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EQing the SI 18D2

Build log for this sub beginsĀ HERE.

With a 3.67 year old, the only time my house is reliably quite is at night. Last night was my third is the last week of evening spent making pink noise and sine wave sweeps. My wife is sweet to tolerate it.

The first few times I will write off as experience. I had some troubles with my UCA-202 producing phantom signals sub 20 hz, so I’m using my M-Audio firewire solo, a Dayton EMM-6 (calibrated by CSL), and a Radio Shack SPL meter. The purpose of the measurements are to help create EQ filters for use with a balanced Mini-DSP 2×4.

NOTES: Unless indicated on the image, the graphs have no smoothing. All measurements were taken with a 60 hz crossover between the sub and main speakers, controlled by the receiver.

These are close-mic measurements taken 1 foot in front of the sub.


This is before any EQ, taken from the main listening position. Graph shows subwoofer alone, mains alone, and both together.


Here are the filters I used.


This is before and after EQ (of the subwoofer alone). I didn’t use very much EQ. A minor Linkwitz Transform to extend the -3dB point from 38 hz to 33 hz, and some filters to lessen the hump from 30 to 60 hz.
Because I have so much power on tap, I did not want to apply much boost to the low end. I plan on building a second one of these, and at that point I might try to find the very limit. For the time being, I am happy to preserve the natural roll-off of the sealed box. At least until Audyssey gets ahold of it (See below).


After the EQ I raised my sub trim slightly. The result is the pink line above. Not bad, but I have a hump outside the passband of the sub that I can’t touch with the Mini DSP. The blue line is after running Audyssey. It tames the 100-250hz hump.


So, nice and flat, right? I have some concerns about the boost in the sub 25hz area. There is a 10 db rise from 25 to 5hz. I don’t know if a little boost can create even more room gain – so I’m unequipped to reverse engineer this, but nonetheless, I am inclined to undo it for now.


This is a zoom in of the sub-40 hz region. Blue line on top is AFTER Audyssey. Pink Line is BEFORE Audyssey. And the green line is what I have AFTER disabling my little LT in the MiniDSP. I will probably be back to the drawing board with this. Though I may just leave it for now and reapproach after adding the second sub. It’s nice and flat, and as long as I don’t crank it up for the heaviest move scenes, I’ll be okay.


Here is the current home for the sub. I moved things around a bit. Moving the sub to the inside of the speaker gave help with a null I was having before. I’ve got room for another one on the opposite side when I have it built.