Bought my BFD and I Have Questions (1 Viewer)

[Bob U]

Hi Bruce,

Actually, this is the same technique I used in the other position. I lowered the peak at 31.5 to match the peak at 22, then lowered the resulting peak with the filter broadly centered at 28. The shelf, at that point, is about an octave wide.

I'll play with the software, and repost sometime today. I did raise the sub level and need to replot bypassed and corrected modes.

I'll try narrowing that filter at 28 as well to see how it effects the very bottom.

-=Bob=-

 

[Bob U]

Ok, another 4 or so hours into this today.
I started by re-graphing the bypassed FR since I had adjusted levels last night. Also tried graphing just one sub and amazingly, discovered my bypassed response is MUCH smoother with 2 subs rather than one. (These are in both front corners, btw) They do have different FR, and ideally, I would EQ each individually then test the combined, but I really don't have the energy for that project. Just the way this has soaked up time, I would guess I would have another 8 to 10 hours to get a curve I would be pleased with.Maybe more in trying to balance the two subs.
So, here is today's work:
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Honestly, I haven't even listened to it yet other than measurements. Took a bit to get here, but it looks pretty good on paper.
I'll post today or tomorrow as I listen.
-=Bob=-

 

[Brian Schucher]

Have to tell yas. I just picked up a BFD to use in the new HT when its done and this scares the hell outta me. This appears complicated as hell!!!

 

[brucek]

Brian,
It sounds more complicated than it really is. There are lots of people around here that will give you a hand.
Good idea to use the information and Excel graphing tool on Sonnies site:
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Do a general search on BFD's and spend a few hours reading and you'll be an expert.
Download the BFD design software I mentioned in an earlier post and play around with it to get familiar with filter curves too....
brucek

 

[Bob U]

Its not. Just follow Sonnie's tutorial. You'll be amazed how quick you get to understand the device.

But, in a bad room such as mine, it is tedious to get it tweaked. And I am a perfectionist.

Best tip I can give anyone here is that I have found that the bandwidth setting always works better set smaller than I would have guessed from looking at the graphs.

And, I just listened to a bunch of tests and this is the best it has ever sounded for me. The "bloom" is gone.

BUT...I have to say that the folks here in other threads talking about being blown out of their chairs, or walls shaking either must have their subs set waaaayyyy too high or have bigger and better rooms than I. I hear what I would expect to hear in the proportionate levels of explosions, the Matrix fight scene, the THX ball, but it never shakes the house. If it did, the bass would either have to be 20dB above 1kHz or I am missing low frequencies that would make the difference.

I'd really like to hear a meticulously tweaked system to compare my audible results to with known material. At this point, I think I have the best I can do with my gear and room. I don't know how it compares to a known benchmark nor if SVS's would make an improvement.

-=Bob=-

 

[Steven Hen]

Brucek,

Does that Behringer software that you mentioned work with windows xp? I dl it and unzipped then clicked on the DSP1100.exe file and nothing happens.

 

[Brian Schucher]

As far as adding a pair of SVSs for you Bob, DO IT! You have lotsa space to fill. I have to believe you would make the house shake with them....Althoug im currently in a rental house while mine is being built, my system was set up in my last house with TONS of volume to fill and a pair of 20-39s SHOOK the house for sure. I was EQing with an ART351 at that time but im sure i didnt have it as smooth as yours..

 

[Bob U]

Hi Brian,

You know, the question is: do I want the house to shake?? I can easily turn up the Sunfires and have pictures fall off the walls, but that isn't accurate reproduction. On the other hand, if I am missing bottom bottom frequencies that would make a difference without raising the sub levels, then yep, I would want to do that. Most importantly, I don;t want the sub to be out of proportion to the volume I am listening to my mains.

-=Bob=-

 

[brucek]

Steven H,

Yeah, I'm sorry, I should have mentioned that. Sonnie told me that last week because he has XP also. He had to use it on a computer at work that had W98. Oh well..too bad, it's very nifty software.

brucek

 

[Steven Hen]

Thanks brucek,

I'll grab a laptop at work that has win98 and check it out.

Also, thanks for your in depth explanation of octaves in your other posts...very helpfull to us newbs!

 

[Rick Radford]

brucek,

How 'bout W2k?

 

[brucek]

Rick,

Don't know about 2000. I only learned last week from Sonnie that XP is a no go...

I had only given the design software a cursory glance originally because I found it easy enough to enter my filters by hand rather than hook up a midi.

