MANUALLY MEASURING THE SPL OF SUB FREQUENCIES
USING MICROSOFT EXCEL WORKBOOKS
Here I will cover the manual measuring procedure I have used in the past and explain how to insert these measurements into the Excel chart. I now use Room EQ Wizard (REW), but this is for those who do not have the convenience or ability to use REW for whatever reasons. You do not have to use the Excel chart to setup the BFD, but it makes it a lot easier to analyze versus using nothing at all.
The first thing you will need to do is create a Microsoft Excel Workbook based on the Radio Shack SPL Meter you own. Obviously these require Microsoft Excel.
Old Analog RS SPL Meter
New Analog and Digital RS SPL Meters
Using the workbook is 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 is a little more difficult but it can be done. It will take a little longer so be prepared to spend some time on this. Again... I cannot emphasize enough the benefits of Room EQ Wizard and how this has made the entire process so much easier and quicker.
If you share your home theater with your family or great room you may want to try to mimic the conditions and surroundings such as shutting/opening doors and blinds as you normally would when watching a movie.
The Excel Workbooks that brucek designed have the new RS correction values built in... if you plan on continuing with the RS Meter. It is 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, there may be correction values provided, however they most likely will be incorrect if they are not the new values. If not loaded then you will need to load them according to the software help file instructions for the software you are using.
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.
Okay...so you may be asking what is 1/6 octave frequencies and/or why use 1/6 octave frequencies. We will go into more detail about octaves when we get into the bandwidth section later on, but I did ask brucek to give us a simple explanation as to why we use 1/6 octave frequencies instead of just using something like 5Hz increments... say 20, 25, 30, 35, 40, etc. Here's what he had to say:
"It is sometimes hard to explain something without a lot of boring detail, but the best reason I can give for measuring sound using octaves is to mathematically comply with the logarithmic nature that is representative of human hearing.
Each octave is a doubling of a frequency. So 20Hz is an octave above 10Hz, and 40Hz is an octave above 20Hz. In that regard, the notes within a scale are not equally distributed in frequency. For example, from 20Hz to 40Hz there are 20 (one hertz) steps for the octave. From 40Hz to 80Hz there are 40 (one hertz) steps. The number of steps are getting progressively greater as the frequency increases. So you can't just divide an octave in half and expect the frequency to be half way between. It requires a formula (that I won't include here). Measuring at equally spaced frequencies such as 20, 25, 30, 35 etc would not be representative of how we hear.
In 'equal tempered tuning' there are considered to be 12 equally spaced notes per octave. It is accepted that if you equalize a subwoofer to 1/6th octave tones, that the response will sound correct even if there are some anomalies between these tones. So we use 1/6 octave tones to do frequency response checks and accept that it's good enough that we won't detect any problems."
When measuring manually I always test 1/6 octave frequencies from 16Hz up to 160Hz. Low frequency tones and sweeps are available for download at this link:
Test Tones and Sweeps ... (You will have to register and/or login to download. Registration and downloads are all free!)
These are all sine waves in MP3 file format but you can convert them back to wave files and record them to disk. Your DVD player may already play MP3 files... if not, you can convert the MP3 files to wave using CDEX, a free program that you may find useful for other applications as well. There are other programs available that will do these conversions. 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 below to begin with. The sweeps may be handy if you have other means of testing such as ETF or Spectra Plus. If you are using a software program then measuring with a sweep is probably the best option. Another reason why we like Room EQ Wizard is because it provides you with a full resolution sweep and will ultimately be more accurate with finding response problems. No downloading of tones is necessary with Room EQ Wizard.
