BFD&speaker problems

Discussion in 'Home Theater Projects' started by PatrickMiller, Feb 7, 2004.

  1. PatrickMiller

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    Im calibrating my sub with the BFD and everything is going good until I tested the satalites and center with the sub. I have test tones 20 - 125Hz. My sub sharply dips from about 90Hz up with a total diff. of about 15dB. My sats and center play down to 56Hz and looks like a roller coaster when graphed. From 100-125hz there is a huge spike in contrast to the subs dip. My center is in an entertainment center in a cubby above the tv which is roughly 8"x20"x20".
    I have a 14'x18'x8'room with an opening in one wall and an entrance to a kitchen and hallway. The sub is corner loaded. I stuff pillows behind the center and it helped some and moving it is not an option. The sats are also in cubbies. I have taken many measurements and Im getting very disheartened. I have pretty flat response from 20-90hz and was hoping to do the 400hz house curve trick tonight! I can smooth it out quite a bit in that upper range by boosting the subs input by 5-10dB but then Im out of headroom for when I get a house curve and raise the level again. My subs volume control is 4/5 the way up to. I dont know how to approach this delima! On top of this Im confused about this;
    Im playing the tones on my dvd player. I cant use a true surround channel because of the cd. Im using pro logic 2 movie. Ive noticed only the center plays these freq. in this mode. In P.L. 2 music they play them along with the center. I also use 3 stereo from time to time with stereo sources.Are there dif. crossover points for diff. sources? This all seems so complicated! HELP!
     
  2. TimForman

    TimForman Supporting Actor

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    I can't comment on your room problems as those are always unique. One thing that comes to mind is your crossover point. If your going to play your mains down to
     
  3. PatrickMiller

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    Im not choosing my crossover point. My receiver gives me no options.How do I use my BFD with my sats and center for midbass equilization? I guess I need to add another piece to the chain, I have a Kenwood receiver and I dont see how I could use the BFD with it except for the sub!
     
  4. ThomasW

    ThomasW Cinematographer

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    Entertainment units are the worst possible places to put speakers. And having speakers in cubbies is problematic too. The baffle step compensation circuit (BSC) in most speakers is designed for them to be placed atleast 24" away from any wall/boundry. So when they're near a boundry (your cubbies)the results are what you see/hear.

    If you want to keep the speakers in the cubbies; then you'll need to change the BSC circuit in the speakers to flatten the response. Or buy and live with another pair of equalizers to flatten the response from all three of the L>C>R speakers
     
  5. Wayne A. Pflughaupt

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    Patrick,

    It’s hard to follow your situation exactly, but here are a few guidelines for EQing and so forth.

    First, the EQ is only for the sub, as you’ve noted. Any equalization you wish to get specifically for the mains, center, etc. will have to come from the receiver. Or you’ll have to get separate equalizers to connect between the pre-outs and main-ins for each channel.

    However, typically EQing the sub is sufficient. Naturally you can expect to see peaks and valleys in response with the sub. If you’re measuring the mains and center as well, you can expect to see peaks and valley there, too. However, you can’t do anything about that, since the BFD is for the sub. So concentrate more on the low frequencies and not so much on the upper range.

    You can expect to see sharp peaks and valleys about an octave above and below the crossover point, due to phase issues. The BFD will be able to address much of this, however.

    When you’re taking measurements generally it’s best to use only the L/R mains, not more than that. It’s impossible to address the phase issues between the sub and every channel, so most people just concentrate on the sub and L/R.

    With all due respect to Tim, I disagree that using more than four filters is overdoing it. Every room is different; some need less than four, some quite a few more. For instance, if you happen to have a non-symmetrical peak or valley – that is, it’s steeper on one side than the other – you can easily “burn” two or three filters just to deal with that. So don't be afraid to use as many filtes as you need. Most of the so-called "rules" of equalizing - cut, don't boost, less is more, etc. - are out the window when you're dealing with subs.

    Hope this helps.

    Regards,
    Wayne Pflughaupt
     
  6. PatrickMiller

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    The problem is my ent. center was made for me by a relative,it really is the center piece of my whole friggin house, so its not going anywhere! It takes up 3/4 of the wall and is only about 6 feet away from my main sitting position. The cubby is above the tv about 6 ft high. I could put it on top but then it would be almost 7ft at about a 70 degree angle if aimed at me! Besides the wife not letting me put it in front on a stand, I believe it would be far to close, especially for other listening positions. The sats are a few inches lower on each side in cubbies. I might get away with using wall brackets for them.
    Heck, Im still arguing with her about sub location! She wants it in the bottom cubby where it only has about an inch of space on every side!Im getting more test tones and experimenting with the speakers(i.e. rearranging, sound dampening, etc.). I dont know how to go inside the speaker to make adjustments. So are the crossover points the same across the board in the diff. modes? Has anyone tried eq'ing the upper range? If I decided to what would be the easiest way put the BFD inline? Thanks for all the help!
     