Then I had this idea about using it to design a house curve. It worked so darned well that I told Sonnie about it and when he tried the software with his XP it didn't work - so this is how I found out about it. It is so useful in getting a feel for how filters work plus the added bonus of finding out your phasing which is graphed along with your filters - very cool...

He tried it at work on 98 to test my house curve theory and said it worked fine for him.....

brucek

 

[Rick Radford]

brucek,
Between the time I posted and came back to see your response, I decided to get off my lazy butt and try out the BFD software.
It definitely runs on my W2k installation.. and is pretty cool! Thanks for the heads up on it. (just what I need.. something else to spend more time on!)
So while I have your attention (it's been a while since I messed with my BFD), I'm curious about BW.
From earlier discussions with you and Wayne, I learned that a 1 octave filter is not split about the center freq but is 1 octave either side of the center freq. Agreed?
When figuring the o.p. (outer parameters) for a filter, do you look for how far the filter goes either side of the center freq?
For example, (using the BFD software) I put in a 20/60 (1/3 octave) filter at 60 Hz and thought the o.p. would be 50Hz to 80 Hz. However, with +3 dB gain, the BFD software shows the effect going from below 40 Hz to above 90 Hz.
Also, the greater the gain used, the greater the freq range affected. For instance, changing the gain to +9, the freq range goes from below 30 Hz to above 100 Hz.
Is the key here that there is very little displacement from zero at the fringes? I guess I would have expected to see the Freq range affected to be stable, regardless of the cut/gain employed. Also, I expected to see the affected freq range start and end at the o.p.
... just a little something to jump start your day.

 

[brucek]

Rick,
OK here's my more detailed explanation of relative and absolute bandwidth as I see it. You're gonna hate yourself for asking. I'll just talk about cuts here in my examples, but the same holds for gains. Gain is the same, but I didn't want to add confusion.
To start, I will clarify that you are correct. When you enter a BW (bandwidth) of one octave into the front panel of a BFD, the filter will be one octave above and one octave below the center frequency - but that's the easy answer. Where I measure the bandwidth of one octave is the rub, and takes some explaination. Try not to go to sleep during the discussion.
Here are the simple rules to follow.
Absolute bandwidth = bandwidth at the 3dB point.
Relative bandwidth = absolute bandwidth divided by the center frequency.
Q = inverse of the relative bandwidth = 1/relative.
Front panel entered bandwidth is the absolute bandwidth divided by two.
For a cut, the absolute bandwidth is defined as the width of the filter at its 3dB down points expressed in octaves. Did you notice I said 3dB "down". Big difference from saying - 3dB cut. This isn't 3dB like the gain dial readout of - 3dB. This is the relative 3dB less than zero dB for a given cut (or boost) value. So the 3dB down point will be different for every cut value. But the absolute bandwidth at that 3dB down point will remain the same for different cuts, but then of course, the bandwidth where the filter flatlines into zero dB will get wider and narrower as the cut is changed.....
For example, that means if the front panel entered cut is -6dB from zero, then you have to use a mathematical expression to calculate the value at which the curve will cross 3dB "down" from zero when we use - 6dB as the cut, (given your front panel octave width selection) . This makes sense because obviously if we cut by - 2dB on the front panel from zero, we couldn't say the absolute bandwidth was measured at absolute - 3dB cut because - 2dB cut is less than -3dB cut. We'd have to calculate for the selected cut of -2dB where 3dB "down" point was located.
Lets take an example of three three filters. The filters maintain a constant absolute bandwidth of 2/3 octave centered around 50Hz. 1/3 octave is entered into the front panel for BW. 1/3 octave less (40Hz) and 1/3 octave greater (63Hz) than 50 Hz. The only variable is the cut of -3dB and -6dB and -12dB.
I have calculated the 3dB "down" from zero points at which the filter must cross the 40Hz and 63Hz absolute bandwidth of 2/3 octave for a front panel entered cut of -3dB, -6dB and -12dB. Each value will be 3dB down from zero at a different spot, but when they are indeed at 3dB down, they all possess the same absolute bandwidth of 2/3 octave from 40Hz to 63Hz.
Here's my three calculations - ignore if you're not familiar with decibel and antilog calculations.
Let x = 12dB cut calculation for value of cut at 3dB down from zero.
x = [(antilog -3dB/20) x cut value ] - cut value
x = [(antilog -3dB/20) x 12 ] - 12
x = - 3.50dB
Let x = 6dB cut calculation for value of cut at 3dB down from zero.
x = [(antilog -3dB/20) x cut value ] - cut value
x = [(antilog -3dB/20) x 6 ] - 6
x = - 1.75dB
Let x = 3dB cut calculation for value of cut at 3dB down from zero.
x = [(antilog -3dB/20) x cut value ] - cut value
x = [(antilog -3dB/20) x 3 ] - 3
x = - 0.87dB
So what am I saying is that for a 50Hz center frequency filter with an entered value of BW of 20/60, with a cut of -12dB, the at 40Hz and 63Hz the cut will be -3.5dB. These are the absolute bandwidth 3dB down points. The filter will of course extend out further until it reaches zero effect, but most of it's power is in the absolute area.
So for this filter example here's the values from my initial list of definitions.
Center frequency = 50Hz
BW = 2/3 octave from 40Hz to 63Hz = Absolute bandwidth = bandwidth at the 3dB down point.
Relative bandwidth = (63 - 40) / 50 = 0.46 = absolute bandwidth divided by the center frequency.
Q = 1 / 0.46 = 2.17 = inverse of the relative bandwidth = 1 / relative.
Front panel entered bandwidth is the absolute bandwidth divided by two = 2/3 / 2 = 1/3 or 20/60
Anyway, the math and the design graph seem to support each other, so I think I have this correct - I may have made some math mistakes. The design graph isn't super resolute, so it's hard to get exact readings off it, but its close enough to use to make filter decisions - it's easier than doing antilogs anyway. Does it make sense to you?
What was your question again?
brucek