For the initial setup of the BFD I test only the sub. Shut down your mains by either disconnecting them or turning off your amps to them so that only the sub is playing. My front/center/surrounds crossover is set at 80Hz on my receiver, but I like to see how much output is above this crossover point up to about 160Hz. Plus, there is a little LFE (Low Frequency Enhancement) information up to 120Hz unless you have a LFE crossover and it is set lower. Some pre/pro's have crossovers for front/center/surrounds and LFE. Typically you would set the mains/center/surrounds to 80Hz and the LFE at 120Hz. It's not that important to worry about frequencies above about 80Hz because there's not a lot of info there as far as LFE is concerned, but it won't hurt to look at it and equalize it either. 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 using 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 a 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 (this is a very old graph of my response many years ago) 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 had to just 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 above graph). Look at the dark blue line (my initial measurements) and you will notice I had a small peak at about 22Hz and a larger one at 31-32Hz and another at 69-70Hz and another at 100Hz. I had a really nasty dip at 55Hz. Eckkk! These are all pretty much as a result of my room. So my work was cut out for me. If you've inserted your numbers (values) in your chart, you already know what frequencies you have to deal with.
Your BFD should still be in the "Bypass" mode from when you were setting the input levels. Push the "IN/OUT" button once so the "IN/OUT" button 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 two 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 have not 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.
[CHOOSING PRESETS AND SETTING THE FILTER MODES]
There are 10 preset programs on the 1120p and 1124p BFD. Programs 4 and 5 are already set up for PA (Parametric Equalizer). If you want to see what the preset programs are, you can look in the manual on page 21 (11.2 Preset table). The 2496 only has one preset.
Look at any of the picture of the BFD at the top of 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" button light up.
You should see one of the following in the display:
"OF" (for Off)
"PA" (for Parametric Equalizer)
"AU" (for Auto)
"SI" (for Single-Shot)
"LO" (for Locked)
These are the different filter modes for each filter within each preset 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 preset 1 filter 1. If you change it the "STORE" buttons' light will blink (this indicates you have made a change). You might wish to go through all the filters for each preset you are not using and turn them to "OF" (for off). If you somehow accidentally use the wrong preset it will at least be off and there will be no processing. Don't forget to press the "STORE" button twice after each change. You will initially 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 another preset, make sure the "FILTER MODE" is set to "PA" for each filter before you setup the filters.
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.
Here is a tip from Gary Kratochvil: For those out there who use a remote to turn on/off the power to the BFD... set up the BFD so that your favorite filters are stored in preset 10. Preset 10 is the default preset where the BFD returns to after losing power. Gary set up his filters on preset 4 initially and most of the time if he lost power it would reset to preset 4, but then every once in a while, it would lose which preset it was on and power up with preset 10, so he just set his favorite filters up in preset 10. Now it starts there every time without fail. Don't forget to change the filter mode to "PA" if you which your filters over to preset 10.
[A LITTLE ABOUT HOUSE CURVES]
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". I will not get into all the technical details about a house curve, but generally speaking most people like a house curve for movies. It will give you more bottom end which is typically desired with movie watching. You can get your response to flat and then read brucek on House Curves as well as House Curve: What it is, why you need it, how to do it. and Minimal EQ, Target Levels, Hard-Knee House Curves.... both by Wayne Pflughaupt, to learn more.
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 had. I did not really noticed that I even had a dip. At any rate, the house curve is worth investigating.
[DETERMINING FREQUENCIES YOU WANT TO ADJUST]
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.
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' light will come on. I may repeat this a few times but it helped me to remember until I get the hang of it.
[CHOOSING A FILTER WITH THE FILTER SELECT BUTTON]
Press the "FILTER SELECT" button once and the button will light up. 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 picture of the BFD at the top of this page. You have now chosen filter "1" to setup.
(NOTE: You will notice that the "STORE" button blinks 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.)
[CHOOSING A FREQUENCY WITH THE FREQUENCY BUTTON]
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 button 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 should 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.
STOP! BEFORE YOU GO TO THE NEXT STEP... READ THIS!
