily. In fact, in order to achieve high sensitivity specs, speaker designers have to make certain construction compromises. While subject to some debate, a low-sensitivity speaker, though power hungry, is potentially higher fidelity than a comparable highsensitivity design. Acme recommends pairing the cab with 1,200–2,000 watt amps.
Given the cab’s power-hungry personality, I paired it with some of the biggest power amps we have on hand. Since big power is often the purvey of PAstyle power amps, this review had the side benefit of (A) giving me a serious workout, and (B) reminding what fun it is to pair rack preamps and power amps for a live rig, a once-popular practice that’s gone out of vogue with the emergence of lightweight high-power bass heads. My numerous rigs included various combinations of Fender TBP-1, Demeter VTB-201S, Kern IP-777, and Noble preamps with Crest CA-9, Crown Macro-Tech MA-3600 power amps. Realizing that most folks don’t want to schlep the absurdly heavy rigs I created, I also used the cabinets with a Warwick LWA-1000 and a Markbass Big Bang, a pair of great-sounding, lightweight Class D/SMPS heads.
Given its design, it would seem that one of the immediate challenges with the Acme is placement. The opposed woofers mean one is always pointing backward (obviously). This can be a boon to a drummer, but a cabinet’s sonic presentation is influenced by placement, with bass reinforcement and other acoustic effects emerging as you alter the cab’s relationship to walls and corners. In practice, though, it didn’t end up being a big deal at all. I began to think of the cab in a more conventional way, and once I did, I never found myself forced into an impractical placement paradox. While placement is something that may require more thought versus conventional cabs, the Acme’s design is not as nutty on the gig as you might predict.
My feelings about the cabinet’s sound are mixed. On one hand, it offered some of the most authoritative, taut, controlled, and rich low-frequency response I’ve encountered. Combined with the big PA amps’ massive headroom, the Low B is just a total beast. But rather than just maul the listener with gritty teeth, it is beastly and articulate, dynamically sensitive, and colorful. It’s a joy to play, most of the time.
Which gets me to the other ingredient in my mixed feeling. This is subjective, natch, but I did not like the sound of the tweeter, especially with passive basses that don’t already offer a ton of highfrequency snap. Somehow it felt a little shrill in comparison to the beautiful intensity of the woofers’ output. Some may like its zippy crackle, but I thought it could have been better integrated into the overall soundscape. Given this quality, not to mention the fact that it’s essentially an industry standard, I wish the Acme had a rheostat or switch to control the tweeter’s output. I think the high-register sound would have cleaned up nicely had I had the opportunity to attenuate it somewhat. [Acme’s Andy Lewis responds: “I’ve never been happy with the best available L-Pad attenuators. Most amps offer better treble control than simple speaker attenuators.”]
Regardless of your own take on the Low B’s sound footprint, it absolutely deserves your attention. It is a genuinely impressive cabinet, and it doesn’t much resemble the sound of anything else. The Acme’s blend of accuracy and dynamic sensitivity with room-filling richness is anything but generic.
Low B Series III 2x12
Pros Incredible articulate tone, exceptional transient response, loud-but-accurate
Cons Tweeter is a bit shrill
Bottom line An expertly designed cabinet, with a distinctive approach to age-old problems, that delivers big-time.
Woofers 2x12" custom-designed Eminence cast-frame neodymium in “impulse compensated” orientation
Tweeter Textile dome Connector 2 parallel Neutrik dual connectors (Speakon and 1/4" jacks)
Impedance 8Ω (4Ω also available)
Power handling 1,500 watts RMS
Warranty 10 years limited
Made in USA