This is the second generation of our servo driver. While designed specifically for our Direct Servo subwoofers, all our drivers are also suitable for conventional use. After extensive testing and comparisons and positive customer feedback, we feel compelled to offer them for sale separately. In a market dominated by products designed to look good on paper, we have created products that feature uncompromising performance. Audiophiles are well advised to keep in mind that drivers that look most impressive on paper may not be very accurate.

Impressive on paper vs real performance

To improve the specs on paper, most existing drivers on the market use more voice coil layers. This requires a wider voice coil gap. As a result, not only the moving mass of the driver is increased, the magnet strength is weakened, and the voice coil inductance is also increased. In many cases, the result is a driver which performs poorly above 40 Hz. The problem is more serious than it may appear. If we play a 40 Hz tone, harmonic distortion products will be added to the original. 3rd order distortion products are particular objectionable, and for this 40 Hz tone will be at 120 Hz. The ear is more sensitive around this range, and as a result, it makes the distortion more audible. It is often thought that a subwoofer that has poor distortion performance can merely be crossed low. The problem with this is that harmonic distortion will be clearly audible and accuracy will be compromised. Most subwoofers are plagued with these problems. Not only are they unsuitable for operation above 40 Hz, they also add a lot of distortion even when crossed this low.

Our approach to driver design

We take a very different approach. Our drivers have low moving mass, high flux density in the magnet gap, and low distortion. We start with two 1" stacked magnets (for a total of 2" magnet height) and a 1.8" long sensing coil with 0.5" top plate to support 1.4" linear peak to peak excursion. In order to achieve the goal of low moving mass, we have designed a lightweight 2 layer voice coil with the tight magnet gap (less than 0.1"). To reduce distortion and low inductance, we added a FEA-(finite element analysis-) designed short circuit ring that is effective above 30 Hz for reducing flux modulation and at the same time reducing voice coil inductance at higher frequency. The cast frame basket further improves the rigidity of the driver. The result is a driver capable of high SPL and that is also accurate.

Conventional vs Direct Servo

For audiophiles who desire the ultimate in accuracy, we recommend our Direct Servo kits. While our drivers are better than most, their performance in a conventional subwoofer will never be as good as a Direct Servo subwoofer. If you are looking for non servo drivers, we recommend that you consider a Direct Servo kit.

Driver features

	Rigid anodized aluminum cone (black or silver)
	Rigid 12 spoke cast aluminum basket
	FEA designed aluminum short circuit ring to reduce 2nd order distortion
	High linear excursion capability of 1.4" peak to peak (xmax)
	High mechanical excursion capability of 2.6" peak to peak (xmech) to reduce risk of bottoming
	Very low inductance
	24 ohm ultra thin sensing coil for servo operation keeps moving mass low
	Woven wire lead in the spider to prevent rattling during high excursion
	Gold spring loaded terminals for easy solderless cable connection
	Single 2.8 ohm voice coil
	Available with rubber mounting gasket (12-5/8" outer diameter and 3/4" depth)
	Mounting without gasket (12-3/8" outer diameter and 3/8" depth)
	Two 1" stacked magnets for a total magnet height of 2"
	Cutout: 11-3/16"
	6-1/2" clearance in depth
	350W RMS max power
	Proudly made in USA

Mounting

There are two mounting methods for this driver. The first method is to use the rubber gasket that comes with the driver, put it on the basket outer ring, and use it as a seal to mount the driver (a popular method for car subs). The second method is to use a foam gasket tape (also comes with the driver) that goes between the driver basket and the enclosure to ensure proper seal. We recommend to put the tape on enclosure, instead of on the driver basket. The main difference is on the cosmetic look and also the recess depth and the final driver outer dimension. In the following, we show the top and side views of the driver with and without the rubber basket.

Our DS12 driver is available in three versions:

Our DS12CV driver is designed to work in smaller enclosures. The low fs and low Qts enables it to work well in a 1.5 cu ft enclosure. While our standard driver, DS12TC is available in black finish, DS12CV is only available in silver. We also supply an 8 ohm version for use in our dualkit, DS12D.

These servo drivers are available for purchase separately to use in a nonservo configuration with the intent to upgrade to a servo sub with the purchase of our servo amplifiers in the future.

	Description	Price	Silver only
	DS12 standard 12" servo driver (black cone)	$180

This distortion comparison gives an idea of how our Direct Servo kits compare to conventional subwoofer drivers currently on the market. We compare the distortion of DS12TC mounted in a 2 cu ft sealed box at 70 Hz at 104db SPL (at 1 meter). "Driver X" (AV15) is a very popular high-excursion 15” driver. The other driver is 12” subwoofer driver, "sh*va" 12." Both are popular among DIY community. The distortion at mid to upper bass frequency such as 70 Hz gives a good indication of how clean the bass will be since human hearing is more sensitive to that frequency range than say 20 Hz.

Impedance curve

The above shows impedance in linear scale with 5ohms for each division. The measured impedance of DS12 is 6ohms at 1khz. The equivalent inductance is actually less than 1mH. The metric to fairly compare inductance among drivers is voice coil inductance divided by voice coil DC resistance (or inductance per ohm). This is primarily because the stability of voice coil inductance vs voice coil DC resistance (similar to the stability of force factor square vs voice coil DC resistance). The inductance per ohm from DS12 is 0.33mH/ohm. Also check the zero-phase crossing point. DS12 has the crossing point at 100 Hz. This point should be as high as possible so that it will not affect frequency response. Now let us check the impedance curve of driver "s**VA", as shown below.

First, the impedance at 1 kHz is 17 ohms. Second, the zero phase crossing point is at 80hz. This driver in a sealed box will produce a hump at 70 – 80 Hz. For LT purposes, this driver will be listed as one requiring shelving-down equalization.

While these distortion charts will not be familiar to all, they show the superiority of the Direct Servo driver. This is due both to the design of the driver and the Direct Servo system. This improvement is not only evident on paper, but also in listening tests.

Currently we are providing the DS12 as a kit. You have two options for construction:

Have the box built by a local cabinet-maker
Build it yourself for the ultimate in value for money view plans

Either option results in considerable savings. The shipping cost is significantly reduced, and we keep our overheads low. Plans are available in the DIY section.

Unlike conventional subwoofers, the frequency response remains flat at all output levels until the output limits have been reached. Without Direct Servo, a flat response will only be achieved at low output levels.