Systems List › DIY › TC Sounds LMSR12 Dual 15" VMP
Some weight is removed from the VMP’s for this test to try and achieve a higher 30Hz tuning. The tuning actually came in closer to 27Hz.
With this tuning of the VMP’s the response shape is pretty good with the peak at about 40Hz and a very gradual roll off of about 5dB total by 150Hz and the low corner coming in at basically 25Hz. The raw response is within a 6dB window from about 23.5-200Hz. For typical use and the high power testing here a 25Hz 18dB/octave 3rd order high pass filter should be employed to protect the drivers below tuning. Response in the time domain shows well controlled behavior with some increased energy near the system tuning with the high pass filter in line as is expected but not enough to exceed 1.5 cycles.
As has been shown in other tests already the LMSR-12 is not going to win any efficiency contests with about 86dB sensitivity with a 2.1V input. However it once again displays exceptional linearity and power handling. The long term output compression testing shows well controlled behavior and good tracking up until the 110dB nominal sweep. There is some minimal compression during the 115dB sweep of less than 2dB. During the 118dB sweep the active driver was over driven and emitted obvious distress noise which shows up in the response near 38Hz, so testing was stopped there. .
Still the system compression was only about 3dB over most of the range which is impressive considering the amount of power needed and the impressive amount of output developed from such a compact system. This is probably due to the massive LMT voice coil attached to the aluminum cone and stainless steel former and the extensive amount of venting built into the driver motor. .
The dual 15” VMP passives with their much larger SD and even longer excursion capabilities were never near their limits when driven by a single 12” driver. Additionally the distortion results show that the output is very clean. Above 25Hz the THD is below 5% during the 110dB sweep. Even during the 118dB sweep the THD stays below 9% above 25Hz. The distortion is dominated by the 2nd harmonic. .
Both the maximum long term output achieved and the CEA-2010 burst testing prove that this system has impressive output capabilities for a compact system. There is some useful output at 20Hz and a generous amount of headroom from 25Hz on up. At 25, 31.5 and 40Hz more output could probably have been coaxed out seeing as the failure mode was relatively high in frequency in the 5th, 9th and 10th harmonic bands which are allowed very little contribution via CEA-2010 guidelines. .