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  • Steve Lee
    commented on 's reply
    One Ping ONLY, Vassilly . . .

  • Jicafold
    replied
    Originally posted by randyohoh View Post
    Using real numbers will push actual measured performance closer to calculated / modeled performance.
    I understand what you are saying here, but I'm not making the Space Shuttle. I'm not going to sweat miniscule differences and do not believe that a hundreth of an inch translates to any significant practical audio difference in the real world environment while I am watching The Hunt for Red October.

    Leave a comment:


  • Jicafold
    replied
    Originally posted by DeZZar View Post

    GASP!! Leave this forum immediately!!!

    hahaha.....jokes. Great first build.

    I'm guessing your internal volume is around 6.5L net with port, crossover etc considered. If that's the case your current ports tune the enclosure to around 58hz.

    Assuming the 80hz high pass mimics 2nd order roll-off the maximum power handling is around 90watts for these two woofers and at this level they are producing just north of 102-104db (a little less with the crossover factored in) but the potential issue is the port velocity with your chosen dimensions is up around 50meters a second (WITH the 80hz high pass filter) - essentially a hair dryer. Its over 80+ m/s without the high pass filter and max power.

    Whether you hear this and find it unpleasant or not is entirely your call.

    Two ports with an internal diam of 1inch and a length of 4.75 inch would provide the same tuning and reduce the port velocity to something more reasonable at typical listening levels (19m/s @ 100db w/ 40watts)
    A hairdryer you say? That’s an interesting and rather alarming analogy. Perhaps I will make those ports bigger. Thank you for that information.

    Leave a comment:


  • DeZZar
    replied
    Originally posted by Jicafold View Post
    ...or just buying the somewhat similar Dayton Audio MK442.
    GASP!! Leave this forum immediately!!!

    hahaha.....jokes. Great first build.

    I'm guessing your internal volume is around 6.5L net with port, crossover etc considered. If that's the case your current ports tune the enclosure to around 58hz.

    Assuming the 80hz high pass mimics 2nd order roll-off the maximum power handling is around 90watts for these two woofers and at this level they are producing just north of 102-104db (a little less with the crossover factored in) but the potential issue is the port velocity with your chosen dimensions is up around 50meters a second (WITH the 80hz high pass filter) - essentially a hair dryer. Its over 80+ m/s without the high pass filter and max power.

    Whether you hear this and find it unpleasant or not is entirely your call.

    Two ports with an internal diam of 1inch and a length of 4.75 inch would provide the same tuning and reduce the port velocity to something more reasonable at typical listening levels (19m/s @ 100db w/ 40watts)

    Leave a comment:


  • Steve Lee
    replied
    Originally posted by Jicafold View Post
    The 0.75 diameter I posted for the PVC was in the inner diameter. It has a 1 inch outer diameter. When measuring with a digital calipers it actually measures 0.79 inches on the inner diameter. I haven't noticed any chuffing when running full range, even when listening to rap.. So I think I'll leave things as is. Thank you.

    I wonder what the size of the single port is on the Daytion MK442 shown below? Looks like it may be inch and unknown length. I also wonder how that speaker compares to what I built but I don't want to buy on just to find out. Does anyone here have one?
    MK442 port dimensions:

    Depth/length = 80mm
    Diameter = 31.8mm

    Leave a comment:


  • randyohoh
    replied
    The dimensions in the chart are US industry standards and any schedule 40 PVC pipe purchased in this country will conform to these dimensions within a small, insignificant, tolerance. Custom manufactured plastic ports are another story and probably measure as advertised within an insignificant manufacturing tolerance of +/-.005 or so.

    It's impossible to get a precise measurement of an inside diameter with a digital caliper due to the width of the blades of the caliper. The measurement takes place at the edges of the caliper blade and not the center, providing smaller than actual numbers. The blades on my cheap, Chinese, caliper measure .078 (2mm) wide which introduces a .010 error when attempting to measure an .824 inside diameter.

