DIY Sub: Port Length and polyfill

Discussion in 'Archived Threads 2001-2004' started by Bryant Brunner, Jan 2, 2003.

  1. Bryant Brunner

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    I've searched a lot of threads and can't seem to find the answer that I'm looking for, so here goes.

    I have an Orion XTR 12" (DVC)driver that I plan on wiring parallel in a vented enclosure. Using WinISD, it seems to me that a 147L enclosure is optimum when tuned to 27Hz. So can I effectively reduce the size by 20% (~118L) and add polyfill @1lb/ft3 and achieve the same response?

    If so, what port length do I use for a 4" port? The length for the 147L enclosure or the 118L?

    Thanks,

    Bryant
     
  2. Patrick Sun

    Patrick Sun Moderator
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    The port length figured for 118 liters would be pretty close if you do the 100% stuffed enclosure route. You might want to see what port length is for 147 liters, and cut the port that length and then chop it down to get the tuning closer to what you are aiming for.
     
  3. Ron-P

    Ron-P Producer

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    I have a similar question that pertains to this topic, sort of.
    I have a Tempest Sonosub that I built a while back. It is a 177L sealed enclosure, 20" dia. x 36" in length and is stuffed with 6.5 lbs of poly-fill. I was told on the Polk Audio forum that I could go louder and lower (into the teens) if I ported the enclosure.
    Can someone recommend a port dia. and length that might help me achieve getting my sub down to 18 Hz or so? I'd have to port through the top of the sub.
    Peace Out~[​IMG]
     
  4. Bryant Brunner

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    I guess you could tune to 20 Hz with a 8.42 inch (4.02 diameter) port. Assuming the fill material would pseudo-create a volume of ~212 L. I think that I read somewhere that the law of deminishing returns kicks in for enclosures over 5ft3 at 20% in a 1lb/1ft3 ratio.
    Thanks Patrick for the input. I'll give it a try and see what comes up.
    Does anyone know how to covert old WinISD files to the new WinISD pro?
     
  5. Ron-P

    Ron-P Producer

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    Thanks Bryant. How'd you come about with that size port? Also, any suggested on line places to land porting kits?
    Peace Out~[​IMG]
     
  6. Bryant Brunner

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    Ron,

    I used your driver specs and the volume you had in WinISD and came up with the port size. I used a volume of 212 L to account for the fill material. I noticed after I posted that you were looking for something around 18Hz. If you want that, it appears that you'll need to increase the port length to around 11 inches.

    As for where to get them, I got a 4" flared port from PE for around $15. I plan on using rubber cement or some other non-permament binder so I can re-use them in the future. I'm not sure what the air velocity at the port would be, but the flared should work perfectly.

    Bryant
     
  7. Chris Carswell

    Chris Carswell Supporting Actor

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    Uh Pat, you do realize that the port for the 147L box will already be shorter the the 118L box [​IMG] . So Bryant, start with the 118L port & chop down from there, don't forget to -the volume of the port, driver, & braces from the original volume. You are correct about diminishing returns kicking in for enclosures over 5ft3. I hope you have a good pair of ears or a modified RS spl meter b/c sometimes it can be hard to tell which port size is best when you are chopping off 1/4" & 1/2" increments.
    Ron, what do you mean exactly by "getting my sub down to 18 Hz or so". Do you want an F3 of 18Hz or just good output at 18Hz? If you go with 2 3" ports 11" long you will have a flat response to ~30Hz and an F3 of 22Hz. At 18Hz you will be about 6dB down, F10 is 16Hz. How does this compare to your current sealed rig: It slowly starts to roll off more so ~60Hz with an F3 of 37Hz. At 18Hz you will be about 11dB down, F10 is 19Hz. So by going ported it will give you +5dB more output at 18Hz or an F3 of 15Hz lower. These #'s are not exact but it will give you a good idea of what to expect. Hope it helps.
     
  8. Patrick Sun

    Patrick Sun Moderator
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    Oops, now that I thought about it, figure out the port length for 147 liters (for use in the 118 liter enclosure) for the desired tuning. If you want to make it make it longer and then chop it down, do a worse port length calculation for around 118 liters (in case you took out all the stuffing) at the desired tuning frequency.

