Systems List › DIY › FocusWorks Audio GUJ21V1 (DBV21 320L Sealed)
NotesMeasurements of the GUJ21v1 driver in the large 320L 21 inch driver sealed cabinet start with the impedance curve as usual. The impedance low is about 5ohms, but this rises to 7.3ohms at 10Hz and reaches a peak of 44.4ohms at 31Hz before dropping back down to 9.5ohms at 47Hz and starting a gentle rise towards 125Hz where the impedance is 12.5ohms. Like the GUJ18v1 driver the 21 inch version has a higher than 8ohm average impedance with the coils in series and should represent an easy load for most amps. The 2.83 volt at 1m sensitivity of this system shows that the maximum sensitivity is about 95dB from 32-40Hz which drops off a bit to 90dB or so towards 100Hz. The sensitivity at 20Hz is just over 84dB. The overall response shape measured at a 2 meter distance exhibits a bit of a droop in the upper bass frequencies but overall manages to fit within a tight 6dB window from 25Hz to beyond 200Hz, which is quite a wide bandwidth for a sealed system with no response shaping. The group delay and spectrogram plots show nothing to be concerned with. Group delay never reaches 1 cycle over the bandwidth of interest.
The long term output compression measurements start with a 4.1 volt signal which produces the baseline measurement for the system of roughly 90dB at 50Hz at 2 meters. The GUJ21v1 driver does not exhibit any significant compression in the output until the 41 volt sweep where a small amount on the order of 0.5dB begins to occur. The next 5dB increase in the drive voltage to 72.7 volts causes only a moderate increase in the amount of compression to about 1dB at maximum. Another full 5dB increase in the signal to 129 volts causes a marked increase in compression of the output and also some clearly distorted noises from the driver indicating it has run out of excursion. The output is now compressing by up to 2.4dB near 10Hz and between 1 to 2dB from 31 to 120Hz. During the loudest measurement sweep the GUJ21v1 was producing 97.5dB at 10Hz, 111dB at 20Hz and peaked at over 121dB at 37Hz. The repeat 4.1 volt measurement showed that there was some heat buildup in the driver resulting from this testing which resulted in a temporary loss in sensitivity of about 1dB broadband.
The distortion results for the GUJ21v1 in the 320L sealed cab are low at the 23 volt drive level. THD is below 4% at 20Hz and remains so until past 200Hz. The 5dB higher 41 volt signal causes THD to increase but it is still under 20% below 15Hz and is less than 6% from 20-200Hz. The 72.7 volt signal causes the GUJ21v1 driver to start to lose composure a bit in the deepest bass where THD has now risen to 40-50% down near 10-15Hz indicating very high excursion. THD remains below 9% above 20Hz though. The final 129 volt measurement pushes the driver to its excursion limits below 15Hz resulting in very high THD. THD dramatically jumps at 20Hz as well reaching 30%. The distortion above 30Hz remains below 9% even at this level. Of note is the narrow spike in distortion at 140Hz. This appears to be a family trait of the GUJ design as it was present in all tests with both drivers. It appears to be caused by some resonances up near 430 and 880Hz. For this reason it would likely be best to operate the drivers as dedicated subwoofers low passed below 120Hz only. During the 129 volt measurements the GUJ21v1 was clearly being driven past its useful limits and it produced some audible distress and overload noises. However the driver did not suffer any long term damage. Similar to the 18 inch GUJ driver, the 21 inch version gives ample warning prior to any damage actually being done. As usual with long throw drivers the distortion is composed primarily of the 3rd harmonic in the deepest bass and a mixture of the 3rd and second harmonics over the rest of the range.
The short term burst output for the GUJ21v1 driver in 320L sealed, is powerful. The output in the 10 and 12.5Hz bands are limited a bit by the 3rd harmonic distortion as evidenced by the maximum output without regard for distortion where the GUJ21v1 is able to produce about 98dB at 10Hz and over 102dB at 12.5Hz. At 20Hz the GUJ21v1 was able to produce 111dB which is very strong for a sealed system. At 31.5Hz it was able to burst 122dB with passing distortion which is a lot of output from driver excursion alone. At 40Hz and above the output reaches 125 to 127dB. The deep bass output is primarily limited by the 3rd harmonic and the upper bass is limited by the available amplifier voltage.