Proper amp for Tumult

Discussion in 'Home Theater Projects' started by Jeffrey Stanton, Jul 10, 2003.

  1. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Hey guys:

    What would be your recommendation for a GREAT pro amp for a Tumult? I just ruined my AV-15 by trying to drive it with a crummy 380 watt Rythmic Audio plate amp. I would like to state for the record that it is NOT a good idea to try to push an AV-15 with only 380 watts. [​IMG] [​IMG]

    I figure to prevent this from happening again I need a decent amp. I've got around $1000 to spend on the amp.

    First, no plate amps. I am not going to cut a hole in my Acoustic Visions box because that'll make it pretty much impossible to retro-fit if the need should arise.

    Also I think there may be a need for a rumble filter to protect the sub, especially the way I will be prone to driving the thing...(could one use a BFD parametric filter as a rumble filter???)

    What are you Tumult users using?

    Any suggestions, comments, ideas?


    Thanks Much

    Jeff S.
     
  2. Brian Bunge

    Brian Bunge Producer

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    Jeff,

    I highly doubt it was a problem with the amp. Sounds more like a problem with the driver itself. I know John has had some issues with a few of the drivers being built wrong. Not his fault at all.

    If it were the amp then I'm sure my dad would have destroyed his DVC 15" driver with a 250W plate amp by now.
     
  3. Darren_T

    Darren_T Second Unit

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    I was kinda thinking the same thing. The AV15 should perform beautifully with that amp based on it's specs and the enclosure designs out there. It is possible that the amp was being driven beyond it's intended purpose and was distorting which could damage the driver but that's the only thing I can think of unless the driver was bad.
     
  4. Kyle Richardson

    Kyle Richardson Screenwriter

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    The only reason the amp was being looked at as the cause is because it would make some clacking noises then shut down.
    Brian, it very well could be a combination of both.
     
  5. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Yeah, it made a real loud snap/clack noise and then the amp was OFF. It never happened with music no matter how loud I got it, only during REAL HEAVY LFE sections of DTS DVDs played at normal (reference or near-reference) levels. But it was after several of these episodes that I started hearing the metallis "chirping" noise coming from the driver when playing music at moderately loud levels...[​IMG]
     
  6. You will not find any non-plate amp with an appropriate rumble filter. You will have to either buy one (like the SVS black box), build your own, or do without.

    I think a great amp would be a crown K1 bridged. This is one hefty amp and does have (IMO) the potential to fry the driver if you really push it. I have a K2 and a single channel is good enough....bridged (If I really wanted to hurt my ears and apartment integrity) could easily toast the tumult as some have proven.

    I know you don;t want a plate amp because you do not want to make a hole in the box (I sure wouldn't!), but you can still do a plate amp like the HS500 or the new powerhouse (the Keiga 1000watt). I have seen people build separate enclosures for the plate amp. ...just a thought
     
  7. Dan Hine

    Dan Hine Screenwriter

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  8. Brian_DR

    Brian_DR Extra

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    Jeff,

    First, very sorry to hear your story. Second I would like to understand the cause of it. It sounds like the driver has been bottomed out very often. Is the sub a vented box? The reason I ask is because vented box has 3 times excursion requirement below resonance frequency. Without a rumble filter, the result will be much worse. Our amps have adjustable rumble filters because each person has different playback habit. For maximum play back level, the rumble filter should be set to highest 28hz setting. Amp clipping is different from bottoming. The amp has short circuit protection for excessive current. However, in vented box, the excursion below resonance frequency does not require a lot of current. So the only way to protect it is with excursion limiter. But the excursion limiter needs to designed specific for a driver. It is not just my amps, any other high power PA amp can do the same thing. Over excursion is particularly problematic with aluminum former. I would like to keep my customers happy. Apparently you are not now.

    Regards,

    Brian

    Rythmik Audio
     
  9. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I don't think you can bottom an AV-15 with only 380 watts. Amp clipping seems a more likely possibility. AV-15's in a 24" cube with two 1600 gm PRs (one 'o Kyle's babies), using 380 watt Rythmic Audio plate amp...

    I also would like to understand what's going on because I do not want to repeat this scenario.

    Jeff S.
     
  10. Brian Bunge

    Brian Bunge Producer

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    Jeff,

    Technically you can't if it's built properly. If the build house screwed up then it's quite possible to bottom the AV15 with 380W.
     
  11. Brian_DR

    Brian_DR Extra

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    Jeff,

    what extension filter setting did you have?

    Thanks.

    Brian D.

    Rythmik Audio
     
  12. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I have experimented with all the setting for rumble and extension. It's not that I am not happy with your amp. I only got it for TEMPORARY USE because the pro amp I originally intended to use with the sub would not work off the LFE output from my amp (with or without a pre-amplifier). I suspect a built in 30 Hz rumble filter may have been part of the problem plus maybe impedance mismatching. In any case, your amp was only for temporary use until I got a larger pro amp (something with at least 700 watts that the AV-15 requires for "full effect". I knew it was not quite enough to make the AV-15 happy, but did not think I could "damage" the AV-15 with it!! I guess the jury's still out on what went wrong, although amp clipping seems a distinct possibility. I think one is just as likely (if not more likely) to damage a driver with too little power than too much. I didn't mean to cast aspersions as to your amp, I'm sure it would do just fine with a driver that needed less power than the AV-15. It's also possible the driver may have had a problem itself.
     
