I've tried everything, but my shiva is still bottoming out!!!

Discussion in 'Home Theater Projects' started by BryanDO, Nov 26, 2004.

  1. BryanDO

    BryanDO Stunt Coordinator

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    Hey guys, I've been having this problem since day 1 with my shiva. It seems to constantly bottom out at frequencies in the 30-40 range. I've tried many different enclosures which include 3 cu ft ported to 22hz, 3cu ft sealed, 2 cu ft sealed. None of the boxes were braced nor did they have any fill. The amp is a 360 watt plate amp which has a boost boost of 4db at 25hz. I would like to know what the possible problem is with the setup because I want to build a 4cu ft ported sonosub for this set-up but I'm afraid it will be a waste of time and will bottom out like all the rest. Any helpful suggestions are greatly appreciated... Money is short as well so buying any new equipment wouldn't be an option.
     
  2. Aaron Gilbert

    Aaron Gilbert Second Unit

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    If you are overdriving it, you're asking too much from the woofer, simple as that. Also bear in mind that the sealed boxes will have slightly higher excursion than the ported box above the tuning frequency, which in my opinion should be 21 Hz or lower for the Shiva. Since you say it's bottoming out specifically in the 30-40 Hz range, that's a sure sign that you are trying to get more output than the woofer can provide. My advice is to get another Shiva or a different woofer with high output capability, keeping in mind that you'll need to double the swept volume for a 3 dB increase.

    You could get higher output by tuning quite high, or using a bandpass enclosure, but not without sacrificing sound quality.


    Aaron Gilbert
     
  3. Chad Kuypers

    Chad Kuypers Stunt Coordinator

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    Doubling the swept volume gets you 6 dB more output. Doubling the power gets you 3 dB more output.
     
  4. BryanDO

    BryanDO Stunt Coordinator

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    Thanks guys, out of curiosity how would a 2cu ft ported enclosure do tuned around 19hz? would it have the same problem? The rumble filter is set at 15hz as well. I emailed the vendor of the amp and I found out how to remove the bass boost. Only one problem, I dont know how to read electronic schematics [​IMG] It says change 2 resistors, r23 and r24. I have no idea where r24 is. The Shiva I think is perfect for what I am looking for, I just made a rookie mistake on buying the amp.
     
  5. stephanX

    stephanX Stunt Coordinator

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    Shiva is DVC isnt it? couldnt you fiddle around with ohm loads so the amp put out a more feasable amount of power for that woofer?
     
  6. BryanDO

    BryanDO Stunt Coordinator

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    I could wire the sub at 8ohm so it will only see 250 watts. Only problem with that is only 1 coil will be hooked up, dont know if that will pose a problem...? I'm not sure if it's the wattage thats the problem or solely the bass boost. If I lower the wattage would the bass boost hurt?
     
  7. stephanX

    stephanX Stunt Coordinator

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    most people on DIYaudio giove it 200-250 watts and you can still bottom it with 250 watts, so 360 should be quite a bit too much. I would say its a combination of both. i think wiring up only one coil raises the Qts too. Don't take my word for it though im still a noob.
     
  8. minhG

    minhG Stunt Coordinator

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    i think the shiva is dual 8ohm right? i'd try wiring them up in series (don't wire only one of the VCs!) for a 16ohm load, that will drop the output considerably and may be enough.

    most people building large vented box shivas only use ~200W amps. that's what i have and i've never bottomed mine out (142L vented box) and i've measured up to bout 100db with a 25hz tone.
     
  9. BryanDO

    BryanDO Stunt Coordinator

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    Im assuming a 16 ohm load would probably give me around 160 watts? With the 4Db boost at 25hz and 160 watts, do you think I'd be able to go for a large vented enclosure or would the boost still bottom it out?
     
  10. Aaron Howell

    Aaron Howell Stunt Coordinator

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    I've also built a LOT of shiva enclosures. With a 250watt plate amp I've bottomed the woofers in all of them, with the exception of the 1.2cuft sealed enclosure which is the smalled shiva enclosure I have built.

    I know a lot people will look down on this, but the most "boom" I've gotten out of a shiva was in a 2cuft net enclosure with a 4"dia x 11" port. I have some extra shivas around since I've went IB, and that one remains for a "party sub". All of my friends like that sub the best for music. IIRC, it has an approx 10db boost in the 40hz range. It sounds muddy and boomy, but for the common non-audio-geek in the 20-30 age group with rap/pop/rock that ghetto enclosure wins out consistently.

    From my personal experience "boomy" bass seems to to be the preference of most people. Most of my friends don't even notice the difference in the bass of different enclosure, just which one is louder than the other.


    This is the way I look at it, if this info is incorrect someone please correct me. If you prefer a large hump in the 30-40hz range, build an enclosure that puts an emphasis in that region. That way you don't put a large load on the amp to reproduce that hump in the response. In other words if the 45hz bass is what you are after and your enclosure naturally increases that range, then you need less power to achieve that output. Lowering your input power to sub output ratio means you'll be putting less stress on that shiva.

