Bass Response / Room Equalization

Discussion in 'Archived Threads 2001-2004' started by Kirk Mango, Jan 21, 2003.

  1. Kirk Mango

    Kirk Mango Stunt Coordinator

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    Well, finally figured out how to use my notch filter on the B&K Ref 30. I ended up notching the frequency at 46hz around -6.5dB, with a width of say 38.8hz-52.3hz. With very ineresting results. Here are my measurements at each hz level without the correction factors added in. These are the numbers right off the meter. First set is the hz, second set is the original numbers, the third is after the notch filter has been set. Remember I am only using a -42dB test tone from my preamp for these readings.

    HZDB LvlDB w/notch
    206262
    226565
    247071
    267069
    287271
    307170
    327069
    347069
    367169
    387269
    407672
    427974
    447973
    468074
    487974
    507672
    527471
    547572
    567472
    587573
    607675
    627676
    647877
    667876
    687676
    707575
    727575
    747575
    767574
    787372
    807070
    826868
    846666
    866465
    886564
    906563

    It was interesting to find that the notch filter not only had an effect on the hz fange I set it at but also a more subtle effect in many other areas of the hz range. Anyone know why that is? Wayne?

    As far as the soound went I noticed a smoother cleaner bass response with music and movies. For example, when I played the scene from matrix where Kiano Reeves walks into the building with all the guns and open hands the gaurd in the chest through to where they are on the rooftop, I noticed more musical bass tones. Same held true with several music CD's I am familiar with. The difference was not huge but it was evident. Also noticed a loss of some bass frequency when the Agents bullets passed by Kiano on the rooftop as he bent backwards. Another interesting note is that even though some things sounded the same there was a drop in SPL. Example, I used to get around 99 dB in the scene from ATOC during the ship fly by at the beginning (The 3rd one coming through the clouds)when I set my peamp to -15 below reference. This same scend now regesters about 97dB. the scene felt and sounded the same but did not register the same SPL. Interesting. I should also note that on some scenes like the fight scene in Matrix between Orfeus and Kiano where Orfeus jumps in the air and his knee crunches through the floor I felt and heard the distinct shock of the crunch but then an after shock that was more felt then heard. Kind of delayed. It was not huge but definately there. Also, In the Ice field scene from Titan A&E there is one part about in the middle of the scene, or first 3rd of the scene, where there is very little sound heard but a definate feeling of pressure in the room as the Ice pieces collide and crunch together. Of course there is a lot of low bass all through this scene along with mid and higher tones accompanying the low tones, however, there is that one area where the room just kind of feels pressurized with very little middle and high tones. Weird. Never noticed any of this before. Well, anyone have any thoughts on this, Wayne chime in.

    KM
     
  2. Wayne A. Pflughaupt

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    Chimin’... [​IMG]

    This is the first time I’ve had the opportunity to evaluate the effects of the Ref 30’s notch filter. I have to say if is very effective and surgically precise – a very tight filter that appears to be narrower than 1/6-octave. Either that or it is an excellent design that maintains excellent Q characteristics (i.e., minimizes “spillover” to adjacent frequencies).

     
  3. Kirk Mango

    Kirk Mango Stunt Coordinator

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    Wayne,

    Thanks for all your responses. The Ref 30 only has one notch filter. They said it would take to much porcessing power to have much more. Originally I thought you had to notch each frequency, however, that is not the case. You set the notch, in my case 46hz, and then expand the width of the notch, in my case 38.8 - 52.2, to fit your needs. It is a one time deal. I set the dB at the 46hz level at -6.5 dB and supposedly it rolls off at around 38 and 52hz. The results is what you see in the numbers I've posted. I have considered notching the smaller hump at 60-70hz and seeing if that would bring down the 40-50hz level as well. What do you think? Should I just stick with the lower end because it is a larger hump of almost 10db from 24hz to 46 hz? That same range only has a 6dB difference now. The biggest difference now occurs between 64hz and 36hz (8dB).

    The only thing I am uncomfortable with is that the 32-38hz range dropping below 70dB. I would have hoped that this stayed in the 70's. If I narrow out the notch width I miss the hump at 40hz, it will jump to around 75dB. Wayne what do you think about all this. Should I leave well enough alone. Talked to B&K and they said that it is considered good to have a 10db or less difference in the lower hz ranges say below 100hz. Getting around 6dB difference is excellent and very difficult to do according to them. One of them also told me that the lowest dB in DVD's is around 25hz per article in Stereophile Magazine. Anything below that occurs because of room resonance. The specific example I was given was in planet of the apes where in stereophile magazine they printed that the director said the low was 25hz. Based on all the talk on this forum you would think that there are DVD's out there that dip into the low teens at reference level. Who is correct?

