Sealed 142.5L Shiva

Discussion in 'Home Theater Projects' started by Russell R, Nov 22, 2003.

  1. Russell R

    Russell R Stunt Coordinator

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    Hello,
    I want to experiment with the setup that I have. It is currently a 142.5L 21.5hz Shiva. What would be the pros and cons of making this setup sealed? I have modeled it in WinISD and notice that the frequency response is not as low, but will it be capable of HT reference levels with a PE250 Plate amp? How low will it play in a small room with the sub corner loaded? Is it safe to assume that it can produce 25hz? Are there other enclosure volumes that may be better?

    I have thought about a passive radiator on the top. Can a PR15 be mounted in a horizontal fashion? I am looking at the Shiva EBS PR alignment. This way, there is no cutting of the sonotube that it is currently residing in.

    Your thoughts,
    Russ
     
  2. ThomasW

    ThomasW Cinematographer

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  3. Russell R

    Russell R Stunt Coordinator

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    Hello,
    I have the upgrade/DIY bug, which is the reason for all of the questions. Here is what I do not understand. Taking the Shiva alignments for example, what would give me the best bang for the buck when it comes to HT use? My current sub needs a port change due to port noise during high levels at certain frequencies, hence the reason to explore other options on this platform. I want to step up from a 4" flare to 6" flare; this should help me out with the chuffing. I modeled a sealed with the same volume and did not like the results, or at least I saw a drastic low end decrease in response. After reading about other sealed recipes, there is data in the mid 20hz, which should be OK for HT use and should be tighter for music use. The sealed coupled with room gain and EQ should give me good results, correct?

    When designing a sub, what factors are taken into account for cone excursion? Are you trying to limit the excursion or increase the excursion, within its design capabilities?

    Back to the alignments, the SBB4 and Adire ported designs seem to have more punch and that is what I am looking for. What doesn't make sense is after room integration and EQ, shouldn't all three ported platforms sound similar? I chose the EBS due to the low extension, but does the other two actually have more punch for HT? Why, after calibration?

    Thank you very much for all of your time and effort on this.

    Russell
     
  4. ThomasW

    ThomasW Cinematographer

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    There should be no port chuffing using a Shiva with a 4" flared port. If the port is too close to an adjacent surface or if the damping material is to near the port those things can cause chuffing. Also some people do hear chuffing with test tones at very high output levels, that type of chuffing isn't audible during every day use.

    To test the sound of a sealed box just cram something in the port, a towel or a rag will do the job. The best method is to get a 'nerf' football or foam rubber ball cover it with kitchen plastic wrap and stuff it in the port.

    Compared to a ported boxes sealed boxes double the excursion of the driver. And they are less efficient.

    EBS are designs play low, other higher "Q" designs have more 'punch' because they aren't being ask to play low with their higher tunings.

    The room is the great 'equalizer' between various "Q" boxes.

    There really isn't a way to answer an abstract question about which alignment will be 'best' in your needs. DIY audio is all about experimentation (with accompaning success/failure). Sort of like learing to fly by playing Flight Sim programs vs taking flying lessons. There is no substitute for hands on experience.

    Something else to consider is whether or not you just need the added output of a bigger driver and additional Shiva
     
  5. Russell R

    Russell R Stunt Coordinator

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    I have chuffing during movies at loud volumes. I have not had the time to investigate "how loud" and "what freq", but I will very soon. I have the 4" port in the center of a 14"id tube. Could that be too close?

    Good idea with the nerf football. I will try that.

    Eventually, I will add another driver to complement the setup.

    Thanks again.


    Russell
     
  6. Frank Carter

    Frank Carter Screenwriter

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    If you can lay your tube down you can add the PR.
     
  7. ThomasW

    ThomasW Cinematographer

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    Ports should be spaced a distance equal to or more than the port diameter from any adjacent surface. So you're close to the minimium distance.

    Did you use a flared port? Flared ports flow as much air as the next larger sized straight port and they drastically cut down on chuffing.

    How long is the port?
     
  8. Russell R

    Russell R Stunt Coordinator

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    I used a PE 4" Flared port. It is around 13" total (including flares) for a tune around 21hz. So, I have ~5" next to the adjacent surface. Could that cause the chuffing? How can you get away with using anything smaller than a 14"id tube? I could not imagine using a 12" and a 4" flare. This sub will eventually be moved to another room for background listening duty, so I will not be pushing it as hard. Don't get me wrong, it does sound good and does go low, but on occasion at high levels, there is chuffing. Not that bad, but an annoying air turbulance. I am sitting in a small room that may not help matters. The sub is placed ~6 feet from the listening position.

    Thanks,
    Russ
     

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