BFD Guide Quick Links | FAQ | Tips - Home Theater Forum and Systems -

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post #1 of 5 Old 04-18-06, 02:36 AM Thread Starter
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BFD Guide Quick Links | FAQ | Tips

This thread is the official BFD Guide Quick Links | FAQ | Tips thread with tips provided by users.

This thread will be locked, but if you have a tip that you would like to share, post it here and I will be notified and consider it for inclusion to this thread. We reserve the right to edit any tip that is provided

Quick Links to the BFD Guide:
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post #2 of 5 Old 04-18-06, 02:56 AM Thread Starter
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Re: BFD Guide Quick Links | FAQ

If this is the first time you've heard of the BFD and are wondering what it is, or why you would need one, and/or what it will do for you, then you are about to learn.

What is the BFD?

The BFD model that most people have been using is the Behringer Feedback Destroyer Pro DSP1124P and is currently priced at around 90-100 bucks at several online stores. There is an older DSP1100P model and a newer FBQ2496, but for the sake of this discussion we will stick with the 1124... it's really the best of the three anyway. This is also the model for which the BFD Guide is written.

What is the BFD used for?

Originally the BFD was designed for the performance/entertainment industry. Think about its name “feedback destroyer”. It is used in recording studios and concerts. The unit is wired into the system, set on auto-pilot, and then it searches out feedback and kills it. However, its functionality and design allows it to be used in the home theater as one of the most flexible parametric subwoofer equalizers available... and the least expensive by far. With the BFD you can pick up to 24 frequencies (1 combined channel X 24 or 2 separate channels X 12), adjust the bandwidth as narrow or wide as you wish (from 1/60 of an octave to 120/60 or 2 full octaves), and either boost them as much as 16db or cut them by as much as a whopping 48db. How many parametric eq's do know of that can do that for 100 bucks or less? Pretty impressive if you ask me.

Why do I need a BFD?

As stated above, the BFD can be used as a parametric subwoofer eq. Subs are professionally measured and tested in either a wide open space or an anechoic chamber/room and the mic is usually placed 1 meter out from the center of the sub speaker cone. How many of us set up our sub in the perfect room and have our listening position with our ears centered 1 meter in front of the sub? When you see the frequency response of a sub measured by the manufacturer you see this:

The manufacturer rates the frequency response as 22hz – 200hz (+/-3db). When we place that sub in our homes there will be two things for certain and one thing for sure… if we measure the frequency response at our listening position, it will not be the same as the manufacturers response. It will look something like this:

This is actually the pre-BFD response of my sub from my main listening position. Obviously yours may look different… the point is that it will not be nearly as flat as the manufacturers rated response. This is not the sub manufacturers fault... they did what they were suppose to do. Our room size, shape, construction, and things we place inside such as cabinets and chairs, as well as the location of our sub, will all have an effect on our sub response. This means what we are hearing from our sub is not what the manufacturer intends for us to hear and it will probably not sound as good as it should. What we can do with the BFD is at least get the response better for the main listening position, and many times it will make it better for those near that main listening position. What we would like to do is get our response to look something like this:

No… this is not a perfectly flat line, it is somewhat of what we call a house curve. This is the post BFD response of my sub from my main listening position. The house curve is what many enthusiasts like for movie watching, while critical music listeners might prefer a flatter response. The house curve generally rises about 10-12db from about 100hz to somewhere aroud 30-40hz and then flattens out. It all depends on what kind of house curve you like. There really isn't a chiseled in stone rule for the house curve. In my case it’s the best I could do since I had a nasty dip at 40hz. So… if we take those two graphs, the pre-BFD response and post-BFD response, we can get a really good picture of what the BFD can do:

How complicated is it to setup and use the BFD?

Well, when I first learned of the BFD I was challenged mentally trying to figure it out. To me it was intimidating and humbling. The manual is just not that specific with regards to using it as a subwoofer eq since that is not its original intended use. I searched the forums and found bits and pieces of info, but I could never find one place that had it all put together and easily understandable. Many of those bits and pieces I found were written by the technical savvy and most of what I was reading flew right over my head. Not to mention I couldn’t find everything I needed to know… I had lots of unanswered questions. Yeah it was frustrating. So I challenged myself again. I decided I’d put together a comprehensive guide dedicated to the setup and use of the BFD that would contain all these bits and pieces of information in an easy to understand language. With the help of mainly brucek, one of Shack Administrators, and a couple of other forum buddy’s (I could not have done this without everyone's help), I was able to put together the BFD Guide. brucek was a major contributor in much of what is written in the Guide and in helping me understand all the technical stuff, while the others had various inputs of importance to it's accomplishment as well.

