What did I do wrong with my svs driver? ..

Discussion in 'Archived Threads 2001-2004' started by Jason Hammerly, Jun 24, 2002.

  1. Jason Hammerly

    Jason Hammerly Supporting Actor

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    I built a ported box that is 85Liter tuned to around 21 hz and I'm not impressed. It bottoms very quickly, especially with stuff like the beginning of Toy Story 2. Did I do something wrong? I have it powered by a 250 watt PE amp. I heard this really loud scratching sound once.

    Just wanted to add that I don't necessarily think it's the driver, but probably something I did as it seems that lots of people are having great luck with it. I do think that one will be enough as I tweak this one or build a new box, so am selling the other one I picked up for the normal $40 plus shipping. Out.
     
  2. Cam S

    Cam S Screenwriter

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    Toy Story 2 is a known sub killer, so I'm not suprised that the sub bottomed out on it. How did you calibrate the sub to your system? My guess is that it was running hot, you turned up the volume too much, and then the movie did it in. Try to get it calibrated with an SPL meter and AVIA, and you'll be set.
     
  3. Brian Bunge

    Brian Bunge Producer

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    You might want to do the amp mod that Pat Sun did on the SVS sub that he built. I'm sure he'll be here before long and say the same thing.

    Brian
     
  4. Patrick Sun

    Patrick Sun Moderator
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    I kept the volume on the PE 250W amp at 1/3, the enclosure on mine was around 4.5ft^3, yours is more suited for a SVS 25-31 model, though 3 ft^3 might be too little. I did do the amp mod (1dB boost around 21-25Hz, with the amp's Fc at 21Hz), which helped a little bit. Calibrating the sub to the rest of the system will help in not over-driving the sub as well.

    I got the Toy Story 2 intro not to bottom out on my SBS at decent volume levels, but there's no hope for the dts Haunting, that DVD should be sold with a rumble filter.
     
  5. Jason Hammerly

    Jason Hammerly Supporting Actor

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    I'll fiddle some more with it. One thing I am notincing is that I get a lot more output from my 100L sealed Tempest with a 150 watt plate amp. I do have the gain on the 250 watt amp up to about 3/4. Maybe that is the problem. I calibrated it, but had the gain on the am,p cranked when I did the calibration. Maybe I'm sending a clipped signal to it. thanks for the input.
     
  6. Cam S

    Cam S Screenwriter

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    WOW, 3/4 volume on the plate amp!!! That is crazy. On my AVA250 the gain is barely up to 1/4!!!
     
  7. Jason Hammerly

    Jason Hammerly Supporting Actor

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    When I try to calibrate it I have to turn up the gain to get the level up. If I leave the level at 1/3 or less, I'm not getting enough juice. Am I doing something wrong with the calibration?
     
  8. Brian Bunge

    Brian Bunge Producer

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    Jason,

    Are you using the sub out from your receiver? If so, you should use the sub out volume control in the receiver to calibrate. If you've got the amp's volume turned 3/4's of the way up I'd imagine that's the cause of a lot of your problems. I just don't feel plate amps were really meant to be run anywhere near wide open, contrary to what I've heard elsewhere. Now pro amps are a different story...

    Brian
     
  9. Mark Tranchant

    Mark Tranchant Stunt Coordinator

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    Another case of people not understanding how volume controls work. Please read my post in this thread.
    The plate amp's amplifier section has a fixed gain: you put a voltage it, it'll multiply it by a fixed factor and put it out to the speaker. The control is done by the volume control, which is a variable factor multiplier. Having this control at 3/4 of full and feeding it a small signal gives the same output to the speaker as having it at a lower setting and feeding it a correspondingly large signal.
    "Wide open" doesn't mean a thing: the only limit is when the input to the power amp reaches a level that causes maximum output. This could be achieved with a very large input signal and the volume control at 1/10 of full.
    Note that it is usually preferable to keep the line signal as high as possible without causing distortion in order to maximize the signal to noise ratio - turn the sub out up on the receiver and adjust the plate amp control down to match.
    Jason - ported boxes are much worse than sealed below their tuning point, as the cone experiences virtually no resistance to movement. Does the plate amp have some sort of high-pass (rumble) filter you could use?
     
