Feedback Destroyer???

[Bing Fung]

I'm considering the purchase of the FD for my DIY sub. Should I just get it or should I just build the sub and let it rock with out this item?

Am I just geeting sucked into purchasing something else I really don't need in a practical sense?




Bing

[Patrick Sun]

From what I've been able to ascertain, if you have bad humps in your room with your sub, the BFD (haha) will allow you to tame the humps (can't do that much for nulls) and then you'd be a prime candidate for a BFD. I think I am (because I have an awful hump from 56-63Hz), but the downside is that the BFD will shut down anything below 20Hz, so that's a bit of a bummer.




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[Andrew Pratt]

Bing before you go spending money again wait till you've built the beast and ran some test tones though it. You may find you don't need it or that a slight shift of the couch or sub will fix the hump etc.

[Bing Fung]

My main purpose for wanting it is to control the cross over point. Currently the Denon will passes 80Hz and down to the LFE. My B&W mains run to about 43 Hz. I would like to dial out any extra overlapping frequencys by having the crossover point set to around 50Hz.

That and the hump adjusting feature...




Bing

[Andrew Pratt]

well it would do that for you. Now that I've got mains that go down reasonable deep as well I'm looking at my options. I think for now though I'm going to just turn the sub down for the direct mode (mains are automatically set to large in Direct mode).

[Bing Fung]

So Andrew, are you saying that for 5.1 having the Xover at 80Hz is okay, it's just for stereo stuff that you want control of?... I not sure I understand. Currently I have my center and Mains set to large.

Do you know of another solution that is inexpensive? If it cost the same as the BFD (hahaha) may as well go with the BFD. I have found one in town, brand new $245 + taxes.




Bing

[Bing Fung]

Pat, does the BFD cutoff the signal sharply at 20Hz or is there still some type of roll off?

It just seems strange that it's a digital process, that theoretically can be adjusted to 0 Hz, why would they cut it off at 20 Hz?

Could it be that 20 Hz is the the minimum adjustable range and it still will pass signals lower than 20?

Is this even a consideration if my sub is tuned to 21 Hz witha F3 of 19.5 Hz?




Bing

[Patrick Sun]

Bing, email Mike Knapp, he's got a BFD (among other personal quirks) and he'll be able to fill you in on it.




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[Patrick Sun]

Bing, glad Mike was able to clear up confusion (i.e. BFD will pass anything under 20Hz with no processing).




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[Bing Fung]

Yes, it is good. I was doing some further reading on the instruction manual, I think it would also fix nulls in the room as well.

I was playing around with the Windows interface of the machine, way cool. Once you have shaped the curve graphically to your desired results, the configuration can then be ported to the BFD via a Midi port. Hey... I happen to have one of those on my sound blaster live!

It has a +/- 16dB for what ever range you have set your filter to. It also seems as if you can cascade or stack filters in the same frequency that will further compound the desired effects.




Bing

[Andrew Pratt]

Bing how exactly does it fill nulls? That seems impossible since nulls are waves canceling each other out...it doesnt' matter how large those waves get (by increasing the volume or eq etc) they will still cancel each other out. The only way I know to remove nulls is to move the sub and therefore the waves that are giving you a problem...or just move the couch to and area w/o nulls

[Bing Fung]

You maybe right on this Andrew, I was assuming because this was done in the digtial domain, that any dip or vally in response can be boosted by + 16dB to fill the hole. Just by processing the signal at that area, it would be seem capable of curing that null because it has now changed that particular freq signal to advoid cancelation.

I was thinking of a Null as dip rather than a total absence of signal.

Still looking at the the dsp1100 editor software, it seems you can change the area that is giving you the null enough that there will be no cancelation, because the signal is now different for that area.




Bing

[Patrick Sun]

Bing, 'Drew's right on this one, the nulls are a bitch to fix, and the fix is room geometry and/or sub placement. But for taming the humps, the BFD will be more suited for that task. Just don't sit in the nulls!




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[Bing Fung]

Yes, I agree...




Bing