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Fiddling with my BFD again...

Discussion in 'Subwoofers' started by AngelEyes, Oct 15, 2005.

  1. AngelEyes

    AngelEyes
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    Hello chaps, Tis me!

    I have been experimenting with the Sub in a more sensible position and seem to be getting on much better now.

    I would still like a little help if you wouldn't mind taking a peek at my SPL readings on the attached Excel document.

    Just for your info I have 3 sets of readings:

    Blue - Tuned to 20hz, raw / compensated readings
    Pink - Tuned to 16hz, raw / compensated readings
    Yellow - Tuned to 20hz BFD PEQ adjusted readings

    So for those of you interested in playing with Port bungs you might get some idea of the affect it may have on your system.

    The Front speakers are set to large as any other crossover setting gives me huge troughs in the graph. However there are 2 peaks, one at 80hz and another at 135ish hz.

    Nothing I have tried with the BFD will even touch these so I have to assume it is related to my fronts and maybe a phase issue. I have yet to tackle this and would welcome any suggestions.

    By the way I cranked the system to ear bleeding levels the other night (before my PEQ efforts) and sat the wife in front of Master & Commander for the opeing 15 mins or so. She was grinning like a cheshire cat... it really is awsome!
     

    Attached Files:

  2. bob1

    bob1
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    I would go with the light blue line, nice house curve. :thumbsup:
     
  3. AngelEyes

    AngelEyes
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    hmmm yes very funny :(
     
  4. bob1

    bob1
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    :D :rotfl:
     
  5. bob1

    bob1
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    You could try moving your front speakers slightly and see if that makes a difference,other than that just leave it ,it could be the reason you prefer the speakers at large.I have a peak around 111hz but have just left it because it sounds good as it is,whats a bigger problem is the huge dip at 160hz. :rolleyes: :suicide:
     
  6. AngelEyes

    AngelEyes
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    Yes that is an annoying one but it has been present on all my sweeps no matter where the sub is placed. It is probably an affect of having an open stairwell and doorway in the room.

    My front speakers are pretty limited to where they are as they are not shielded and there really is any physical room to place them anywhere else.

    Just out of interest, should a rooms idea curve be like the 'unused' one on my Excel doc? I mean starting higher up and sloping away gently? I have been trying to get a perfectly flat curve using the BFD, is this wrong?

    (bear in mind I listen at 'normal' volumes most of the time and so would prefer a bit more bass than the other frequencies?)

    ...with this in mind do you think the 16hz tuning would be a better bet...?
     
  7. Mr Incredible

    Mr Incredible
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    Angel,

    You say "Nothing I have tried with the BFD will even touch these so I have to assume it is related to my fronts and maybe a phase issue"

    Just re-run some tests with a few phase changes. Try 0, 90 and 180 to start to see how much that affects your overall response. Your statement infers that the graphs are of the sub + mains working together? Getting a flat as possible line for this is the best way to go.
     
  8. Mr Incredible

    Mr Incredible
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    ....oh, and just double check the Frequency selection on the BFD. I had a simialr "issue" in not tackling a peak. Turned out I had twiddled the frequency dial on the BFD to 1khz instead of 100Hz. Easily done.
     
  9. allinthemind

    allinthemind
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    hi folks,

    Excuse my ignorance here but what is a BFD? and what does it do?

    Thanks
     
  10. psflynn

    psflynn
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    Big Friendly Dragon.

    If you get a big sub, you will need one to keep it safe from the wife.



    But seriously, Behringer Feedback Destroyer. Not used as such by the peeps in this forum, but can be used to produce multiple fixed notch filters to help smooth the frequency response of their subs to match to the main speakers.

    Amazing value, £50quid ish on ebay.

    Cant wait to get one and post super geeky graphs!

    Cheers

    P.
     
  11. bob1

    bob1
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    By movments i ment small movments ,the phase could help but if the bfd didn't do anything at that frequency the phase won't either as it must be the speakers that are causing the peaks.
    Here's my latest geeky graph.

