Difference between PR's and Porting

Discussion in 'Archived Threads 2001-2004' started by TonyiBe, Mar 9, 2003.

  1. TonyiBe

    TonyiBe Stunt Coordinator

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    I want to know the difference between using Passive radiators and Porting.

    Thanks
     
  2. Seth_L

    Seth_L Screenwriter

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    There is no frequency response difference in theory. They're both Hemholtz resonators.

    However, in practice you can have port compression and issues with the airspeed in the ports, which can cause audible chuffing. A PR bypasses these issues.

    I don't have my Tumult, so I can't comment on the sound of a PR'd enclosure yet, but I'm told they sound different from ported enclosures, more like a sealed box, despite having identical frequency responses (or at least they can have identical responses).

    Seth
     
  3. Travis Cain

    Travis Cain Stunt Coordinator

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    Like Seth said, they both work on the same principal.. I, personally, think that PR's sound a little cleaner and tighter than a port. There are many port advocates that will claim the opposite.

    Neither one will yield a higher SPL than the other though.

    So, unless you have a personal preference to the type of sound one or the other produces, then you're probably going to be happy either way.

    Some things to consider...

    Cost- Ports are far cheaper than PR's.

    Enclosure size- If you're building a smaller cube sub with a higher excursion driver, it may not be possible to fit enough porting into the enclosure.. PR's will avoid that problem.

    Physical appearance- I really think PR's look cool, myself.. I like to see moving cones, the more the better.

    Tuning adjustment- Although it's not too often anyone needs to alter the tuning of their box, PR's make it simple.. Add or remove weight. With a port all glued in place, you can always trim it, but you can't make it longer (unless using a flared port kit and you don't actually glue the flares in place)

    Either way you go, if it's the same box size and same tuning, you're going to get the same SPL and response, with only slightly differences in the sound which is really just a user preference..

    I just bought a Tempest and 2 PR-15's so that shows how strongly I favor PR's over ports..

    Hope that helps.. [​IMG]
     
  4. Travis Cain

    Travis Cain Stunt Coordinator

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    Oh, and one other advantage PR's have over ports is driver protection below tuning..

    With a port, once you get below it's tuning point, it unloads the driver completely making it very easy to push your driver beyond it's mechanical limits to a point of damage.. Passive radiators will still begin to unload the driver below their tuning point, but not nearly as fast as a port so you still have *some* protection..
     
  5. TonyiBe

    TonyiBe Stunt Coordinator

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    Thanks guys for the repsonses.

    I knew Jack would chime in. I have seen some of the enclosures you built and i know you know PR designs well. Yuo build some nice enclosures. Thanks for the link as well.
     
  6. Mark_E_Smith

    Mark_E_Smith Second Unit

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    As usual I learn something from the "fortunate son"[​IMG] ! I have a comercial pr system that sucks, I thought all prs did, but the Stryke FAQ makes since and has changed my mind. Maybe i'll take a look and see if I can tweek the system I have.
     
  7. ThomasW

    ThomasW Cinematographer

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    There are some 'misconceptions' on the Stryke site too.....

    Properly design and implimented ports do not chuff or create compression. Nor do they create transient impulse 'ringing/overshoot' inherent with high mass PR's

    If you need the smallest box possible then use a PR.

    If you want 'vented' sub that has the best pitch definition and least 'coloration' use a port. But understand that the port MUST be flared. And it MUST be of sufficient diameter, to avoid issues like compression/chuffing.

    Obviously this is just my $0.02.....[​IMG]
     
  8. Jack Gilvey

    Jack Gilvey Producer

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    When space/Vb permits a large enough ("properly designed" [​IMG] ) port, I'd always go/suggest that route.

    I do not find that PR alignments sound "somewhere between a sealed and ported box" , as I've seen suggested, and I do not find that they offer more driver protection from unloading below Fb (I don't see how this could be the case unless there was little enough PR Vd available so as to negate the prime {or sole} advantage of PR's anyway).
     
  9. Seth_L

    Seth_L Screenwriter

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    Thomas,

    I think the problem is how you define a "sufficient diameter" port. How much airspeed is allowable? Most (if not all) commercially available ported subs are underported.

    Seth
     
  10. Jack Gilvey

    Jack Gilvey Producer

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  11. ThomasW

    ThomasW Cinematographer

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    Seth

    I think the general tendency is for undersized ports everywhere, given the co$t and box volume occupied by larger ones.

    IMO 6" flared is the mininium size for a single high excursion 15". And 4" flared is appropriate for 12"s.

    Now I'm certain that there are many people that will disagree with this. My experience is that 'overporting' to some degree is the best way to avoid the potential performance drawbacks of a ported design.

    I don't get to fixated on mach numbers. It is important with 'woofers' reaching into the lower midrange. Subs on the other hand are more forgiving of slightly higher Mach numbers and or distortion. But unlike some, I feel that 10% distortion is too high [​IMG]
     
  12. TonyiBe

    TonyiBe Stunt Coordinator

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    Where can i get 6" aeroports. Will one be enough for an AV15...

    Thanks Guys, i learned alot from reading the stryke site as well.
     
  13. Joey_N

    Joey_N Agent

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    This was a good read, thanks for the info guys!
     
  14. David Lorenzo

    David Lorenzo Stunt Coordinator

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    Dual 3" flared ports would also work well for an AV15. It gives the same mach as a single 6", and they would be much shorter.
     
  15. Seth_L

    Seth_L Screenwriter

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    I don't think so David. The cross sectional area of two 3" ports and 1 6" port are not the same. a single 6" port has 2x the cross sectional area of two 3" ports and as a result has twice the length and half the air velocity.

    Seth
     
  16. David Lorenzo

    David Lorenzo Stunt Coordinator

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    Well then something weird is going on in WinISD. I never did any math. I just went by what WinISD came up with. A single 6" port measured a mach of .10, of course that would change with different tuning, and with 2 3" ports the mach given is still .10. You are right, however, about the area. So I don't see how the air speed can be equal. Any thoughts? Is WinISD wrong when calculating mach?
     
  17. Seth_L

    Seth_L Screenwriter

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    Are you sure you had the same input power? I used WinISD to come up with my numbers.

    Seth
     
  18. Patrick Sun

    Patrick Sun Moderator
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    WinISD doesn't seem to be strong in calculating the mach numbers.
     

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