    The port length you end up with be under that 2nd length, and may be just near the 1st length (but you'd rather be too long and have to cut it down, than too short and be inventing new cuss words).

    (Corrected to reflect my brain farts).
     
  9. Chris Carswell

    Chris Carswell Supporting Actor

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    A 4" flared port 11" long will work nice just like Bryant said but the dual 3" flared ports will have a lower port air velocity. For simplicity reasons, I'd probably just go with the 4".
     
  10. Ron-P

    Ron-P Producer

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    Thanks for the help guys!
    What is exactly ment by the F3..F10, etc.? Also, what are the benefits of using multiple smaller porst vr. one larger port?
    I am mainly looking for good output in the lower 18Hz range. Currently, with the sub in the new room, I am rolling off at 25 Hz.
    One more question. If I port the sub, should I remove any of the 6.5 lbs. of poly fill?
    Peace Out~[​IMG]
     
  11. Ron-P

    Ron-P Producer

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    Thanks Chris, you answered one of my questions before I posted it.
    Peace Out~[​IMG]
     
  12. Andrew Bowzer

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    Bryant,

    I will chip in a little word of advice, the driver will bottom out like there is no tomorrow if driven with 250 watts. I use an Orion XTR 12" SVC when im messing with my shiva. My box is tuned to 21hz, but you most likely will bottom out on movies and music if you turn it up high. I've had the sub in a 5 cube enclosure, and a 3.65 cube enclosure. Alot better results came from the 3.65 cuber, and I imagine probably better if I went smaller. It just doesn't like a big box.
     
  13. Chris Carswell

    Chris Carswell Supporting Actor

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    Keep the poly fill.
    F3= where the speaker is 3dB down in output.
    F10= where the speaker is 10dB down in output.
    You want a port with lower air speed but no so big that it kills you with surface area & volume. Also the wider you go the longer it has to be to reach a certain tuning point. If your box is 20" long but the 4" port needs to be 22" long it won't work. You would then use a smaller diameter port or multiple ports depending on application.
    Hope it helps [​IMG]
    -Chris
     
  14. Chris Carswell

    Chris Carswell Supporting Actor

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    Oh yah BTW, Andrew is right on about the sub. Hope you like Rice Krispies [​IMG] J/C [​IMG]
    "Once car audio, now home audio" I'm glad you have joined our side Andrew.
     
  15. Andrew Bowzer

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    Chris, I'm glad I changed too, it was a weird story. I'm 17, Regional Golf Tournament for my high school, 18th hole my ball ricocheted off a hidden root in the rough, and flew straight into my eye. I finished the round, shot a 80, although I got a 9 on the last par 4. Two stitches later, waking up in my bed, I said, "what the hell is wrong with me, I've spent over $1500 for an audio system in my truck (only paid $3000 for the truck) and for what? A large headache everytime I drive somewhere." Ever since that day last September, I sold everything car audio I had, and made the switch, and I'm loving every minute of it.

    Good thing I hit myself in the head with a golf ball.


    Sorry about the off-topicness
    Bryant, I'd watch what you use that sub for and don't be surprised if it can't take the power. Especially if you have a DVC 4ohm running off a P.E. 250 watt amp @ 2ohm. Way too much power will be going to it at 2 ohm, and there is already too much power for it at 4 ohm.
     
