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Shiva Subwoofer-please help,something just not right.

Discussion in 'Archived Threads 2001-2004' started by Marc_D, Jan 18, 2001.

  1. Marc_D

    Marc_D Extra

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    Let me start by saying it is not the actual driver from Adire, but MY alighnment/enclosure.
    Previous set-up:
    2- 8" 100watt subwoofers that are built into my Infinity RS-8 main speakers. output range:32Hz-110Hz.
    I want more quality bass and more quantity of bass.
    Current Set-Up [​IMG]Tell me where I went wrong!)
    I am NOT acheiving the SPL that I had expected. Also at loud volumes when a loud explosion happens on my dvd, the driver POPS really loud. (I turn down immedialtly to not dammage the driver). The driver distorts too easily at high volumes with music or movies.
    Shiva in a 4.8 ft^3 effective size (total size minus driver, port, bracing etc..)enclosure made from 3/4" MDF. Port is a Lightning Audio 3" flare port, which tunes enclosure to 23Hz. Parts Express 250Watt plate amp (same a Adire, but still has 30Hz "boost"). The Shiva is wired with both (+)'s on the voice coils connected to the (+) on the amp, and both (-)'s connected to the (-) of the amp. Thus giving a 4 Ohm load to the amp (I think)?
    I have a H/K AVR 500 receiver.
    I have all my speakers set to small (100hz-20Khz) and set in the middle of the range (0db) The subwoofer is set on (20Hz-100Hz) and also set at 0db. The bass is set at the middle detent. On the PE plate amp, the level is straight up and down.(halfway between min and max). The cross over is set in the middle (halfway between 40hz and 160Hz) 100Hz. Polarity is adjusted a best as I can determine with my head stuck back there where I can reach it.
    Here are the enclosure particulars:
    The Internal dimensions are 22.875" X 23.4375" X 18.25"
    =9784.424 in^3
    - 183 in^3 (driver displacement)
    - 50.53 in^3 (port volume)
    - 632.85 in^3 (internal bracing)
    - 620.5 in^3 (bricks) *see below*
    --------------------------------
    8297.55 ft^3 =4.8 ft^3
    *I had to adjust my volume due to the fact that the internal piece to my port would be less that an inch, which would not work. So I had to fill some space in the enclosure to get the port length and the enclosure volume right. Thus the bricks I added for volume and weight. This thing weighs a TON. Is there something else I can us to take up space w/o the weight?
    The length of the port is calculated according to the following equation.
    Lv= 8466.4 X (Vr)^2
    ------------------------ - 1.463 X Vr
    Vb X (Fb)^2
    where:
    Lv= Vent Length
    8466.4 = contstant
    Vr = vent radius = 1.34"
    Vb= Enclosure volume (ft^3) = 4.8 in^3
    Fb= Tuning Freq = 23Hz
    1.463 = contstant
    =4.02" Lv
    cut center piece of port 3" less to achieve proper length.
    = 1.02"
    WHAT IS WRONG?
    Is the driver wire incorrectly?
    Is my alighnment off?
    Is the enlosure volume/tuning incorrect?
    Will someone please help me!!!!??
    I have spent over $350 and a lot of time to get a sub that is SUB standard. [​IMG]
     
  2. ThomasW

    ThomasW Cinematographer

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    For a 4.8 cu ft box, tuned to 23Hz, using 3" diameter port with dual flares, the port length should be 5.514".
    Take out the bricks [​IMG]
    Check for air leaks, set your mains to large, turn off any bass boost in the plate amp. Make sure that the sub and the mains are "in-phase"
    If the popping sound continues, I'd suspect the amp is being driven into clipping.
     
  3. Eric M Jones

    Eric M Jones Second Unit

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  4. Marc_D

    Marc_D Extra

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    Thomas.
    Thanks for the quick reply!
    What equation did you use for the port length? The one that I used and posted is from the port manufacturer. I would assume it to be correct. Did I do the math wrong?
    If I take out the the bricks, the volume of the enclosure will increase, thus screwing up the alighnment.
    No apparant air leaks, no bass boost to turn off. How can I make sure the mains and sub are in phase? Positives are connected to positives and negative are connected to negatives.
    Marc
     
  5. ThomasW

    ThomasW Cinematographer

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    Marc
    Dyslexic Norwegians don't do forumlas. [​IMG] I simply modeled your sub in BassBox Pro.
    The easiest way to check for proper phase is play something with good bass. Then gently touch the edge of Shiva and the edge of one of the 8"s at the same time. Make sure they are moving in and out together. Having mains out of phase with the sub will result in bass cancellation.
    You can also check by reversing one of the speaker input leads. If the amount of bass you hear drops they were in phase. If it goes up, they were out of phase
     