  7. ThomasW

    ThomasW Cinematographer

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    Sorry but changing to wall brackets won't make any difference. The speakers are still too close to the wall or boundry.

    In order to use EQ you'd need to put the device through the L>C>R channel preamp outputs, if your receiver has these.

    However the correct way to fix the situation, is to rebuild the crossovers (that's where the BSC circuits are), to reflect where the speakers are placed.
     
  8. TimForman

    TimForman Supporting Actor

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    I should know better than to make wide-sweeping generalizations by specifying a number. To rephrase: I believe that less is better based on my own experience and watching others go crazy trying to make "ruler-flat" response graphs with a BFD.
     
  9. PatrickMiller

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    I dont think my receiver has preouts. It sounds like to much trouble to eq each channel. How diff. is it to adjust the crossovers? Where can I learn more about it? Thanks!
     
  10. Wayne A. Pflughaupt

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    In your receiver's and sub's manuals.
     
  11. Kevin Deacon

    Kevin Deacon Second Unit

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    Adjusting the crossovers in the speakers for a novice can become a nightmare. There are whole books dedicated to speaker xovers and they just scratch the surface. In your situation you are stuck, unless you want to spend a bunch of money. You have probably thought about using room treatments to tame some of the freq peaks and valleys, but the wifey will put a stop to it once you try. You are in a difficult situation. Try to get the subwoofer freqs tamed as best you can and live with the rest. Does your system sound bad to you? Play some movies and music - If it sounds good, put the meter away.

    Oh, use as many filters as you want on that BFD. I'm using all 12 for my IB subwoofer and it sounds unbelievable. I found that by bringing all the levels down to meet my valleys was the key in using the BFD. Try not to boost any freqs, just use more filters to bring those levels down.

    Good luck on keeping the sub placed in the corner! I'm very lucky as I have my own room and the wifey can't dictate.
     
  12. Wayne A. Pflughaupt

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    Kevin, this is one of those “rules of equalizing” I mentioned before that doesn’t necessarily apply to EQing subs.

    Actually, boosting or cutting is often academic and ends up with the same results.

    The primary issue the “cut, don’t boost” fans claim is that boosting increases headroom demands on both the amplifier and driver. That’s true, but it’s certainly not the end of the story.

    For instance, let’s say you had two low points at 22Hz and 63Hz. If you follow the “cut only” rule, it would take numerous filters to cut everything else to get the response curve down to where 22 and 63Hz were. After equalizing you would find that overall gain was down substantially, maybe 10dB or even more. Certainly that “bought” you a lot of headroom, but now the sub level is too low to use. Of course, you will have to recover probably that full 10dB to get the output back up to where you had it. So you have to boost the sub right back up. Well - say goodbye to the “free” headroom!

    After re-adjusting your sub level, it would appear that you are now driving your sub as hard as you were before equalizing, right? Nope. The situation now is that you have much flatter response. This means the frequencies that were underrepresented before ( 22Hz and 63Hz) are now being driven harder than they were before equalizing. That’s right – you’ve succeeded in boosting those low areas, whether you intended to or not.

    So – anyway you cut it, subwoofer equalizing places increased demands on the amp and driver. It’s unavoidable. So don’t worry about setting filters for boost if it’s a more efficient way to flatten response. It would have made much more sense to use a couple of filters to boost the low spots instead of multiples to lower everything else, and it would have accomplished the same thing in the end.

    Regards,
    Wayne A. Pflughaupt
     
  13. Kevin Deacon

    Kevin Deacon Second Unit

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    Hi Wayne, point well taken. In my situation I had two low points that no matter what I tried, wouldn't boost. These two points I was told were room nulls and were almost impossible to equalize. So by using the 12 available filters I was able to achieve a flat response up to 125hz.

    Thanks for your insight.
     
  14. Wayne A. Pflughaupt

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    Kevin,

    Yes, room nulls can’t be equalized – even by cutting everything else down to their level. When you boost the sub’s gain back up, the nulls will re-appear.

    Regards,
    Wayne A. Pflughaupt
     

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