 

[Rick Radford]

>What was your question again?<
Uh, I forget!
>You're gonna hate yourself for asking.<
Not at all! This is really good stuff. Thanks for taking the time to explain. You, WayneP and Vince should pool your thoughts for an advanced primer! ^2
>the absolute bandwidth is defined as the width of the filter at its 3dB down points expressed in octaves. Did you notice I said 3dB "down". Big difference from saying - 3dB cut. This isn't 3dB like the gain dial readout of - 3dB.<
You caught me! This is why I used 3dB. I'd remembered just enough of some other reading about "Q" and 3dB down to be dangerous.
>the absolute bandwidth at that 3dB down point will remain the same for different cuts, but then of course, the bandwidth where the filter flatlines into zero dB will get wider and narrower as the cut is changed.<
>So for this filter example here's the values from my initial list of definitions.
Center frequency = 50Hz
BW = 2/3 octave from 40Hz to 63Hz = Absolute bandwidth = bandwidth at the 3dB down point.
Relative bandwidth = (63 - 40) / 50 = 0.46 = absolute bandwidth divided by the center frequency.
Q = 1 / 0.46 = 2.17 = inverse of the relative bandwidth = 1 / relative.
Front panel entered bandwidth is the absolute bandwidth divided by two = 2/3 / 2 = 1/3 or 20/60<
I see how it's done now. Hmmm.. ain't nothing ever simple, is there? Just out of curiosity, if you used a cut of less than 3 dB, would x have been a positive number, or still negative, but just approaching zero?
This is interesting stuff to me. For someone doing this manually, I have a hard time understanding how they'd begin to know what values to plug in without having some understanding of all this. Sure helps me be appreciative of ETF/SDA mode!
IAC, I think I see why my manual BW calcs have sucked so badly. How are you guys doing this manually with any degree of accuracy short of all the math? I find it hard to believe you go to all this trouble to figure a BW parameter.

 

[brucek]

Rick,

IAC, I think I see why my manual BW calcs have sucked so badly. How are you guys doing this manually with any degree of accuracy short of all the math? I find it hard to believe you go to all this trouble to figure a BW parameter.

