BFD setup samples

Discussion in 'Archived Threads 2001-2004' started by MikeHalder, Feb 17, 2002.

  1. MikeHalder

    MikeHalder Stunt Coordinator

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    Well I am collecting data for setting up my BFD tommorrow and wanted some suggestions on filter placement/setting based on my data. The two worksheets show the freq response with my base management in place @50HZ and the mains turned off (A/B switch), and the second with a direct feed of the tones without base management or crossovers in line. This is my first attempt at EQing using measured data instead of personal preference, any help or suggestions would be GREATLY appreciated.[​IMG]
    Mike
    Base Management
    No Base Managemnt/Crossovers
     
  2. Larry Rasmussen

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    I've been following the equalizer set up threads with interest because I plan to get a BFD to use with my SVS. I believe that you would want to measure with the crossover or bass management you are going to use on and the front main speakers also on. I bet if you post that measurement you would get some specific ideas. You may find that you have a hump or a dip around crossover depending on the response of your mains.
     
  3. MikeHalder

    MikeHalder Stunt Coordinator

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    All the folks who have poated on this subject have recommended EQing the sub only w/o the mains. I put both grapphs on the same chart and foun that the follow the same pattern with or without the base management except for a few dB drop after the 50HZ where the crossover slope comes into play. If I figure there should be a 12dB/Octave slope in the graph at 50 HZ...I think thats the way it should look with base management in place.

    Mike
     
  4. brucek

    brucek Second Unit

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    Mike,
    What you have done is quite correct. You don't want the mains involved at this point.
    I think one piece of information that is really useful when you're doing this is to know what effect the room has on your sub. Although you don't have an anachoic chamber, doing a near-field measurement tends to give you a better look at what your subs output looks like if you took away the room influence.
    This information would tell you if the dropoff below 25Hz and the rise between 22Hz and 45Hz is caused solely by the room or you have a great room and this is simply the response of your sub.
    In that regard, I suspect the room is giving you the 22Hz to 45Hz peak because since your cross is at 50Hz, you got a typical 4th order drop from 50Hz to 100hz if you corrected the dip directly at 50Hz.
    My attack would be several cut filters (maybe 3 @25 @31 @40) spread across to correct from 22Hz to 45Hz (don't spread your bandwidths too wide) and then a bit of a boost at 50Hz. And then assume the drop below 22Hz is natural for your sub. You could maybe try and cut @80 a bit too.
    That would be my starting point. Regraph after that and make further decisions..... Others may disagree.. [​IMG]
    brucek
     
  5. Nick P

    Nick P Second Unit

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    O.K. guys, I'm confused as to why you are equalizing with the mains off. Most (or at least some) people have a peak or a valley when the mains crossover. If you EQ with the mains off and then turns the mains on there will still be either a boost from the mains sloping in or a valley from cancellation. Right?? I'm going to try the BFD also in the next day or two also but it doesn't make sense to me to EQ with one of the main problem areas addressed. At least it's a problem in my situation.
     
  6. brucek

    brucek Second Unit

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    Nick,
    You may misunderstand here. The recommendation is to carry out the equalization with the sub only and to remove all the peaks created by the room. This is the function of a sub equalizer. At this point you're not interested how well your processor takes care of its bass management duties at the crossover points. Most of the problems caused by the room will be concentrated in the very low end anyway.
    Once you're satisfied with your equalized sub, then by all means turn on your mains and carry out a new set of readings and evaluate the new graph. Now any interaction between the mains and sub because of phasing or crossover points can be tweaked if necessary.
    That's my take on it anyway. [​IMG]
    brucek
     
  7. Patrick_T

    Patrick_T Agent

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    I'm with Nick on being confused about calibrating with mains off. Aren't we interested in flattening the reponse of the system, not just the sub. Say that we have a mode around 60Hz with a crossover frequency of 80 Hz...both the sub and mains will be outputing at this frequency and will lead to an overall larger bump in the output at this frequency, and thus we would want to cut the output at this frequency on the BFD. If we did this before putting the mains in then when we put the mains in we would get a bump at 60Hz again. A previous poster mentioned calibrating without mains and then repeating with the mains afterword....why do this twice...what are the benefits? I in no way doubt the posters who have done this more than I...but I was just wondering if someone might explain specifically the reasoning. Thanks again.
     
  8. brucek

    brucek Second Unit

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    Patrick,

    My feeling is that you want to eliminate as many variables as possible when you are doing this. It is a time consuming and difficult enough task without trying to guess whether a peak is coming from an interaction between two speakers or as a result of the room.

    As I previously said, most of the peaks, and the most effect of adding these filters will be in the lower frequencies less than the crossover. It is the sub we are trying to equalize, it has most of the energy less than the crossover, so the first order of business is to equalize the sub. The energy from the mains in your example is quite a bit less at the frequency below cross. Once the peak is filtered out for the sub, the lesser energy provided by the mains at this frequency isn't likely to overcome the filtered sub.

    Once you've accomplished this "sub only" equalization and add in your mains, you will likely (if at all) only have to touch up. If you see a peak at this point after adding in your mains, it may be an interaction and perhaps not a room mode. This then might call for some phase adjustment or slight speaker movement rather than a filter. Doing it this way arms you with more information overall when you're finished.

    Again, this is the way I did it and it seemed to work. I know others have had success this way and found it difficult to get accurate readings when all the speakers were turned on. But if anyone thinks having all the speakers on is an easier way, then they should definitely try it.

    brucek
     
  9. gomez_a

    gomez_a Stunt Coordinator

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    Brucek, I see your point about plotting the SPL of the sub only, then going back and plotting the system's overall SPL with the mains and sats on, now at this point, I woukld think you would want your mains set to "SMALL" as the sub(s) provide plenty of low end anyway, right?
     
