Systems ListDIYRE Audio MX-18D2 Sealed

Measurement Details

AmplifierPowersoft Digam K10
Outside Temperature82 F
Date TestedSept 15, 2012
Settings & EqualizationNone...

Notes

The sealed MX18 system results in a frequency response with a moderate hump at about 37Hz with a gradual and shallow roll off of about 5dB to 100Hz where the response plateau's and stays basically flat out till almost 500Hz. Indeed this driver looks like it could be used up as high as 500Hz or so if needed. The response hump is likely a result of a higher than average system qtc than inductance as the motor seems to have extensive inductance combating measures. The MX likes larger enclosures due to the high moving mass and low BL. The sensitivity of this driver is low. With a 1.7 volt input into the 2.8ohm minimum load the result is about 90dB sensitivity at 40Hz and decent sensitivity for this enclosure size below that point, but the sensitivity has dropped to about 85dB by 100Hz and stays in that range up until 500Hz or so. The response in the time domain shows nothing of note as expected with a sealed system. No ringing or energy smearing issues are found in the group delay or spectrogram charts. 

Looking at the long term output compression testing the MX system needed 4.1 volts to produce about 90dB at 50Hz at 2 meters. Due to the response shape this is a bit more voltage than most drivers. the compression performance is great up through the 110dB nominal sweep which is an input of about 41 volts. By the 115dB, 73 volt sweep, compression is in effect with 2 to 3dB of compression over most of the range. The driver still sounded fine at this level and not really in distress so a final 120dB sweep was attempted. At this point the deep bass compressed mightily as the driver was clearly out out clean stroke. The compression ballooned to 4 or 5 dB across most of the range. By this time the driver was receiving about 130 volts which would be about 6000 watts into the minimum impedance. Impedance rise from heat in the motor had likely set in which would lower the actual power applied somewhat but needless to say it was substantial amounts of power. A large part of the compression may be due to the driver running out of excursion linearity combined with the rapid heating of the 4" coil. The levels of output achieved below 40Hz are impressive for a single driver but at 50Hz and above the output is lackluster due to the very low sensitivity. 

The CEA-2010 burst output which does not induce heat related compression shows that the MX18 sealed system has decent short term output 50-125Hz but nothing to get excited about. Over the 20-40Hz octave the output is impressive with nearly 108dB available at 20Hz and over 114dB at 25Hz. Below 20Hz the distortion increases rapidly so the SPL levels reached with passing output are not quite as good but still decent. If distortion is ignored the maximum output are higher than normal reaching almost 96dB at 10Hz. The distortion results are a little mixed. During the 115dB sweep at 73 volts the THD stays below 10% until below 22Hz which is impressive. Even during the 120dB sweep THD stays well below 10% above 35Hz. Overall the THD is decent to good but it exhibits a dramatic increase below about 20Hz. The THD is composed mostly of a mixture of the 2nd and 3rd harmonics. 

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