Playing with the "House Curve"

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

  1. ColinM

    ColinM Cinematographer

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    I just got my ART351 in line with the old driver 20*39CS and a PE250, and flattened it out according to 1/3 RTA and Spectra. Sounded a bit weak, and while I like accurate and all, I decided to try this...

    Using an SPL meter on a tripod, right at the ear's sweet spot, I cal'd it to zero/80db at each slider up to 100Hz. This meant having to boost 20Hz by 8db or so, taking away slightly on a couple, and boosting another by 2-3.

    I can get away with -6db from ref on the THX ball in TPM, anything louder SCARES ME. I haven't tried it yet full up, and likely won't because my HK AVR110 runs out of poop with NHT's all around.

    Music sounds fine. I listened to the entire Tommy album and it was better than ever before.

    Anyone think I'm nuts? It's been a long winter.......
     
  2. Ned

    Ned Supporting Actor

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    +8db at 20hz is a pretty big drain on headroom. Did you order the driver upgrade yet? It is a very significant upgrade. With the old driver TPM THX intro would always bottom out at even -3db under reference in my small (10x12x8) room that has no openings to other rooms. I have the ART351 also and highpass filter at 19hz so that gave me a little more headroom even.

    The new driver can play it at -3db easily and the whole room pops when the ball explodes and then the floor vibrates near the end when the THX logo comes up. There were a few places in the Pod race where I could hear the old driver reaching it's limits but the new driver plays through them easily and at even louder volumes.

    So if you haven't already ordered it, definitely consider it. The upgrade is anything but subtle.
     
  3. ColinM

    ColinM Cinematographer

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    I almost have to look every time I fire it up, it seems as if the ISD is already in there, but it's not.

    I checked the accuracy of that 'rumble' filter with a 20Hz tone, and found that it starts to roll off the 20 when dialing up to ~16. So actually you may be cutting off the stuff slightly above 20. YMMV, as tolerances may not be tight. But my RF is set to ~14, which is where I couldn't discern any attenuation of the 20Hz tone.

    I could play full ref +1-3db easy before EQ. The mains were likely clipping, but the sub didn't bottom, with either 165 or 250 watts behind it.

    I have yet to bottom the thing.

    Maybe I need 300+ watts to do it, but that would eclipse the performance of the rest of the system, so not necessary...yet.

    2400 sq ft, one stairway with an open door at the top, another open door in the back of the room.

    I need more power for the mains.

    - C
     
  4. Wayne A. Pflughaupt

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  5. ColinM

    ColinM Cinematographer

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    You know how the SPL meter drops off down low?

    I just kept the needle at zero with the EQ.

    Playing around again last night I hear that some fine tuning is in order, but I love the effect on movies.

    - C
     
  6. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    ?
     
  7. ColinM

    ColinM Cinematographer

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    Yup.

    hehe

    I've heard "gentle 8dB rise to 20hz" describe the house curve theroy, and If I follow that plan and keep the needle at zero, I am also eq'ing the room at the same time.

    Seems to work.

    When the invasion landing craft decends from space and then flies over your head in TPM, I could tell there was bass there, but nothing really happened before EQ. Now my couch shakes 1/4" back and forth at about 18Hz, -6 from ref.

    Qwazy....
     
  8. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    I used the same method (zeroing each slider to let the meter's inaccuracy dictate the curve) to EQ my 20-39CS+ and I really like the results. I graphed the corrected response afterwards, and other than an unavoidable 5db drop at 56Hz, I've got a nice steady curve. In my room, I was able to play SW:TPM at about -2 from reference before I stopped for fear of blowing the windows out, and that's the only time I've seen the clip light even flicker on the Samson 1000.
    Of course, my cat decided to play with the ART's sliders last night, so now I have to do it all again. And thus, the cat must die. [​IMG]
     
  9. Ned

    Ned Supporting Actor

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    Colin-

    I set my highpass using a 20hz sine wave rather than trusting the markings on the knob. For what actually filters at about 19hz and under, shows 12 on the markings. So may as well scratch the labels off completely because they are totally wrong.
     
  10. Chris PC

    Chris PC Producer

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    This reminds me of how much I miss the old loudness control. I listen to music at lower volumes sometimes and I used to use my old amps loudness control to give me that fuller bass when the volume wasn't high. With my newer receiver, I find that unless I turn it up, the bass is a little low. With the subwoofer its ok, so I have choosen to use the subwoofer level control as my personal manual loudness control, but its not quite the same. I miss that loudness control.
     
  11. Lewis Besze

    Lewis Besze Producer

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    Actually the house curve should rise till @32hz or so,having about 7db rise compare to 100hz [gradually],and shoud be flat below that to 20,which would create the a "roof" line on a spectra or similar program's graph with the peak at 32hz.

    At least this is my understanding from the lenghty posts of Wayne P. and others.
     
  12. ColinM

    ColinM Cinematographer

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    I actually did tweak down the 20 and 25 Hz sliders 2db each.

    This is the sound I was looking for.
     
  13. Wayne A. Pflughaupt

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  14. Richard Greene

    Richard Greene Stunt Coordinator

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    The "house curve" should be whatever sounds like a flat frequency response to YOUR ears.

    There is no correct "house curve" for ALL ears.

    There is no reason I can think of that a "house curve" must extend only to 32Hz., and not below 32Hz., for ALL ears.

    The Radio Shack correction factors we so often see on the internet are not used solely to adjust for Radio Shack meter "errors". If the Rat Shack sound meters were that far off in the bass frequencies, we should not be using them to measure bass.

    The published correction factors are primarily to adjust from C-weighting to U-weighting (see list of bass correction factors from C-weighting to U-weighting typed below) AND secondarily to adjust for the fact that the Radio Shack meter does not measure C-weighting perfectly (pretty close though).

    "C-weighting" includes a built-in "house curve" versus an unweighted SPL (U-weighting) that is intended to adjust the readings for the fact that human hearing doesn't work as well as frequencies decline. A flat C-weighted frequency response should sound like a flat frequency response to the average person at normal SPL's. Of course how loud something sounds is quite subjective and who among us has "average" ears?

    C-weighting to U-weighting (unweighted SPL)

    conversion factors:

    10Hz...+14.3dB

    12.5...+11.2dB

    16Hz....+8.5dB

    20Hz....+6.2dB

    25Hz....+4.4dB

    31.5Hz..+3.0dB

    40Hz....+2.0dB

    50Hz....+1.3dB

    63Hz....+0.8dB

    80Hz....+0.5dB

    100Hz...+0.3dB

    125Hz...+0.2dB

    160Hz...+0.1dB

    The C-weighting "house curve" works well for my ears

    so I make no adjustments to the raw dB readings from my

    Radio Shack sound meter -- if my system measured absolutely flat on my Radio Shack meter using C-weighting (in my dreams!) then it would sound flat to my ears when I listen to music in the 75-85dB range.

    I see no logic in adjusting the raw C-weighted dB readings from my Radio Shack sound meter using correction factors derived from someone else's Radio Shack sound meter.

    I do note that the treble corrections for that other person's meter do NOT correlate (not even close) with my 1989 model Radio Shack meter, so I have no reason to expect the bass corrections for the other person's meter are correct for my meter.
     
  15. ColinM

    ColinM Cinematographer

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    So, I am NOT a revolutionary.....I guess I am in agreement that if one wants good 'ol wallop to his bass, keep the needle at zero all the way down, and tweak to taste.
    Enjoy your stuff while you can. Now that it's getting nice out I have a yard that is screaming for attention...
    [​IMG]
     

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