PARAMETRIC EQ





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GENERAL INFO

If you own or you are about to own a BFD (Behringer Feedback Destroyer), then you may find this page helpful.  Especially if you are like me and read about equalizing subwoofers somewhere and wasn’t sure about how to accomplish it.  There's a lot of information available but it's scattered about and sometimes hard to piece together for understanding. This page should help combine the necessary information into one reference. This page is certainly all about equalizing a subwoofer, using of course, the BFD.  Call it, if you please, “The BFD Instructions for Dummies” or “The Beginners Handbook to Using the BFD” or whatever you wish.  This is very long and detailed but it's written for someone who knows very little about equalizing subs. If you are better educated and/or experienced then you might find some sections boring and may wish to simply skip over it. Either way it will probably be a good idea to print out these instructions so you can refer to them while working with your BFD.


(NOTE:  If this is your first introduction to the BFD and you are not familiar with all the terms, then I should warn you... this will not be a quick tutorial.  This takes time to do it right and it also takes a lot of experimenting, especially for the newbie!  But it is fun; at least it is to me. Remember too that the more you work with the BFD the easier it gets.  So try to enjoy and once you have finished and have a smoother frequency response for your sub, you should feel a sense of accomplishment and your system should sound better.)


In these instructions I will do my best to explain how to setup and use the BFD as a parametric equalizer to smooth out your sub’s frequency response.  The BFD is a fairly complex piece of equipment to setup for some.  To some it will be simple, but I’ve seen many, many, posts in forums asking for help in setting up the BFD.  Thanks to *Ken Bruce (brucek), an e-mail buddy and forum buddy in the HTGUIDE FORUM and the HOME THEATER FORUM, I was able to setup my BFD and chart/graph it using a Microsoft Excel Workbook, initially created by Ken and modified with my values (measurements).  If you have Excel you can use the previous link to go ahead and download the workbook and later you can input your own values to see your results.  You don’t have to be able to understand Excel Workbooks to use this chart.  As I continue these setup instructions, the Excel Workbook will make more sense. Furthermore, I will give you step- by-step info on how to plug in your values. 


*Ken Bruce is also my most valuable source of information in reference to these setup instructions.  Ken has reviewed the BFD and completed technical measurements.  I encourage you to read his review.  It is a wealth of information with corrections to some misleading FAQ’s: Review of the BFD by Ken Bruce.   Very much worth a reading!


***** I want to give special thanks to Ken Bruce, Rick Radford, and several others in the various home theater forums, for their knowledge and contributions to this site.  I continue to update this page because of the continued contributions I am receiving. Please come back and visit with us every so often.


It would be a good idea to read the BFD MANUAL thoroughly as well.  The manual is in PDF format.  (CLICK HERE to download a free copy of Adobe Acrobat 5 that will allow you to read the manual.) This information on this page is not 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. You might wish to read all the manual and this page, experiment a little with the BFD, then read it again. It will be clearer the second time around and after you have experimented a little.


If you are a BFD user and see any mistakes or have any comments or suggestions to add to this page, please feel free at anytime to e-mail me.






CONNECTING THE BFD

The first step of course is to get your BFD connected. Try to use a power source (pre/pro or other) that will power on the BFD prior to your sub amp being powered on. This should eliminate the 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. If you notice any hum after powering up your BFD you can use a cheater plug to eliminate the ground terminal on the BFD power plug. If you have only one sub in your system you can use either the right or left Input/Output. You will need either ¼ 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 ¼ inch adapters at Radio Shack. You should be able to understand the connection process from the MANUAL (PDF Format). 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 (button depressed). Once you have your BFD connected then you are ready to set the input level.






