# BFD Connection Question



## drrick (Nov 16, 2006)

Ok, I searched around to see if this had been answered before, but I didn't see anything. My BFD is on the way, and I'm trying to visualize how I'm going to use it. My sub is currently not hooked up to the sub out of my receiver--I have my main speakers set to large and use the L and R channels to run into the speaker level inputs of my subwoofer. I then use the internal crossover of my sub to determine the crossover point (around 90 Hz). Now, I'm not completely opposed to hooking my sub back up to the sub out, but I like the way it is now. 

Here's my question. Can I use these speaker level inputs to input into the BFD, then into the sub, and even if I can, is it a good idea? My reasoning for doing this would be that if I used this method, I could then use the BFD to attempt to Eq my front speakers in addition to my sub. Is that practical, or is that going to be problematic when I try to put that many filters in (I'll be using REW, by the way)? Thanks for your help guys! I'm new to the shack, but I've been reading a bit around here. Let me know if I'm making this far more complicated than I need to. Thanks!


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## Sonnie (Apr 11, 2006)

Hi drrick and welcome to the Shack!

You will want to go back to using your receiver's sub out with the BFD. The BFD will not accommodate speaker level inputs/outputs. You will also need the sub out level adjustment to set the input of the BFD.

You could still leave your mains set to large if you wanted, but initially I would recommend setting them to small and crossing them over at about 80Hz. Then look at your sub only response via REW, your low end response with sub + mains, and then you might consider looking at using your mains set to large. It is really going to all boil down to if you need the mains set to large and/or if they might interfere with your sub response... their low end response could defeat what the BFD does for your sub.

Add to that... I believe the consensus is that the BFD should not be used for full range. It's not quite up to par and could possibly hurt more than help.


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## drrick (Nov 16, 2006)

Sonnie,

Thanks for the very helpful reply. I thought that would probably be the case, but I wanted to check and make sure before I just started trying to connect different things :bigsmile: I'll go ahead and use my receiver's bass management to cross over my speakers at 80 or 100 Hz (I'll have to see which works better). My mains really aren't full range (45 Hz +/-3db), they were just set that way since the sub was connected to them--so that I could use the sub's internal crossover. So, I'll set my mains back to small, although I may try them set large too, just to see. Thanks for your help and for sharing your knowledge with newbies like me!


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## Sonnie (Apr 11, 2006)

No problem at all... we are here to help... :T

It would be good for you to go ahead and download REW and take some measurements, if you haven't done so already.


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## Gson76 (Dec 18, 2006)

Sonnie said:


> You will want to go back to using your receiver's sub out with the BFD. The BFD will not accommodate speaker level inputs/outputs. You will also need the sub out level adjustment to set the input of the BFD.


Sorry to break in, but I will hook up the BDF on the pre-out (main L+R) NOT the sub-out because the receiver does´nt activate the sub-out in Direct Source which sounds so much better.

So, this make me not be able to adjust the input signal to the BDF? How will it affect by doing like this?

One more thing, I will also in the near future buy a passive pre-amp between the receiver and the BDF to be able to adjust the volyme of the sub. The bass information are as you know very "up and down" in velocity depending on the source... Do you think it can work? Receiver-->Preamp-->BDF-->Active Sub.

Thanks and Mery Christmas to you all


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## brucek (Apr 11, 2006)

> I will hook up the BDF on the pre-out (main L+R) NOT the sub-out because the receiver does´nt activate the sub-out in Direct Source which sounds so much better.


You will have to use a Y-splitter so as not to pass your mains signal through the BFD (which would have a negative effect)
Then you will have to create a crossover for the sub with the BFD filters before doing any equalizing.



> So, this make me not be able to adjust the input signal to the BDF? How will it affect by doing like this?


The signal level going to the BFD will be the same as going to your mains amplifier. It would be nice to have a bit of trim control there, but nothing you can do about that.



> The bass information are as you know very "up and down" in velocity depending on the source... Do you think it can work? Receiver-->Preamp-->BDF-->Active Sub


So your idea is to use a passive pre-amp (basically an attenuator) to lower the signal level feeding the BFD if it's too high? Why not just turn the sub up and down? Is it a matter of convenience?

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

> The bass information are as you know very "up and down" in velocity depending on the source...
> Do you think it can work? Receiver-->Preamp-->BDF-->Active Sub.


 I have something like that, but my dedicated sub pre amp is remote controlled so I can adjust sub level “on the fly” if need be, without having to get up from my chair. Unless the pre-amp you want to use is remote controlled, I can’t see any reason to use it at all. You can get up and adjust the sub’s level just as easily as the pre-amp’s. Unless maybe the pre amp will be more readily accessible than the sub – maybe then it would be worthwhile.

Regards,
Wayne


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## Gson76 (Dec 18, 2006)

Hi Brucek and Wayne,
The pre-out L+R is still active when I run the main speakers with the internal power of my receiver so I don´t need to split the signal. The active sub has it´s own adjustable low cut filters, selectable 12 or 24dB/oct. The BDF will only be hooked up with the sub signal.

The reason to add a pre-amp (remote controlled) is to make adjustments from the sweet spot, nothing else. The ordinary sub-out can be controlled with the receivers remote, but unfortuanately is this output not activated in Source Direct mode...:crying: 

What will happen if the signal is kind of low into the BDF, let´s say I only reach half the blinking leds when I listen with normal to high volumes? I mean, if you listen with only 10 % of the potential volume, will the BDF make the sub sound less good? I don´t understand :dontknow: 

Anyway, a BDF is ordered! :jump: I will get a pre-amp if I feel it´s necessary after the installation of the BDF/REW.

Thank you so far  
Martin


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## brucek (Apr 11, 2006)

> if you listen with only 10 % of the potential volume, will the BDF make the sub sound less good? I don´t understand


With any system that uses an analog to digital conversion, the goal is always to optimize the input level to take advantage of every bit available so as to maximize signal to noise ratio and dynamic range. This means the softest signal is above the noise and the loudest is using every bit before clipping. In the context that we use the BFD where the input is controlled with a volume control rather than a fixed line level, that goal is nearly impossible.

I highly doubt you would be able to hear any problems when used with a sub as a result of a lower input level to the BFD. You work with what you have. If you find that the level is insufficient, then you can add an active line amp. I doubt you'll need it.

brucek


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## Gson76 (Dec 18, 2006)

Ok, thanks Brucek.

It starts to clear up in my nearly melted brain


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