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Servo 15 update. My Thoughts and BFD results.

Discussion in 'Home Cinema Speakers' started by Phil Hinton, Nov 11, 2003.

  1. Phil Hinton

    Phil Hinton
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    Most will know that my experiences with an SVS were not great, so I swaped for two servo 15's. Last night I finally had a chance to plot their response in my room and was shocked at the result (blue line) with a huge dip. Anyway after reading up as much as i could i applied some small gains accross the many freqs of the ip and now have quite a nice flatish response and it sounds good as well. I made sure to leave a laod of headroom for the subs amps when i orginally plotted the blue line so the Pink (bfd) will not cause to many problems, I couldn't see any other way to correct the Huge dip. Here's a look at the chart. Comments welcome.
     
  2. alexs2

    alexs2
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    Very nice work indeed,considering you didnt have a digital equaliser and room correction setup to work with.
     
  3. Apocalypse

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    Hi Phil, I'd add a filter at 36Hz and 71Hz to curb those minor peaks, aside from that you have a very nice response there, nice one.

    Why don't you do as I've done and create your own figures, I have 21 measurements but they are all from 20Hz to 80Hz, it means you can get a more accurate picture of your sub's performance. You might be surprised at the findings, when I first did it I uncovered a huge room node at 52Hz that previously wasn't detected due to the large gaps between frequencies in the default graph.
     
  4. Phil Hinton

    Phil Hinton
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    I think Liam has a copy of a disc which gives 1hz increment tones, I'll see if he can copy it for me and have a closer look.
     
  5. dunkyboy

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    That's a good idea, but where do you get correction values for the SPL meter?

    Also, it looks from that almighty dip like your two Servos may be cancelling each other - have you tried messing with their positioning? If they are cancelling, then I imagine fixing it by BFD can only be bad....

    Dunc
     
  6. Nic Rhodes

    Nic Rhodes
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    looks more like a square room to me with at least two dimensions being very similar.
     
  7. CYRUStheVIRUS

    CYRUStheVIRUS
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    looks like a room with a tv,chair,dvd and probably audio equipment to me.:D
     
  8. Phil Hinton

    Phil Hinton
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    Hits the nail on the head again. 13.5ft x 14ft x 9ft(h) thats the size of it. I am going to try stacking them on the left side and retrying my measurements.
     
  9. Phil Hinton

    Phil Hinton
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    Will also try the 12 and 6 approach Nic ;)
     
  10. deckard

    deckard
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    That same dip is almost exactly the same problem I get with one CHT-15 in a ~14.5x14x8 ft room. I managed to tame the dip by putting my sub at the half way point of the left wall.

    Although from what I've read on two sub set up, the 12 and 6 o'clock position has been found to be the optimium. Have a look here IIRC: http://www.harman.com/wp/pdf/multsubs.pdf
     
  11. buns

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    Surely to get correction values all you need do is interpolate between the correction values we do have..... they follow a general trend so i really doubt there will be aby big deviations.

    ad
     
  12. lmccauley

    lmccauley
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    That's all I did.

    Cheers,
    Liam
     
  13. dunkyboy

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    Hmm, inter.. intepr... interperpolate.... D'oh, does that mean I'll have to go into the part of my mind labelled "Things I Learned In Maths Class For The Finals And Then Promptly Forgot"...? I hate it when I have to do that....

    Or did you just guess? :D

    Dunc
     
  14. ShinObiWAN

    ShinObiWAN
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    Interpolate means to go in a specific number of even steps between two points.

    ie. 30 - 70 in 10 unit increments would be interpolated as:

    30 40 50 60 70

    Surely everyone knows this? :)
     
  15. MuFu

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    Wow, you said your room was bad but that looks scary - it's sucking the life out of the damn things.

    How much gain did you have to apply to get rid of that trough? I had a go with my sub this evening and discovered that there don't really seem to be any rules at all when it comes to EQ, just a lot of experimentation! The main trough took +10dB to correct whilst the big peak (no doubt the primary resonant mode of this room) required a staggering -18dB attenutation. :eek:

    I was a bit worried that I was just killing a tiny frequency range but have done higher resolution tests to check it's actually flattening things out evenly and it looks fine. I'm also not so keen on the +10dB application, but that should be fine once I recalibrate to 85dB. Now I can see how much of a problem I had before....

    [​IMG]

    Definitely worth doing. I can completely understand why people start using BFDs etc and never go back to a non-EQ'd setup. The improvements are very apparent.

    MuFu.
     
  16. jag77

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    I agree with the major suck out. Sucks big time.

    I too agree there isn't any rule to EQ-ing. So long it sounds good.

    Mufu, you could insert in a house curve. House curves tend to make flat response bass sound better. Many feel flat response doesn't sound good. A house curve gives a slight downward slope from 30hz onwards.

    You cn try to insert a suitable house curve for your room by doing this.

    Play a 100hz tone. Remember how loud it is to your ears. (Don't use the SPL meter anymore). Now play a 30hz tone. This 30hz tone is expected not to be as loud as the 100hz tone. Use the BFD to insert some gain until the 30hz sounds just about as loud as the 100hz. The final part is just to get a nice slope from the now boosted 30hz point to the 100hz point. (Now you can use the SPL meter to help you plot the final curve and settings.) Thats your house curve.

    Definately worth doing the house curve. Will definately further heighten the appreciation of the BFD.
     
  17. MuFu

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    I don't don't have a BFD, I'm using an impulse convoluting plugin with parametric EQ for a software player to correct the sub's output (just for stereo use). I'll give what you suggest a go sometime - should be fairly easy to do just using the standard graphic EQ.

    Cheers,

    MuFu.
     
  18. Ian J

    Ian J
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    You've just made that up :D
     
  19. MuFu

    MuFu
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    Heheh. Had to get the ol' flux capacitor fired up first, of course. :D

    jag77, I did a little reading about house curves. Apparently C-weighted calibration already applies boost in the sub 50Hz region to make frequency reponse more "subjectively flat". Since I'm already adding 11.5dB@16Hz to try and correct the meter readings I'm not sure it'd be wise to push the sub any more. It's a pretty modest unit with a 10" driver and 200W amp.

    Phil, I assume you're using the correction values supplied in the snapbug spreadsheet as well (?).

    MuFu.
     
  20. MuFu

    MuFu
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    I'd recommend doing this as well. I found similar things by recording a 16-160Hz sweep using the RS meter (shown in green) and overlaying it onto the meter plot:

    [​IMG]

    Look at how much detail is missed by using 1/6 octave intervals! Bear in mind that the sweep recording isn't calibrated, neither does it use the same vertical scale as the discrete meter readings.

    MuFu.
     

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