# Can I use a BFD?



## Regg (Jun 24, 2007)

I'm sorry about the newb question, but I just got a sub recently and have begun to try to integrate it with full range monitors for two-channel audio...so far I'm not completely satisfied. 

Can anyone take a look at my profile and see if I would even be able to use a BFD? Any suggestions would be appreciated.:help:


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## Otto (May 18, 2006)

Hi Greg, and welcome to the Shack.

I had a look at your profile, and I don't necessarily see anything that would preclude you from using a BFD. In general, if you have a line-level signal coming from a preamp to your sub, you can insert the BFD in that signal path.

I understand about not being satisified with mains/sub integration for 2-channel listening. It's a never ending battle, but a lot of fun at the same time. What are your current complaints?

If you have an SPL meter and a PC, I might suggest that your first step be a simple REW measurement. You can do this with your mains off, to see the response of your sub by itself, as well as with the mains on, to determine their integration with the sub. Once you have a look at these frequency responses, you'll have an idea if a BFD will do any good for you. Most of us can make use of a BFD. 

So check that out and let us know. We'll be happy to help.

Have a good day.


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## Otto (May 18, 2006)

Having another look at your profile, I got hooked up a bit on this:

"The amp for the high-level connection to the sub is a B&K Sonata Series EX-442 Dual Mono amp."

I believe the LFM-1 has an internal amp, so are you running a speaker-level signal to this sub, or a line-level signal?

I think that either way, there's a line-level signal in there somewhere, and you should be able to manipulate it with a BFD...


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## Regg (Jun 24, 2007)

Hello Otto,

Thanks for your quick response and the welcome.:bigsmile:

I was running to the low-level sub input from the alternate pre-outs at first, but I could never seem to get that right. I could only connect to the left _or_ right channel. If I used a Y splittler, I think the L & R channels would become blended so I would lose the stereo image altogether. And using a single channel for the sub made me get a sense that I was not recovering all the information from the bottom end.

I already had the B&K amp, so I just used it for the speaker level connection to the sub. Do you recommend that I should use a mixer of some sort instead?

I'm definitely interested in checking out the REW software, as I believe this room probably has some bass resonance that needs to be ironed out anyway. My digital front end utilizes a PC with an RME DIGI96/8 PAD...any issues with REW and RME soundcards?

The SPL meter I have currently is an old 33-2050. Will this do the job or should I upgrade to something else?

Again, thanks for all your help, and sorry about all the questions.


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## brucek (Apr 11, 2006)

> If I used a Y splitter, I think the L & R channels would become blended so I would lose the stereo image altogether.


You're not actually allowed to do that, since you would be shorting the output stages together.

You need to use a mixer (also called a combiner) to mix the two signals together into a mono signal without creating any crosstalk between your mains channels. Inexpensive resistive mixers tend to cause crosstalk problems, so active or transformer type are the best.

I looked around and came up with one that would probably be fine. 

It's an unbalanced stereo to mono transformer from EDCOR . You could attach it after the BFD, at the LFE input to the subwoofer. Inexpensive, seems to have decent low frequency response for the price. The transformer used appears to be this one. It's only off a half dB at 30Hz, so easily compensated with the BFD.

Others may have different ones they prefer.. 

brucek


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