Can a BFD flatten this?

Discussion in 'Archived Threads 2001-2004' started by Gregg Petrarca, Apr 11, 2002.

  1. Gregg Petrarca

    Gregg Petrarca Auditioning

    Joined:
    Apr 11, 2002
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    Hi, I just received my 16-46PCi and I'm wondering if a BFD could flatten my room response. I ordered one and should get soon but I'm wondering if a satisfactory result is possible. Basement HT 21' long x 14' wide by 7' high closed off room. Mains along the short wall with sub in front left corner. Here is the raw curve.
    http://link.freepichosting.com/image...pg?x=600&y=400
    Please advise your thoughts!
    Regards,
    Gregg
     
  2. Steve_Ma

    Steve_Ma Second Unit

    Joined:
    May 7, 2001
    Messages:
    420
    Likes Received:
    0
    Trophy Points:
    0
    Holy Cow! That's some serious woofage below 30hz. Is it fair to assume you've already calibrated and experimented with placement as much as possible?

    Although I don't own the BFD (yet), I would think that you could still bring down that peak at 80 and level off the
     
  3. Richard Greene

    Richard Greene Stunt Coordinator

    Joined:
    Mar 5, 2001
    Messages:
    148
    Likes Received:
    0
    Trophy Points:
    0
    The BFD is the least expensive solution to your problem.

    I recommend that you use it to pull down frequency peaks

    and ignore the frequency troughs.

    The 80Hz. peak is from the floor-to-ceiling axial room mode

    (565 / 7'(floor-to-ceiling) = 80.7Hz. room mode
     
  4. brucek

    brucek Second Unit

    Joined:
    Dec 29, 1998
    Messages:
    335
    Likes Received:
    0
    Trophy Points:
    0
    Gregg,

    It shouldn't be too much trouble to make that response a lot better.

    I guess this graph is including your mains since there is no roll off indicated. You might want to start with the sub only when you begin equalizing.

    Obviously you'll have to bring down the 80Hz area and then work on that large peak from 28Hz and lower, that I suspect your room is boosting too much. If you reduced that area to about 90dB, it would go a long way to smoothing the sound.

    Play with the Excel graph a bit by entering values now into the "filters with BFD" column to get a feel for "what if" I reduce this area etc. First copy the "no filters" values into that column for a reference and then play with values you would like the EQ to work on. This will give you a good feel for what will be required when you actually need to start entering values into the BFD front panel.

    brucek
     
  5. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    1
    Trophy Points:
    0
    Double check the deep boost switch on the PCi amp to make sure that it isn't activated.
     
  6. Sonnie Parker

    Sonnie Parker Second Unit

    Joined:
    Dec 11, 2001
    Messages:
    407
    Likes Received:
    0
    Trophy Points:
    0
    That dip could get really nasty to deal with, but, I definitely believe you could get a nice house curve going.
    Don't you think so Ken?[​IMG]
    That a very unusual looking response to say the least.
     
  7. Matthew_Judd

    Matthew_Judd Extra

    Joined:
    Jul 14, 2001
    Messages:
    24
    Likes Received:
    0
    Trophy Points:
    0
    OK. I'm pretty new to HT but had thought I had gotten beyond the "what the heck are they talking about" stage. I guess not. What is a BFD?

    I read through a few posts on BFD, but if you don't already know what they are talking about it is pretty obtuse. OK, I get the general idea, but would like a more comprehensive source of information?

    Perhaps someone could post a link?

    Thanks
     
  8. Steven Hen

    Steven Hen Stunt Coordinator

    Joined:
    Feb 26, 2002
    Messages:
    143
    Likes Received:
    0
    Trophy Points:
    0
  9. Gregg Petrarca

    Gregg Petrarca Auditioning

    Joined:
    Apr 11, 2002
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    Bruce, you were right, I did have the mains on. I did a new curve with the mains off. It looks quite a bit more manageable.
    Sonnie, my BFD came in today and I just started playing with it after printing out and reading your page and following the links to Bruce's work as well.
    It does appear the dip will be troublesome. I tried to increase the gain at 70hz by +16 and could only raise it 1 db. Would it be best to work the the lower freqs down by 20db towards the 71hz? I've got plenty of headroom as the receiver is about 25% and the BASH amp is 1 click before 1/2 way.
    Thanks guys for all your efforts and the education. Starting to see things clearer. I'll try and post some results. If you have any suggestions feel free[​IMG].
    Here's the redone raw curve
    http://link.freepichosting.com/image...pg?x=600&y=400
     
  10. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    Gregg,

    This is a bit of topic but what program did you use to make that chart? I've been wanting to make one for my sub but could not find a program that would let me.

    Ryan
     
  11. Wyatt_Y

    Wyatt_Y Stunt Coordinator

    Joined:
    Jan 22, 2002
    Messages:
    74
    Likes Received:
    0
    Trophy Points:
    0
    Re: Big Dips....

    I had a big dip at 63hz bordered on each side by peaks. I got everything pretty flat except for a narrow -8db dip at 63hz - this with a filter set at 63+0;BW=17;gain +16.

    For the heck of it I added a second filter at 63+0;BW=5;gain +7 and it the resulting measurement came out very, very flat. I don't know about the advisability of multiple filters at a single center frequency (phase, etc.???) but it worked to eliminate the dip.....

