Group delay query (Sealed vs vented Tempest sub design)

Discussion in 'Archived Threads 2001-2004' started by MarkJD, Apr 15, 2002.

  1. MarkJD

    MarkJD Auditioning

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    Hi

    I'm a complete newbie at this stuff, so please bear with me.

    I built a couple of vented 300 liter sonosubs tuned to 16Hz based on the Adire Audio "Tempest" driver last year. They sound terrific for home theater. By accident rather than by design, the subs look to be similar in LSPCad's "Free air SPL at 1m distance" to Adire's "Vented EBS Box" design.

    Adire state that their vented EBS box is designed for audiophile bass. I am interested in opinions of the difference between Adire's sealed Q=.577 design and their vented EBS box. In particular, the group delay of both subs don't appear to have significant differences at above 20Hz.

    If I were to build one of Adire's desinged sealed Q=.577, how would it sound different from their vented EBS design?

    Thanks

    Mark
     
  2. Richard Greene

    Richard Greene Stunt Coordinator

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    I doubt if you will hear from anyone who has built both a sealed and ported Tempest subwoofer.

    I built a sealed Tempest in a 230 liter enclosure stuffed with eight pounds of polyfill which should result in a Qtc in the neighborhood of 0.577. A sealed Tempest will have significantly less bass below 30Hz. than a ported Tempest unless equalized to boost bass below 30Hz.

    Concerning any differences in group delay (that are probably less than 20 milliseconds) -- here are several factors that would interfere with your ability to hear these group delay differences:

    (1) Sound coming from the main speakers masks the sound coming from the subwoofers

    (2) Room bass resonances will cause bass frequency response deviations in the neighborhood of +/- 10dB or more (deviations can usually be cut in half by using a parametric equalizer)

    (3) Room ringing (slow decay) at several room bass resonance frequencies will last perhaps 200 milliseconds until the sound attenuates by 30dB

    Considering (1), (2) and (3), I would guess that group delay differences would not be audible at all, especially with the low port tuning frequencies used in extended bass shelf designs.

    So why would anyone build a sealed Tempest rather than an EBS design to extend bass lower? For me the answer is that my walls rattle loudly at 18-20Hz., even with concrete slabs leaning against them, so I don't want full output at

    18-20Hz. in my room. For me an EBS design would be a real "wall resonator" (I'm too lazy and too cheap to rebuild my living room walls)
     
  3. Pete Mazz

    Pete Mazz Supporting Actor

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    Plug the port with something and let us know! [​IMG]
    I found the bass to be more controlled when I tried a sealed enclosure. The lower Q enclosure(twin Tempest .6 Q) give me all the bass I could want in my room.
    Pete
     
  4. MarkJD

    MarkJD Auditioning

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    Thankyou both for your replies.
    I guess I could try plugging the ports on my vented subs to check it out. Good thinking dude! [​IMG]
    Question is, as the ports are 8 inch diamater, what can I use to plug them?
    Thanks
    Mark
     
  5. Mike Strassburg

    Mike Strassburg Second Unit

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    You could use some foam out of a couch cushion or maybe a ball of newspaper wrapped in duct tape. If it's only for a test and no one will see it that is [​IMG]
     
  6. Ryan T

    Ryan T Second Unit

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    you could just take a wadded up T-shirt and stick it in the port. Or if you have any poly batting laying around that should work also.

    Ryan
     
  7. Brandon B

    Brandon B Second Unit

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    Use a balloon.

    BB
     
  8. ScottZol

    ScottZol Auditioning

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    So I'm curious as to the results. The reason I am curious is that I have almost completed a vented 192L enclosure (haven't cut the port and driver hole in the bottom yet) for a Tempest, but have not yet decided if I want it vented or sealed. If I go vented, and then plug the ports if I like the sound better, is there any reason to believe a truly sealed box of the same dimensions would sound better that a vented/plugged one?
     
  9. Dustin B

    Dustin B Producer

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    Well I haven't done very extensive comparisons and they weren't blind. But I thought I noticed a very slight improvement in the detail of the bass when I plugged the port in my 260L Tempest tuned to just over 16hz. But for the big HT explosions, I had a definate preference for the port not being plugged.
     
  10. Jack Gilvey

    Jack Gilvey Producer

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  11. ChristopherD

    ChristopherD Stunt Coordinator

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    Jack, that's what I'm planning for my Tempest project. Is there an alignment that would be more conducive to getting the most out of my "VTF" Tempest? I'm thinking EBS at this time.

    Gracias!
     
  12. Jack Gilvey

    Jack Gilvey Producer

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    I like the EBS for this type of project. Really low reach for HT, and a nice, "low-Q" sealed sound.
     
  13. ChristopherD

    ChristopherD Stunt Coordinator

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    Thanks!

    Finally a decision has been reached!
     

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