    [​IMG]
     
  12. Mr Incredible

    Mr Incredible
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    Perhaps the mains are running a little hot impacting the FR above the xover more than below the xover. If the BFD on the sub is genuinely not making any difference to the peak at 112Hz, then it is unlikely it would be affected by turning up the gain a little on the sub. That may help to "level" the apparent peak.
     
  13. Mr Incredible

    Mr Incredible
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  14. Sonnie Parker

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    Hi ya Bob... thought I'd drop in on you guys. Btw... I ordered up a Behringer mic and amp to use with the REW. It shipped out today so I'll be tackling the REW very soon. I may need your help with that.

    You guys like flat huh? I think you'd be happier with a house curve if you'll try it out.

    I'd try measuring the sub alone to start with and later kick in the mains. The BFD is only going to be working on the sub response so you really don't need the mains initially. Just cut off the amp to those or unplug them.

    Here's somewhat of a house curve... mind you, they are subjective...

    [​IMG]

    Check out the GUIDE to see more examples at the bottom of the page.
     
  15. bob1

    bob1
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    Hi Sonnie, i think anyone with a bfd will know who you are, welcome to the forum.
    I have tried a house curve and did like it, to be honest i have so many filters set i forgot which one was the house curve,some of the filters were set up with either speakers set as large or small so i could really do with starting all over again. :rolleyes:
    I did try just using the sub with the bfd and was quite easy to get a smooth graph but as soon as i put the other speakers into the mix everything was miles out.
    You can check out some of my graphs here
     
  16. Sonnie Parker

    Sonnie Parker
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    Thanks bob1... I appreciate the welcome. I think it was Bob (Malice) who actually told me about you guys.

    You've got some good looking graphs. I also have two presets set up... one flat for music and one house curve for movies. I usually just leave it on house even on what little music I listen too, which is mostly DVD concerts.

    When you get a chance, and if you don't mind, combine your raw (pre-BFD) graph with your corrected house curve onto one chart. I'd like to place it on the BFD GUIDE at the bottom with all the other graphs. I'm trying to get a collection of graphs. You know... it would be nice to have a flat graph too.... so if you will do both, I'll place both of them on the page.

    That goes for any others of you that don't mind your graph being placed on the page. You can shoot me an e-mail... I'd also like to put your name on it if you'll provide with a name of some sort.
     
  17. AngelEyes

    AngelEyes
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    Hi Sonnie,

    I have heard house curves mentioned as well as flat curves but haven't ever found a reasonable explanation for the benefits of each.

    Would you be kind enough to do the honours? :)

    Thanks.
     
  18. Mr Incredible

    Mr Incredible
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    :hiya: to Sonnie
     
  19. Sonnie Parker

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    What's up Bob... didn't think I could find ya huh? heehee

    Absolutely AngelEyes... be glad to offer my 2 cents worth on the subject.

    A “house curve” is a cascading response curve that slopes downward from the lows to the highs. This sounds warmer and more natural to the human ear than flat in-room response. It's not always the case for everyone, but generally speaking, critical music listeners want flat. They don't want it any more or any less than what the recording engineer recorded... even though flat typically sounds... well, flat (thin and unnatural). However in movies... most (not all) will generally want impact, rumble, sometimes over-emphasis to feel the effects, as if you were there. A flat response usually won't yield these effects. In my situation, when I got my response as flat as I could get it, I knew I was missing response in the bottom end... the house curve gave that back to me. The house curve gives us a more realistic perception of what we hear, or how our ears hear.

    To be a little more technical... I'll quote Wayne Pflughaupt... he can say it better than I can:

    "A lot of people, especially if they are new to room measurements and equalization, are distressed to see their readings are not flat. However, when they equalize for flat response at the listening position they find that the results are overly bright--very unpleasant, if not unlistenable.

    The mixing engineer is listening to either near-field monitors or other speakers when he/she is laying out the final 'sound' of the music that is being mixed down to 2 (or more) channels. If the physical space and hardware that the mixing engineer is using has been designed properly (including the choice/location/eq. of the speakers for monitoring), the frequency response at their listening position should be flat from 20 Hz to 20 kHz.

