Axiom Home Page Forums General Discussion Technical Questions DSP vs EQ

Unless it's a Cylon.

Just a quick update... The BFD came in the mail yesterday. I was able to play around with it for an hour or so last night, and just by manually applying 3 filters I was able to drastically improve the REW response (I had to enter parameters manually because the MIDI cable has not yet arrived).

I applied 2 reductions at 28Hz and 72Hz, and one gain at 45Hz and the resultant REW curve appears to be within +/- 2db of my programmed house curve from 20-100Hz. This was a heck of a lot easier than I thought it would be (even entering the parameters manually), and was certainly easier than constantly moving the EP500s around the room (with much better results).

I'll post some details and REW screen shots this weekend after I have some time to fine tune things and really get them where I want them to be. But for 60 mins work and only 3 filters, I'm very happy at this point.

One thing I did notice however was that the BFD appeared to apply a 9db gain across the board from 20-100Hz, even with no filters programmed. I had to attentuate the SW output in the Denon to adjust for this. Is this normal? I am using the 1/4" jack input/output with 1/4" to female RCA adaptors, and using the -10db setting on the back of the unit. Is this happening because I am mixing balanced / unbalanced inputs?

Very interesting thread. It is inspiring me to maybe download the freebee version of TrueRTA just to get a rough baseline of what current, square, hard floored, relatively empty room looks like compared to the new HT room when it's done.

If it works OK with my setup mike from the Denon, I would imagine I will have to spring for one of the more powerful versions than the free one as 1 octave measurements are probably not going to give me much of a comparison.

Would that be safe to say? If so, what would be reasonable for basic room comparisons and maybe a little curious tweaking down the road?
1/3, 1/6,....1/24th ?

Some part of me is telling me this is a bad idea but that voice has never been one I listened to in the past. Why start now?

Okay, I was able to work with REW and the BFD last night. The results are pretty staggering. This is my 20-100 Hz response before (2 EP500's, 0 Degrees, Full, XO Bypass on Sub and 90 Hz in AVR). Note that the more straight line is my goal, a 75db hard knee house curve that adds 6db between 20-30Hz:



And here are the results after the adjustments.



I used 4 filters:
26.98Hz, -9.0db, 0.500 (9.5Hz BW)
37.67Hz, 2.5db, 0.333 (8.9Hz BW)
49.66Hz, -4.5db, 0.200 (7.0Hz BW)
69.35Hz, -7.0db, 0.250 (12.3Hz BW)

I tried lower XO settings in the AVR, but the responses were always better to start with at 90 Hz. Plus, I'm able to control more of the curve with the XO higher. Interesting note. Before the adjustments (the 1st curve), my AVR was set at -12db for the sub (with the subs at 6:30pm). After adjustments (2nd curve), the AVR is now set at -6db (subs again at 6:30pm).

This adjustment was very easy to do, and actually pretty fun. The improvement in the bass was very obvious. It sounds much cleaner and tighter now. Although the low frequencies were by and large reduced, the bass actually sounds lower now, and much more realistic.

Interesting. Especially that it did not sound like an expensive box. Thanks for sharing.

have you tried the 500's on flat versus full, will help reduce your hump in the 30hz area.

Sroo,

I haven't played around with equalizers so forgive me for asking basic questions. How did you choose the goal line? Why for example didn't you select a flat goal line? Have you tried a single sub as opposed to two?

REW accounts for the RS meters flaws, and creates a slope goal.

Looking good though I would suggest half trim rather than full, if only to avoid that boost of 37.67Hz, 2.5db, 0.333 (8.9Hz BW). Boosting filters may make that line look flatter but it comes at the cost of eating into amp headroom and introducing more ringing and phase errors. Hopefully at half trim you can remove that boost entirely and just rely on cuts to get a nice flat curve.

Thanks for the input guys. I did try half and flat, but even at half, I dropped way off in the 40Hz-60Hz range by like -7db. The room is eating up 40-60Hz, and amplifying >60Hz range.

I do want to try to remove the +2.5 Hz gain. I may wind up narrowing the BW of the 26.98Hz filter and maybe moving it down a Hz or two. The +2.5 gain is necessary now due to the -9db at 26.98.

I chose a +6db house filter to adjust for the human ear's reduced sensitivity in the 20-30Hz range. I tried a flat curve, an this sounded much better to me. There are advocates of house curves, and of the flat response. In the end, you wind up setting it the way it sounds better to you. Randy's right to. REW has adjustments that you load in to account for your measureing equipment. I loaded the Radio Shack sound meter adjustment, and also calibrated my sound card (though that was not as much of an adjustment as the meter).

But overall, this is a 2x improvement from pre-equalization.