To answer the question above, the BFD is not very complicated to setup and use with the Guide as a tool. For the newcomer to the technical world of subs and parametric equalizers it will most likely be very time consuming, but it's not that difficult once you dig in and get started.

You can learn much more about setting up the BFD and it’s various functions within the Guide itself. Get yourself a BFD and join in with the fun! Hey... if you run into problems you got the perfect place to ask questions.

Everyone needs a BFD!
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post #3 of 5 Old 04-18-06, 05:31 PM Thread Starter
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Re: BFD Guide Quick Links | FAQ

The BFD has created a hum in my system... what can I do?

If you a 50 or 60hz hum that is introduced into your system after connecting your BFD, there are a few links I will provide for help. Yes, you may have heard of people using cheater plugs (an adapter that converts a 3-prong plug to a 2-prong plug) to eliminate the hum. However I offer this WARNING and quote from brucek:
brucek wrote:
The cheater plug effectively eliminates the third prong on the AC plug. The 'third prong' is the electrical safety ground and is there to protect you and anyone who uses your equipment from electrocution. This safety ground is a cold conductor designed to provide a path to ground for safety protection against internal shorts inside your equipment when equipped with the three prong plug. The third prong connects back to your service panel (where it is bonded to the neutral wire), and from there is connected either or both to your house plumbing or external ground rod. On equipment with a third prong, the metal case and external metal parts are all connected to this safety ground when you plug the electrical cord into the wall. If a component fails inside a piece of equipment and the 120 volts shorts to the equipments case, then that case is now live and can electrocute you. If the safety ground was attached, then a breaker would trip to indicate you had a fault.
With that warning, cheat at your own risk, if you choose to cheat! There are better alternatives to using a cheater plug. Below are a few links to help you eliminate ground hum via ISO transformers. This is the correct way to eliminate hum and this is really good reading that I highly recommend, rather than place yourself and/or anyone else that might come in contact with your equipment, at risk of being killed by electrocution.

Jensen Transformers' FAQ on hum, buzz and transformers.

Hum & Buzz Whitepaper: A very technical whitepaper on hum and buzz in stereo systems.

Possible solution with DCI Specialty ALH1

Possible solution with Ebtech's Hum X Filter

Possible solution with Ebtech's Hum Eliminator

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post #4 of 5 Old 04-21-06, 12:09 PM Thread Starter
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Re: BFD Guide Quick Links | FAQ

What are Correction Values and how are they used?

For years most enthusiast have used the Radio Shack SPL Meter as one of the tools for measuring their sub response. The big drawback with using this RS Meter is the mic in the RS Meter is not accurate. Traditionally we have used what is known as the RS Correction Values to offset the inaccuracy of the RS Meter. By adding these values to the corresponding frequency, it causes the RS Meter to be more accurate. Below is the traditional RS Correction Values (although we now recommend not using them - keep reading):

Although these values have been generally accepted, they are not accurate. How do we know this? Well on more than one occasion there have been individuals, including myself, who have measured the RS Meter mic with these correction values against a professional calibrated mic with a flat response. For on my latest test of the newer analog and latest digital meters... see this thread. Bottom line... the gool ole traditional RS Correction Values are NOT accurate. If you use them then you will most likely be seeing an inaccurate response from your sub... especially in the extreme lower frequencies.

So... having explained this, we now have a new set of RS Correction Values and instead of them being 1/6 octave, they are 1/60 octave from 10hz to 200hz, which is the typical range measured for sub response. There are new *.cal files with these correction values for the older analog meter, the newer analog meter and the latest digital meter. You can download the new *.cal files by logging in and going to the Downloads Page. These are the *.cal files for use with Room EQ Wizard. If you need to know how to load them into REW, see the first post in this thread.
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post #5 of 5 Old 05-04-06, 12:57 PM Thread Starter
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Re: BFD Guide Quick Links | FAQ | Tips

Using the BFD Presets

contributed by Malice

My experience with the BFD and REW has shown that I prefer different house curves for different source material. For movies I like the curve to be flat, and for music I like to have the lower frequencies boosted a little. But how much boost?

This is where the BFD's multiple profiles or presets can be used to good effect to create multiple versions of your preferred house curve.

What I would say, however, is that without a MIDI connection to the BFD from the computer I would have found this a complete PITA! So my advice is to get a MIDI set up as soon as you can.

Then you can easily create multiple profiles like the ones below.

The red (top) is the unfiltered resposnse, and you can see the other presets I've dialled (well Midi'd) in. #1 is for movies and #2 for music. #3 and #4 are good, but #2 has the edge.

I would have had even less hair if I had not used a MIDI set up to get all those filters in place.

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