  16. Bryant Brunner

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    Forgive my ignorance, but I'm a little confused. Why would the XTR DVC freak out with 250 @ 2ohms when the spec sheet I have in front of my indicates 800 Watts Pmax at 2 ohms. I show Fo at 23.57Hz and Vas at 5.54 according to manufacturer specs.
    zUIfgerho;
    dsgvsadh'o dasfho' sho'dasjlfdjkadfsg
    - my head banging on the keyboard. [​IMG]
    Alright. So do I even try it? I've got a PE 250 amp and a 4" flared port kit on the way. I'm on a relatively tight budget (just upgraded to M&K 150s) and I would have like to use the two never used Orion XTRs. Actually I was just planning on using one for the time being. Do I just scrap the project and go for a Shiva or Tempest or something similar? Suggestions?
    Bryant
     
  17. Bryant Brunner

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    [​IMG]ouble post:
     
  18. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Bryant,
    I'm wondering if you're the same guy named Bryant who has been conversing via email with Tom Simms and myself regarding using Orion XTR DVC drivers for a HT sub. The fact that you're in Frisco makes me think that this is more than a coincidence.
    First, remember that when the manufacturer states maximum power they're usually telling you the maximum power that the voice coil can dissipate without cooking itself to a crisp. In other words - the electrical power limit. But you also must consider the physical limit of excursion that the woofer can handle. There's three points of interest here.
    1) There is a limit of how much excursion the woofer can sustain linearly - before significant distortion sets in. This is called Xmax.
    2) The suspension limit (Xsus) is usually a little larger than Xmax. If the woofer trys to move past Xsus you'll "bottom out" the woofer. This is usually accompanied by a loud clacking or popping sound and it can damage your woofer if allowed to continue.
    3) The amount of power it takes to reach Xmax or Xsus will depend on the enclosure that you put the driver in.
    What these guys are telling you is that this woofer is going to bottom out in most enclosures long before you feed it 250 watts.
    Regarding tuning: Using WinISD pro and the specs for the XTR DVC on www.orioncaraudio.com I get a peaky response with 147L tuned to 27Hz. If you're wanting a smaller enclosure I'd try something like 120L tuned to 24Hz with no stuffing. With 7.5mm of excursion (I assume that's each way, not peak-to-peak) you'll be excursion limited to 80 watts. But you'll get over 106dB from 30Hz and up. A 3 inch flared port would be plenty.
    Now if you are that same guy then you mentioned using 2 of these woofs in the email. So either build two or build one double-sized enclosure. That'll get you over 112dB from 30Hz and up with 150 watts or so. Very respectable. And you could use a single 150 watt plate amp from PE to power it. The 150 watter has the undesirable built-in bass boost, but I can disable it for you. Or you could go ahead and get the 250 watter for $20 more and you'll have plenty of power in case you swap to a higher excursion driver later.
    I'm curious about the 800 watt power spec. Everything I see for this woof, including the Orion website, says 250 watts continuous and 500 watts peak. The XTR pro is rated 500 watts continuous and 1000 watts peak.
     
  19. Chris Carswell

    Chris Carswell Supporting Actor

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    Ryan, you couldn't have written it any better. [​IMG] I agree with you 100%.
    Bryant; so.... uh... ya..... I take it that you have the 12" DVC woofers that are 4ohms per coil & you are going to wire them in parallel to get a 2ohm load via this statement:
    "I have an Orion XTR 12" (DVC) driver that I plan on wiring parallel" & this one:
    "....XTR DVC freak out with 250 @ 2ohms......"
    Not a good idea. I was thinking along the lines of a Tempest which is an 8ohm DVC sub so wiring them in parallel yields a 4ohm load. This is fine since the PE 300-794 is rated to handle 4 ohms. If you run it a 2ohms you will burn it up in no time. It's not rated to run at that low impedance. Although.......... you never know, it might be fine since it probably won't have to put out much more than 80 watts anyway before the V/C jumps out [​IMG] Just use one coil. Unless you are that same guy that mentioned using 2 of these woofs. If that's the case then wire the subs coils in parallel then connect them in series with each other so you will still have a 4 ohm load. Good luck.
     
  20. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Somewhere along the way, I became lost... [​IMG] I'd also like to know the answer to the original question.
    Say, you have a 100 liter box. With 100% stuffing, you get a 120 liter box. (Approx.). So the port should be tuned using what volume? 100 liters or 120 liters? This could have a big impact on the overall design.
    Off the top of my head I'd think the vent should be tuned for a 100 liter box since that's the actual volume, and the polyfill is only there to "fool" the driver into thinking there's actually more volume inside. Am I wrong?
     

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