SETTING THE INPUT LEVELS ON THE BFD

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 the home user.  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.  At home we vary our volume level because we have several different input sources and different listening levels at different times. Our sources are usually fixed outputs and 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), we are using it as a parametric equalizer to tame frequency peaks…we surely don’t want to eliminate them.  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 buttons’ small green 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. Play a CD or DVD with some good deep bass (U-571 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 the green LED’s and the yellow LED 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 movie.  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. (Your volume control on your sub has nothing to do with the input level.) I had my pre/pro 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.  It is okay if the red LED blinks occasionally, but you don’t want it to blink frequently or stay lit constantly.  You would then be driving the unit into clipping territory and could possibly invite abrupt unwanted noise and improper filtering.  Obviously that’s why they labeled the red LED as “CLIP”.  Remember, the input level of the BFD should be set in the “BYPASS” mode (the “IN/OUT” buttons’ green light 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.  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.  I now measure my sub output at about 10db louder than my mains.


NOTE:  When the BFD is in its normal filtering mode and you are watching a movie or listening to music, pay close attention to the LED’s for a few days.  A continuous red LED indicates the unit is near clipping. You will need to revisit your initial input level settings and decrease your pre/pro or receiver’s sub output level.  If you do, you will need to again level match your sub vs. mains, but when doing so, make sure you use your sub volume for matching and not your pre/pro or receiver’s sub level.

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 add a foot to the distance you tell your pre/pro or receiver that your sub is from your ears, then it will advance the sound the 1 msec required. This will compensate for the BFD's delay.






MEASURING SUB SPL LEVELS
&
USING MICROSOFT EXCEL WORKBOOK


If you have a sub 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 because unless you have the perfect setting (anechoic chamber or room) you will probably need it.  If you use Spectra Plus or ETF software then this may be boring to you.  Skip it if you wish.  But for those just beginning maybe this will be of some help.


Here I will cover the measuring procedure I use and how to insert the measurements into the Excel chart.  You do not have to use the excel chart to setup the BFD but it makes it a lot quicker and nowadays computers come preloaded with Excel.  If you download the Microsoft Excel Workbook, it’s as simple as clicking on a cell (a block with a number in it) and typing in your own number (your numbers will be from your measurements).  If you don’t have Excel then you can just write the measurements down on a piece of paper.  It’s a little more difficult but it can be done.  It will take a little longer so be prepared to spend some time on this.


I have a Radio Shack Analog SPL Meter that I use in measuring my sub output levels.  I measure from my listening position. I use a small camera tripod, which allows me to mount the meter directly to the tripod.  The tripod sits in my recliner.  I angle the meter mic up about 45 vertical degrees and towards the front of my room, and stick a couple of small couch pillows behind the tripod (this represents a much smaller version of my body).  The mic ends up being about where my ears are while sitting in my normal listening position.  There are different opinions on how to aim the mic.  Some point it straight up and others tilt it. Some point it towards the sub and others point it straight forward. You can choose whichever you like.  It’s good to try and mimic the conditions and surroundings.  Shut/open doors and blinds as you normally would.  I pull up a small chair behind my recliner and with remote, pen, and paper in hand, begin playing my test tones. If you have a laptop you can enter your values as you take your measurements.


The mic on the meter is not accurate so we have to use correction values to compensate. These are referred to as the “Radio Shack SPL Meter Correction Values”.  The Excel chart that Ken Bruce designed has the correction values built in. It’s much easier to have formulas to auto update the added values rather than to add values each time you measure.  If you use Spectra Plus or ETF, you can use the correction values provided with the software.


If you look at Figure 1 below you will see 1/6 octave frequencies in the far left column.  In the middle column you see “RAW SPL” values.  These were my very first measurements with the BFD connected and in the “BYPASS” mode with no active filters. The third column, “SPL (comp)” is the corrected values with the RS Correction Values added in.  I don’t have to enter values in the (comp) columns because the formula updates them automatically as I type in my "RAW SPL" values.


I tested 1/6 octave frequencies from 16hz up to 160hz. Low frequency tones and sweeps are available for download.

IF YOU NEED TEST TONES OR SWEEPS CLICK HERE

Once you are at this page you can right click on any of the files and a pop up box will appear.  Click on “Save Target As” and another pop up box will appear.  Navigate to the folder on your computer where you want the file saved.  Click “Save”.   These are all sine waves in MP3 file format but you can convert them back to wave files and record them to disk. Or your DVD player may already play MP3 files.  Each sine wave (frequency) is 10 seconds long and fades in/out the first and last 10% of the tone.  You actually get 8 full seconds of sine wave.  You may wish to only download the 1/6 octave frequencies listed in Figure 1.  These will be the only frequencies you will have correction values for (using the RS SPL Meter). The sweeps may be handy if you have other means of testing such as ETF or Spectra Plus.

