Wednesday, November 30, 2011

Dialed back 26 Hz boost to 0.1db

On Wednesday morning, I was finding it somewhat difficult to crank the volume level on Bass Ecstacy by Bass Erotica (a very low-bass-heavy album).  So then it occurred to me that after I extended the deep bass to 16 Hz this weekend by adding one subwoofer port plug on the left side and two on the right and lowering the low frequency cutoff accordingly, I may well have been adding back in much of the circa 26Hz bass the boost had been intended to restore.

So I dialed the 26 Hz EQ (in the DCX 2496 crossover) back from 3.5dB, where I had set it most recently, to 0.1dB, effectively disabling it without removing it.

Then the extreme bass became more tolerable, and I was able to raise the level by a comfortable 10dB, making the lyrics and effects much more open sounding.  I was even dancing.  But I think the bass still needs more refinement.  I believe I can still listen to this very difficult album louder in the master bedroom, where I have custom equalized the bass with parametric and graphic EQ using a Behringer DEQ 2496.

Might be time to bring back the keyboard, which was put away on Saturday Night to prepare for a party on Sunday.  I was even thinking about using a real oscillator, but might be nicer to program a frequency offset slider into my keyboard sine program.


Back on Friday night, when I found another bass port plug for my left subwoofer, I measured the effects of decreasing the low frequency cutoff frequency on 16Hz playback, and the effect of adding the one plug.  Adding the plug did increase output by a few dB, as did changing the cutoff to the one-plug recommended setting (which is 18 Hz).  Adding the plug had a bigger effect than turning the cutoff to the two-plug recommended setting (which is 16Hz).  I had the numbers written down, but they did not get copied to this blog.  Now I've found a second plug for the left subwoofer, and thinking about doing a whole matrix of measurements.  But I need to replace the C cells in my Genrad 1933 SPL meter, which conveninently has a "flat" setting and 1 inch microphone.  I was measuring levels between 89 and 100dB SPL at 16-20Hz.  I believe I boosted response at 16Hz from 89 to 92dB.  The bass plug not only increased 16Hz response, it flattened the hills and valleys between 16 and 25 Hz.

SVS shows the flattest response (ruler flat) to 20Hz with no port plugs.  They show 2.5dB loss at 20Hz with one plug, but improved extension to 15 Hz before cutoff.  They show 6dB loss at 20 Hz with two plugs, with little visible knee in the curve, but lots of drooping, so response isn't actually extended until you get down to 13Hz or so.  Three plugs produces 8dB loss at 20Hz, with no indication from the curve that this offers additional frequency response extension at any frequency.  According to their graph, I think I would prefer the 1 plug modification, very little difference at 20Hz but nearly flat extension to 15Hz.  The two plug seems to sacrifice too much response at 20Hz, but seemed better when I measured on the right speaker.

Here is the 

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