linkwitz for my Tumult?

Discussion in 'Home Theater Projects' started by Brad Dixon, Feb 28, 2005.

  1. Brad Dixon

    Brad Dixon Stunt Coordinator

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    After doing a bunch of reading this has me interested. Now the deal would be this,

    1. keep my current 110-115L sealed box.
    2. replace the Keiga amp with the ADA1200 amp from Adire.

    Using the linkwitz spreadsheet plugging in:
    Box volume = 115L
    Target Fsc of 15hz
    Target Qtc of .7
    Amp rated power = 1200w
    EQ power applied = 100w

    excursion limit is not exceeded
    amp power is exceeded ~13hz
    I did NOT enable the input or subsonic filter as I wasn't sure if it's an option on the ADA amp.

    Where I'm confused is when I use Unibox to model my current sealed box with 1000w and compare it to a 150L ported/PR'd box tuned to 16-17hz with 1000w I have a difference of about 6db at 20hz. IE the reflex boxes have 6db more output than my current sealed box at 20hz.

    If I'm understaning the linkwitz spreadsheet correctly, my current box would be "speaker" on the graphs and "target" would hopefully be the response with the LT. If this is so then I'm gaining 7.5db of output at 20hz over my current box using the LT circuit(and 10db at 14hz!).

    So I'd be looking at output similar to what building a ported/PR'd box would give me(if I keep the Keiga amp and build a ported/PR'd box)?

    If this is the case then I think I'd go this route. It's more money but the box is already built and my wife really likes it(size and design).

    Can anyone see a problem with my proposed LT circuit? I really don't know what to shoot for(Fsc or Qtc, I just used numbers like I've seen mentioned in posts) so I was just kinda running numbers to get lower extension while not exceeding the amps(or Tumults) limits by much.

    Also I forgot to ask, since I'd be extending the response will I actually end up with LESS output/volume since a lot of the amps power have to get used for that? This is the main thing I can't seem to figure out.

    Thanks for any input,
    Brad
     
  2. David_P

    David_P Stunt Coordinator

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    not sure about this...

    It appears to me that excursion is exceeded at about 16hz.

    My understanding?

    The EQ power applied means that the amp is assuming 100W output at some higher frequency (above rolloff). The power vs frequency graph tells you where (frequency-wise) the amp runs out of juice attempting to maintain "the curve" assuming whatever input level drove it to 100W at the higher frequency is applied all the way down "the curve".

    In this case it appears that the excursion limit is higher than the power limit, therefore the tumult will bottom?

    Or maybe I totally don't get it.

    David
     
  3. Brad Dixon

    Brad Dixon Stunt Coordinator

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    I'm at work at the moment so I can't double check myself. I wonder if I did have the subsonic/input filter activated and didn't realise it. I don't think so becuase I'm sure the buttons said "enable" on them. To me this would mean they are currently disabled.

    I won't be home till nearly 11:00pm tonight but if I remember I'll double check everything. Who knows, maybe I have one of the Tumult specs input wrong.

    Thanks,
    Brad
     
  4. David_P

    David_P Stunt Coordinator

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    It's entirely possible that I just don't understand how the spreadsheet works.

    Best bet is to ask the Adire folks. On the other hand, some one (Brian bunge?) mentioned in another thread that his LT'd Tumult setup could be bottomed at very low (infrasonic) freqs with only 800 watts (IIRC).

    We (me) need a definitive explanation on how to read the LT spreadsheet properly.

    David
     
  5. Brad Dixon

    Brad Dixon Stunt Coordinator

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    Well I didn't go out tonight so here is the info I'm using for the linkwitz spreadsheet I have.

    Name - Tumult
    Number Of Drivers - 1

    Fs - 19.00 Hz
    Qms - 4.3
    Qes - 0.39
    Qts - 0.358
    Vas - 160l
    Xmax - 34.0 mm
    Re - 3.2 Ohm
    Impedance - 4 Ohm
    Diameter - 35.0 cm
    Wattage - 1600 w
    Sd - 962.1 cm
    Vd - 3.27 L
    nO - 0.275%
    Spl 1w/1m - 86.4
    Max Spl - 118.44 dB

    Transform Information
    Target Fsc - 15.00 Hz
    Target Qtc - 0.70
    F3 - 15.15 Hz
    K > 0 - 4.18


    Amplifier Information
    Amp Resistance - 0.00 Ohm
    Series Resistance - 0.00 Ohm
    Rated Power @ 4.0 Ohm - 1200 w

    Eq Information
    Power Applied - 100 w
    Peak Spl - 106.40 dB

    Volume of box is 115L

    Input buffer and subsonic filter are disabled.

    Speaker excursion never exceeds max, although it is pretty much maxed at 10hz.
    Amp exceeds power rating at 13hz.

    I'm using the spreadsheet linktranadv28.11.xls
    I'm running Windows 98 and use excel 97 if that may make any difference.

    Thanks,
    Brad
     
  6. Dan Wesnor

    Dan Wesnor Second Unit

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    Target 25Hz for a big room, 35-40Hz for a small room. The shallow slope of the sealed sub will pick up the rooms gain and sound much more natural than going down to 15Hz. I currently have Fc=~37Hz, Qts=0.71, and it can shake the chairs in a 15'x13' room.

    Don't use an amp with boost for an LT sub.
     

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