IF YOU NEED TO CONVERT THE MP3 FILES TO WAVE YOU CAN USE CDEX AVAILABLE HERE


For the initial setup of the BFD I test only the sub.  I unplugged my 5-channel amp so that only the sub is playing. My front mains crossover at 80hz on my pre/pro, but I like to see how much output is above this crossover point.  Plus, LFE (Low Frequency Enhancement) signals are usually up to 120hz unless you have your LFE crossover point set lower.  My pre/pro has crossovers for Front/Center/Rear and LFE.  All are set to 80hz except for the LFE, which is at 120hz. I start by setting the meter to 70/slow/c-weighting. I then play the 16hz tone and set the volume so that the meter reads +3db to +5db (which results in approximately 84db to 87db spl with the correction values added).  I suppose you can start anywhere you like.  You may wish to start at the same level that you start with when you match your mains to your sub.  At any rate, get a starting point and go with it.

You will probably want to use your DVD player to take your measurements to set up the BFD preset for movies. Then if you want to set up another preset for music, use your CD player for the measurements. Different sources may have different bass sound qualities, so set up the BFD presets for the sources you listen to.


Play each frequency and write down each spl measurement on a piece of paper or a printed table from your computer.  You may have to change the meter setting from 70 to 60, 80, or 90 if you have some moderate valleys or peaks.  If the meter needle pegs out one direction or the other then obviously you’ll need to change the setting to get an accurate reading.


If you’ve downloaded the Microsoft Excel Workbook, you can click on the first row of “RAW SPL” (it will look just like Figure 1 within the Excel Workbook), which has a value (or measurement) of 73.  Type in your measurement for 16hz. You will see the “SPL (comp)” column change for the same row based on the corrected value.  Go down the “RAW SPL” column and input all of your measurements.  If you look at Figure 3 (the graph) you will see the dark blue line also changes as you type your numbers in the “RAW SPL” column. The graph will show the corrected values.  The dark blue line is your unfiltered frequency response.  Be sure to save your Excel Workbook.  Figure 2 is used after you have input your filters and taken new measurements. (I’m getting a little ahead of myself here.)  After each filter change you should take more measurements because it may (probably will) affect some frequencies far away from the filtered frequency. You will insert your new filtered measurements into the “RAW SPL BFD” column (Figure 2).  The corrected values in the next column will auto update and the magenta (purple/violet) line in the graph will be your new filtered (equalized) frequency response.  I will reference Figure 2 again later.


Figure 1

Figure 2



Figure 3






SETTING UP FILTERS ON THE BFD

Now that you have completed your initial measurements you should be ready to examine your graph and determine which frequencies to experiment with. I've found that I just had to keep experimenting and adjusting to become familiar with what was happening.  I believe you will understand once you have input a few filters and take new measurements.  It’s really amazing how a lower frequency filter can affect a higher frequency response far away from the filtered frequency.


Take a look at Figure 3 (the chart above).  Look at the dark blue line (my initial measurements) and you will notice I have a small peak at about 22hz and a larger one at 31-32hz and another at 69-70hz and another at 100hz.  I have a really nasty dip at 55hz. Eckkk! These are all pretty much as a result of my room.  So my work is cut out for me.  If you’ve inserted your numbers (values) in your chart, you know what frequencies you have to deal with.


Your BFD should still be in the “Bypass” mode.  Push the “IN/OUT” button once so the “IN/OUT” buttons’ green light is no longer blinking but fully lit.  You are now in the active “IN” mode but no filters are set.  Don’t touch any other buttons yet. The only button lit should be the “IN/OUT” button with the exception of the “ENGINE L” and/or the “ENGINE R” buttons, one or both should be lit depending on what you choose.  If there happens to be other buttons lit, go ahead and press them once to turn the button light off.


