Copyright 2001- BFD Guide - All rights reserved!


Welcome to the BFD Guide. If you are new to using the Behringer Feedback Destroyer DSP-1124P, (or the older model DSP-1100P), or the FBQ-2496 as a Parametric Equalizer in your Home Theater System to tame your subwoofer response, then perhaps this guide will be of some help to you. For good reasons enthusiast have found the BFD somewhat intimidating, but after you start working with it for a while it becomes easier and easier to understand.

The BFD Guide is designed to help you connect the BFD to your system and set it up manually to be used as a parametric equalizer. This page will deal mainly with connecting the BFD unit, setting the input level and preparing to measure the frequency response of your subwoofer or subwoofers.

The first page of the guide has been shortened tremendously from its previous days due to the fact that very few people actually work with the BFD manually anymore. Now that we have the BFD Forum here at Home Theater Shack home theater forums for daily discussion and the and the REW Forum for discussion of the Room EQ Wizard, an excellent room eq software... it has become easier to automate the process of equalizing your subwoofer. If you are one of those who have been working with the BFD in slow motion (manual mode), then it is time to speed up and check out the Room EQ Wizard software. If this is your first experience with the BFD, then it is advisable to not even bother visiting the manual measurement page... go straight to the Room EQ Wizard after you have your BFD connected and the input level set.

I also want to give special thanks to brucek, Rick Radford, Wayne Pflughaupt and several others in the various home theater forums, for their knowledge and contributions to this guide.

To start with, it would be a good idea to read the BFD Manual before you go any further here. The manual is in PDF format. (CLICK HERE to download a free copy of Adobe Acrobat that will allow you to read the manual.)

The information in this guide is not intended as a replacement to the BFD Manual but rather a supplement to the parametric equalizer sections. If nothing else at least read pages 10-12 (section 4. CONTROL ELEMENTS), but please, go ahead and read it all.

DISCLAIMER... Home Theater Shack, LLC., its Members/Partners, nor myself are not in any way form or fashion affiliated with BEHRINGER or BEHRINGER Spezielle Studiotechnik GmbH. I DO NOT guarantee the performance of their products nor do I guarantee the performance of any software, development tools, or any other files you might download from this site or any site related to this site.


The first step of course is to get your BFD connected to your system. Try to use a power source such as your processor or receiver to power on the BFD prior to your sub amp being powered on. This should eliminate any thump or loud pop at turn on. The BFD draws very little current so you can leave it on all the time if you wish to do so. My BFD stays on 24/7/365.

If you have 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. One thing to check is your cable TV feed, or an improperly grounded satellite feed can also cause hum. Simply disconnect the feed and see if the hum disappears. 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: "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 metal 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 and Buzz Whitepaper

Possible solution with Ebtech's Hum X Filter

Possible solution with Ebtech's Hum Eliminator

Of course there is always the BFD Forum for discussion of hum problems. There have been a few threads concerning the issue. However, not everyone has hum.

If you have only one sub in your system you can use either Output/Input connection on the rear of the BFD.

Output/Input 1 = Engine L or the Left Channel, effects all "L" labeled LED's on the front of the unit.
Output/Input 2 = Engine R or the Right Channel, effects all "R" labeled LED's on the front of the unit.

You will need either inch or XLR type connectors on your cables. If you already have RCA type connectors on your sub cable(s), you can pick up a couple of RCA to inch adapters at Radio Shack for temporary use until you can order some RCA to inch cables. The adapters are cheaply made and they create another connection point for your signal to travel through, so I recommend purchasing some better complete cables.

You should be able to understand the connection process from the BFD Manual. On the rear of the BFD, above each Input/Output you will see an "Operating Level" button. Make sure this button is pushed in (the "IN" position) which is for the -10dBV (HOME) setting. Do not use the +4dBu (STUDIO) setting (leave this button in the out position). Once you have your BFD connected then you are ready to set the input level.