*** When you first rotate the jog dial to your desired frequency... (go ahead and rotate the jog dial counter clockwise all the way until you see 20HZ with no decimal point to the left) ...go as low as it will go frequency wise and then start from there choosing the frequency you want to adjust. The reason this is important is because if you are not careful you will be adjusting a higher frequency than you think you are. For example... .63 (with the decimal point to the left of 63) is actually 630Hz NOT 63Hz. To get to 63Hz you need to rotate the jog dial counter clockwise until you get to the 63 WITHOUT the decimal point to the left of the number. This has caused some people to scratch their heads for hours on hours. They went through and adjusted frequencies that were not even in the bass region and thought their unit wasn't working properly... which it wasn't because they didn't have the right frequencies adjusted.
[FINE TUNING THE FREQUENCY WITH THE FINE BUTTON]
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.)
[UNDERSTANDING AND SETTING BANDWIDTH WITH THE BANDWIDTH BUTTON]
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: (If you understand bandwidth you can scroll on down a little.)
An octave is the doubling or halving of a frequency. I don't know if you have ever used a graphic equalizer in your home or car 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 equalizers before, then you should have a head start.
"FREQUENCY" is dialed in and your "FINE" is 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 the Excel graph in Figure 3 we looked at earlier, 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 was 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.
brucek has some very interesting comments about bandwidth. He 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 he has to say:
brucek on Bandwidth.
Furthermore, here's another link to some good information on bandwidth, written by Wayne A. Pflughaupt (Another generous fellow, like brucek, offering a lot to help us all understand bandwidth and sub equalization)... definitely worth a read:
Wayne Pflughaupt on Bandwidth (excerpt from a forum post).
[SETTING THE GAIN WITH THE GAIN BUTTON]
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. Boosting can eat up a lot of dynamic headroom extremely 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. Remember just because you've cut frequencies does not magically give you more room for boosting. Also remember that if your dip is a room null then boosting will not help it. The room is causing the dip and in this situation it's all but impossible to boost it. If you find you have one or more nasty dips you might try moving your sub around, even a few inches to a foot can have a noticeable and measurable effect on the response, and in some cases may eliminate a null or move the dip to another frequency than can be adjusted by a small boost. If you must boost... listen carefully and make sure you are not putting too much strain on your amp. The bottom line is try everything else possible before boosting.
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.
[STORING YOUR FILTERS WITH THE STORE BUTTON]
Now that you have finished your first filter you need to store and save your work. Remember above I stated that the "STORE" button is blinking because you've made changes. Now that you finished the filter, press the "STORE" button twice. You have now saved filter 1. The "STORE" button light will stop blinking and go off.
[SUMMARY AND RECAP]
You should now measure your response again before continuing to filter 2. Refer back to Figure 2. After you have entered in a few filters and get the hang of seeing what the filters are doing you may decide to tackle inputting several filters or adjusting several filters before taking new measurements. 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.
1. Set input level. (This only has to be done once.)
2. Set preset to 4 and make sure "FILTER MODE" is "PA" for each filter. (One time only.)
3. Take measurements and determine frequencies to filter.
4. Set "FILTER SELECT". (For each filter you setup.)
5. Set "FREQUENCY". (For each filter.)
6. Set "FINE" (If necessary to achieve desired frequency. Use chart to determine.)
7. Set "BANDWIDTH". (For each filter.)
8. Set "GAIN". (For each filter.)
9. Press "STORE" twice to save. (After each filter is set.)
Optional: Take new measurements after each filter setting until you understand how the filters will effect your measurements.
If you want to copy one preset you have setup to another preset (i.e. copy preset 4 to preset 5)... follow the instructions below. This might come in helpful if you want to change only a filter or two for different sources. For example: you have flat response curve setup for music and you want a house curve for movies. You can copy the flat response preset over to another preset and make minor adjustments for a house curve.
1. Select the preset you want to copy.
2. Press the "Store" button, it will now be blinking.
3. Rotate the jog dial to select the destination preset.
4. Press the "Store" button again, the preset will be copied, and the "Store" button will stop
Now you can make minimal adjustments to the new preset without having to go through every filter.
If you see errors, corrections that need to be made, broken links, have new information or suggestions... or just have a question... please post them in the BFD Forum of Home Theater Shack.
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