(NOTE: If both the “ENGINE L” and “ENGINE R” buttons are lit, this is “COUPLE MODE” and is okay, but you will be entering the filters for both left and right INPUTS/OUTPUTS if both buttons are lit. Initially both will be lit.  Press both buttons simultaneously and “ENGINE L” button will be lit with the “ENGINE R” button not lit.  You can now press either to activate or deactivate that channel. If you do cut off one channel, make sure the correct channel you are connected to, has the button lit. Warning:  If you don’t like lights then make sure you cut off the channel you are not using, this will eliminate LED’s lighting up for that channel on the display.)

This has been confusing for some who use 2 subs and want to create different filters for each sub. Here is the section from the manual on coupling:

*Use the ENGINE L key to select the left audio channel.

*Use the ENGINE R key to select the right audio channel. If you wish to process the left and right audio channels simultaneously (COUPLE mode), press both ENGINE keys together. In couple mode both engine LEDs light up. Whenever you edit one of the two audio channels and then switch to couple mode, the parameters of the active channel will be copied to the other; i.e. if you press ENGINE L before ENGINE R, left will be copied to right.

I don't have 2 subs so I haven't actually made the connections and tested this, but as I understand it, by pressing both ENGINE buttons at the same time, both buttons with either light up or go out. When the buttons are lit by the pressing of both buttons at the same time you are then in COUPLE mode. Pressing both buttons at the same time again will turn off COUPLE mode and neither button will be lit. To make each channel work independently you will press both buttons to make them light, but don't press both at the same time.


There are 10 preset programs on the BFD.  Programs 4 and 5 are already set up for PA (Parametric EQ).  If you want to see what the preset programs are, you can look in the manual on page 21 (11.2 Preset table).

Look at any of the pictures of the BFD on this page and you will see the number “160” lit up green on the far right of the display.  Now look at your BFD and you should see 2 dashes instead of the green “160”.  If you rotate the jog dial the 2 dashes will change to numbers 1 thru 10. These are the preset programs.  (Note:  If you rotate the jog dial and the numbers are not 1 thru 10 then you are not in the preset program select mode….check to see if any other buttons are lit (other than the “IN/OUT” button and appropriate “ENGINE” button), and if any are, press that button once to turn the button light off.)  Rotate the jog dial to preset program 1.  “1” will appear where the “160” is above. Now press the “FILTER MODE” button once (all the buttons are labeled). Don’t press any other buttons yet, just press the “FILTER MODE” button once and you should see the “FILTER MODE” buttons’ green light come on.


You should see one of the following in the display:


"OF" (for Off)
"PA" (for Parametric EQ)
"AU" (for Auto)
"SI" (for Single-Shot)
"LO" (for Locked)


These are the different filter modes and will change if you rotate the jog dial.  It’s okay to rotate the jog dial now so you can see what I mean. You are now changing the filter mode for filter 1 of preset 1.  Rotate it back to “SI” which is the preset filter mode for this preset. If you change it the “STORE” buttons’ red light will blink (this indicates you have made a change).  You might wish to go through all the filters in each preset and turn them to “OF” (for off).  Just in case you somehow accidentally use the wrong preset the filters will at least be off. Do this in the “COUPLE” mode.  Press both “ENGINE” keys at the same time.  Both buttons will be lit.  Rotate the jog dial to preset 1.  Press the “FILTER SELECT” button (button will light up).  Rotate thru the 12 filters stopping on each one and pressing the “FILTER MODE” button and rotating the jog dial to “OF”.  To save the change press the “STORE” button twice.  The “STORE” buttons’ red light should go off.  Now if you rotate the jog dial you will be rotating thru the preset programs 1 thru 10 again.  You can go thru all of the presets and change all of the filters to “OF” except for preset 4.  All of the filters in preset 4 are already set to “PA”.  Don’t forget to press the “STORE” button twice after each change. You will use preset program 4 to set up your filters.  You can later go back and use preset program 5 (or any other preset) to set up other filter programs if you want one program for movies and one for music. If you do use other preset programs make sure the “FILTER MODE” is set to “PA” before you setup each filter.


