Drivers ListFocusWorks Audio DriversGUJ21V1

ManufactureFocusWorks Audio
Motor TypeUnderhung
Driver Size21 "
Driver Weight35 lbs
Coil Diameter4.5 "
Coil MaterialAL
Manufacture's Xmax30 mm

TS Parameters (Measured by

Fs22.5 Hz
Res4.9 Ω
Le 1khz3.01 mH
Sd0.155 m2
Vas321.8 liters
Mms520.2 grams
Cms96 μm/N
BL25.93 Tm
BL2/Res137.2 N2/W
L/R Time Constant0.61 milliseconds
SplSens90.2 dB


The GUJ18v1 18 inch bass driver and it’s brother the larger GUJ21v1 21 inch, are both from a startup company called Focusworks Audio. Both drivers are ightweight, long throw designs suitable for larger sealed systems or perhaps very large EBS style vented systems. Some of the driver engineering expertise and assembly for these drivers are provided by Funk Audio, which explains some of the shared family traits.

The GUJ21v1 is built very similar to the 18 inch unit. The 21 also uses a large 6 spoke style cast aluminum frame and includes a rubber wrap around gasket. The motor and voice coil used for both drivers sizes is the same as is the spider used and the terminals etc. To recap...The design of the GUJ21v1 is also an underhung topology with an inner neo magnet slug. There is an aluminum pole sleeve covering the entire pole and gap area of the driver to lower and linearize inductive distortion. The motor also includes a large center pole vent and is also quite compact and relatively lightweight. The frame of the GUJ21v1 is not machined like the 18 but rather has a large spider spacer with a bunch of 0.75 inch holes in it to provide the venting above the gap.  The voice coil is the same very large 4.5” diameter 4 layer wind, which is said to have a higher winding height than normal for an underhung topology. Xmax for this driver is said to be 30mm at 70% BL with Xmech at 40mm. The suspension for the driver consists of a large 10 inch diameter spider and a large half roll foam surround. The cone itself appears to be a heavy pressed paper but it does not have the carbon fiber front face that the 18 inch unit does. The same inverted aluminum dust-cap completes the front of the driver though. The driver is a dual voice coil design with a pair of spring loaded binding posts for each coil.

Testing of the GUJ21v1 also produced a set of parameters that were in close agreement with the factory ones provided, similar to the 18 inch GUJ driver. The driver is essentially a nominal 6ohm or possibly 8ohm driver, with the coils in series, just like the 18, since they both use the same voice coil wind. The BL^2/Re of the driver is a bit higher on the 21 than the 18, at about 137 and the Fs came in a bit higher at 22.5Hz despite an MMS about 100g heavier at 520g. This may be due to the larger 21 inch surround being thicker and stiffer or perhaps the 18 has had the suspension worked out much more. Either way this is all well within normal production tolerances. The GUJ21v1 also ends up with a low EBP and a Qts of about 0.50. This driver does like a bit of air volume to work with for best results. Inductance seems to be well mannered and under control judging by the distortion results from testing this driver and the shape of the impedance rise after the driver resonance. Unsurprising since the motor/coil system is the same as the 18 inch version. Free air testing of the GUJ21v1 indicated it is quite clean and mechanically quiet up to somewhat past 2” peak to peak and at about 2.75” peak to peak it starts to develop some chatter that indicates it is becoming increasingly non linear. Again the same as the 18 inch model. It was pushed to about 3” peak to peak without issue other than high levels of distortion and air noise. Mechanically it also seems well built and abuse tolerant. If anything the 21 seemed like it may be a bit better behaved at high excursion. Both GUJ drivers do quite well with large power inputs for an underhung design. Generally underhung designs have lower efficiency and less coil mass so they do not do as well with large power inputs. The GUJ drivers are an exception to that due to extensive cooling in the motors and relatively massive voice coils. Distortion on these drivers was quite low until the drivers were pushed to huge amounts of excursion. Both the 18” and 21” drivers give warning sounds of overload and distortion well before any mechanical damage can occur which is always good.

The GUJ drivers are expensive with MSRP of about $850 for the 18 and $900 for the 21 but the street price may be lower. TBD. These drivers are lightweight weighing less than 40lbs and offer a ton of displacement with low distortion. I can’t think of any other underhung drivers that will take the amount of long term power that these will so overall these are a bit of a different breed from most other drivers available. Focusworks Audio indicate that these should be available for sale to the public soon. 

FocusWorks Audio 21" GUJ21V1 Systems