PR18 Specs / Drawing / Photo(s)?


  • Member
    Stereodude on #1364

    1) Specs

    This old thread from 2009 has these specs.

    18″ Passive Radiators : Sd=1200cm^2 – Vd=9.14L – Vas=1840L – Xmax=76.2mm p-p – Cms=0.9mm/N – Maximum mms allowed : 2500g (dual spider)
    Part # ……….. Fs ………. Mms ………… Qms
    PR18-1600 ….. 4.2Hz …… 1600grams ….. 74
    PR18-2100 ….. 3.66Hz ….. 2100grams ….. 85
    PR18-2500 ….. 3.36Hz ….. 2500grams ….. 92

    The product page on the website has this:

    PR18-1600:
    Fs: 4 Hz
    Qms: 85
    Vas: 1840 L
    Mms: 1600 g
    Sd: 1200 sqcm
    Vd: 9 L
    Xmax: 60mm p-p

    There are no specs listed for the 2100 or 2500. What specs are correct?

    2) Drawing

    Is there a mechanical drawing for the 18″ PR?

    3) Photo

    Are the PR18 photos in this directory representative of what is currently being built / sold?


    Member
    Stereodude on #11403

    Another question…

    PR18-1600:
    Fs: 4 Hz
    Qms: 85
    Vas: 1840 L
    Mms: 1600 g
    Sd: 1200 sqcm
    Vd: 9 L
    Xmax: 60mm p-p

    How does a passive radiator with a Sd of 1200cm^2 and 60mm of peak to peak xmax displace 9L? That’s 7.2L of displacement, not 9L.


    Member
    Stereodude on #11404

    Not that I’m getting answers to my questions here, but i’ve been told via e-mail that the specs on the website are correct and the PR18 is dimensionally the same as the TD18 without the motor on the basket. Which means this drawing is basically applicable.

    Unfortunately, it doesn’t have the diameter of the mounting holes in the frame.


    Participant
    Adhoc on #11405

    I scrapped the gaskets which came with my TD18’s, really it isn’t very good. You get better sealing ability with common cellular EPDM used around window frames etc. If you scrap the gasket and want to recess the metal basket rim, you get a snug fit by routing Ø 465 mm, 10 mm deep. I used Ø 5 mm screws for wood, if I remember correctly the screw hole diameter is 8 mm. You may get into trouble if you use M8 machine screws though, you have to be very precise when you drill and there will be little extra wood around the screw. (Whoever made that drawing must have missed geometry class, 8 evenly divided holes with 60 degrees in between … :mrgreen: )


    Member
    Stereodude on #11406

    @adhoc wrote:

    I scrapped the gaskets which came with my TD18’s, really it isn’t very good. You get better sealing ability with common cellular EPDM used around window frames etc. If you scrap the gasket and want to recess the metal basket rim, you get a snug fit by routing Ø 465 mm, 10 mm deep. I used Ø 5 mm screws for wood, if I remember correctly the screw hole diameter is 8 mm. You may get into trouble if you use M8 machine screws though, you have to be very precise when you drill and there will be little extra wood around the screw.

    I was planning to keep the rubber gasket. I used them without issue on my AV15-H drivers. I’ll be using English hardware, not metric since I plan to use hurricane nuts from PE.

    Generally I try to make the driver’s hole undersized a tad and then use a mild roundover on the “corner” so the driver fits flush but there’s a little extra wood for holding the fasteners.

    (Whoever made that drawing must have missed geometry class, 8 evenly divided holes with 60 degrees in between … :mrgreen: )

    I noticed that when I looked at it too.


    Participant
    Adhoc on #11407

    The supplied gasket offers more of good looks than good function. (My personal view, after being in seals and gaskets business since 30+ years.) Put a drip or two of wood glue in the threads of the hurricane nuts to improve airtightness of your box.


    Participant
    stryke on #11408

    The gasket is not intended to provide a seal, but is a cosmetic addition to cover the outside edge of the surround where it is glued down. We always use a closed cell foam tape behind, typically 1/2″ x 1/4″ thickness. This compresses and makes a good seal.

    We either use #10 washers and #10-24 socket heads that will fit through gasket properly, or we use 1/4-20 button head screws. If using 1/4-20 you have to pull back the gasket so you can put the screws in, then let the gasket go back into place once the screw is in.


    Member
    Stereodude on #11409

    @adhoc wrote:

    The supplied gasket offers more of good looks than good function. (My personal view, after being in seals and gaskets business since 30+ years.) Put a drip or two of wood glue in the threads of the hurricane nuts to improve airtightness of your box.

    @stryke wrote:

    The gasket is not intended to provide a seal, but is a cosmetic addition to cover the outside edge of the surround where it is glued down. We always use a closed cell foam tape behind, typically 1/2″ x 1/4″ thickness. This compresses and makes a good seal.

    Well I must be a schlub. I didn’t put any foam gasket tape behind the rubber gasket on my AV15-H sonotubes. They sealed just fine with the rubber gasket against the finished Baltic Birch (5 coats of poly). I also didn’t make any attempt to seal the threads of the fasteners. Who knew I’ve been doing it wrong all this time. 😯

    So, how about all the other PR18 related questions John? Since I’ve already paid for and have several of them on order, the most important question to me is what’s the x-max? 30mm or 38.1mm (each way)?


    Participant
    stryke on #11410

    The suspension will do 38mm maximum before damage, this would be the Xsus, or overall suspension limit. Based on the compliance rise though, if rated as a woofer, the Xmax would be 30mm. From 30-38mm is really operating outside the normal compliance range.


    Member
    Stereodude on #11411

    Okay, thanks for the clarification.

    By the way, what is the diameter of the mounting holes in the metal frame?


    Participant
    stryke on #11412

    Unfortunately the diameter of the holes changes from batch to batch it seems. That is why we just suggest those screw sizes. They are either .300″ or .325″.


    Member
    Stereodude on #11413

    @stryke wrote:

    Unfortunately the diameter of the holes changes from batch to batch it seems. That is why we just suggest those screw sizes. They are either .300″ or .325″.

    Okay, thanks. I think I will go 10-24 this time even though Parts Express doesn’t sell 10-24 hardware inserts. McMaster-Carr to the rescue! I didn’t have the best experience with 10-32 fasteners last time. It was hard to get the 10-32 socket cap screws to start in some of the hurricane nuts even though all the holes were carefully drilled on a drill press. Hopefully the coarser threads on a 10-24 will help with that problem some.


    Participant
    stryke on #11414

    This is what we use for inserts.

    http://www.mcmaster.com/#92105a010/=wsji0s

    We screw them in with epoxy to give a little extra holding power. I always run a 10-24 tap through them after installing them in the cabinet. They are brass so they do warp a little and often times just aren’t tapped overly well. It makes it so much easier to get the bolts in.


    Member
    Stereodude on #11415

    @stryke wrote:

    This is what we use for inserts.

    http://www.mcmaster.com/#92105a010/=wsji0s

    We screw them in with epoxy to give a little extra holding power. I always run a 10-24 tap through them after installing them in the cabinet. They are brass so they do warp a little and often times just aren’t tapped overly well. It makes it so much easier to get the bolts in.

    I was thinking to use these:

    http://www.mcmaster.com/#90267a695/=wsjk80

    But those look better. I can’t see why epoxy would be needed when screwing them into Baltic Birch though.


    Participant
    stryke on #11416

    Not a necessity. We just don’t like to take any chances.

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