  10. Nick P

    Nick P Second Unit

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    Bruce,
    I follow what you're saying but it just seems like you're doing things twice by EQing the subs w/o mains and then going back and re-checking w/ mains. I can clearly see on my graph for my system were the peaks and valleys are under my crossover point and I can address those. I then have a whole new set of problems 10db under and 5db over my receiver's crossover at 80hz. With my mains off I don't have these problems. If I EQ everything with my mains off then I still have those problems with my mains are turned back on. All I'm suggesting is it might be better to leave the mains on. All these people EQing with the mains off may think they have a super flat response only to unknowingly have a non-flat response when they hook their mains back up. Just thinking out loud here. [​IMG]
     
  11. gomez_a

    gomez_a Stunt Coordinator

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    Dr Wayne [​IMG] , what's your take on this debate?
     
  12. Larry Rasmussen

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    Mike, I'm the guy that suggested mains off. I wanted to say I stand corrected (perhaps).
    As a matter of course I measure response for my subs and mains (both with and without
    X-over) even though I am not equalizing. Given the recommendation to EQ the sub first then go back and do again with mains engaged I believe it would be very educational to have you post your responses for this second step. It would be very interesting for someone to EQ using the two step method vs the one step with sub and mains on and see if there is any variation in ultimate
    settings. You wouldn't think there should be. Anyway this is one of those good learning threads, thanks posters.
     
  13. Dennis B

    Dennis B Stunt Coordinator

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    I've been doing this the way brucek has described, since it's also the way others have suggested, and find that although the ultimate goal is to flatten the response along the whole frequency range, doing it speaker by speaker and staring with the sub has given me a great level of understanding of how each speaker contributes to the overall result and how they interact with each other. It's very time consuming, though, that's for sure.
     
  14. brucek

    brucek Second Unit

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    Dennis is nicely making the point I have been trying to get across. Ultimately you want to have an equalized sub that integrates with the main speakers. This isn't a race to the finish - it's a hobby, and the more information you can gather the better. There are an enormous amount of interactions between speakers and subs and rooms. If you can eliminate as many variables as possible, you make less assumptions and more true information is gathered, although it takes more effort to get there. In the end, this information may help you better understand and setup your system.
    In setting up my system, I had quite a few peaks to work on with the BFD. Once completed, after adding in the mains, there were no surprises. Maybe I got lucky. My feeling was simply that once the sub was equalized by itself, that the energy from the mains, common to the sub frequency range, would be much lower because of the mains cross and wouldn't have enough effect to disturb my equalization.
    If you read the DEMO ROOM tutorial for ETF5 spectrum analyzer software at:
    http://www.acoustisoft.com/index.html
    it goes through the method of setting up a set of speakers in a demo room. They go one step further and do the sub alone first with no cross and then each main speaker alone without a cross and then the sub and mains together with the cross to integrate them. Interesting stuff on this site. Lots to be learned there.
    I guess if you're in a hurry and you're feeling lucky, why not turn on all your speakers and setup your BFD filters all in one shot. I guess in Nicks and Patricks defense, thats how we'll ultimately use the system. You'll have to let everyone know how it goes when you're finished.
    brucek
     
  15. BruceD

    BruceD Screenwriter

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    Brucek makes a valid point here.

    You don't really know how all the speakers are interacting with each other if you measure with all of them on at the same time.

    How can you optimize the location of each speaker when you are measuring all at the same time? You can't.

    Maybe your current speaker locations are not ideal for your room. You may never know measuring everything at once.

    I've been using ETF5 software for the past 2 years and can't say enough about how much it has taught me. Their demo room example is a very good model for optimizing sound quality from speaker/room placement.

    I would recommend everyone serious about getting the best sound out of their system to go there and read it.
     
  16. Rick Radford

    Rick Radford Supporting Actor

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    >If you read the DEMO ROOM tutorial for ETF5 spectrum analyzer software at:<

    I forgot about the Demo Room for ETF5. That would probably answer my question about integrating the mains and the sub using ETF.

    Ah well. Back to the ETF site!
     
  17. Kevin C Brown

    Kevin C Brown Producer

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    There's another bonus you get when you do them separately (sub alone, and mains alone) then together (mains + sub):

    You get to make sure that you phase is set correctly.

    Slightly below, at, and slightly above the crossover point should measure higher with both mains + sub playing, vs sub alone or mains alone.

    And one last bonus, is that I actually tried to *depress* some of the peaks in my sub to compensate for peaks I *also* had in my mains (near the crossover point). Didn't work very well.

    (That's why I'm still looking at trying to eq my mains, once I make my test disc and measure...)
     
  18. Larry Rasmussen

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    Ok, now I get the reasoning. Measure separately to gather information to better understand what is going on. For years I have measured subs and sats separately with and without Xover, together with sat full range and then with X-over, varying X-over range if available with whatever pre amp I happen to have, then listened extensively to the combination of choice, tweaking as I go. I guess I thought this would be a given for everyone considerating equalizing, how else would you know you need an equalizer?

    My assumption was that a person would have sub location, X-over settings, relative levels, phase etc dialed in before even getting out the credit card for the BFD. I'm convinced to do the sub first though when equalizer arrives given this thread. As pointed out, it's not a race. I appreciate the perspectives offerred.
     

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