Ports?

Discussion in 'Archived Threads 2001-2004' started by Will Pomeroy, May 8, 2002.

  1. Will Pomeroy

    Will Pomeroy Stunt Coordinator

    Joined:
    Feb 9, 2002
    Messages:
    144
    Likes Received:
    0
    I have designed a sub, its internal volume is about 2.3 cubic feet. In order to tune it to 20Hz, I would need a port about 34" long. I am wondering if it would be okay to make the port all curvey to fit it in the enclosure, or am I making a huge mistake even bothering trying to tune it so low?

    Thanks very much,

    Will.
     
  2. James W. Johnson

    James W. Johnson Screenwriter

    Joined:
    May 26, 2001
    Messages:
    1,055
    Likes Received:
    0
    2.3cuft is not much. What driver are you using?

    Yes its ok to curve your ports and 20Hz or lower is a good tuning point for an HT sub but a 34" port wether its 3 or 4" wide will hog up alot of space bringing your net volume down.

    Why so small?
     
  3. Joe Meissner

    Joe Meissner Stunt Coordinator

    Joined:
    Jan 31, 2002
    Messages:
    204
    Likes Received:
    0
    From my ventures into the diy arena seems like everyone recomends a passive radiator when going that small. i didnt want to spend any more money so i went with a bigger box. and went ported. and i used a 90degree elbow in my box just to get a 19.5 inch port
     
  4. Will Pomeroy

    Will Pomeroy Stunt Coordinator

    Joined:
    Feb 9, 2002
    Messages:
    144
    Likes Received:
    0
    I see... I just want something small, and I want to save moeny and not use a passive radiator.

    I'm planning on using a shiva...

    and an ava250
     
  5. Kyle Richardson

    Kyle Richardson Screenwriter

    Joined:
    Jan 1, 1998
    Messages:
    1,073
    Likes Received:
    0
    What diameter port are you thinking about? Is your 2.3 feet gross or net volume?
     
  6. Neil Joseph

    Neil Joseph Lead Actor

    Joined:
    Jan 16, 1998
    Messages:
    8,332
    Likes Received:
    1
    Real Name:
    Neil Joseph
    That must be net volume. The amount of volume a 34" port would take inside such a small enclosure would almost eat up the entire 2.4 cubic ft. Are You designing a box or tube enclosure? Or are you using an existing enclosure off another sub? Note that you could accomodate a larger enclosure easily with a sonotube design if you wish, without the enclosure being too bulky.

    With a net volume of 2.4 cubic ft and a tune of 20Hz, you would see rolloff much earlier and a -3dB point of around 30Hz. If you use a bigger enclosure like 4 cubic ft for instance, you would have a -3dB point of around 25Hz. Your port for this design would be a 4" port at 18" long. If you use a sonotube design, you won't need a bend in the port to fit it in the enclosure.
     
  7. Will Pomeroy

    Will Pomeroy Stunt Coordinator

    Joined:
    Feb 9, 2002
    Messages:
    144
    Likes Received:
    0
    Yeah, I realize the benifits of sonotubes, but I really don't like the looks of them. I had something like this in mind...
    I'm also considering sealing the box, but with a box this small, would it have a HUGE impact on the SPLs?
    oh yeah, I realize that the shiva is not a kevlar cone, I just think it looks cooler for rendering purposes... [​IMG]
    [​IMG]
     
  8. James W. Johnson

    James W. Johnson Screenwriter

    Joined:
    May 26, 2001
    Messages:
    1,055
    Likes Received:
    0
    You are tackling the most difficult kind of subwoofer

    to build.

    You can forget about using a Shiva in 2.3cuft , it won't work well at all. Go 5cuft or don't even bother.

    If you want a small 2.3cuft sub to extend into the 20s and put out 100db down there its going to be costly and hard to do.

    You might come out ahead if you just go out and buy one of Bob Carver's Sunfire subs.
     
  9. Jeff Rosz

    Jeff Rosz Second Unit

    Joined:
    Sep 24, 2000
    Messages:
    335
    Likes Received:
    0
    gotta agree with JWJ. with that long of a port its acting like a sealed box anyway. you hit the brick wall. the port is compressing for ~full octave down low with a big drop in SPL over the span of the lowest octave. go sealed. my $1/50.
     
  10. Will Pomeroy

    Will Pomeroy Stunt Coordinator

    Joined:
    Feb 9, 2002
    Messages:
    144
    Likes Received:
    0
    Okay, looks like i'm going sealed. Would the Shiva still be a good performer in a sealed setup? If not, what other considerations should I take into consideration? (that sounds like a line from austin powers). I realizes that the performance will be comprimised, but I can handle that, as long as it will still sound really good.
     
  11. Joe Meissner

    Joe Meissner Stunt Coordinator

    Joined:
    Jan 31, 2002
    Messages:
    204
    Likes Received:
    0
    will,
    look at this thread http://www.hometheaterforum.com/htfo...threadid=68450
    this is the sub i just finished. there is a link in there that will take you to my other post with more detail and an early construction pic. this sub ended up being around 3.20^3 using a 19.5 inch port which tuned it to 21-22hz. it looks awesome and has a high WAF[​IMG] . this thing was shaking my pant legs watching JP3 and I am using an old 120watt amp on it. also it is using an original SVS driver.
     
  12. James W. Johnson

    James W. Johnson Screenwriter

    Joined:
    May 26, 2001
    Messages:
    1,055
    Likes Received:
    0
    I realizes that the performance will be comprimised, but I can handle that, as long as it will still sound really good.