    Near-field monitors reduce room reflections due to their close proximity, but they do not escape interaction with the room. Furthermore, they are voiced and designed (in a general sense, via the use of wide-dispersion tweeters and other methods) to resemble the sound of regular speakers at a normal listening distance. Therefore, the house curve function applies to studio situations, too. Measured flat response in the studio sounds as bad as it does in the home. (In actuality, if the studio speakers exhibit truly flat response, the engineer will overcompensate. The result to the end user (that’s us) will be a product that is extremely and unnaturally bass-heavy.)

    The same is true, even more so, with subs. I can’t count the number of threads I have seen where someone lamented, 'My sub’s response is within 2dB from 100 to 25Hz, but it still sounds bad.'

    As we know, most every sub will exhibit one or more response peaks, and eliminating them will result in an improvement. However, eliminating peaks may or may not result in listenable bass. For instance, if the sub is an 8 or 10 incher and the listening area is large, say 6000 cubic ft., the bass will sound anemic at all but low-to-moderate volumes. This is because the little sub does not have the power or extension to properly blend in and 'hold up' its end of the house curve. Likewise, even an adequate sub for a given room may naturally roll out before response reaches 20Hz. If the goal is to achieve response and extension as good as the studio (hopefully) had, there is nothing wrong with applying a gradually increasing boost toward the lower frequencies in order to achieve that objective.

    Actually, achieving a natural-sounding house curve is the best way to 'listen to what is on the recording' and to 'what the mastering engineer heard at the studio.' I used to equalize the bass on many recordings to make it to sound the way I wanted it to. Since I have achieved proper room response, I am confident I am hearing what was recorded, for better or worse."

    Again... remember that not everyone want's a house curve, and not everyone believes they need it. As you can imagine, I've seen a bus load of graphs over the last several years. When you write something like the GUIDE and offer your help to anyone, a LOT of people will take you up on that offer. I've lost count of how many final graphs I've reviewed and nearly (probably 99%) prefer the house curve over flat. That has to speak for something.
     
  20. eviljohn2

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    I'm not a great fan of house curves myself (I'm in the less is more camp) but I can appreciate why people might want them. It's important to emphasise that using a BFD to boost a signal isn't really a wise plan unless you have a massively over-specified amplifier for your sub. :)
     
  21. Sonnie Parker

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    True... boosting should always be used in consideration of your amp. Although it's better to boost one or two frequencies than to cut 7-8 and then have to turn the volume up to compensate, thereby boosting more frequencies. It is all dependent on your amp and your raw response.

    We apply the house curve by cutting.... if you can't naturally build a house curve, you can usually get a flat response and then apply something similar to a shelf filter at 366hz 2 octaves wide and it will give you that nice house curve.

    Here's an example... in some cases it may take more than a 15db cut... you adjust to your preference:

    [​IMG]
     
  22. stevefish69

    stevefish69
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    Sonnie.

    All good and well plotting nice graphs for people to play with regarding house curves but laymen need easy settings (366Hz = ?????? Frequency +- ??????? Fine) if you know what i mean. I found the actual BFD settings for a house curve somewhere on your site but lost them when i re-tuned to 16Hz.

    I'm currently running flat, and wifey is sick to deaf of test tones but sub sounds great, although worried that increased gain for house curve + SVS tuned to have 1 port blocked @16Hz may be eating up Amp headroom, as you increase the main sub gain to match the peak SPL's you are used to.

    BTW i do run my Sub about 5db hot :devil:

    Steve
     
  23. Sonnie Parker

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    Okay... according to the ISO Frequency chart in the BFD Manual (I only have up to 160hz on the GUIDE)... 366hz will be setting your FREQUENCY (using the FREQUENCY button and jog dial) to 400hz. The display will actually read .40khz. You then will set adjust the FINE (using FINE button and jog dial) to -8. This will dial you into 366hz. Then you will adjust your cut accordingly depending on how much cut you need to achieve your house curve slope.

