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Technical information ~ Listed

Mag soft parts
Mag XBL^2 motor
BM soft parts
BM XBL^2 motor

Technical information ~ PDF download

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Mag D2

Soft parts

First and foremost, the soft parts of a speaker (the surround, cone, and spider) are a critical part of performance. We at Stereo Integrity know how important the cone, surround, and spider are so that's where we started when we re-designed the Mag D2.

Suspension linearity is a critical factor in how good a speaker sounds and we started with the very first part, the surround. The surround of the new Mag D2 is made of rubber and provides just the right mix of compliance and linearity for performance.

The cone used on the Mag D2 is a unique blend of paper along with Kevlar and Carbon Fiber strands that give it a massive strength-to-weight ratio. The content of our paper cones was specifically formulated to reduce cone resonances. Less cone resonance means cleaner, un-distorted sound. Sure we could have just used an ordinary cone, but why use something ordinary? There's nothing on the new Mag that's ordinary. Even though it may look like just another paper cone, it's far from it.

The spider on the Mag D2 is 8" diameter and has woven-on tinsel leads. Read carefully - we said woven-on, not woven-in. Woven-on tinsel leads don't damage the integrity or linearity of the spider like wove-in tinsel leads do. You see, woven-in tinsel leads make micro-tears in the surround and over time the voice coil leads start to saw the spider in two. Our tinsel lead attachment method eliminates all of those problems and provides our customers with reliability. As we stated on the Mag D2's web page our sewn-on leads also eliminate lead slap. Basically, the spider and woven-on tinsel leads are just another thing that we do here at Stereo Integrity to provide you with the most distortion-free subwoofer possible.

XBL^2™ motor

So what's an XBL^2™ motor and what does it mean to you? An XBL^2™ motor uses a proprietary motor topology that stabilizes BL (a force created by the motor) which in turn stabilizes the speakers parameters as the cone moves back and forth. The more stable and linear the cone remains, the cleaner the sound is going to be. The BL curve on a Mag D2 isn't much of a curve at all - it looks more like a plateau. A typical subwoofer BL curve looks just like a bell curve. When a BL curve looks like a bell curve, or hill, it means that the more the cone moves, the more the speakers parameters will shift, causing a change in the way the speaker sounds. The new Mag maintains BL throughout its stroke, resulting in a significant stabilization of parameters. For a little bit more clarification, here is an excerpt from a press release on www.audiojunkies.com:

You can see the FEA results on the new motor in the graph below, along with a graph of how much variance a very good overhung motor can have as a comparison.

The graph shows the new Mag's BL linearity over a portion of the drivers throw and varies less than 1% each way over 20mm of one-way stroke. A good overhung design can vary as little as 3% and can extend to 15% in some cases. We are using XBL^2™ on the new Mag's and have defined a flat BL curve with the new motor. A flat, constant, BL curve allows T/S's to stay stable and minimizes compression throughout linear travel.

We have also added a nice little touch called a Faraday ring inside the motor. We had the pole piece anodized copper and then diamond CNC machined it down to the desired diameter. What this does is give you the benefits of a shorting ring without any BL-sucking air gaps inside the motor.

So why add a shorting ring? Put simply, a shorting ring helps lower inductance. What is inductance and why did we reduce it? Inductance is the rise in voice coil impedance as frequency increases. High inductance subwoofers have a very narrow bandwidth, which has a major impact on how the subwoofer blends with the rest of your system. The inductance on the new Mag is 0.8 mH. Our previous Mag was 3.5mH. Most high-power subwoofers range from 2.5 mH to 4 mH. Just look back over those figures for a little bit. 0.8 mH compared to an average low of 2.5 mH. The reduction of inductance we were able to achieve with the new Mag will give you blending and imaging like no other subwoofer out there.

The reduction of inductance has one major draw-back though; it makes the Mag very detailed and very critical. The Mag D2 will probably play back information you aren't accustomed to hearing.

BM 12"

Soft Parts

Since the BM's were designed for ultra-shallow performance we had to ditch a normal cone and go with a flat diaphragm. The major benefits of using a flat diaphragm are increased clearances and shallower mounting depths. The diaphragm on the BM is a Rohacel and Nomex composite. Our composite diaphragm reduces weight as much as possible while still keeping strength really high.

Using a flat diaphragm also allows us to mount the spider and the motor of the subwoofer closer to front of the subwoofer, which reduces the mounting depth considerably. Without a deep cone, the spider can be mounted closer to the cone.

The spider on the BM series is a massive 10" diameter spider! We have a proprietary glue joint where the spider meets the cone (equivalent glue area between the cone and voice coil is equal to a solid 5" circle!) so we had to increase the size of the spider from 8" to 10" to accommodate the kind of Cms (have the Cms term link to the PDF on compliance) curve we wanted.

The surround on the BM subwoofers is an inverted foam surround. We inverted the surround to allow the use of most normal speaker grilles. No more searching the internet for hours on end trying to find a grille for your subwoofer because almost any grille will fit on a BM without clearance issues. The surround on the BM series is made of foam to achieve the correct compliance to allow the ultra-tiny enclosure specifications.

If you look at the overall height, you'll notice that the BM's surround and cone don't protrude from the front of the speaker. Minimal (or none in the case of the BM's) obtrusions from the mounting surface of the subwoofer affords you the benefit and flexibility to use whatever grill you want to protect your BM.

XBL^2™ motor

Just like the BM's big brother, the Mag D2, the BM's use a BL-stabilizing XBL^2™ motor nestled neatly inside the bottom of the basket. The XBL^2™ motor keeps linear excursion more linear, giving you the cleanest, most consistent bass possible. The BM series also feature reduced inductance over conventional subwoofers due to the reduced voice coil height that XBL^2™ offers. Inductance is even further reduced by an aluminum shorting ring which is housed inside the top plate of the motor....