    >>>>>>>>>>.

    Define 'sounds really good' and what you expect from

    a subwoofer.

    What subwoofer are you using now or is this your first?

    What subs have you heard that you like?

    What purpose do you have for this subwoofer?

    How big is your room?

    I have played around with Shivas in small sealed enclosures and I was'nt very impressed, but

    I have heard an EQ can help these small sealed

    boxes quite abit.

    How much are you looking to spend?

    A Shiva, EQ and amp will set you back a min. of $300,

    by the time you build it your looking at around $400

    min.

    For $399 you could get a Rava which has a Shiva , 250watt amp and a custom EQ built into it.

    Its totally up to you , you might be happy with a small sealed Shiva sub that is not EQed. In my opinion it would'nt be worth doing because at this price point there are a few commercial subs that are already build and ready to go that will give it a run for its money.

    Now stick the Shiva in a 7cuft enclosure , tune it to 17Hz and run it with 300 quality watts and we have a different animal. A Shiva sub like this is worth doing because nothing could compete with it for the same amount of money.

    Add another 3cuft and use a Tempest driver instead and you have lept up yet another level for only a few more bucks.
     
  13. Will Pomeroy

    Will Pomeroy Stunt Coordinator

    Joined:
    Feb 9, 2002
    Messages:
    144
    Likes Received:
    0
    Thanks for all of your help, first of all [​IMG]
    Hmm... I'm being very tempted here. Of course this brings in a whole new ball game. I'm pretty sure that i'm going to stay with the shiva, beacuse i'm really trying to keep the cost down. Now that i'm thinking about it, a 7cuft sub, would really only be a 2' square (minus the driver and amp and stuff-i'm a assuming). So lets say that that is fine and dandy with the PAF (parent AF), I just have a few questions about the sealed vs vented- I have a vented sub for my computer (yes, I realize that this is just computer unit, but it is THX certified, and i does have an 8" driver, and it is pretty good, I can shake the house with it) I was doing some experiments with it by plugging the port, and the sound that comes out from it as a sealed sub is completely different. I was wondering, in my simulations, the sealed and the ported come out as pretty much the same SPL, but would the ported provide more pant shaking base compared the sealed although its at the same SPL?
    and now to your questions:
    1. "Sounds really good" to me would be being able to flow seamlessly to my mains, but yet still be able to go the extra mile with some good ole rumbling without any type of distorstion, like port noise and what not.
    2. This would be my first home theater sub.
    3. The only subs that i've heard are those tiny ones you can get from future shop and crap like that, so i'm pretty sure that i'll be able to surpass that. Oh yeah, and my comp sub, but I put that in my TV room for a bit and I was not too impressed, the room just washed out any type of base that thing had.
    4. This sub would probably be 50/50 music hometheater, my taste in music is very varied, but I do really enjoy nice cello music, so I would like something that would sound alright producing the lows of cello. But also be able to pump some nice base for base lines, and be able to produce good movie atmosphere.
    5. My listening room is about 11.5' by 23' with 9' ceilings. The narrow part is where the TV goes.
    Now with these high demands you're probably wondering what i'm smoking, but just so you know, it doesn't have to be ultra loud, I just like something to complement the movie, and not hurt my ears... I have no idea what my listening levels are in terms of dB, but I don't think they're that high, like movie theater level (absolute max) and lower.
    Oh yeah, my current setup is pretty bare bones:
    For the mains we have KEFs from the mid 80's, Reference 102s I believe.
    We have a Yamaha natural sound amplifier from the same vintage (CR -620)
    Our DVD player is an Onkyo DV-S535
    Right now, we are just using the stereo outs fromt the DVD player to go into the amp, so I would just use the sub out from the DVD player as well.
    I think thats all, but i'm sure you'll see the little "last edited" thing at the bottom of this post in no time [​IMG]
    THANK YOU ALL VERY MUCH! Sorry about making this long, but thats my story, and i'm sticking to it...
    Oh yeah, if we could keep the price under $100....
    just kidding [​IMG]
     
  14. Joe Meissner

    Joe Meissner Stunt Coordinator

    Joined:
    Jan 31, 2002
    Messages:
    204
    Likes Received:
    0
    Will,
    If you looked at my sub^^^^^ the table top to it is 21-1/2"
    by 20" total height is 30". this could be built using the dayton DVC12. (i used an old SVS driver) but this thing blends in with my mains beautifully. plenty of punch with movies and sounds great with music. I am only using a 120watt amp and really dont see the need to upgrade since i couldnt watch movies at the volume it takes to push this sub to its limits. maybe just for showing off the system but thats it.[​IMG] . well good luck. im just throwing stuff out there for you to think about[​IMG] you could build this sub for under $300.[​IMG]
     
  15. Will Pomeroy

    Will Pomeroy Stunt Coordinator

    Joined:
    Feb 9, 2002
    Messages:
    144
    Likes Received:
    0
    Yeah, your sub looks nice... I like the way it doesn't really look like a sub... [​IMG]
    So James? are you going to reply? thanks!
     
  16. Greg_R

    Greg_R Screenwriter

    Joined:
    Apr 9, 2000
    Messages:
    1,996
    Likes Received:
    0
    Location:
    Portland, OR
    Real Name:
    Greg
    Will,

    I like the look of your sub rendering. Keep in mind that you should make the enclosure out of MDF or BB plywood (so you'll need to veneer the surfaces to get a wood effect).
     

Share This Page