  6. Geoff L

    Geoff L Screenwriter

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    I too am comeing up with the same for you.----
    3 inch port 5.30 inches long for tuneing of 23HZ in a 4.8 cubic ft box.
    Re-check your wireing for phase on the driver and amp connections.
    Check for air leaks around driver, amp, port and all wood joints.
    REMOVE BRICKS - the small VOLUME difference will not be much of a factor. (Assumeing with-out the bricks your volume is 4.8 with everythng subtracted driver amp and port.)
    Though I have not used the shiva in any of my designs, Im sure the amp your running (have used this--parts plus AMP-250) is not over-driveing sub power wise.
    Amp clipping is much more likely!
    Maybe some others can offer some more ideas as possible problems.
    You maybe tuned to high and as such when the driver reaches below port tuneing, the driver rapidly looses control of itself. I dont remember what your port lenght was so this may not have been an issue.
    Check these we have listed and get your port to proper length and check back. We all will try to help as at some point we all have been where you are. [​IMG]
    ------------------
    Smoothe
     
  7. Marc_D

    Marc_D Extra

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    Thanks for the advice guys!
    I appreciate your looking at my port length, but for some reason I can't imagine that the formula that came with the port not being right.
    Are all flared ports created equal?
    The manf. knows all the nuances of the port such as flare radius, flare length, etc... Where unless the modeling program used the exact same port for its measurements, how can it be correct without having the exact flared port dimensions?
    On the brick issue. If I takeout the bricks, the enclosure volume increases to 5.16 ft^3. Tuning becomes difficult then because the port length becomes to short (According to the manf. formula)
    I am going back to double check connections and improve sealing around woofer and port, although I cannot feel/hear and air leaks.
    Should I change to the following alignment (Adire alignment)
    142.5L tuned to 18.1Hz?
    The curve is smoother, but according to WINISD, my current alignment has a sharper drop off, and has higher output from about 80Hz to 25Hz (from memory).
    P.S
    The port and the driver are downfiring with about 3" clearance to a bottom plate. Do I need more clearance?
    The amp is the 250Watt Parts Express amp (180watts RMS into 8Ohms, and 272watts into 4 Ohm according to PE), but on the transformer and the circuit board, it say "sub 150" am I getting hosed?
    Thanks for your help!
     
  8. ThomasW

    ThomasW Cinematographer

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    Don't know anything about the port mfgr, or how they calculate the lengths.
    If you use 5.16 cu ft, the port length simply changes to 4.999" this keeps the 23Hz tuning. If you want 18Hz with the same size box, the port size changes to 9.412".
    These lengths are the total length including the flares.
    I'm not familar with the amp. But "popping" is usually clipping.
    Do you have a Radio Shack SPL meter? How loud is the sub playing when the popping occurs?
     
  9. Patrick Sun

    Patrick Sun Studio Mogul

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    I suggest going with the 18Hz tune and going with the 9" long ports that ThomasW suggested.
    And yes, please list exactly which DVD/scene you are getting the sub to pop for you at high volume. Please don't tell me it's the dts version of The Haunting, that's a sub-killer.
    ------------------
    PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; LDs
     
  10. Marc_D

    Marc_D Extra

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    The formula they (Lightning Audio) uses to calculate the port length is as follows:
    Lv= 8466.4 X (Vr)^2
    ------------------------ - 1.463 X Vr
    Vb X (Fb)^2
    where:
    Lv= Vent Length
    8466.4 = constant
    Vr = vent radius = 1.34"
    Vb= Enclosure volume (ft^3) = 4.8 in^3
    Fb= Tuning Freq = 23Hz
    1.463 = constant
    =4.02" Lv
    cut center piece of port 3" less to achieve proper length.
    = 1.02"
    Does everyone agree I should blow off this calc and go with BassBox suggestions? I am willing to try other lengths, but the inside port piece is in limited supply, I have a 1" piece and a 11" piece left.
    Unfortunately, I do not have a SPL meter to measure.
    The DVD I am using is the Matrix. The scenes that I have played with a where popping occurs are as follows:
    When rescuing Morphius they fly the chopper down the side of the building an start unloading with the Gatling gun.
    When the chopper hits the building, the second part of the explosion scene.
    At the end when he realizes he is "the one" and jumps into the agent and explodes him. Mainly when the walls fluctuate and the WHOOOMOOOM (technical term) part.
    I have not played the whole movie, just a few parts while tweaking.
    ThomasW, can you tell me the "optimum" alignment that BassBox suggests?
    ------------------
     
  11. Greg Monfort

    Greg Monfort Supporting Actor

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    The formula I have for flared vents is:
    Lv = [(8466*R^2)/(Vb*Fb^2)] - (1.463*R) + 1
    Lv = [(8466*1.34^2)/(4.8*23^2)] - (1.463*1.34) + 1
    Lv = ~5.03" total
    Considering that this vent is 2.68" dia, and TW, etc., are quoting 3" dia, 5.03" seems right in the ballpark since a smaller diameter would be shorter than their sims, and what I would use if ~23Hz is the goal.
    That said, ~23Hz is a bit high for HT, so I agree with the others that it needs to be tuned lower, or a sub-sonic filter be used to roll it off below Fb.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  12. Geoff L