After powering on the unit you will need to set the input level. The BFD is more commonly used in recording studio's and concerts, etc. It was not really designed for use in home theater systems nor for equalizing home audio subwoofers. When setting up a studio or concert, the level is usually the same. Most concerts I've ever been to keep the volume level the same (very loud!) during the entire event... they set it and forget it. At home we vary our volume level because we have several different input sources and different listening levels at different times. Our sources (DVD Players, CD Players, Tuners, etc.) usually have fixed outputs and they are in the audio chain prior to the pre/pro or receiver. The BFD is in the chain after the pre/pro or receiver. Plus we are not setting this on auto pilot and letting it search out frequencies to destroy feedback as the name of the unit would imply. It can cut a feedback frequency by up to 48db. We are using it as a parametric equalizer to tame subwoofer frequency response peaks... we surely don't want to eliminate them completely. Thus, we have to set the input level on the BFD so that during our maximum listening volume, it doesn't clip.

On the top right front of the unit you will see the "IN/OUT" button. Press and hold this button for a moment until the button light blinks. You are now in the "BYPASS" mode with no filtering active. You can only monitor the setting of the input level in the "BYPASS" mode. The input level is monitored by the LED's in the far left section of the display window. If the unit is not in the "BYPASS" mode then the LED's will monitor the "output" level. We want to monitor the "input" level. Play a CD or DVD with some good deep bass (U-571 with the depth charge scenes is a good one to use if you have it). Play the source at the maximum level you would listen to it. You should notice the green LED's moving up and down. You may only see part of or all of the green LED's lit or you may see all of them lit up along with the yellow and the red LED at the top lit (they will vary with input). The red LED at the top is labeled "CLIP". Your goal is to see the yellow LED close to the top blink on loud bass sections of the music or movies. It is okay if the red LED blinks occasionally as well... as long as it's not constantly lit. Remember... there's a reason it's labeled "CLIP". To adjust how far up the LED's blink you will adjust your sub output level on your pre/pro or receiver's speaker level menu or sub level control. (Your volume control on your sub has nothing to do with the input level.) On one of my pre/pros I had my sub level set to zero initially. After I connected my BFD I raised the sub output level to +3. This allowed the yellow LED and occasionally the red LED to blink during the loudest scenes of movies. Remember, the input level of the BFD should be set in the "BYPASS" mode (the "IN/OUT" button will be blinking). Once you have set the output level on your pre/pro or receiver you can then adjust the output level (volume control) on your sub to equal your mains. I used the AVIA DVD to match the levels of my speakers. AVIA instructions are easy to follow and the DVD will give you a host of other tools to use for video and audio calibrations. There are other DVDs and CDs available for this... such as DVE (DIGITAL VIDEO ESSENTIALS). You will also need to repeat the reset of the sub vs. main levels once you later complete the filter setups. You may find that once you have smoothed out peaks that your sub level doesn't seem loud enough. I had to turn my sub volume up for my taste. Remember not to adjust the volume of your sub via your pre/pro or receiver after you have set the input level... use you sub volume or the volume on the amp connected to your sub, which should be inline after the BFD.

NOTE: Something that you should remember to do when you are setting up your BFD is add a foot to the value you enter for sub distance in your pre/pro or receiver set up. The 1 msec DSP processing delay in the BFD would account for approximately a foot in distance.


If you have a home audio subwoofer and want to equalize it, then you may already understand how to complete your sub measurements. This is probably why you purchased the BFD. You have completed measurements to see if you need the BFD, right? It's okay if you haven't... unless you have the perfect setting (anechoic chamber or room) you will probably need it.

