Measuring the effects of polyfill...would this work?

Discussion in 'Home Theater Projects' started by Frank Carter, Sep 24, 2003.

  1. Frank Carter

    Frank Carter Screenwriter

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    Just finished my TP tubes and I have 9 20oz bags of polyfill to play with. Instead of just stuffing a bunch in, I want to know if this would be the correct way to measure how much my effective volume is with the polyfill.

    1.) By using WINISD I know at the tuning frequency a woofer's excursion is at it's lowest. With my SPL meter near the woofer's cone I'll measure the the freq where output is the lowest to find the tuning frequency of the enclosure with no polyfill.

    2.) If I now add one bag of polyfill, and I remeasure the tuning frequency and it's lower this means the polyfill did it's job.

    3.) By using this new lower tuning frequency and my known port size/length, I can work backwards and find what internal volume would be needed to get the new tuning frequency using my ports.

    4.) Repeat steps 2 & 3 until I get my desired effect or it doesn't lower the tuning frequency any more.

    I just wanted to know whether this would work before I take the time to do this. Does anyone else do this(or some other method) when they add polyfill? I plan on sharing my results so if anyone's interested they can read.

    Thanks

    Frank
     
  2. ThomasW

    ThomasW Cinematographer

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    Normal fill rate is .5-1.5 lbs/cu ft.

    I usually start with 1 lb/cu ft. Then add increments of 1/2 lb at a time for fine tuning. With each addition the bass should 'tighten'. When it stop tightening and only the efficiency drops remove the last amount added.

    I have some serious test gear and software, but find that final tuning by ear provides the best results. Software modeling programs just can't accurately do this kind of thing.
     
  3. steve nn

    steve nn Cinematographer

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    Hi Frank! The AV15 Brian B. built for me just has fill in the top half. Maybe he will step in and tell us just how much he put in? 1-1 1/2 lbs into 220 L? After we ironed every thing out it sure has proven to be one hell of a woofer. If I recall correctly you are shooting for 18 Hz? Mine is tuned to around 20.7 Hz and does it perform. If I don't sell mine soon I'm going to run it with my three 25-31CS+'s with their port plugs in. (I have come to like the 20Hz tune better) I am working on my wife and I think I am close? I will have to buy her a leather chair with ottoman to replace the love-seat though. [​IMG] All in the name of bass right? I need space!

    Yikes! Frank those tubes are going to be something. It's interesting to see a face behind all the words also. I thought you would have been a more handsome guy but you look better than me. Pic your way soon.

    Steve- PS>> Send me a PM and tell me what you think of the 5660 Yammy receiver?
     
  4. Frank Carter

    Frank Carter Screenwriter

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    Hey, hey, hey...don't make me go ghetto and put the smack down on ya[​IMG][​IMG]. Maybe I should send you a pic showing my other better looking side[​IMG].
     
  5. Mark Hayenga

    Mark Hayenga Supporting Actor

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    I wouldn't add polyfill to a vented sub unless I had good test software to measure the effects. I did 50% fill on a Tempest subwoofer of mine and measured the imedance with Laud. Tuning frequency dropped a whopping 2Hz with a corresponding tremendous drop in Ql - the new impedance curve looked like crap. YMMV....
     

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