Too much for the Shiva

Discussion in 'Home Theater Projects' started by RobertFirment, Jan 4, 2005.

  1. RobertFirment

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    I just built a 95L vented box with a 12" Shiva downfiring and Rythmik 350 amp. I am not sure but I think I may have damaged the speaker or amp. After playing some heavy bass it started making a crackling/buzzing sound that is especially noticable when the sub is not actively playing. The gain is at 12 o'clock and the level from the RX-V1500 receiver is about midpoint. I had also reconnected the sub cable without turning the power off, which I now understand is a bad idea. I had been playing a song called "Gangsta Bounce" which someone recommended and it must get down to around 25-30hz and was at 108db at 10 feet. Not my kind of music but I was just trying to test the sub. The room is about 40'x25' with 10ft. ceilings.

    I did put the sub in the corner and it seems to work best there. Also, I bought a splitter so that i am feeding the left and right input jacks on the amp. I did notice a significant increase.
     
  2. ThomasW

    ThomasW Cinematographer

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    It's a huge room, most people would use at least a couple 15"s with a big amp.

    The sound is probably the amp clipping. So called 'hard' clipping can result in a mechanical sound
     
  3. RobertFirment

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    It had been working for some hours before this without making these sounds. It would bottom at certain times but this is something different. Is it possible I blew the driver?

    I can see where a 15" driver should be used for this big a space. I consulted several places before building the box and no one mentioned using a 15" driver. This is my first sub of any kind so it has been quite a learning experience.
     
  4. ThomasW

    ThomasW Cinematographer

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    What's it sound like now?

    If you actually blew the driver it would make no sound at all. It would be hard to blow a Shiva (aka melt the voice coil) with a 360 watt amp.

    It's possible that you bottomed the voice coil and warped the former. That will create a constant fuzzy scraping sound due to the former rubbing in the gap.
     
  5. RobertFirment

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    It still makes that crackling sound when not receiving any signals. It works but the bass sounds unclear. Is there a way for me to easily view the coil or do a manual test?

    Is it correct to use a splitter to feed both the l and r inputs? I only saw it mentioned once on theis board.
     
  6. ThomasW

    ThomasW Cinematographer

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    I doubt that the splitter is the issue. You could remove it and see if anything changes.

    I suspect you damaged the amp.

    If you carefully cycle the cone in and out by hand (pushing on the edges of the dust cap) it should be obvious if the VC is rubbing.

    If you toasted the voice coil you'd know it, the driver would smell like burned electrical insulation
     
  7. RobertFirment

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    The only sound I get when pushing on the cone is sort of like nylon rubbing nylon but it moves smoothly.
     
  8. Geoff L

    Geoff L Screenwriter

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    If you push the driver in by hand, ~{must be with even pressure around the cone and pushed "straight in"}~, is their any sound, a scratchy scraping type sound while it goes in and out. Do this while subs Amp is off..!

    I don't think it's the driver from you basic description..

    The Rythmik amp might have some caps going bad. It will make a slight buzzing to even crackling sound, especially noticable if the Amp is ON ~{but NOTHING is playing}~. If this is the case it will usually get worse with time. Brian started changing out the stock caps and upgrading them sometime last year.
    You might have one of the older NO CAP UPGRADE amps, or even a upgraded one, and it's starting go bad.

    He will fix it free if that turns out to be the problem.

    I have a Rythmik NS-350 doing the same annoying thing. A slight buzzing especialy noticable when ON but NO signal being sent. It's one prior to the cap upgrade he now dose on all of them before shipping. I talked to him months ago and he said no problem send it in and he'd take care of it.
    I've just been to busy and not got around to it. Having other subs to run certainly has not help me speed up getting it to him..:b

    First you need to know if the driver is fine and not damaged. Hook it up to another power source if you have to, so you can see if the "supposed" driver noise continues. Thus taking the Rythmik amp out of the equation.

    Also be sure and use the adjustable SS filter on that thing, it will help with premature bottoming of the driver once you get this figured out...

    Regards
    Geoff ¥
     
  9. ThomasW

    ThomasW Cinematographer

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    Pull the driver out of the box and slowly cycle the cone in and out. Make sure that you keep absolutely even pressure on the cone, if not your hand will cause the VC to rub.

    With evenly distributed pressure on the cone, there should be no noise at all when cycling the cone in and out.
     
  10. RobertFirment

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    I emailed AcousticVisions today and am waiting to hear from them. Thanks for all the help guys.

