Originally Posted by buddhamus
Hey Alan, I have 4 x Submersives 1000w subs so they are all identical subs
... Funnily enough it's my nearfield subs that are running out of gas with the Farfields not even clipping while running 5db hot. Could be a placement problem... Hence why I wanna try and work this problem out. Thanks again!
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FWIW, I ran some tests that might be of interest to you. First test was to check the output levels of the subs, measured at the MLP, using a REW 60Hz test tone played at -3dBFS, with AVR MV=0 and sub trim=0. The results are shown in the first thumbnail below. Note that all four subs are identical, and are meticulously gain-matched. Two subs are in the front of the room, and the other two are immediately behind the MLP. The first thing that you notice is the varying output levels, which shows the impact of the room and the sub placement. The right front sub is close to a couch, which is likely to be absorbing some of the low frequencies. Second thing to note is that the combined level of the subs at the MLP is 107dB, which is pretty loud (but I rarely play my system at reference).
Test 2 shows the results of REW measurements for a single sub with the mic placed near field. As Matt predicted, the mic clips at levels starting at -15dBFS, so two of the three measurements may be flawed. The next two clips show the output sweeps (notice measurement 3 shows the sweep distorting because of the clipping), and the distortion for each measurement level. Even though the THD at 20Hz is rather high at 23%, THD falls rapidly to 3.4% at 30Hz.
Test 3 shows a measurement at the MLP for all four subs, first at MV= -10 (a typical listening level for me), and then at MV=0 (reference). The 18.7% THD
with MV=0 shows the extreme case, with THD rapidly falling off to 1.4% at 30Hz.
In all of these tests, the MiniDSP Input level and all four Output levels were set to zero. Watching the output meters on the 2x4, the max output reached -18 on the scale, which is right on the border between orange and red.
In summary, I did not find anything in these tests that would be cause for concern, especially since my listening levels are nowhere near as aggressive as the levels used in the test, and 20Hz content is equally rare. I welcome observations and comments from others regarding the results as well as the test methodology. And hopefully the tests will provide some guidance to
WRT evaluating his own sub setup.