    KM
     
  4. Kirk Mango

    Kirk Mango Stunt Coordinator

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    Wayne,

    Went ahead and played around with it a little more today. I should mention that I have Mirage OM5's as mains in my system. These speakers have two woofers in them with their own 250watt amp per speaker for low bass frequencies (rated down to 22hz +/=3dB). They also have the ability to tune the woofers with two dials. One is + or = up to 6dB the other dial is for the range you want to dial this dB + or = in at. Say from 30 to 150hz. As I said in my last post I was trying to increase the dB level in the lower hz range without disturbing the notched area between 40 & 50 hz. Well adjusting my mains did the trick here are my results along with the first results from at the top of this post:

    HZ / no notch / w/notch / w/notch and adjusted OM5

    20626262
    22656566
    24707171
    26706970
    28727173
    30717073
    32706971
    34706969
    36716969
    38726969
    40767272
    42797473
    44797373
    46807473
    48797474
    50767272
    52747170
    54757271
    56747271
    58757373
    60767575
    62767675
    64787776
    66787677
    68767676
    70757575
    72757575
    74757575
    76757474
    78737272
    80707070
    82686868
    84666666
    86646564
    88656464
    90656362


    As you can see I accomplished this however when you add in the conversions for the SPL meter I end up with a hump of around 77dB at the 28hz level. When I listen to Hotel California on the CD Hell Freezes Over the drumb beat has some kick, however, when going back to the Matrix DVD where Orfius knee crunches the floor the sound blends together with the second lower bass tone. Kind of covers it. Other music tends to be a little boomer, but hard to notice. What do you think is my best set of numbers? Before the OM5's are adjusted up 3 dB or with them left as is?

    KM
     
  5. Wayne A. Pflughaupt

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    Kirk,

     
  6. Dean Mar

    Dean Mar Stunt Coordinator

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    Kirk

    You are getting a nice flat response. As Wayne says, whichever sounds best to you is the way to go.

    I have a B&K AVR305 and it also has the notch filter. I have played around with it a little bit, but I am waiting to get my sub up and running (DIY) before I get serious about room eq. It is nice to see that the notch filter works as well as it does.

    I just hope that it works as well for me and that I can get a response that is that flat ! Every room is obviously different but I never imagined anyone could get that good of a response without adding a separate equalizer of some sort.
     
  7. Kirk Mango

    Kirk Mango Stunt Coordinator

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    Wayne & Dean

    I have to say that I have done some extensive testing and listening. At this point I have decided to just bumpt the 0M5's up just a tad. The set of numbers with only the notch filter engaged had the OM5's settings at 70hz down 3 dB. The last set of numbers, which gave me a hump at the 28hz level and a larger nul at 36hz has the OM5's set to 70hz and 0dB dectrease. Essentially what the manufacturer would call flat. I find that some music with good quality bass in it, not boomy bass, is a little bit to strong. The bass just seems cleaner with the 3 dB drop at 70hz. This is also true with movies. So I have decided to just bumpt it up to a 2.7 dB drop at 70 hz and leave it. So far I am finding that there are definately differences using the B&K notch filter. I am noticing more lower frequencies shaking things with less loud bass which was caused by the hump I had at 46hz. Example. When the Octupus thing in the DVD Lord of the Rings brings down the entrance to the Caves of Mora. I hear less volume but more shake. This is expecially evident in Titan A&E in the Ice Maze scene. There is a spot in that scene right after one of the wings is broken off the ship where there is now real sound you can hear but my couch is definately moving. You can feel pressure in the room but little volume. Before any of these changes I would have to say that I heard more bass then I felt. Now the volume has dropped and there is more feel to what is going on on screen.

    I will keep testing the OM5 settings and may tweak it up a little more. As long as it does not negatively effect the bass in my music.

    I suppose I should note that the differences I hear in the music are very subtle with regard to the OM5 Changes. Most people would not notice the difference.

    My goal has always been and always will be to get exactly what the director intended for me to hear out of any CD or DVD. Clean Clear Solid bass without distortion and which does not step on other sounds, unless the director intended it to do so (as in an explosion), is part of that goal.


    KM
     

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