    I wasn't relating the use of a splitter to this problem. I was just wondering if using a splitter is done by others.
     
  11. Geoff L

    Geoff L Screenwriter

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    Splitter is fine.

    Sorry Thomas you explained the things while I was typing them out.

    One finger typing Joe here...[​IMG]

    Should be no audiable sound like Thomas mentioned when pushing the cone in and out.
     
  12. ThomasW

    ThomasW Cinematographer

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    If you're going to be talking with Kyle, you might ask him about a driver or drivers that would be more appropriate to the size of your room.
     
  13. RobertFirment

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    He is the one who recommended the Shiva.
     
  14. ThomasW

    ThomasW Cinematographer

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    He recommmended the Shiva knowing it was going to be used in a 40' X 25' X 10' room? Or was it instead recommended for a specific budget?
     
  15. RobertFirment

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    I sent him my house floorplan and drew in the component layout. Budget wasn't an issue.
     
  16. Kyle Richardson

    Kyle Richardson Screenwriter

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    Robert,
    I replied to your e-mail immediately after receiving it but judging by the time of your last post you must not have received it. Basically, it said exactly what Thomas suggested.

    I don't remember recommending just a single shiva for a room that large. For some a 12" driver would be fine for even that large of a room for lower to medium SPL levels, but it is all up to the individual listener to determine how loud they want it. If you want to get to HT "boom" levels then at least a 15" is needed or multiple drivers for a room that massive.
     
  17. RobertFirment

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    The sound level it was producing was fine for me, until this problem started. I am at work right now so I will need to wait until I get home to look at it again. The best I could describe the sound when manually moving the cone the last time I tried it is like rubbing nylon. I was careful to apply even pressure.

    I don't have another amp to try but can I just disconnect one of the mains from the receiver and wire it to the sub for testing?

    -----Original Message-----
    From: Acoustic Visions Sales [mailto:[email protected]]
    Sent: Tuesday, November 09, 2004 10:42 PM
    To: Firment, Robert E.
    Subject: RE: Reccomendatons

    I would go with the Shiva and a 250 watt plate amplifier. You can go with the Rythmik 350 watt amp for more sound shaping features and not a lot more money although you don't NEED quite that much power its extra features make it nice. The DPL12 is a good woofer, but I would use it if you were using it in a 2 channel set up more than TV or movie viewing so I would have to give the nod to the Shiva in your application.

    No need for PR's with the Shiva. I'd just port it using either the 85L Adire alignment or the 95L SBB4 alignment (both plans are downloadable on the Shiva page on my site).



    Thanks,

    Kyle Richardson

    Acoustic Visions

    --------------------------------------------------------------------------------

    From: Firment, Robert E. [mailto:[email protected]]
    Sent: Tuesday, November 09, 2004 7:56 PM
    To: [email protected]
    Cc: [email protected]
    Subject: Reccomendatons



    I am looking for suggestions on a DIY subwoofer. I have Polk LSI 9 fronts and a Yamaha RX-V1500 receiver. This is going to be a 5.1 system eventually. My room is very big as you can see from the attached picture. I was thinking of a 12" either Shiva or DPL. Not sure how big an amp is needed for this room or if I should add a passive radiator. I don't need it super loud, just something appropriate. This is going to be used 90% for tv viewing.
     
  18. Allen Ross

    Allen Ross Supporting Actor

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    how many times did you bottom it out? cause that could have misaligned the VC.

    Sounds like from the email the shiva would be fine for what you were going to do with it, (90% TV) but prob did something to it when you tried to push it further then it was capable of.
     
  19. RobertFirment

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    It bottomed out several times over a few minutes and I adjusted the gain to stop it. Is there any way for me to visually inspect the driver? Does my description of rubbing nylon make sense?
     
  20. ThomasW

    ThomasW Cinematographer

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    The very first time it bottomed was the indicator to immediately turn it down.

    Unless you tear the driver apart, it's impossible to look at the voice coil.

    HERE's a graphic about the construction of loudspeakers.

    Any of that gangsta rap especially a disc that's recommmended for subwoofer demo, will have extremely over emphasised bass and midbass. So that combined with your very large room, was a recipe to kill the sub.

    When you said 108dB at 10', do you understand that sound attenuates at a rate of -6dB for every doubling of distance from the source? So your 108dB at 10' means the sub was playing 114dB at 5', 120dB at 2.5' and 126dB at the driver itself. And if you were measuring with a RS meter they aren't accurate that those SPLs, so the actual output was probably even higher
     

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