Built my sub, not pleased... Please help...

Discussion in 'Home Theater Projects' started by BryanDO, Feb 16, 2005.

  1. BryanDO

    BryanDO Stunt Coordinator

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    I finished building my Adire Shiva project a while back. I've had alot of time to play around with poisitioning and settings but it never sounds the way I want it to. Out of the sub I wanted a very smooth, controlled (tight), and defined bass. Instead I got a sub with peaks at all different frequencies, it's not smooth and can be plain harsh, shaking everything at one frequency and not audible another. My very first sub was a Velodyne CHT-8 and I really liked the sound of it, but it didn't go quite low enough or loud for my tastes. The sub is in a 3 cu ft ported enclosure tuned to 19 Hz. The amp is giving the sub 150 watts and has a 4db boost at 25hz. I wish I could defeat the boost but I can't. I cant afford another amp either. I would like to build and enclosure with the amp and Shiva that will net me the results I want. Is it possible? Can you guys give me some designs ideas for the box? Thanks everyone...
     
  2. Darren_T

    Darren_T Second Unit

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    Hmmmm... you may be used to the boomy sound of a commercial sub. I had a Velodyne 10" and while they are good bang for the buck they are quite boomy. When you move to a high quality sub such as the Shiva in your case you may have to adjust your listening expectations. The Shiva will reproduce clean tight bass but you also have to take into account the fact that depending on your amp you probably don't have bass boost or anything else the Velodyne used to increase output.

    Give it a while, you'll grow to appreciate accurate bass. You'll get earth shaking bass when it is actually called for.

    As a side note, if you built the enclosure yourself be sure you have good tight joints and the woofer is sealed well. Any cracks or holes can drastically affect the performance of sealed or ported enclosures. I built a Tempest as my first DIY sub and forgot to put in one T-Nut and it killed the performance of the subwoofer.
     
  3. BryanDO

    BryanDO Stunt Coordinator

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    Thanks Darren, I'm going to tear the box down and cheack all joints... I think the bass boost on my amp now is hurting more than anything. I want to build a box around it so it doesn't hurt the quality and sounds smooth. I found the Velodyne smooth because it seemed the response was much flatter than my current Shiva. Do you think a small sealed box for the Shiva would make a difference? Around 2 or 2.5 cu ft? I can tell the difference between a boomy sound and a more natural sound. But the Shiva's response right now doesn't seem smooth at all.
     
  4. Darren_T

    Darren_T Second Unit

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    I'm no expert on the Shiva or any subwoofer for that matter but a smaller box will probably tighten it up a bit but you'll loose low frequency extension. Is this for music or HT? You may require a bigger amp if you go sealed or smaller ported. I'm just throwing out thoughts here, it's been a while since I built anything other than proven plans.

    You may be experiencing room gain, have you measured your response? You could have a severe hump.

    Others will probably chime in with good troubleshooting advice but that is a start for you.
     
  5. Greg_Hammond

    Greg_Hammond Agent

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    Bryan - There are all sorts of tips and tricks for adjusting the sound of your enclosure that you could try before giving up. Padding the inside of the box with carpet or tacked-down polyester fiber fill is one trick, as well as putting in a few solid wood blocks and screwing them to the inside of the cabinet to reduce free air space.

    I think a sealed cabinet might provide tighter bass, but low-end frequency response might suffer. Again, you could always cover the port with a block of wood and see what effect it provides.

    Greg
     
  6. Rob Formica

    Rob Formica Stunt Coordinator

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    Sounds a lot more like room modes than subwoofer response. A subwoofer may have a peak at one frequency or it may roll-off early, but it's highly unlikely that it'll have peaks at all different frequencies.

    On the other hand, that description matches exactly what you'd expect from room modes... with nulls (0db) at peaks (+15db) at multiple frequencies.

    I'd measure my room response first...
    Rob
     
  7. BryanDO

    BryanDO Stunt Coordinator

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    The room is definitely not sound friendly. All hardwood flooring open concept, plain walls and lots of hard surfaces. I tore the sub down to bare MDF and noticed a few leaks. Around the sub where it's mounted and the amp. I'm going to get some foam to pad the inside but as for sealing the sub, amp and port, is there some sort of gasket I can use thats found at common stores like Wal-Mart? I live in a small town and don't have many large fabric or hardware stores.
     