  13. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    It had a rumble filter...15, 20, and 28 Hz as I recall...
     
  14. RichardHOS

    RichardHOS Second Unit

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    I agree, damaging a driver with too little power (clipping) is probably more likely than damaging one with too much, though both do happen.

    Also, I would think that 380W in a PR'd enclosure would be plenty to driver the speaker to bottoming below resonance. Low frequencies don't require much power at all to reach large excursions. A 10Hz signal at loud volumes might be enough to kill an AV15 without a rumble filter.
     
  15. Brian_DR

    Brian_DR Extra

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    Brian,

    Technically, it is possible to bottom out with a 380WRMS amp, though incorrect driver parameters can acerbate the problem. Here is the reason.

    The power rail is 80V DC for my amp (no load). That does not mean it will output 800W RMS @4ohm. Because under 4ohm loading, the power rail will drop to 60V and output 350WRMS @4ohm. For vented and PR subwoofers, there is an impedance peak below box resonance frequency (approximately 0.7 times resonance frequency). The impedance is not a constant. The peak can go as high as 40ohms. That is almost like no-loading. So the amp can output 80V instantaneously for these signals. This is like getting 40% more excursion requirement. One of the critics I have for simulation programs is that they don't take this output vs impedance dependency into account and just blindly assume it is a constant voltage source. In real world, the problem most likely occurs in the very beginning of transition from no signal to full signal. That may also explain why Jeff does not have problem with music (continuos signals). Why sealed box does not have this problem? Because there is no additional impedance peak below box resonance frequency. As the cone move along, the charge on the power rail has been partially dissipated and when it reaches the excursion peak, the power rail already drops to 60V. Most people overlooked the importance of rumble filter in the vented box /PR configuration. A lot of, if not all, commercial vented box subs have at least 6th order roll-off. Some even have 8th order.

    Can someone provide T/S parameters so we can all do a simulation here?

    BTW, while it may appear it is over-driven, but it is not that far off. It is not like driving a 1000WRMS woofer with a 100WRMS amp and try to play at 120db level.

    Brian D.

    Rythmik Audio
     
  16. Jeffrey Noel

    Jeffrey Noel Screenwriter

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    Jeffrey, did you hook up the amp to any other speaker? That's a sure-fire way to see if the amp is 'damaged'.
     
  17. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Nope. I really don't care if it's damaged, as it works now as long as I do not turn it up loud. It's going to be "retired": I'm going to go with a Mackie 1400i pro amp (WITH adjustable rumble filter...5-170 Hz)...1400 watts mono- bridged. And a Tumult. Already ordered the Mackie. Ordering Tumult tomorrow from Kyle R.

    I be tired of monkeyin' 'round. Bet that Mackie won't clip.

    Jeff S.
     
  18. Craig Treusdell

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    I am running a Tumult in a PR enclosure with a QSC RMX 2450 bridged at the moment. When the second one gets fixed I will switch to one sub per channel. Not sure if 750x2 will be enough. Kinda makes me wish I had bought the PLX 3402 (1100x2), but I won't be sure until I hear both Tumults.

    Right now I have the gain knob at 16dB, with 34dB being max, and movies are incredible. I have not had any clipping as of yet, even when playing bass cds and cranking the gain knob way up. I was previously using a Tempest in a ported enclosure, and while it was impressive, there is no comparison.

    So for $560 and a 3 year warranty, the RMX 2450 is IMO a good choice. It does have some fan noise, but not enough to bother me or my wife. I thought I read about problems with the K2 going into sleep mode when no signal was present for a period of time and then having a delay to wake-up. Any thoughts?
     
  19. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I have been informed that the first batch of AV-15s had a problem: insufficient excursion before the voice coil hit the back plate. I have also been informed that once the VC hits the back plate, the driver is screwed. SO, there probably was no problem with the amp clipping causing the above problem. I had jumped to the conclusion that I had a good driver, which evidently was not the case.

    Oooops,

    Jeff Stanton
     
  20. John E Janowitz

    John E Janowitz Second Unit

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    Hi Jeffrey,

    Until the driver is taken apart, it is still unclear whether there was a driver problem, or a problem due to clipping the amp. Some drivers had problems with misaligned coils. The coil would hit on the back plate, and if it is done continually it will actually bend the VC former. Try hitting the end of a piece of copper tubing in the ground, and it will begin to bend and fold. Once the former bends it can make contact with the pole piece or the gap plate causing scratching and will eventually cause the driver to fail. If that is the case, the drivers will be replaced at no charge.

    However, it is still possible to have similar results due to clipping the amplifier. When the VC is moving back and forth, the motion aids cooling. The more current you put through, the more it moves and the more the motion helps keep it cool. When you clip an amp you chop off the tops of the signal. Instead of a back and forth motion, you actually pause the driver at the ends of it's motion. So now you are putting in high amounts of current with no motion to cool the VC. This is the easiest way to damage a VC and much more dangerous than having too much power. When this happens, glue on the vc former can fail, windings can come move around, you can actually warp the former due to heat on some occasions, etc. Lots of problems can lead to the VC rubbing after this.

    It is very possible the driver was built wrong from the start. It is also possible that the amp clipping was the cause of damage. In any case it is being taken care of. The driver will no longer be an issue after the repair.

    John
     

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