***Official Linkwitz Transform Thread***

Discussion in 'Archived Threads 2001-2004' started by Anthony_Gomez, Aug 14, 2002.

  1. Admin Note - This thread is now been designated the Official Linkwitz Transform Discussion Thread. Please post all questions on LTs in this thread. Thanks.
    (please forgive any spelling, grammar errors or typos)
    What is a Linkwitz Transform you ask?....
    Quite simply, an LT (LT=Linkwitz transform) is a piece of active circuitry that functions as a very special kind of bass boost for SEALED ENCLOSURES ONLY (or infinate baffle).
    The really really really rediculously good:[​IMG]
    What it does is artificially takes ANY sealed or IB sub and give you ANY response you want!. YOU choose what you want the QTC and Fb of the box to be. If you want the box to be the size of a tissue box and have a Qtc of 1.00 with an Fb of 10hz, you can have it!! The size part is the SAF dream come true[​IMG]
    The bad:[​IMG]
    This device is not magical. Being able to have any response comes at a price. For every 3db you boost, you require 2x the amplifier power. With this power, you now start chewing up xmax rather fast and given enough power, you will start to run into driver compression (driver compression is where you do not get what you put into the system. Going from 500-1000watts should give you 3db more gain, but compression might yield only a 2db gain).
    More bad:[​IMG]
    So as you can see, the more extreme LT systems require high excursion drivers (may have to then contend with an inductance hump)and a hefty amp which together yield a hefty price tag.
    BUT, not all LT'd systems are extreme. Some could only add 3 db which isn't less than most bass boosts but you yield a superior driver response...so normal amps and drivers can be used! Others like myself and Jack Gilvey will go a little more extreme and get a 1000+ watt amp with a monster driver in a little box or an infinite baffle.
    Lets see an example:
    The new Tumult 15 driver is a superior LT driver. It has really high LINEAR excursion, high Surface area (15" driver) with monster power handling and no inductance hump (and it should be selling pre-order at a super price!). You want to drop it into a 17" cube and after subtracting all the bracing and driver displacement, you end up with a 42.8L enclosure. You then open up a modeling program like UNIBOX (linked below) and use it to calculate your actual Qtc and Fb. I like to model with no leaks and heavy stuffing. This yields a Qtc=0.707 and an Fb=36.8hz. You don't care so much about the sub being really really loud, but rather have it play really low with a loq QTC for your organ music that you love so much. So you WANT a Qtc of 0.55 and an Fb of 18.5hz (yields an F3=25hz which the program should calculate).
    This equalization yields total boost of about 6db at 20hz and raises up to about 8.5db after you account for the input buffer. Lets say you are really cool and have a Crown K1 amp [​IMG] that puts out 1500watts RMS into 4ohms bridged. If we just consider 20hz and up, your 6db gain has already cut that amp effectively down by a quarter...or 375watts..but if you want to consider down to 10hz, you only have ~210watts to work with (but the driver is beyond it's linear excursion at 10hz with 255watts). Back to 375watts for 20hz and up. The single driver is rated about 85.5db 1w1m. With 375watts, you can get a maximum db of 111db at 100hz and 106db at 20hz (-5db down) and the driver happens to be at its xmax.
    How can you model these things yourself?
    Simple...download one of the many spreadsheet programs that are out there. Below is a link to the FRC consortium that has UNIBOX and an TL program that I helped to author.
    http://www.pvconsultants.com/audio/frdgroup.htm
    How can I get one of these?
    If you are interested in an LT, you can work up a breadboard by yourself, or get one of the high quality PCBs from Rod Elliot at www.sound.au.com. You will also need to get a power supply built for this too which I know Rod sells as well (there are other sources for these PCB's). OR you can get an adjustable (on the fly) LT from Marchand Electronics under the name BASIS at http://www.marchandelec.com
    If you don't want to build your own and cannot afford the Marchand Bassis pre-built option, then you should have a look at this thread:
    http://www.hometheaterforum.com/htfo...threadid=88950
    Enjoy!!!
    Hope I didn't confuse the heck out of you with all of that!!![​IMG]
     
  2. Scott Simonian

    Scott Simonian Screenwriter

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    Very nice FAQ there Anthony. [​IMG] [​IMG]
    With the prices of gigawatt amps coming down and down, LTs should become even more popular. People need to learn more about them (including myself :b ).
     
