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SUbwoofer building - ports square vs round ?

Discussion in 'Amps and Cabs [BG]' started by 4Mal, Aug 29, 2007.


  1. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    My design calls for qty 2, 4" round, 10.5" deep ports. As a 4" dia circle is about 12.5 sq in, can I achieve similar results using a shelf style port that provides the same sq". That would be 25 sq in with a divider that 1. supports / braces the shelf and makes it 2 chambers rather than 1 ?

    The cab itself is meant for small PA support. It will handle the 50 to 125 area and take the strain off my EON 15 tops. I'm thinking about the occaisional job where it would be nice to mic the kick...
     
  2. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
  3. tonejunkie

    tonejunkie

    Dec 11, 2006
    Cape Coral, FL
    Thanks for asking this question 4mal! I am in the middle of building a sub for myself and I substituted a rectangular port for a round one. I just figured that the issue is the area so that the volume of air can go in and out. If the area is too small, the air will start to make "chuffing" noises and you'll have to add flares.

    It's good to know someone thinks the way I do. Wait, that's kinda scary...
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    WinISD does a good job of calculating both circular and rectangular ports. It's free to download, so I'd do it as a double-check.

    Or, let me know the cab details and I'll run the figures for you (Cab volume and intended tuning frequency is all I need.)
     
  5. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Mal's looking at doing a <3 cu ft cab., max, unless he changed his mind since yesterday.:cool:

    His Eons don't get real loud, and the single BMS 12" driver he bought will work pretty well with them, I think.
     
  6. questhe

    questhe

    Jul 17, 2007
    mesa, az
    Round is better, less turbulance.
    Best would be a flare on BOTH side of the cylinder, but most expensive. Turbulence sounds like the chuffing.

    Pretty high-fi to flare, may not be noticeable for bass cabs.
     
  7. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    Ah, baby subwoofer! Is that the 12N630 he's using? Looks a really nice woofer if you don't need it to play up into the midrange.

    Alex
     
  8. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Aye, and aye, AFAIK.;)
     
  9. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Wow. Assistance Audio actually followed through?

    I guess I'd go about 1.6 cf with this and tune it a little higher than a quasi butterworth.
     
  10. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    http://www.brownellsound.com/

    The Website has the phone for contact and that is about it. I generally deal with Talot or Kurt. Yes it is the BMSPRO 12N630. They had a few in stock when I grabbed mine the other day.

    For my uses, a sub doesn't need it to do anything but woof in a very tight band. I'm planning on a steep 50 hz hi pass on it and feeding it 125 and below. Maybe not the most elegant, broadest subwoofer design but - for a small / medium club where I'm wanting to mic a kick it should help keep my EON's from damage and richen things up on the low end. This would be blues, root's rock, surf - no techno/DJ/hip hop... for my uses I think 50 is as low as I really need.

    The box itself is 2.25 cu ft internal and according to the designer it should do 99 db 1 watt at 56 hz, something like 124 with around 400 watts. So a really practical box considering I move my 4x10, mixer in a case, 2 4 space racks, basses, poles, 2 EON 15's and monitors - in a Subaru outback wagon... I'm all about small and practical - after bracing i'm at something like 14.5 x1 5.375 x 19 PW's suggested I think about a 21" dim rather than the 19 for stackability. It's a good point and I gotta think on that.

    When the Van's "Warped Senior's"* tour call's me up I'll ask for a truck!

    an old friend Kurt Bever's is the proprietor at Brownell. So no - to date I've never had a call returned by Assistance Audio. I think I'm too small a fry to pop up on their radar. Kurt is bigger fish though ... great guy to deal with as well. If he tell's ya it's blue- when it get's to ya it will be blue, not a shade of green ...

    So part of what I've heard tell's me that the shelf style port has the potential to muck about with your tuning to a degree that the round port doesn't. This may be due to friction build up in the port itself. So is it that the wood itself is more 'friction prone' than the plastic of the 4" pipe or is it really the square vs round shape.

    I'm hoping to have this little beast off the paper and listenable next week some time.

    *Vans Warped Senior's Tour. Kinda like the PGA Senior's but for those with a warped but musically inclined outlook on things - anybody out there want to sponsor that ? I can probably coax The Crackertones onto that tour. If our song "I Love Lesbian's" doesnt qualify ... I don't know what will..


     
  11. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge

    not so far but then you know me pretty well ...
     
  12. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    In a 1.7 cf box tuned to 33 Hz or so the driver doesn't even start to fall off until 50 Hz, - 3 dB at 34.5 Hz. For what you want it, you could easily fall back to 1.5 cf and tune it say to 37 Hz.

    Not what I'm seeing, perhaps I need to see if BMS has upgraded the driver. It's one I was looking at last year and I think it's a really good small box deep bass extension driver. Little else reaches that low actually, when it's in the box size you are mentioning. But you might actually like a slightly higher cutoff and more power handling.

    I was considering a 212 of 3.5 cubic feet myself.
     
  13. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    What kind of efficiency would you see with that 1.7 ft box ? To tune it that way what would the porting look like ? I'm planning on running the 50 hz filter on my QSC. I've got 425 into 8 ohms for it so efficiency is important.

    I've got the tools. I may do a couple of itterations. The 2.25 cu ft design and then maybe a 1.7 Passinwind and I can do a comparo and see how they stack up.
     
  14. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    What program are you looking at that in? WinISD suggests that some of the supplied parameters are wrong and calculates what they should be from the other bedrock figures of

    mms
    cms or fs

    then

    sd
    bl
    re

    then

    qms
    xmax

    etc

    It pegs some of the datasheet and website figures as wrong and from what I've observed I'd have to agree.
     
  15. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Oddly enough though some of BMS's figures are suspect, they recommend enclosure volumes much like mine.
     
  16. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    ummm, Im not actually using a program. The box size was recommend to me by Brownell. He's used the driver in a number of portable and fixed install applications - custom design and build is a big part of what he does... I'm winisd impaired. Partly it's because I work in software development as my day gig. Between that and Pro Tools - there just isn't any mental shelf space left for Win ISD. So I'm a beggar when it comes to box design ...
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
     
  18. chadds

    chadds

    Mar 18, 2000
    Blaming your pants for "chuffing" noises is irresponsible (unless you are wearing corduroys). While we are on the subject of pants I'm not wearing flares anymore!
     
  19. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Indeed. I'm glad you brought that up, Petebass. I was going to address that and got so carried away on the other part of the post that I forgot to.

    Like you, I think shelves are a great way to deal with port velocity in a given amount of real estate.
     
  20. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Friction between the air mass and the duct walls does exist. The effect only extends a few millimeters from the wall and for the most part is negligable in impact. However, a sufficiently narrow 'shelf' style duct can exhibit a lower than anticipated resonant frequency when the airmass within a few millimeters of the walls is a substantial percentage of the airmass in toto. For this reason one should not make shelf style ducts less than an inch across in the narrow dimension.
     
    PawleeP likes this.

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