Systems List › DIY › Focusworks GUJ18V1(DB18V Cab)
NotesThe GUJ18v1 driver is loaded into the new DBV18 cab with all of the ports sealed off for this test, which provides a large airspace of about 290L for the driver to operate in. The impedance of the system exhibits a resonance at about 27Hz and a minimum impedance of about 8ohms at 10Hz and about 9ohms at minimum above the resonance. This system should be considered an 8ohm load. The 2.83v at 1m sensitivity of the system shows good low end extension and low bass sensitivity due to the large air volume of the enclosure but middle of the road top end sensitivity. At 20Hz the sensitivity is roughly 84dB which is good for a sealed system. The sensitivity peaks at 36Hz at 92dB then gradually rolls off to about 88dB from 60-150Hz. The overall response shape fits within a 6dB total window from 22Hz to 193Hz which is quite good for an un-equalized sealed system. The response shape and impedance curve show a few resonances in the 170-230Hz range which are related to both the large enclosure dimensions and the slot vents. Even though the vents are blocked off it appears that they still exhibit a strong pipe resonance internally. This being the first test using this new cab it is likely that a bit more damping material can help damp these resonances down a bit more. This will likely be investigated further. Regardless the response is useful up to the 125Hz range or so which is really the upper bandwidth consideration for most subwoofers. The measurements investigating the time domain response of this system show nothing worth worrying about in the bandwidth of interest. Group delay is well under 1 cycle and no appreciable ringing or smearing shows up in the spectrogram plot.
Long term output compression measurements of this system show generally good behavior. Note that the 90dB sweep was mistakenly referenced to 40Hz instead of 50Hz as usual. The 90dB sweep required a voltage of 4.1V in order to produce the required 90dB nominal level at 2 meters ground-plane. The GUJ18v1 driver in this large 290L sealed system performed very well in this test and exhibited very little output compression even at the highest output levels recorded. With a 72.7v input corresponding to a nominally 115dB level the output is compressing less than 1dB over the entire 10-125Hz bandwidth. The loudest measurement was a 3dB increase from the 72.7v level to an input of 103v. Even this input is only causing about 1dB of compression which is very good. The repeat 90dB or 4.1v measurement showed barely 0.5dB of compression due to heating in the driver. However testing was stopped at the 103v level as the driver ran out of excursion below 20Hz and produced some clear distress noise. Assuming a minimum impedance of 8ohms and the 103v input results in a calculated maximum power input of about 1300w to the driver. The 103v 118dB nominal measurement shows that the GUJ18v1 system was able to produce almost 109dB at 20Hz over 115dB at 30Hz and then a slight drop to around 113dB above 60Hz.
The distortion measurements for this system are captured at the same drive levels as used for the long term output compression sweeps. With a 23v input signal the THD is well controlled being 5% or less above 17Hz and rising to about 13& at 10Hz. An increase of 5dB to the signal results in 40.9v to the driver however the distortion results are still quite good with 5% THD or less above 23Hz, 7% THD at 20Hz and a rise to 17% at 10Hz. Another 5dB increase in the signal to 72.7v pushes the driver excursion much higher below 15Hz and distortion there rises to the level of 40-58%. Above 28Hz THD remains low and stays at or below 5%. The final 103v measurement produces driver distress and mechanical noise as indicated by the THD reaching 100% or greater below 20Hz. Thankfully the GUJ driver platform does not bottom easily and gives warning well before damage. THD during the 103v measurements stays below 10% above 28Hz where cone excursion is much lower. The harmonic makeup of the THD is comprised primarily of the 3rd harmonic in the deep bass where excursion is high and the 2nd harmonic in the upper bass where excursion is lower. There are a few blips in the distortion related to cabinet internal resonance issues. One in particular near 155Hz. Still the actual amount of THD produced at these spikes is well under 2.5% even at the highest output levels.
Short term burst distortion limited output shows that the GUJ18v1 offers a lot of low frequency displacement in this cabinet. It was able to produce a passing output of 92.1dB at 10Hz which is always difficult for any system. A result of just under 104dB was recorded at 16Hz and a solid 109dB at 20Hz. At 40Hz an output of about 121dB was recorded. Output plateauís a bit from there and reaches 123 to 124dB from 50-125Hz. At 60-125Hz the amplifier was able to apply its maximum burst voltage to the driver without endangering it mechanically. In the deepest bass near 10-12.5Hz the system could produce a bit more output before running into dangerous excursion levels with the driver. At 16-40Hz there was only another half to 1dB of extra output before the driver became in danger.