Systems List › DIY › Focusworks GUJ18V1(DB18V Cab)
NotesThe final test for the GUJ18v1 driver in the DB18V cabinet is with all 3 slot vents open. The impedance curve measurement shows that the in band impedance minimum is at about 23Hz and about 7.3ohms. the in band impedance maximum is at roughly 36Hz and about 52 ohms. The second impedance miniumum in band is about 9.5 ohms at 50Hz similar to the other tests in this cab with this driver. the impedance curve and driver behavior indicate an effective vent tuning somewhere near 24Hz. The raw frequency response shape is a bit peakier than the sealed or lower vent tunings, but overall it fits within a 10dB total window from 23-164Hz. The transition to the steep roll off below vent tuning doesn't become apparent till about 19Hz which is a little odd. Up top we see the ragged notch in response related to the vent pipe resonance which makes the response unusable from about 150-200Hz. The 2.83v sensitivity of the GUJ18v1 in this cab with all vents open is about 90dB over the 65-130Hz octave and reaches a quite sensitive peak of 98.5dB at 37Hz. Down at 20Hz the sensitivity is still about 85dB. Looking at the time domain data for this system configuration we see that there is a slight peak in the group delay near 37Hz which still just barely reaches one cycle even with the HPF in place and nothing of note below that point even with the HPF in place in which case it just reaches one cycle down near 16Hz. The waterfall shows just a hint of ringing near 37Hz which is mild and likely to be inaudible and no other significant ringing in the 10-125Hz bandwidth. The high pass filter used for protection of the driver below vent tuning is a 3rd order Butterworth filter at 24Hz. This protects the driver a bit better than the 2nd order filters used for the deeper vent tunings.
The long term output measurements of this system start out at 3.25v which produces about 90dB at 50Hz at 2 meters ground plane. There is no significant compression in the output until the 57.8 volt measurement where there is just 1-1.5dB of compression near the vent tuning. The next measurement with a 5dB hotter signal is at 103v. At this point there was just a hint of vent air noise and a little bit of driver distortion in the deep bass. Compression still remains low with just 1-1.7dB broadband. Another full 5dB increase in signal strength calls for an input of 183v into the GUJ18v1 driver. At this point driver distress noises became apparent as well as what might be a resonance in the cabinet somewhere. The output compression at the 183v level is still moderate and is just 2 to 2.5dB on average from 18-45Hz and 1 to 1.5dB above that point. The repeat 3.25v measurement indicated some temporary sensitivity loss after this measurement.
The distortion measurements show that this configuration produces 3% THD or less above 24Hz at the 18.3 volt level. With a 32.5 volt input the THD remains below 5% above 23Hz and is under 20% down to 16Hz. With a 57.8v measurement the THD remains at or below 7% above 23Hz and below 30% down to 16Hz. The 103v measurement is beginning to drive the GUJ18v1 driver quite hard. At this point the system is producing 10% or less THD above 23Hz except for a spike in THD up near 170Hz related to the vent resonance. From 15-20Hz THD has now risen to 30-50%. The final 183v measurement produces a lot more THD from the system indicating that it is being driven very hard. THD is up over 65% below 20Hz indicating very high driver excursion and also reaches almost 19% at 37Hz again indicating high driver excursion. Note that the spike in THD at 170Hz likely corresponds to the cabinet noise noted during the tests. This will require investigation later. It may be possible that one of the braces is not fully secured in the cabinet.
Distortion limited short term burst output for this system is about as expected. There isn't much below 20hz as this is well below the vent tuning but at 25Hz and above there is a lot of headroom. Below 63Hz the system was distortion limited. At 63Hz and above the system was amplifier voltage limited.