  3. Kyle Richardson

    Kyle Richardson Screenwriter

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    Very nice Anthony...now I just need a K2 [​IMG]
     
  4. Bill Leber

    Bill Leber Stunt Coordinator

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    A gigawatt amp! Where do you find a 1,000,000,000 watt amp? [​IMG] (just kidding Scott. I know you meant kilowatt.)
     
  5. Brian Bunge

    Brian Bunge Producer

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    Bill,
    It's right next to the Flux Capacitor! [​IMG]
    OK, FAQ #2: What is a grit?! Discuss...
    Brian
     
  6. Jason Hammerly

    Jason Hammerly Supporting Actor

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    If I was running a 122L sealed Tempest with a Q of .707 and wanted a Q of .577, would my 250 watt plate amp be enough to get me there with the LT. Would it pretty much be plug and play? I want the benefit of the lower Q, but don't want a huge box. Thanks.


    Jason
     
  7. Stephen Dodds

    Stephen Dodds Second Unit

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    Can a flexible EQ device such as the Behringer FD or Ultracurve give a similar result?

    Thanks

    Steve
     
  8. Chris Carswell

    Chris Carswell Supporting Actor

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    Ah yes Grit, ask Joe Peshie [​IMG]
     
  9. Stephen. Yes and no. If your system has a sufficiently low F3 and has a low enough Q (0.6 is my personal minimum), then the answer is yes. However, you do not end up with as good of a responce as a LT would give. Also, your system will dive quickly after 20hz where an LT will maintain the proper rolloff.
     
  10. Scott Simonian

    Scott Simonian Screenwriter

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  11. Scott?...you don't have one? I already got a pair of them! The electricity company even helped me pay for them because in the long run, I will represent 1/2 of their income=)
     
  12. Jack Gilvey

    Jack Gilvey Producer

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  13. Dan Pawlowski

    Dan Pawlowski Stunt Coordinator

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    Jason Hammerly

    I EQ’ed (+6dB @ 25Hz) my AVA250 amp to turn my Tempest sub from a »Butterworth alignment (.707) to a »Bessel (.577) alignment. Pretty easy too, used only 2 capacitors. The overall trade off I experienced was SPL. I measured my system, Dennon amp kit281s and AVA250 amp Tempest and found the following: I can only power my kit281s at »45 Watts Peak (115 dB SPL @ 1M @ 2Khz) before the AVA250 amp starts to clip (»350 Watts Peak @ 15Hz). Adequate volume for my room although a bit more would be nice. I also modified the crossovers in the AVA250 for Q=0.5 and 6db down at 55Hz.

    Dan
     
  14. Dan, those mods are really nice if you just want to change the Q of the boost (also know as the bandwitdth on parametric EQ's). However, it doesn't actually yield a new Q sub responce.
    ..i guess it all comes down to what you want your sub responce to look like=) It is a trade off of $ vs responce vs ease of use.
     
  15. Dan Pawlowski

    Dan Pawlowski Stunt Coordinator

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    "However, it doesn't actually yield a new Q sub responce. "

    Why not??

    doesnt the low pass filters, the response of the speaker and box all equate to the total system q of the sub??

    in other words isnt an lt just a low-pass filter with a selected response added to a hi pass filter (speaker + box) to give a result of a hi pass filter with a lower 3dB point.

    dan
     
  16. Isaac C

    Isaac C Stunt Coordinator

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  17. Dan, download my lated program for the BFD...you can add a parametric boost and you will see what I mean=)
     
  18. Dan Pawlowski

    Dan Pawlowski Stunt Coordinator

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    Anthony
    "download my lated program for the BFD"
    This program is where??[​IMG]
     
  19. Dan Pawlowski

    Dan Pawlowski Stunt Coordinator

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    Anthony


    Never mind i found it

    hey im new to this forum

    dan
     
  20. Dan Pawlowski

    Dan Pawlowski Stunt Coordinator

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    Athony
    ok i see where the confusion is
    i was answering Jason Hammerly's post not Stephen Dodds.
    you do not need a parametric eq to accomplish a LT just a low pass filter.
    By the way your link to Rod Elliot’s page is incorrect (has an extra "/")
    it should be: http://sound.westhost.com/index.html
    later
    dan
     

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