BFD and "home curve"

Discussion in 'Home Theater Projects' started by JohnGil, Jan 12, 2004.

  1. JohnGil

    JohnGil Stunt Coordinator

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    Well I bought a BFD the other day and have been reading post after post on EQing subs. Im fairly new to the EQing realm and all these posts are starting to make my head spin. The more I read the more I'm convinced that using "Home Curve" is the way to go. Now through all this reading I have yet to read how to determine exactly what the "Home Curve" is and how I go about determining it in MY room.

    From what I gather, the home curve is the natural response of the room taken with the RS SPL "C" whighted and "slow" response with no correction factor. Then you would use the BFD ParEQ to tame the peaks based on this raw data.

    I'm trying to take the info I need and apply it without too much technical junk getting in my way (keeping it simple).
     
  2. Wayne A. Pflughaupt

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    John,

    I could set you up with some "all about" links regarding a house curve, but my computer is down for repairs so I don't have access to my references right now.

    It's not hard to do a house curve. All you need is a program source with 1/6-octave sine-wave test tones, some graph paper and an SPL meter.

    As you may have already figured out from your research and reading, a house curve is response that sounds flat rather than measures flat. This means that with a house curve, lower bass frequencies will measure higher than upper bass frequencies.

    The reference points I like to use are 32Hz and 100Hz. To get the house curve your room needs, those two frequencies should sound like they are the same volume. Measured response between those two points should be as flat as possible, which means you end up with a rising slope. It usually sounds best if response is shelved (measures flat) below 32Hz.

    Hope this helps,
    Wayne A. Pflughaupt
     
  3. Allen Ross

    Allen Ross Supporting Actor

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    what kind of slope/gain are you looking at from 35-100HZ?
     
  4. JohnGil

    JohnGil Stunt Coordinator

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    I could set you up with some "all about" links regarding a house curve, but my computer is down for repairs so I don't have access to my references right now.

    It's not hard to do a house curve. All you need is a program source with 1/6-octave sine-wave test tones, some graph paper and an SPL meter.

    As you may have already figured out from your research and reading, a house curve is response that sounds flat rather than measures flat. This means that with a house curve, lower bass frequencies will measure higher than upper bass frequencies.

    The reference points I like to use are 32Hz and 100Hz. To get the house curve your room needs, those two frequencies should sound like they are the same volume. Measured response between those two points should be as flat as possible, which means you end up with a rising slope. It usually sounds best if response is shelved (measures flat) below 32Hz.

    Hope this helps,
    Wayne A. Pflughaupt
    -----------------------------------------------------------

    Thanks Wayne, The info does help. I plugged in the BFD last night and went thought the on line crash course. After going through it a couple times its very easy once you rember how to operate it. I will try and attach some graphs when im done. I did have a 13db rise from 18-24hz then it droped off quite a bit with a large dip centered at about 39hz (bad spot for a dip) which was down 13+/- then after that just a couple small peaks which are no big deal.

    Now,if I were to lets say bring all my levels down to compensate for my large wide dip at 39 (which would bring down the level of the sub) would I then just adjust the gain on the sub to make up for the reduced levels?
     
  5. Wayne A. Pflughaupt

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    I don't recommend doing that. It makes no sense to equalize everything in sight except the place there the problem actually is - it certainly isn't econnomical use of an equalizer.

    It sounds to me like you hooked up with one of those threads where someone said you should always cut, not boost - supposedly because boosting "burns" headroom and cutting does not. That's well and fine when EQing the upper frequencies, but for subs it's nonsense.

    For instance, say you did cut everything across the board down to the 39Hz low point, so it appears you've gained lots of headroom. But then (as you noted) you have to increase the sub's gain to get the volume back up. Well - say goodbye to the "free" headroom!

    Also consider that you now have flat response, whereas before you had a hole at 39Hz. So - you've actually succeeded in boosting that 39Hz low spot, even though you never applied a boosting filter.

    Bottom line, any equalizing will place additional demands on both your sub and amp, so you have to have sufficient headroom going in. So don't be afraid to use whatever equalization you need to get the response curve you're after. IMO it's best to get the job done with as few filters as possible. In most cases, this is accomplished with a combination of both boosting and cutting filters.