    Wyatt
     
  12. Gregg Petrarca

    Gregg Petrarca Auditioning

    Joined:
    Apr 11, 2002
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    Ryan, follow the link to Sonnie's BFD Comprehensive Setup Guide on Steven's reply and at the bottom of the page there is the link to the Microsoft Excel Workbook or else get it here Microsoft Excel Workbook.
    Wyatt, I'll look into your suggestion. Thanks...need some sleep.
    Gregg
     
  13. brucek

    brucek Second Unit

    Joined:
    Dec 29, 1998
    Messages:
    335
    Likes Received:
    0
    Trophy Points:
    0
    Gregg,
    I don't think you mentioned what your crossover is set at for this graph - is it 60Hz or 80Hz?
    Your axial resonances as calculated from your dimensions would be at 26.9Hz/40.3Hz/80.6 Hz.. That would seem to be in line with your results.
    I'm sure you already know, but you have to be careful with introducing "gain" with an EQ. If you have some headroom, give it a try. I would not go over +10dB. That's asking a lot of your amp.
    Sometimes no matter what you throw at a frequency, it just sits there, like a black hole. Giving it more boost from the equalizer just eats up headroom. There are some valleys in your response you sometimes have to live with that can't be EQ'd away.
    Moving a seating position can help with that, if possible. Usually we EQ for the prime listening position or average for the front row.
    You have enviable low end extension, which would probably be attributed to your large closed room and a capable sub. Most people would love to have your "problem" from 28Hz down to 16Hz..... [​IMG]
    brucek
     
  14. Gregg Petrarca

    Gregg Petrarca Auditioning

    Joined:
    Apr 11, 2002
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    Bruce,

    I've got the subs crossover disabled. With the main speakers set to small on the Yamaha the crossover is 90 Hz. The main speakers are Diva 6.1's which extend to 30 Hz. Any recommendations?

    Thanks

    Gregg
     
  15. Sonnie Parker

    Sonnie Parker Second Unit

    Joined:
    Dec 11, 2001
    Messages:
    407
    Likes Received:
    0
    Trophy Points:
    0
    Gregg, you know with that dip at around 70hz, you might try setting your crossover to 70hz. That's still a full octave over the Diva's limits. It's an option to consider playing around with anyway.
     
  16. Gregg Petrarca

    Gregg Petrarca Auditioning

    Joined:
    Apr 11, 2002
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    Sonnie, the Yamaha crossover is fixed at 90hz. I won't be able to get seriously into the BFD until tomorrow evening. Thanks,

    Gregg
     
  17. Wayne A. Pflughaupt

    Moderator

    Joined:
    Aug 5, 1999
    Messages:
    6,187
    Likes Received:
    51
    Trophy Points:
    9,110
    Location:
    Katy, TX
    Real Name:
    Wayne
    Others here have written:

     
  18. Sonnie Parker

    Sonnie Parker Second Unit

    Joined:
    Dec 11, 2001
    Messages:
    407
    Likes Received:
    0
    Trophy Points:
    0
    Gregg,

    If your Yamaha crossover is fixed at 90hz then you'll probably have a time working with that one 70hz dip. But you still should be able to get a nice house curve.

    From my witnessing and experience with the BFD, I believe you'll do fine if you use a few filters to cut the lower portion of your response a little. You could try a filter or maybe two on the dip. It may work out good, then again, it may not. I would not try to use too many boosting filters.

    Either way, only you can be the ultimate judge of which is going to work for you.

    I look forward to seeing your results.
     
  19. Richard Greene

    Richard Greene Stunt Coordinator

    Joined:
    Mar 5, 2001
    Messages:
    148
    Likes Received:
    0
    Trophy Points:
    0
    Troughs in the frequency response that are caused by room acoustics can't be fixed by equalization, so if you want a flatter frequency response using equalization, you have only three choices:

    (1) Reduce SPL of non-trough frequencies to match the

    SPL of the trough (not useful here because the trough is only 70dB and won't get much louder no matter how much you turn up the volume, as Wayne correctly explained in his last post)

    (2) Reduce SPL of non-trough peaks (and "plateaus") to an SPL you can live with (less than 100dB)

    (3) Ignore the trough(s) and boost all OTHER frequencies

    to match the SPL peaks at about 100dB

    I would use (2) because I listen to music at an average SPL of only 75-80dBA with my subwoofer 3-6dB louder ... but it now occurs to me that some people prefer bass a lot louder than I do -- they should consider (3) if they prefer 100dB or higher bass.

    A better alternative is to experiment with different seating positions (if feasible) -- the trough may quite a bit shallower if you move your seat three to five feet.

    The frequency response chart showing the loud frequency response "plateau" from 16Hz. to 28Hz. is a very unusual

    shape for a single 12" woofer.

    Given the high SPL (100dB) used to measure these very low frequencies, I would expect that a portion of the SPL measurement is doubling (harmonic distortion) primarily one octave higher ... and possibly some room noises too.

    To test my theory, I would recommend that these measurements be done again at about 80dB, rather than 100dB, to get a more accurate measurement of actual output below 28Hz. (with a lower level of harmonic distortion and room noises at other frequencie included in the numbers).
     
  20. Sonnie Parker

    Sonnie Parker Second Unit

    Joined:
    Dec 11, 2001
    Messages:
    407
    Likes Received:
    0
    Trophy Points:
    0
    Very good point on the starting point Richard. I usually start with a reading of about 74-75db spl on my RS Meter (which with compensation results in about 85db). This could indeed give you a different looking response.

    And as you mentioned....location could be key.

    Gregg, do you have the sub shoved all the way up in the corner? You might try moving it around a little and seeing what response line you get. I would start by getting it as close to the corner as possible.

    Also, you mentioned above that you had tried a boost of 16db at 70hz and only got a 1db increase. While you may not be able to increase 70hz, you might be able to narrow the dip by trying a couple of filter boost somewhere around 63hz and 75hz (on both sides of the dip). I know this has worked for a few others, including myself.
     

Share This Page