Newbie DIY PR sub help,lots of help

Discussion in 'Home Theater Projects' started by MarkRoberts, Feb 21, 2004.

  1. MarkRoberts

    MarkRoberts Stunt Coordinator

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    I am looking into building my first sub. I have allot of ?'s. First off this will go in my suv for now.Hope that doesn't offend anyone, doing it for fun and experience.
    I want to make a PR enclosure. Would like to keep the box dimensions down around 18"x18"x18" or smaller if possible. I don't have all the necessary tools right now so I am considering pre-made cabinets from parts express and flat kits from acoustic-visions. I am thinking a 10" driver and 2 10" PRs.
    I know the PR's are supposed to be bigger than the driver but I think I read somewhere that if the enclosure is smaller you can use more than one same sized PR?
    Driver I am looking at is either a 10" titanic mkIII or the 10" peerless XLS (4ohm car version). and for the PR's 10" peerless XLS. Now for the questions. I know virtualy nothing about all the math and jargin envolved so please go easy on me. I will be feeding it 300w RMS.
    1.Are the pre-made cabinets from PE any good?
    2.Does this sound like it can be done?
    3.Will I need to add mass to the PR's?
    4.What is the easiest way to add mass?
    I want the driver on front and the PR's on each side. I would put terminal cup on back. That way if I want to move into the house all I have to do is open the hole up for a plate amp. I have enough clamps to assemble a flat kit just not all the power tools to build from scratch. Sorry if this long.I tried to find the info on my own but all the box calculators didn't say anything about PR's just port size and length.
     
  2. MarkRoberts

    MarkRoberts Stunt Coordinator

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    Okay maybe you guys will help me with these questions.
    Can someone explain to me how to determine the mass needed for the PR's. I have downloaded WinISD beta. I also have been to diysubwoofers.org. I don't understand the math involved. I am not an idiot though I am feeling that way. If someone could explain the process step by step. Like take this multiply by that ect. This may seem annoying to the more expierenced of you DIYer's but at some point you were inexpierenced too. If you put the rms amp power and the listening distance from the sub in the plot tab of WinISD does that give you a rough idea of real world response your sub will have?
     
  3. AndersP

    AndersP Stunt Coordinator

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    Hi.

    I´ll try to answer som of your questions the best I can but first thing´s first:

    Do NOT use the car version of the XLS as it will not give you near the low level extension of the basic model. The car version is optimized for small dead closed spaces.

    1. No idea.

    2. Of course it can be done.[​IMG]

    3. You will need to add mass. The PR,s come on the light side to be adjustable to different alignments.

    4. The Peerless PR,s come with a bolt on the back where you can easily attach about anything with a hole in it. Thick washers are a hit. You secure the weight with a locknut.

    The adding of mass is, as you surely understand, a part of the tuning process. The trick is to add the correct mass.

    The tuning requires measurements to be really good, but if you have a good understanding of how these thing work you could may be do without it.

    The tuning affects the very low end of the frequencu spectrum. To little mass will give a "disco"- like one note bass and to much will roll off the deep bass to high in frequency. You will need a record with test tones or down load some off the internet. Then you take som crude measurements yourself preferably outdoors as you will be fooled by standing waves and resonances in your listening space. The Radio Shack sound level meter is handy.

    http://www.d-s-t.com/main/tech/appxls.htm

    When it comes to boxes I know that there is an exellent bussiness in the USA called Home Depot. There you can get your MDF or whatever material cut to your measurements with such a precision that you easily can glue it together at home. They also have the lot for woodworking at decent prices. Building simple subwoofer boxes takes very little tools and you don´t need pro tools either. You can do with the simplest hand tools.

    To conclude, the biggest obstacle will be what mass to add to the PR,s. My advice is to buy a readily assembled kit with the driver, PR,s and som box plans. Then you can cook with a proven formula.

    If I was in your shoes I would go for the XLS 12" with 1 PR. There are lots of kits for those.

    Good Luck!

    //Anders Persson
     
  4. MarkRoberts

    MarkRoberts Stunt Coordinator

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    Thanks for the help Anders. I think I am going to use the Titanic MkIII 10" and two of the peerless 10" xls PR's. I am getting some pretty good results with WinISD. The only problem I am having is figuring out the mass needed for the PR's. I used a 1.00 cu ft enclosure tuned to 26Hz . A 14"x14"x14" box dimension. Like the finished cabinet from Parts Express pn 302-800.
    I plugged in a port measurement of 16" and it gave me a length of 774.11 in. There is a formula on the diysubwoofers.org site but I don't understand how to do it correctly.I'm somewhat mathmatically challenged. If I am using WinISD right I'm getting down around 26Hz before the -3db line and on the SPL graph it doesn't go below 90db til around 20Hz. That is with 325w and a distance of 4 meters. Am I doing this right?
    The plan is to throw this in my suv for know and maybe adding a 250w plate amp and bringing it in the house later.
    Does anyone out there know if the internal bracing on the premade cabinets will get in the way of the PR's? I would go to Home Depot but I live in the sticks nearest one is 50 miles away. The local lumberyards will not cut MDF down and only order 4x8 sheets. Wont fit in my Isuzu.
     
  5. Rory Buszka

    Rory Buszka Supporting Actor

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    Look around. Why don't you see many passive radiator subwoofers in cars? Because the forces of motion (braking, accelerating, going over bumps, etc) can cause the weighted passive diaphragm to have big excursions, which can even damage the active driver by causing the voice coil to jump the gap, etc. What happens when you push in on a PR in a single-PR speaker? The cone moves out. Also, when you go over bumps and cause the passive radiator to move from its center position, it may already be vibrating at large excursions and offsetting the center point of excursion by shifting the basket can cause huge stress on the surround. The spider can probably take it, but over time the surrounds may start to tear free from their adhesive. PRs in cars are generally not done for this reason. If they could be done, we would see a lot more of it, becuase PRs let you use a smaller box at a deeper tuning frequency. But the problems outweigh the advantages of a car passive radiator system.
     
  6. MarkRoberts

    MarkRoberts Stunt Coordinator

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    Rory,
    Thanks for the advice. I didn't really think about that but it makes sense. I have 2 JL 10"'s in my suv now I was just hoping to get some of the space back without losing the bass. Also after reading about all DIY projects on here sounded like it would be fun too. I still want to build it, but now I won't put it in the suv.
     

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