Tempest Porting Question

Discussion in 'Archived Threads 2001-2004' started by Andrew S, Sep 19, 2002.

  1. Andrew S

    Andrew S Stunt Coordinator

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    Being 16 and 4 months away from my license, I want to put the Tempest I bought this summer in a box to go into the trunk of my dad's old car, which will be passed down to me if it's still running by then. I've been reading a lot at teamamp.com in the Adire forum, and I THOUGHT I had my box perfectly planned. It was gonna be:
    34" wide
    18" deep
    14" high
    These are all internal dimensions so the box will be about 5 cubic feet before displacement. I've read man post where Dan suggested this size, so I'm pretty set with it. The port is what I'm really unsure of. I originally planned on a 4" internal diameter by 12.5" long pvc pipe to tune it to about 23hz, if I've read correctly, which is supposed to give really good SPL while maintaining good SQ. But then I started reading about people having a higher tuned port for SPL and just plugging it for daily listening. What I wonder is, can I somehow keep my 23hz tuning and have another higher tuning for when I feel like having it really loud? Maybe having two ports with two different tunings, and just plugging one depending on your mood? If this is impractical, then I'll gladly just stick with the 23hz tuning and be happy with it. Just thought I'd ask anyway.
    Also, if it IS possible, can anyone recommend the higher tuning frequency that would yeild high SPL?
    Any info would be greatly appreciated.
    Thanks,
    Andrew
    P.S. I've read all the posts in the AFter Hours lounge about those damn teenagers blasting their music at all hours, and just wanted to say that I'll be considerate [​IMG]
     
  2. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Uh-oh, another teen loosed on the world, and he's going to have a Tempest sub! The boom-boom-booming will reach your ears before his car comes into view. My son turned 16 last Sunday and his older sister gave him her 1985 Honda Accord, so there's no telling what hes' going to want to do...AND, he got an elctric guitar too [​IMG]
    Andrew, thanks for being considerate[​IMG] You'll get good advice from others, I just wanted to vent here.
     
  3. Andrew S

    Andrew S Stunt Coordinator

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    Well don't worry, the only time I'd really turn it up is if somebody asked me what kind of "no name" crap I have in my trunk, or if someone claimed their sony xplods can take my sub anyday...
    Besides... I'm too cheap to pay the few dollars at the border to get into the states, so I wouldn't be worried about me waking you at night [​IMG].
    Andrew...
     
  4. Andrew S

    Andrew S Stunt Coordinator

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    Anybody?
     
  5. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    Andrew,

    I'm not by any means a car audio expert, but I'll give my two cents anyway. I don't believe there is anything wrong with doing a 'two port' system. I don't see it much different than doing the 'plug the port for sealed' setup. As far as what the higher tuning frequency should be, I think most people in SPL contests find the frequency which is most naturally boosted by the car, and tune their enclosure to that frequency. Just my thoughts.
     
  6. Darren_T

    Darren_T Second Unit

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    I'm no "expert" but I think it would work.
    With a ported enclosure I believe you can get away with a bit more, meaning that the "weak" spot that the seal around the plastic port creates as compared to the rest of the enclosure won't be as critical as if it was sealed. I'd think that if you had two ports and plugged one to create a different tuning frequency you'd be ok as long as both tuning frequencies created by the ports didn't allow the driver to extend beyond xmax within your operating parameters.
    Wow, that kind of sounded like I knew what I was talking about, or not. [​IMG]
    Darren
     
  7. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    If what you're looking for is sound quality, then I would lower the tuning point to 18hz.

    If you tune a 140L box to 24hz you get a mid bass hump at about 45hz. If you're trying to achieve a smooth response then perhaps a lower tuning point would work out.

    If you want to tune the box higher you'll achieve a considerable hump in the response which may be desirable if you want a one tone car boomer.

    For instance,

    tuning the box tos omething like:

    40hz will provide a gain of about 7db at 48hz.
    60hz = 11db @ 66hz
    70hz = 12db @ 75hz
    30hz = 4db @ 42hz

    AFter those calculations, you can also calculate the cabin or trunk resonance frequency of your car. This can be done simply by playing test tones and measuring which tone is the loudest. (Should be below 80hz). Then tune the port on the box so it provides maximum gain at the cabin resonance frequency.

    The response won't be smooth, but it'll be loud when you play test tones or songs that have your "booom" frequency.

    So in the end you'll be switching between the port that provides a maximum bass hump and the port that provides an even response.
     
  8. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    The people with cars that have smooth frequency responses you don't have to worry about.

    It is the people with huge bass humps that have done their homework that you gotta watch out for. They're the ones capable of tones at around 150db.

    Imagine how hard it would be to produce 150db in an infinite baffle/anechoic environment. hehe, it would take 1 million watts for a tempest to output 150db.
     
  9. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Chris,

    You've got to remember the huge amounts of cabin gain you get in a car at low frequencies. That mid-bass hump might even be dwarfed by 20Hz output in some cars. Often car guys will tune to mid 30's or low 40's in an effort to get flat output down low.

    If car audio alignments don't work well in HT then the reverse is also true.

    -Ryan (not a car audio expert)
     
  10. Brian Bunge

    Brian Bunge Producer

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    I'd do a single port tuned between 30-40Hz for max SPL and then plug it up to create a sealed enclosure for SQ.

    Brian
     
  11. Jon Torres

    Jon Torres Second Unit

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    I second what Brian said. You don't need to tune to 23 Hz for car audio. Home audio is totally different.
     
  12. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I guess cabins/trunks are different volumes so I shouldn't be suggesting a tuning point. I also don't know the volume of the trunk. What I don't understand is how would he get very low frequencies if he tunes the sub to 30-40hz? Will a trunk boost frequencies in the 20hz-30hz range?

    I guess I think too much of my case where I drive with the windows down a lot so that's why cabin gain plays less of a roll.
     
  13. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    As I understand it there are two types of "room gain":

    1) The gain from being enclosed in a certain volume of space. This would change based on whether you have the windows up or down.

    2) The gain from boundaries near the sound source. This means that much of the energy that starts to travel backwards, towards the trunk gets reflected off that boundary back into the enclosed space. Same for the sides, front, top and bottom. Basically (ha!) its just tough for the energy to escape all these boundaries. It still happens certainly. But much of the energy is reflected back.
     

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