    Geoff L Screenwriter

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    Marc--- as Thomas stated tuneing at 18Hz will require a length of 9.412 inches and at 23Hz 4.999 inches, in your 5.16 box.
    Patrick and also I suggest that you go with the 18Hz. Your port companys tell you to subtract 3 inches from the length for the flares so do so.
    6.5 tube + 3 flares = 9.5inches=18HZ tuneing
    You can always shorten the port lenght and bring your tuneing freq up!
    ------------------
    Smoothe
     
  13. Marc_D

    Marc_D Extra

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    According to Greg, it looks like my formula is off by the +1 on the end.
    I will be taking out the bricks and tuning to 18.1Hz in the morning to see what happens.
    Another development. I was doing some experimenting with my main speaker size and get this: When my mains are set to "Large" I get distortion from my sub at X listening level. When I set them to small I do not get the distortion from the same level. I would think that by setting the main to "Large" less LFE would go to the sub thus reliving some of the strain on it, and By setting it to "small" there would be more signal passed to the sub and create more work for it an more distortion. What is up with that? I even though that the two subs (8" from my main speaker and the Shiva) were fighting for air space, but I turned off the 8" on the main speaker and it still distorted. That does nat make any sense to me at all.
    ------------------
     
  14. ThomasW

    ThomasW Cinematographer

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  15. Scott M

    Scott M Agent

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    I'm curious as to why you guys think 18Hz is a better tuning point for HT as opposed to 23Hz and if this holds true for any given enclosure size and driver?
    I'm an HT newbie planning on building a sonosub in the near future(based on the shiva) and I'm in the process of gathering as much info as possible. Thanks.
    ------------------
    -scott
     
  16. Patrick Sun

    Patrick Sun Studio Mogul

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    Scott, the main reason for a lower tune, like 18Hz, is to use the enclosure the protect your driver when the DVD LFE has insanely high level of sub-20Hz material (like Titan A.E, dts Haunting, etc) and when the DVD is play at a loud volume level, the LFE can cause your sub's amp to clip or the driver to lose control under the tuning frequency.
    The drawback to the lower tuning is that you sacrifice a little bit of SPL in the 25-35Hz range, but for HT applications, it's a fair trade-off.
    Now if you are mainly building the sub for over 50% music use, then you would not tune as low (and might just go with a sealed sub).
    But it's up to you as to what's more important for your subwoofer use.
    ------------------
    PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; LDs
     
  17. Scott M

    Scott M Agent

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    ok, a few follow up questions.
    So any large signal below your tuning frequency is potentially dangerous at higher volumes because the driver can't maintain control and pulls higher current from the amp? Is this due to lack of damping from the enclosure becuase the larger wavelength?
    So that's why people with higher tuning freq's sometimes refer to using sub-sonic(below 20?) filters to prevent this?
    BTW Marc_D please post your results after altering the tuning freq because my setup is going to very similar to yours and I'd like to see if you are happy with your changes.
    And Patrick thanks for the help, both now and from your site, it's been a great reference.
    ------------------
    -scott
     
  18. DanWiggins

    DanWiggins Second Unit

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    Marc,
    If I were you, I'd SERIOUSLY reconsider your design. A 23 Hz tune will result in a 2 dB peak around 30 Hz. Add in the 6 dB boost at 25 Hz, and you've got a WICKED 8 dB peak at 28 Hz, with rapidly diminishing bass capability below 23 Hz or so. At 18 Hz, it's pretty much gone.
    My suggestion? Tune lower, to around 18 Hz, and see if you can disable the EQ boost. The EQ boost of 6 dB cuts your amp headroom quite a bit; you may be clipping the amp, in addition to losing all the deep bass reproduction capability you desire.
    Hope this helps,
    Dan Wiggins
    Adire Audio
     
  19. Scott S

    Scott S Auditioning

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    I run a Shiva in a 110L EBS like alignment tuned to ~18hz. I get some very nice extension. I too can bottom out my Shiva (and it is a loud "metallic pop"), but I can get about 105+ dB out of it before it calls shows signs of strain. I don't run any Sub-Sonic filtering..>>but perhaps I should? It really depends on you needs, and how loud you like your explosions. If you are happy with 105 dB then the lower tuning should be fine. As Dan says I would eliminate the base boost....you wont need it with an EBS alignment.
    Also, if I'm reading the curves correctly, the larger boxes will give you greater extension, but I beleive will be more prone to running into excursion limitations (especially with a ported system below the cut off frequency)
     
  20. Geoff L

    Geoff L Screenwriter

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    Well Marc hope you have not been bummed out as to your minor sub problem you inquired about! The information given was hopefully helpfull and upon makeing the adjustments hope you find your project pleaseing to the ears,or maybe I should say your body!
    So when you have a moment please find your way back to the thread and post your results as we all are pulling for you. [​IMG]
    Good luck
    ------------------
    Smoothe
     

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