    The idea behind the chart was to make sure that designers realize that the nominal dimensions of PVC pipe are not the actual dimensions and if used the nominal dimensions will introduce errors into port calculations and subsequently enclosure tuning. A 1-1/2" PVC pipe actually has an actual inside diameter of 1.610. The area of 1-1/2" diameter is 1.767 square inches while the area of the actual 1.610 pipe inside diameter is 2.036 square inches, 15% larger. The area of .750 (3/4") diameter is .442 square inches while using the actual .824 diameter provides an area of .533 square inches, 20% larger.

    Using real numbers will push actual measured performance closer to calculated / modeled performance.

    Leave a comment:


  • Jicafold
    replied
    The 0.75 diameter I posted for the PVC was in the inner diameter. It has a 1 inch outer diameter. When measuring with a digital calipers it actually measures 0.79 inches on the inner diameter. I haven't noticed any chuffing when running full range, even when listening to rap.. So I think I'll leave things as is. Thank you.

    I wonder what the size of the single port is on the Daytion MK442 shown below? Looks like it may be inch and unknown length. I also wonder how that speaker compares to what I built but I don't want to buy on just to find out. Does anyone here have one?
    Attached Files
    Last edited by Jicafold; 07-18-2021, 10:45 AM.

    Leave a comment:


  • randyohoh
    replied
    I posted this chart a long time ago and it shows what a small change in port diameter does to the area and subsequently to box tuning. Also the actual PVC internal diameters are not the nominal size of the pipe.

    Click image for larger version

Name:	Pvc Dims.jpg
Views:	424
Size:	190.8 KB
ID:	1473273



    Leave a comment:


  • Jicafold
    replied
    Originally posted by wogg View Post
    Probably not a big deal if your AVR is set to high pass at 80Hz anyway. If you're attempting to put out bass from that thing though, I'd agree with Chris.
    Yes. It is set at 80 Hz. I will think about it. I can move it to the 2 channel system and crank it up to see how it performs. Thank you.

    Leave a comment:


  • wogg
    replied
    Probably not a big deal if your AVR is set to high pass at 80Hz anyway. If you're attempting to put out bass from that thing though, I'd agree with Chris.

    Leave a comment:


  • Chris Roemer
    replied
    Not so much from a tuning/FR point, but from a chuffing point, I'd say yes.
    For my TM (in 0.09cf) I used a 1-1/4"id tube. For a pair that'd be equivalent to a single 1-3/4" tube. (You're about at an equiv. single 1"id tube now.)

    Leave a comment:


  • Jicafold
    replied
    Originally posted by Chris Roemer View Post
    I'd (personally) probably have tuned the box a bit higher (and gone w/larger dia. ports).
    A pair of 1.0" id x 4" long ports seems about right (a single 1-1/2" x 4" port would also suffice).
    So changing those ports like you say would change the tuning frequency from 59hz up to 64hz. Does that really make that big of a difference?

    Leave a comment:


  • Jicafold
    replied
    Thank you. I initially did have the woofers closer together exactly for that reason. However, aesthetically it just looked a little wonky. So I moved them a tad further apart. But I did choose the nested design to help with off axis response.

    Box is still essentially unfinished. My router job to flush mouth the drivers could be better. I will likely do some additional standing, wood filler, caulk, and paint to improve its appearance.

    Leave a comment:


  • Chris Roemer
    replied
    EXACTLY !

    Looks really good for your 1st design. Box size/tuning is "reasonable", and XO SEEMs okay.
    (Just to nit-pick):
    Bringing the woofers closer together would probably improve/reduce off-axis "combing".
    I'd (personally) probably have tuned the box a bit higher (and gone w/larger dia. ports).
    A pair of 1.0" id x 4" long ports seems about right (a single 1-1/2" x 4" port would also suffice).

    Leave a comment:


  • djg
    commented on 's reply
    I can get most of mine under the queen bed with a four poster frame. The rest just sit around.

    It's nice to give them as gifts too.
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