    Just watch out for a low point that won't respond to equalizing. That will be a null, so don't waste any headroom there. However, you'll probably find that most low points will equalize nicely.

    Hope this helps.
     
  6. Troy R

    Troy R Stunt Coordinator

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    I've got a question about the BFD if you don't mind a small thread hijak? [​IMG]

    I've read that the BFD causes a 1ms delay in the signal. With an HT rig you can just change the distance to the sub to account for the delay. However, I was thinking of getting one in the future to EQ a sub in my two channel rig, how could I account for the delay on a 2 channel rig that cannot change the distance to the sub?

    Or would I be better off with another type of EQ?

    Thanks,
    Troy
     
  7. Wayne A. Pflughaupt

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    The particular equalizer is pretty much irrelevant. The best way to deal with delay is to have a sub with a continuously vafriable phase control. Or get a digital delay processor from the pro audio world.

    Regards,
    Wayne A. Pflughaupt
     
  8. Troy R

    Troy R Stunt Coordinator

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    Thanks Wayne, that's what I wanted to hear.

    I plan on using a cossover (like the paradigm X30, or Outlaw ICBM) with the BFD. Now if I could just afford to buy it all! [​IMG]
     
  9. JohnGil

    JohnGil Stunt Coordinator

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    It sounds to me like you hooked up with one of those threads where someone said you should always cut, not boost - supposedly because boosting "burns" headroom and cutting does not. That's well and fine when EQing the upper frequencies, but for subs it's nonsense.
    -----------------------------------------------------------
    As a matter of fact thats exactly what I did and I read it probably 15 or more times.

    I'll take some readings forward and back from my primary seating position and see and if I can get out of the null. Im sure it is a null too. I boosted levels in that area to see if I could make a difference but the changes were very minimal.

    Thanks for all the help Wayne its very helpful.
     
  10. ChuckRG

    ChuckRG Agent

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    Wayne:

    A couple of questions and one comment:

    (1) Do you recommend setting the "house curve" into the BFD prior to making the adjustments or afterwards?

    (2) Is your house curve flat to 30Hz (from 20Hz) and then drops to 100Hz (down 3 or 4 db)?

    I can assure you that adding boost, if not done with common sense, can easily bottom out any sub/and or clip any amp. For example, add about 8 db at about 50 Hz with a fairly narrow Q and play about any DVD with big bass. So while some boost is OK, it must be done judiciously.
     
  11. Wayne A. Pflughaupt

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    In most home theaters the slope will be much steeper than that - unless your room is as big as say, a cathedral. It's not uncommon to see slopes with differentials of 12dB - or even more.
     
  12. Saurav

    Saurav Cinematographer

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    FWIW, here's my before and after plot with my BFD:

    [​IMG]

    This is with the sub running 'full-range' and no mains, with the mains mixed in they're both crossed over at 12dB/octave at around 100Hz or so.

    Here's the full thread if you want to read it:

    http://hometheatertalk.com/httalk/viewtopic.php?t=2988

    It goes without saying that none of this would have happened without the help of people like Wayne.
     
  13. ChuckRG

    ChuckRG Agent

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    The "fixed" curve is obviously a lot better (that is one nasty bump at 36HZ---what are the dimensions of your room). However, you still have a fairly substantive bump (8 to 10db) from 45HZ to 70 HZ. Do you have any sense of boominess at all???
     
  14. Saurav

    Saurav Cinematographer

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    Actually, it's a dip at 45Hz that doesn't really want to go away. 50Hz and up is close to 40Hz and down. And if you look at the average, it sorta slopes down from 25Hz to 80Hz. I'm still playing with boosts at 45Hz and 71Hz, they help a little at my listening position but they become overpoweringly loud when I stand up (so it's a vertical standing wave, I think), so I'm not sure if they're worth it, considering the neighbors and all [​IMG] I got this curve with 3 filters active, so I have room to experiment with EQing the smaller peaks and nulls.

    It's probably still a little boomy, but it's *so* much better than what I had before. I just came back from a day at CES, and I think the bass in my room (regular living room, no room treatments) was better than 90% of the rooms I heard. Most rooms either didn't go down low at all, or were really boomy.
     

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