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Maxiumum Octave Range for BFD or FBQ

1759 Views 6 Replies 3 Participants Last post by  mpotoka
I am modeling a small sealed sub that would fit inside my Ikea Expedit bookcase. The hole is 13.25"x13.25" I already have 1 Dayton DVC 10" driver so I figured I'd pick another one up. Not the idea drivers but a neat little experiment non the less.

I was researching building an LT for this box but was able to basically reach the same values by adding a few PEQ cuts of the 12 dB range. However the Q I was using in WinISD was that of .08. Is this a range capable by either the BFD or the FBQ? I know I have seen 120/60 listed before--is that the max width? The conversions I have looked at here: http://www.sengpielaudio.com/calculator-bandwidth.htm suggest that a 120/60 is a Q of .667, and that my .08 Q would be 7 octaves (or 420/60). Are my numbers correct? Does that mean I would just need to use a series of 2 octave cuts? Although if my sub is being cut by the receiver at 80 hz then it "seems" I wouldn't need more than a couple octaves anyways...
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Can you explain what it is you're attempting to do?

I don't understand?


Yeah, its a bit peculiar what you're asking. 0.08 Q = 7 octaves; the FBQ has bandwidth settings up to 10 octaves, but from what I can see modeling its filters in REW, it's not accurate above about 2-octaves. The 10-octave setting is more accurately a 5-octave filter.

That said, there has to be a fundamental miscalculation or misunderstanding somewhere on your part. Keep in mind that the entire audio spectrum from 20Hz-20 kHz is 10 octaves. Also, a so-designated 7-octave filter will affect that much both above and below the center frequency. As such, a 7-octave filter will effectively wipe out the entire audio spectrum. Somehow I doubt this is what you really want/need to accomplish...

Well--I guess doing this during the day works out a little bit better. I want to take my two subs (modeled as 2 drivers in 1 box but actually will be 2 boxes 1.2cf each (I can't go any bigger)

Instead of making a Linkwitz Transform for the subs I want to use a BFD. I want to turn the yellow line into the green line. I cannot use an LT because I don't have a high excursion or high power handling driver. But this is a living room in an apartment with neighbors--and I feel this is not a bad result from 2 $40 drivers and a small sized amp.

So I am limited to 96.5 db (plus room gain). I would have an f3 of 22.8hz and an f10 of 14.5hz. All theoretical of course--but I have one of the drivers and an amp, so for the cost of one more driver, some MDF, and a BFD it sure seems like a fun experiemnt.

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Man those pictures turned out small. Anyways--I guess really the only bigger than 2 octave curve I am using anymore is for the house curve--but I didn't put the lowpass of my receiver in the model either so who knows what I'd actually need. Of course some REW will show me once they are built...

Would you like to have this moved to our DIY Subwoofers Forum? You can probably get better-informed answers about these things there.

No thanks--I don't really have any questions anymore--I should be able to use the 1124 just fine.
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