The first thing you will need to measure your subwoofers' frequency response is an SPL meter and a microphone. We have recommended the Radio Shack SPL meter in the past as a combo mic and SPL meter, but we have found too many varying accuracy issues with it to recommend it any longer. The mic in the RS meter is not consistently accurate. If you use it "as is" then your response will not be correct. You may have heard of or read about the "Radio Shack Correction Values", "Compensation Values" or "Compensation Charts", that have been floating around the Internet for several years. These are values that you use to compensate for the linear inaccuracies of the RS meter's response. MOST OF THESE VALUES ARE NOT ACCURATE! At least they are not accurate for any of the RS meters we have tested, and we have tested quite a few. Maybe for the older model 42-3019 analog meter these values would be okay, but this model is a number of years old and we have not seen too many of these in a long time. We have tested and created new correction values for the various RS SPL Meters that we have been able to get our hands on. We did not just test one, we tested several of the same models. These new correction values are available on the Downloads page at Home Theater Shack as a calibration file (*.cal file). These files can be opened with Notepad. You will have to register and login to obtain these files. However, we will still caution you on using the RS meters, from meter to meter we have discovered some significant variances... you are still risking the accuracy of your measurement.

Your best option is to look for a Galaxy CM-140 or its Voltcraft clone. We have tested quite a few of these and found them to be very consistent, however they still need correction values. We have created these correction values as a calibration file and they are also available via the Downloads page at the Shack. These are typically going to cost from $99 to $129. There is more info about these in the forums.

Note: C-Weighting does not compensate for response inaccuracies on these meters... they MUST have correction values added to be accurate.

Other options are measurement microphones with microphone preamps, however, unless you spend $1,000 or more, most likely you will not get a perfectly flat mic... it will still need some correction. How much correction depends on how low of a response you plan on measuring.

A popular choice has been the Behringer ECM8000 measurement microphone. I have sent my ECM8000 mic to West Caldwell Calibration Laboratories for professional calibration. This will generally cost about $100-150. You may use my calibration file available via the Shack Downloads page, but if you want to make absolutely sure your mic is accurate, send it off for professional calibration.

If you choose to use the ECM8000, you will also need a mic preamp with phantom power and a mic cable. The Behringer Xenyx 802 Mixer (Mic amp w/ phantom power) and a 15' Microphone Cable is needed. You can search the Shack Electronics Store or Parts Express for these products at discounted prices.

Once you get your mic, whichever route you decide to take, you will pretty much be set to take some measurements. When you get ready to measure you can use a tripod to mount the SPL meter on and sit it in your listening position. Face the mic straight up towards the ceiling. If you are using the ECM8000, simply sit in the position you want to measure and place the mic at your ear or nose. I have ran tests and there was only about 0.5db variance between my left ear, nose and right ear. You can test it yourself to see if there is any significant variance. When I set my SPL levels with the SPL meter I hold it out in front of my nose far enough to view the readings and then generally I place the mic right at the tip of my nose. There are different opinions on the methods used, you should be able to figure it out though.

Now that you understand how the BFD parametric equalizer is connected and setup, and how to prepare for measuring, the next step is to start measuring. This is where you will have to decide whether you are going to use a room eq software such as Room EQ Wizard or measure the old fashion way. My suggestion is head on over to the Room EQ Wizard site and look at the features. If you register and login at the Shack, you can download the latest version for free. There is plenty of help in the REW Forum, but the first thing to do is download the software and read the HELP files. John Mulcahy has done a fine job of developing this software and the HELP files. Please read carefully... the software is not hard to understand if you will take the HELP files one section and one paragraph at a time. The HELP files will walk you through connecting everything up to your computer and it will walk you through the proper settings. The HELP files do everything but hold your hand. I can assure you, learning this software is miles of mountains better than the manual measurement method.

A great primer on connecting REW has been written by Shack Administrator brucek: REW Cabling and Connection Basics

If you just insist on punishing yourself, or maybe you do not have a computer you can setup where your subwoofer is located, you can view the Manual Measurement Method instructions. These instructions take you through the basics of measuring with 1/6 octave test tones (using sinewaves) and inputting them into a Microsoft Excel Workbook, which will graph the response for you.

Links related to the BFD that may be of interest to you:
(You may have to register and/or login to view some pages.)

Room EQ Wizard (REW) Information Index - |Links|Guides|Articles|Stickies

Test Tones

BFD Manual (PDF)

Room EQ Wizard Software Download

Behringer Website

Next:   Manual Measurement Method

All information is made available compliments of Home Theater Shack

Copyright 2001- BFD Guide - All rights reserved!


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