After you have stored the last preset filter, rotate the jog dial back to preset 4.  Remember that the only button that should be lit right now is the “IN/OUT” and appropriate “ENGINE” button.

Now that you are at preset program 4 you can begin to enter the information for your filters.  These filters will equalize your sub to the best response it can be equalized, considering your sub and its’ surroundings.


As mentioned earlier, you may wish to set up a couple of different presets for music and movies. You may wish to consider a "House Curve". A simple explaination is my own example. If you scroll down to the bottom of the page you will see my second setup which represents a house curve. Notice it slopes gently from 20hz to 80hz. I won't get into all the technical details about why you might wish to have a house curve but a good link to read is here in one of the forum threads. You can also do a search for "house curve" in many of the home theater forums and find more info. I will say though, once I flattened out my response to the best I could, I noticed I was missing some low end. I ended up liking the house curve because it gave me back some of that low end without any boomy peaks. As well, it helped me with my nasty dip I have. I haven't really noticed (with my hearing anyway) that I even have a dip. At any rate, the house curve is worth investigating.


The first step is to determine what the first frequency is that you wish to filter.  In my graph above I chose 22hz for my first filter.  I needed to bring it down a few db’s.  Then I chose 25hz.  Look at Figure 4 and you can see the settings I used to achieve my results and you can see how it affected my curve. This is not my final filtering, just the response from the very first filters I set up.



Figure 4




Choose your first frequency.  Theoretically let’s say you only have one 10db peak in your entire curve and you want to flatten it out.  Let’s say the very top of the peak is centered at 35hz and is fairly narrow (it’s starts at 32hz and runs to 38hz).  The next step will be to determine the input information for your filter.

Complete each step one by one.  As you press a button, that buttons’ green light will come on.  I may repeat this a few times but it helps me to remember until I get the hang of it.

Press the “FILTER SELECT” button once and the buttons’ green light will come on.  Now you can rotate the jog dial and see the numbers 1 thru 12 appear.  This is because there are 12 filters you can set.  For your 35hz peak you should only need one filter since it is fairly narrow.  If you have a wider peak you may use 2 filters and in some cases you might find yourself using 3.   Rotate the jog dial until you see the green number “1” displayed.  All numbers and letters will be displayed where the green “160” is displayed in the pictures of the BFD on this page.  You have now chosen filter “1” to setup.

(NOTE: You will notice that the “STORE” buttons’ red light is blinking because you have made a change.  Don’t worry about it.  It will continue to blink until you finish all your inputs.  Then you will store the filters.)

Press the “FILTER MODE” mode button once and the buttons’ green light will come on.  “PA” should show on the display. If it doesn’t for some reason, rotate the jog dial until it does.

Press the “FREQUENCY” button once.  You should see “125” in the display.  This is the preset frequency for filter 1 in preset program 4.  You will change this after you have determined what frequency you want to filter.  Next, use the frequency chart below in Figure 5 or in the manual, to determine if your chosen frequency is in the “ISO” column.  There are 31 “ISO” frequencies you can dial in to. (Note: The Figure 5 chart image below is cropped for a smaller image and does not include all of the ISO frequencies since we are mainly dealing with the lower end.)  If the frequency you have chosen is not an “ISO” frequency then you will have to look under the “FINE” frequency columns on either side of the “ISO” column.  I’ll explain how to use the “FINE” button to dial in a non “ISO” frequency in a moment.  The “FINE” frequencies are under the column headings “-9/60” , “-8/60” , “-6/60” , “+2/60” , “+4/60” , etc.

Look anywhere on the chart for your first frequency you have chosen to filter.  If it isn’t there find the next closest frequency.  In this instance you are trying to find 35hz.  The closest you will find (34.9), is under the heading +8/60 on the third row.