    To determine how much cut you will need in your slope you have to take a couple of measurements. With your response curve adjusted to flat, take your SPL meter and set 28hz to 90db... just play a 28hz tone and turn the volume up until the meter reaches 90db. Pay close attention to how loud it sounds. Then play a 100hz tone and forgetting about the meter for a minute, adjust the volume until it sounds as loud as the 28hz tone... most likely you'll be turning it down. Once it "sounds" the same level, then measure the SPL of the 100hz tone. You may think I'm crazy when I say this... but the 28hz tone is usually going to measure 8-12db higher than the 100hz tone, even though they sound the same. Whatever the difference measured is the amount of slope you want from 28hz to 100hz. IOW... if you measure the difference to be 10db, your goal is to keep the area from 20hz (or 16hz if your sub is capable) to 28hz fairly level or flat... then it will slope down gently by 10db out to 100hz. The 28hz tone will measure at 90db while the 100hz tone will measure at 80db... or 10db less.

    Now to get that 10db slope using the shelf filter at 366hz, you may have to cut 366hz by 15-20db. This will simply take adjusting and measuring.

    Don't worry about overtasking your amp (especially your SVS) because it will appear to sound louder in the bass region at the same previous volume level you are accustomed to, even though you have actually slightly cut the response from 28hz to 100hz.

    How's that from a bonafide country redneck hillbilly. Trust me... I am definitely a redneck, and a hillbilly, and I live in the country on a farm.



    28hz to 100hz are not the chiseled in stone beginning and starting points either. Some like to start at 31.5 or 36hz and only go out to 80hz (typical crossover point). Some start at 25hz. Some slope their entire response. There is a lot of subjectivity in setting a house curve, all depending on your sub, amp, room, taste, etc.
     
  24. kit1cat

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    Hi Sonnie, interesting stuff about the house curse but are you referring to a sub only graph or sub + mains graph. I found it easy to get a flat response with sub only but as soon as I turned the mains on I lost it.

    Thanks for the guide, I would have been lost with out it when I first goy my BFD a couple of years ago.

    Barry
     
  25. eviljohn2

    eviljohn2
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    The end goal when treating any room with EQ is to treat the effect of sub and main speakers combined. Otherwise the main speakers will just ruin the integration as you've found. :)
     
  26. AngelEyes

    AngelEyes
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    It sounds like a house curve is what I am after... I like to feel the bass effects without being deafened by the dialogue (which I am right now).

    To think it too me a month on and off to get a flat response *sniff* :(

    Looks like I will have to send the family away for a week :D
     
  27. SimonO

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    Sorry to highjack the thread, but the BFD forum is down and I want to start tweeking... Before I start, can someone please explain why I would want to measure the sub on its own..? This doesn't make much sense to me as (a) the mains are going to affect the overall frequency response and (b) the eq will only directly affect the sub output...
     
  28. recruit

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    Simon - what frequency is the sub crossed at and are you're main speakers set to large ?
     
  29. eviljohn2

    eviljohn2
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    Measure the sub on it's own to establish what response that has. Measure the speakers on their own to establish what response they have. Then measure both together.

    By looking at the 3 plots you can establish exactly where any problems might be coming from and treat them accordingly.

    For example, if neither the sub nor the speakers exhibit a huge peak at about 80Hz but when combined there is one then you know that it's the interaction between them which is the problem. This is best fixed by tweaking the phase or location of your sub.

    Similarly, any problems caused by your speakers will be difficult to fix so it may be easiest to ignore them first of all rather than spending hours tweaking your BFD and sub trying to fix a problem that's not even related to that part of your equipment.

    The secret is to try and get the best overall picture you can of how your speakers and sub are integrating within your room and then go after each large peak individually one at a time and in the right manner. :)
     
  30. SimonO

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    Xover @ 80Hz and the speakers all set to small, what you've suggested is what I intended to measure first off, it was the interaction at/around the xover that was concerning me...
     

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