Systems List › DIY › Fi Car Audio SSD 18D2 Sealed
The raw frequency response of this sealed system exhibits a pronounce peaking centered at 45Hz and increasingly rolled off further away from that frequency range. The system sensitivity with a 1.7v drive level corresponding to roughly 1 watt of power into the minimum impedance resulted in an output of slightly over 93dB at 45Hz which is rather good for a system of this type and size but by 100Hz the sensitivity has dropped by 8dB to 85dB and by 190Hz it is only 82.5dB. Sensitivity at 20Hz clocked in at just over 76dB.
The response in the time domain showed no energy storage or ringing issues of concern but there was a slight increase near the response peak. It would not be audible in use as it is far below 1 cycle of delay and fairly low in frequency. Moving on to the long term output testing The SSD 18 sealed system shows good behavior and signal tracking through the 110dB sweep where the compression remains below 2dB across the spectrum. By the 115dB sweep level the compression has increased slightly but still remains below 3dB at any point and below 2DB for the majority of the range. The 120dB nominal sweep shows greatly increased compression and response shifting. The final nominally 122dB output sweep shows dramatic compression reaching 6dB at one point and 3dB over a large bandwidth.
During the 120 and 122dB sweeps the system was clearly past its point of linearly responding to input power with the driver running into heavy thermal compression and running out of linear stroke. Interestingly this driver also exhibits a shifting of response shape that includes compression at 50Hz coupled with output expansion at 35Hz which reaches about 1.5dB during the 115dB sweep. The distortion results indicate good behavior above 25Hz with distortion below 10% through the 115dB sweep and below 15% for the most part even at the very high power levels used for the final 122dB sweep. Deep bass distortion below 20Hz is rather elevated though and already indicating 15-20% THD even during the modest 105dB sweep level.
Looking at the component makeup of the distortion below 20Hz the 3rD harmonic dominates but above that point the 2nd harmonic is predominant. This indicates that the distortion that is present above 20Hz may be more benign audibly than a driver with a higher 4th harmonic or a 3rd harmonic which dominates.
The CEA-2010 short term burst testing shows this system to have powerful output capability down to the 25Hz range but somewhat diminished output below that point. This coincides with the distortion data well which indicated elevated levels in the deep bass. If distortion is ignored there is greater headroom available in the deep bass especially below 20Hz.