  8. stephanX

    stephanX Stunt Coordinator

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    Weather stripping, and believe it or not duc tape makes a pretty good woofer gasket as long as you take your time putting ltos of small pices on and cutting where they overlap.
     
  9. lee ison

    lee ison Stunt Coordinator

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    use some silicon caulk to seal the leaks ,stuff the port with foam
     
  10. Max F

    Max F Second Unit

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    Sounds like you have a difficult room. Also, a ported sub will likely make things more difficult for an already difficult room. You could buy some expensive bass traps and such or just get yourself a BFD. With the BFD, you can take out that bass boost at 25 hz if that really is the problem.

    Definitely get yourself an SPL meter and measure the room response.
     
  11. brentl

    brentl Cinematographer

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    IF some of the leaks are on the joints just add more glue.

    What type of glue did you use??

    There should be gaskest tape around, actually any 2 sided tape used to stop leaks on exterior doors would work fine.

    HEY, I'm in Uxbridge, so I know small town too!

    Brent
     
  12. Darren_T

    Darren_T Second Unit

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    Ok, you found several leaks...that's gonna make a huge difference in the performance. Just use silicone or latex caulk on all the inside joints. Use weather stripping for the woofer seal and amp seal (the kind for doors etc which is a foam strip with sticky on one side).

    Let us know how it goes.
     
  13. Andrew Pratt

    Andrew Pratt Producer

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    brentl Uxbridge is a nice small a town[​IMG] My parents now live near Port Perry and I get back there every few months.

    Once you get the sub back together we need to establish just where the problem is. To do that I'd highly recomend plotting out its freq response using an SPL meter and some test tones. That will help establish a base line that we can then work from...otherwise its all just guess work.
     
  14. BryanDO

    BryanDO Stunt Coordinator

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    Ok, subs is back together after taking most of the day to do some reapirs. Ford glue on the box I used carpenters glue. Here's everything I did:

    - Sanded the box down and added some glue to the joints.
    - Sealed off all old screw holes from sub, amp etc ...
    - Lined the entire box inside with foam, including braces.
    - Used weather stripping to seal sub and amp to box. Caulking for the port.
    - I also took the bass boost off my amp by replacing a couple resistors on the sircuit board. The sub is now seeing 360 (wired it in series) watts instead of 150.

    The result... Very happy!!! The sound is alot more accurate and realistic. It seems like all the little squeaks and rattles that came from the box are gone. Unreal what a few little things can do. I will be getting a SPL meter soon when moneys a little better. Only real problem is when I'm pushing for a little more bass the sub bottoms out on some frequencies. I should really step up to the Tempest! [​IMG]

    Thanks a bunch guys for all your input and ideas. It really made my day to hear the sub how it was meant to be. I'll report back when I have an SPL meter and can plot the output. Thanks again.
     
  15. Darren_T

    Darren_T Second Unit

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    In case it wasn't mentioned...Radio Shack has an analog SPL meter for about $25.00, get that and download the test tones and you are set for testing.
     
  16. Patrick Sun

    Patrick Sun Moderator
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    You mean wired in parallel, I hope.
     
  17. BryanDO

    BryanDO Stunt Coordinator

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    Oops, parallel, my mistake. I went to Radioshack and there SPL meters go for 70 bucks CDN for the analog. I'll have to wait a bit for it. I'm just curious if theres a program for the PC I can use to map out the frequencies using a microphone, or record the sounds then put them on here. I thought I seen a program like that before, I could be wrong.
     
  18. Jasen Chandler

    Jasen Chandler Stunt Coordinator

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    It is amazing how much the enclosure has to do with the way the box sounds. Vented boxes really need to be braced well. The pressures inside a ported box can get crazy and in some cases at certain frequencies are twice what they would be in a similar sealed box.

    Glad your sub is pounding away. Give the Shiva some break in time. You'll probabably find a bit more low end.
     
  19. BryanDO

    BryanDO Stunt Coordinator

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    Thanks Jasen, I finally got a hold of a RS APL meter and I've mapped out the frequencies on paper. I want to put them into a graph using Microsoft office. I have a spreadsheet open but am completely lost, can someone help me out with this process? Thanks guys...
     
  20. Patrick Sun

    Patrick Sun Moderator
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    Have one column be the frequencies, another be the measured SPL readings, and if you want to get fancy, have another column add in the correction values to the measured values to arrive at the corrected values.

    Then just set the frequecies column as the X-axis, and the other other colums for the Y-axis values (should you want to plot the measured vs. corrected values).
     

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