You have already pressed the “FREQUENCY” button and the buttons’ green light is lit.  Rotate the jog dial until you get the number “32” to display (representing an ISO of 31.5hz – see center “ISO” column).  Make sure the tiny red “HZ” is lit next to the “32” in the display.  You choose 32hz because this is the “Display” frequency in the columns on the far left and far right of the Figure 5 chart below, on the same row as 34.9.  Now you have to zero in on the 34.9 using the “FINE” button.   See the next step for this.



Figure 5




Press the “FINE” button once.  If you rotate the jog dial you can see that it ranges from –9 to +10 to coincide with the headings –9/60 to +10/60.  Rotate the jog dial until you see +8 displayed.  This sets the frequency to 34.9.  Use +8 because that’s the column heading for 34.9.  If you had wanted to filter 34hz you would have looked on the chart and found 34.1 and dialed in +6 for the “FINE” selection.  If you wanted to filter 48hz you would dial in 50 for “FREQUENCY” and –4 for “FINE”.  If you wanted to filter 50hz you would dial in 50 for “FREQUENCY” and +0 for “FINE”.  (If the frequency you want to filter is in the ISO column then the “FINE” should always be +0….you do not have to fine tune “ISO” frequencies.)

Now that you’ve zeroed in on the target frequency you need to set the “BANDWIDTH” (a/k/a “Q”).  This sets how wide the filter will be (how far the filter stretches on each side of the center frequency you choose).

Press the “BANDWIDTH” button once.  You should initially see 60 displayed.  You can rotate the jog dial from 1 thru 120. This represents from 1/60 octave to 120/60 octaves.


To help you better understand:



An octave is the doubling or halving of a frequency.  I don’t know if you have ever used a graphic equalizer in your car or home before, but usually you will see the slides on those divided into “full” octaves as below:



You might even see 16 HZ on some equalizers, which represents one full octave below 31.5 HZ.  If you played around with parametric eq’s before then you should have a head start.

“FREQUENCY” is dialed in and your “FINE” dialed in as well.  Now decide how wide the “BANDWIDTH” needs to be to lower the peak.  This is where you may be doing a lot of experimenting.  If you dialed in 10 for the “BANDWIDTH” then you would have a 10/60 or 1/6 octave “BANDWIDTH” being filtered.   To give you a general idea of how bandwidth works you can look at the examples below.


Figures 7, 8, and 9 show how bandwidth slopes from the center frequency you select.  Figures 7 and 9 are logarithmic graphs instead of a linear graph like my Excel graph in Figure 3 above, so the vertical lines are not equal distance apart.  But it will still give you a good idea of how the bandwidth will slope.



Figure 7

Figure 8



Figure 9




If bandwidth is confusing for you to understand, like it is for me......don't worry. It will be like on the job training when you start experimenting with different bandwidth settings. There are calculations to use, but I don't use them myself.  I found it works much easier and better to start out using very narrow bandwidths and work up. I started by dialing in small bandwidths of 2 or 4 and took more measurements to see how it affected my graph (curve). If I thought it needed to be wider I might raise it to 6 and re-measure.  It doesn’t take that long to measure through 1/6 octaves from 16hz to 160hz.  It’s only 21 measurements at 10 seconds or less each (depending on what tones you use). You might try experimenting with 4 to 5 different bandwidth settings. Just do it to get the hang of how various bandwidths will effect your response. Once you've completed a few it will become easier to look at a peak or valley and get a better estimated starting bandwidth.

Here's a good place to try to get to know the BFD Software if you haven't already. Behringer built a program that will allow you to see what a filter will look like and will even let you load filters in the software and transfer them to your BFD. I haven't done any transferring so I can't tell you much about it. I understand you have to do some midi port configuring on your computer for it to transfer properly. None the less, it's a great tool to see exactly what bandwidth looks like within the BFD.

Here's the latest version that will work with most versions of Windows (including XP): BFD SOFTWARE

And here's a sneak peak screen shot of what it looks like. Notice the 50hz 1/6 octave 10db cut filter I dialed in for the fun of it.





Ken Bruce (brucek) has some very interesting comments about bandwidth and using this software. Ken is dedicated to helping everyone understand sub equalization, thus he spends a lot of time working with it. So before you go any further, check out what Ken has to say:

Ken Bruce on bandwidth and the BFD software.