  10. Brian Bunge

    Brian Bunge Producer

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  11. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    All the advice I've read says to turn up the plate amp volume and adjust LFE on your receiver or pre/pro. This makes sense. Say you set your plate amp volume knob at what you estimate is 3/4, then you adjust your receiver LFE output in 1 dB increments. Then later, for some reason the plate amp volume knob is moved, there goes your calibration. So you move your plate amp volume knob back to your estimate of 3/4 volume and your receiver LFE setting is now not producing exactly the same spl as before when the plate amp volume knob was set at the supposed 3/4 point. It just seems to me that if your plate amp volume control has a fixed point that it can be set at, then your receiver LFE output level 1 dB adjustment settings will be reliably repeatable. That fixed point is all the way up. Works for me. I dunno, maybe some people's plate amp volume knobs are quicker/easier to adjust than their receiver's LFE settings.
     
  12. Patrick Sun

    Patrick Sun Moderator
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    Hank, your advice works for pro amps, but doesn't quite work for these popular PE plate amps. 1/3 (10 o'clock position) is as high as I would go on the plate amp before using the receiver's subout trim to calibrate the sub's output to the rest of the speakers.
     
  13. Jason Hammerly

    Jason Hammerly Supporting Actor

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    do you think it will be better with a Shiva? I actually built the Adire ALignment from Adire's site. I'm thinking about selling both my SVS drivers and picking up a Shiva. What do you guys think?
     
  14. Chris Carswell

    Chris Carswell Supporting Actor

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    Yes Jason get the Shiva. SVS=bad, Shiva=good. You will like it better, It will match your Tempest[​IMG]. Then what will you do with the other SVS????? HMMMMMM, I got it. Sell it to me since I'm buying your other one [​IMG] (I sent you an email about that) I really do need a pair since I don't want to use the SVS and a NHT 1259.
    ----------------------------------------------------------
    Now for my 2 cents:
    In all honesty I think the Shiva does spec out a little better but not 100% on that, specially in that small a box. I would definitely try to re-calibrate it and turn that plate amp down. Are you using the current PE #300-794 250 watt amp? Try the bass boost removal. I also read you use a 150 watt for the tempest. Is that the #300-800? I'm using that one for my tempest but I'm going with ~215 L (not finished yet so I can't comment). 85 L does seem a little small. Did you try to stuff the hell out of it?
     
  15. Kevin Beck

    Kevin Beck Stunt Coordinator

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    Patrick,..
    Is there a way to explain your thoughts on the plate amp aproach vs the Pro amp aproach for us lesser electronicly educated folks. You hit on something I was going to ask, only in a different manner. My question concerning this problem was,...If you have a plate amp,..or other, have the gain wide open, and the receiver's sub out adjustment clocked all the way down, still isn't enough to tame the signal. What then? Seems the only thing to do, would be balance the two adjustmets, in a manner that is best suited the material most comonly listened to. I'm sure this can be explained in better words,..but would this be the idea?
    >>>--->
     
  16. Brian Bunge

    Brian Bunge Producer

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    Kevin,

    That's exactly Pat's and my point. I have 2 PSA1 amps from ACI (nearly identical to the KG5150 that Madisound sells). If I turn the volume up half way (12 o'clock postition) on the plate amp and the sub out at minimum I cannot calibrate. I have to leave it turned to the 9 o'clock position and then increase the sub out on my receiver.

    Another issue, is that with the sub out level so low the plate amp's auto sensing circuit is constantly clicking on and off, which is annoying as all hell.

    Could it be that the plate amp's control really is not an input gain like what the pro amps use? With my K2 I leave the gains wide open and CAN calibrate with the sub out. I leave it around the -5 setting.

    Brian
     
  17. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    They're both gain controls. But pro amps are designed to work with stronger signals. So at the "wide open" setting on both amps the plate amp will have a lot more signal gain.
     
  18. Pete Mazz

    Pete Mazz Supporting Actor

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  19. Brian Bunge

    Brian Bunge Producer

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    Pete,

    So as I thought, on most plate amps this is a "gain" control that affects the amp's output signal; not the input signal. This would explain why using a very weak input signal from the sub out and then "amplifying" it gives poor performance. You've killed your S/N ratio.

    Give me a stronger input signal that requires less amplification any day of the week over a weak input signal that requires more amplification.

    Brian
     
  20. Pete Mazz

    Pete Mazz Supporting Actor

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    Whether this is a true gain control is debatable, I guess, but anything that affects the input signal would affect the output from the amp. I would guess that it attenuates the input signal strength and the amp has fixed gain, but who knows for sure???

    I remember reading something about a test that was done on sub outs from equipment and how a high level setting caused greater distortion in the signal. I don't remember where I read it, tho.

    I used to set up my plate amp so that the signal from the sub out was just strong enough to keep the auto-sensing circuit going, and then adjust the sub volume control.

    Pete
     

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