    If you can't spend more money on equipment, and you want more bass, this an option. It's not ideal, but it could get you by until funds are available.

    With all of that said, feel free to flame me for encouraging boomy bass. [​IMG]
     
  11. KyleGS

    KyleGS Second Unit

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    Unfortunately- I've found this to be true also.
    But don't let your audiophile friend(s) hear that sub. [​IMG]
     
  12. Aaron Howell

    Aaron Howell Stunt Coordinator

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    Tell me about it! I just hope I don't get banned! lol
     
  13. BryanDO

    BryanDO Stunt Coordinator

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    Thanks for the suggestion Aaron. The box I'm looking for is something with a flat response and decent extension in the 20hz range. It's going to be used for 100% home theatre. The best design I have come up with so far is a 2 cu ft ported enclosure tuned to 19hz. Simulating the bass boost in WinISD with that box and 160 watts, it looks like the subs excursion is quite low through the whole freq. range. It's also a fairly flat curve.
     
  14. DanWiggins

    DanWiggins Second Unit

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    Bryan,

    Rather than change the wiring of the driver, how about turning the gain knob of the plate amp down? That will also lower the delivered power...

    Also, don't trust WinISD - it's worth about what you paid for it. UniBOX is a MUCH better freeware modeling package that's also free. And you can also use the highest precision modeler out there for free; see the "Company" section of our website for a free download of LspCAD with Shiva pre-loaded. Extremely accurate, pretty easy to use.

    Dan Wiggins
    Adire Audio
     
  15. BryanDO

    BryanDO Stunt Coordinator

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    I got LSPcad and it's a pretty neat program, I was playing with it all night, my gf was kind of peaved [​IMG] I think it might be easier to wire it to 16ohm that way theres less chance of bottoming it out with too much power. Also, with only 150 or so watts, it seems ok to use a wider variety of box sizes. I think I'm going to go with an 85L box tuned to 20hz, the adire algnment.
     
  16. BryanDO

    BryanDO Stunt Coordinator

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    I've decided on a sonotube design of the adire alignment. The sub is going to be places right beside my listening position. The sonotube will be 30" high, if the port is on the top will I hear alot of noise coming from the port (chuffing, sub working, vibrations etc etc..)? Would it be better to place both the sub and port on the bottom of the tube or would it matter?
     
  17. Aaron Gilbert

    Aaron Gilbert Second Unit

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    Dan (or anyone else),

    I've seen many comments of late criticizing WinISD's abilities. Thus far, I've used it to design my half dozen or so vented boxes, and all have come out as expected. What am I doing wrong? [​IMG] Now, I am not using WinISD pro, so maybe that's the difference? I don't have excursion graphs, and so really I'm just using it to show the relationship between box size, tuning point, frequency response, and group delay.

    I tried UniBOX last year I believe, and found it MUCH more difficult to use in all respects, although certainly some of this can be expected, since it offers so many more features. Is it still true however, that you require MS Excel to run UniBOX? If so, then is it really free if you don't have MS Excel? Or are there freeware Excel file readers out there?

    I do like the LspCAD though!


    Aaron Gilbert
     
  18. stephanX

    stephanX Stunt Coordinator

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    You wont get any port noise if the port is big enough in diameter! look at the flared ports from partsexpress if you cant fit enough length of large diameter pipe in maybe. I believe that winisd has a vent mach calculator as well. I am using two striaght 4" abs lengths for my ports(when i get around to ordering stuff)
     
  19. BryanDO

    BryanDO Stunt Coordinator

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    Just thought I'd give an update... I finished building my sub. It's a 95L ported box tuned to 18Hz, well braced and a lil polyfill along the walls on the inside. The Shiva's downfiring along with the port. The sub is wired at 16ohm and gets about 150 watts. After dialing in the gain, I am very very happy with my sub, no more bottoming out at any frequency and it sounds great. The output is no different than my past setup with 360 watts and its a heck of alot cleaner to my ear. Thanks guys for all your help and suggestions...
     
  20. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Aaron,

    I agree with you. I've always thought WinISD (pro in my case) is much easier to use than either Unibox or LspCAD. I just plotted a Shiva in an 85L box with 7.6cm x 34.6cm port (its silly that LspCAD only accepts metric inputs) with 250 watts into 4 ohms in both LspCAD and WinISD. And as I expected, the results were very, very similar. SPL magnitude was different by about 1dB but otherwise it looked virtually the same. Tuning was within half a Hz.

    I do notice that cone excursion and port airspeed graphs are a bit different - WinISD shows 15-20% lower excursion and ~20% higher port air speed. This is probably what the fuss is about. And I can see wanting to get that extra bit of accuracy before you start ordering parts and cutting wood. But I think WinISD is just so much easier for a first pass at trying a driver in a prospective alignment.
     

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