Furthermore, here's another link to some good information on bandwidth, written by Wayne A. Pflughaupt (Another generous fellow, like Ken Bruce, offering a lot to help us all understand bandwidth and sub equalization): http://www.hometheaterforum.com/htforum/showthread.php?postid=708407#post708407 ... (Post #40)


Now that you have set the “BANDWIDTH” you are ready to adjust the “GAIN”.  Press the “GAIN” button once.  Rotate the jog dial to the desired cut or boost.  Be careful not to boost too many frequencies.  A 3db boost will have an affect of requiring double your power.  It can eat up a lot of dynamic headroom quick.  Boosting frequencies above say 50 - 60hz is not quite as bad as boosting a lower frequency around 25-30hz.  Try not to boost any but rather cut the peaks.  If you do boost, try to keep it low as possible.  Always start with your lowest frequency to filter and proceed to the highest.  (You will have to experiment to see how it affects your response curve by taking new measurements after you have set the first filter.)  After you have entered all your filters then you might need to go back and adjust the previous filters after you complete more measurements.  You may have to re-adjust the “FREQUENCY”, “FINE”, and/or “BANDWIDTH, as well as the “GAIN”.  Again, there is no replacement for experimenting.

There are 12 tiny red horizontal LED’s in a row in the display section (labeled “24 FB-D FILTER”).  You will see “L” to the left of the top row of LED’s and “R” to the left of the bottom row.  In between the two rows are numbers 1-12, each representing a filter.  If you programmed only one channel then only one row will be lit red (one lit LED per filter).  If you programmed both channels (leaving the “ENGINE L” and “ENGINE R” in “COUPLE” mode) then both rows will be lit red.  A red LED will not light until you have made a change in the “GAIN” adjustment.  Once you enter the “GAIN” for a filter then that filter’s LED in the display will light red.

Now that you have finished your first filter you need to store and save your work.  Remember above I stated that the “STORE” buttons’ red light will be blinking because you’ve made changes.  Now that you finished the filter, press the “STORE” button twice. You have now saved filter 1.  The red light will stop blinking and go off.

You must now take your new measurements before continuing to filter 2.  Refer back to Figure 2. The “RAW SPL BFD” column is where you will insert your new values (measurements).  Again the values in the right column “SPL (comp)” will automatically update as you enter the values in the left RAW column.  As well, you will see the magenta (purple/violet) line move as you input your values.

RECAP:

Set input level. (This only has to be done once.)
Set filters in presets 1-3 and 5-10 to “OF”. (This only has to be done once.)
Set preset to 4. (This only has to be done once.)
Take measurements and determine frequencies to filter.
Set “FILTER SELECT”.  (For each filter you setup.)
Set “FILTER MODE” to “PA”. (Verify for each filter to be sure.)
Set “FREQUENCY”.  (For each filter.)
Set “FINE”  (If necessary to achieve desired frequency.  Use chart to determine.)
Set “BANDWIDTH”.  (For each filter.)
Set “GAIN”.  (For each filter.)
Press “STORE” twice to save.  (After each filter is set.)
Take new measurements after each filter setting.

If you have the filters available, you may wish to add the following filters:
-48db @ 1.0 khz, -48db @ 1.25 khz, -48db @ 1.63 khz, -48dB @ 2.0 khz.  These filters supposedly eliminate the harmonic distortion and/or buzzing that often occur with subs.  I have not experienced these noises that I can determine and can not verify if this tweak actually works, but I can not see how it would hurt.  I have added 3 of these filters to my BFD as I only had 3 filters available.

I’m still working on this so if you see errors or corrections to be made please e-mail me and let me know.

Hope it helps you!

Thank you!

Sonnie Parker







KEN BRUCE BFD REVIEW

KEN BRUCE ON BANDWIDTH AND THE BFD SOFTWARE

MICROSOFT EXCEL WORKBOOK

TEST TONES

BFD MANUAL

BFD SOFTWARE

BFD WEBSITE






Here's my latest graph in our new HT room.