You hit the nail on the head there. No one in their right mind would make these calculations. Either use the BFD design software or trial and error the BW entries knowing generally what the effect will be. Just say to yourself that if I enter a BW value it will affect mostly that entered bandwidth value above and below the center frequency, and the greater the cut or boost, the wider the filter will have its effect before I get to zero effect.
************
BTW, I didn't tell you what my "house curve" theory was all about - you might be interested.....
The last time I moved my equipment around I had to go through the routine of re-doing my BFD filters because the response of my sub changed significantly in it's new position.
I did such a swell job this time that it was ruler flat from about 16Hz to my crossover at 60Hz. While I was happy that I did such a nice job of taming my peaks and valleys resulting in such an enviably flat response - it sounded like, well, crap..........I could see Wayne P standing there asking me why I didn't add a house curve.
It was such a pain to get all those filters to create a flat response, I knew it would be even worse trying to get an even smooth house curve designed in. I was wishing the BFD had a shelf filter that I could hinge at about 30Hz and evenly drop my entire sub response by a predetermined amount while leaving my other filters intact.
Then I had an idea, that if I added a single filter up around 400Hz with a very wide bandwidth and a large cut, designed so that its final effect would reach down to about 30Hz, that I would have a smooth drop from 30Hz all the way to 400Hz. It would essentially tip or hinge the shelf at 30Hz and continue to drop increasingly, all the way to the filters center frequency.
This would be a pain to calculate so I decided to try the BFD design software to get a look on a graph what values would work. Well, I found it so easy to enter this single filter into the design software and make adjustments while watching its graph until I found a filter that would work. I then added all my other filters into the design software to see if the effect I was looking for worked. It worked very well. If I enter just my filters that create the flat response in my system they (not suprisingly) look like an exact mirror of the "no-filters" Excel file of my system. Then if I add my "house curve" filter along with my other filters, I get a very nice tilt starting around 30Hz and dropping smoothly from there. I could easily increase the tilt by altering the single "house curve" filters cut and I could easily change the frequency where it starts to take hinge effect by altering the single "house curve" filters center frequency. The filter that I am using that works well in my system is a 366Hz filter with a bandwidth of 120/60 and a cut of -15dB. The phasing problem that occurs at 366Hz from this filter is outside the range of my sub, so it can be ignored. I wouldn't have wanted to try and create the value for that filter without the design software, so that's why I recommend it..............
Now, of course, once this filter is applied, I had to add a small wholesale increase to my subs level control to compensate, but the change was not large and I could afford the small loss of headroom.
This allows me to have two programs, one with the "house curve" filter and one without, for a flat response. Or, I could have several programs with various single house curve filters for example, one for movies, one for music etc..... What do you think?
I hope we haven't scared Brian S off with all this stuff.
brucek

 

[Bob U]

Bruce,
Great stuff. I wish you had posted about your house curve solution BEFORE my last 10 or 15 hours of tuning
Btw, someone reading this forum who happens to live 10 or 12 miles away and owns an SVS sub invited me over to listen. I'm looking forward to hearing the difference and seeing if I feel a need to make a change of subs.

 

[Rick Radford]

>I didn't tell you what my "house curve" theory was all about - you might be interested.....<
Nope.. you didn't! But that is fascinating! What a great idea.
Well I just have to drag my PC back into the HT room and redo all my filters. I have yet to use the RS correction file you defined some time back. So I have a lot of work to do.
I want to do this anyway since I just upgrade my SVS driver to the "i" driver. I had to lower my Samson's gain by 2dB when I recalibrated.
Side note: after replacing the SVS driver, I've noticed the BFD output LED's show much more activity (the clip light occasionaly lites up) than before. Is it conceivable that the new driver could change that? Maybe I need to revisit my input level settings for the BFD before I re-filter.
Is your response curve just the sub only? Or did you integrate the mains as well? I'd like to see your graphs if you still have them.
That's another area I need to revisit... integration of the mains with the sub, that is.
Anyway, I like the idea of one preset with a flat response.. and another preset with the house curve.
I haven't had time to play much with the new software yet. Is there anyway to plug in the data from my low freq response measurements and then apply virtual filters? That would be cool to simulate it and then see how close the real sub response & filters are to the model.
Super info! Thanks a bunch!
PS. I was sorta disappointed that WayneP didn't like my built in house curve idea (EQ the LF response to flat with uncorrected data). Then, when the RS correction file is applied, you have a nice 6-8 dB rise from about 80Hz to 20Hz. And here I thought I'd come up with a slick way to create the house curve without really trying!

 

[brucek]

Rick,

Is your response curve just the sub only? Or did you integrate the mains as well? I'd like to see your graphs if you still have them.

I only kept the readings of my sub only. It shows 4 things, (1)"no-filters" - (2)"filters" - (3)"filters + house curve filter" - (4)"filters + house curve filter + wholesale increase of sub volume". I'll send you a copy when I get home...

brucek

 

[Matt Meyer]

I know this was probably mentioned before, but what freq do you guys use as your baseline and at what spl?
Matt
Some of this stuff is way over my head.