Sub Wattage

Discussion in 'Archived Threads 2001-2004' started by AbelM, Jan 20, 2002.

  1. AbelM

    AbelM Second Unit

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    What does this role play in getting a sub? I mean don't you just care about it's frequency rate (96Hz) and what inch?

    Thanx!!
     
  2. Paul_Fisher

    Paul_Fisher Screenwriter

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    I'm pretty sure the bigger the actual woofer is the more power you need to drive that woofer. The higher the RMS the louder the subwoofer can play.
     
  3. Sebastien David

    Sebastien David Second Unit

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    well ,a larger woofer could push out higher levels, however, that is not the main benefits, or so i understand, of having a bigger woofer.

    all other things being equal, a bigger woofer will have more presence, it will move more air, thus creating that breathy kind of sound that realy moves you.

    also, it will usually go lower.

    there are disadvantages, however, such as the loss in speed. thnka about it: a bigger woofer will have more mass, thus more inertia. therefore, it will have a tendency to be harder to stop (and start). the sound will thus "linger" a bit, so quick peaks like a kick drum sound will be less defined, less neat.

    it might also give up some impact at relatively higher frequencies compared to a smaller woofer.

    now, as i said, these are generalizations, and there are exceptions to every rule. therefore, the best way to judge, as always, is to audition.

    as fore the power, well, up to a certain point, more power is better. it will allow you to move that big driver with more authority, and prevent the amp from clipping or reaching its limits before the woofer does. it does no good to overpower a woofer, however, as the driver will bottom out before the amp reaches its limits. but, as almost always, more power can only be better.

    feel free to pitch in and correct me if i'm wrong, guys!
     
  4. Dustin B

    Dustin B Producer

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    A bigger cone is not slower than a smaller one. It's all a function of the drivers specs (which will also give the strength of the drivers motor) and the enclosure. The motor strengths on the big drivers today make them anything but slow.
    The biggest factor in a subs sound is the enclosure. It comes down to a Q value. This Q value is dependent on the mechanical Q of the driver (qms) the electrical Q of the driver (qes) and the size of the enclosure. There is a qts which is a combination of the qms and qes and when you factor in the enclosure you can come up with an over all Q for the system. This Q value will tell you the sub is either underdamped, critically damped or overdamped. If it is underdamped the cone will tend to, ah I'm not gonna get this out right so I'm just gonna quote a section from a secrets of hifi essay:
     
  5. AbelM

    AbelM Second Unit

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    Thanx a lot guys', that helped out a ton!!
     
  6. ling_w

    ling_w Second Unit

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  7. Dustin B

    Dustin B Producer

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    I'll agree that I could be wrong (more than likely am) about the slope being steeper. But I don't think overdamping increases efficiency above the roll off's starting point.
     
  8. Greg_R

    Greg_R Screenwriter

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    Also, a 3dB increase in SPL requires a doubling in power (watts). This is assuming that the rest of the design remains static...
     
  9. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    >>Overdamping does not mean the slope will be steeper, it just means that the rolloff starts earlier, but at a gentler slope. That could be corrected by equalization. The added benefit of overdamping is the increased efficeincy at freq before rolloff, thereby giving more headroom.40hz). And to get this *advantage*...you'll be forced to introduce EQ down low---sometimes a LOT of EQ---to boost the response of the design. So you end up eating amp headroom,and forcing 2-4x(or more)the voltage thru the driver simultaneously.(so now there's the issue of VC heating).

    TV
     
  10. ling_w

    ling_w Second Unit

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    A overdamped setup with a gentle rolloff starting at 40hz would result in a 5-6dB decrease in efficiency at 20hz. That does not mean you would need 4x the power to produce 20hz signals at the same SPL compared to a critically damped setup since the overdamped sub would have more or less equal efficiency at the 20hz point. The added benefit of the overdamped system is higher efficiency at the critical freq range that is most relevent to HT, which is in the 35hz range.
     
  11. Dustin B

    Dustin B Producer

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    But the roll off will start higher than 40hz. And if the sub is down 6dB at 20hz it will take 4x the power to bring it back up to level. Every 3dB increase in output requires a doubling of input power. So you will need 4x the power (two doublings) at 20hz to get a sub that is down 6dB back up to being down 0dB. And that also assumes it can take 4x the power that a critically damped system applies at 20hz. More than likely it will be well past Xmax with that much power applied.
     
  12. ling_w

    ling_w Second Unit

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    It will not require 4x the amp power since at above 40hz, the underdamped system will be more efficient, so the rolloff will result in roughly equal efficiency at 20hz, and at below 20hz, with the overdamped system having a gentler rolloff, it will require less power.
     
  13. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    What systems are talking about Ling? Most of the thread was very general...and you seem to be comparing two very specific systems...can you back up your claims? What IS the exact 20hz system sensitivity for your *overdamped* design?

    Even assuming the BEST case scenario for you...and believe me...it's quite an assumption at this point...

    As this *ling* system has it's volume increased...it may stay flat at lower volume levels,but it's going to rolloff as the volume is increased....you'll eventually reach a point where the EQed response is no different from the crappy non EQed response which has the major rolloff beginning in the 40-60hz range. So, a lot depends if you are trying to design a system to measure good at some industry standard 85dB, or if you want the system to sound good at more typical HT levels(105dB+).

    TV
     
  14. Dustin B

    Dustin B Producer

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    What I'm saying, which is what I think Tom said above. Is that if you took a vented EBS allignment that could play flat to 20hz and compared it to an over damped allignment (same driver) that was down 6dB at 20hz. The eq to get it back up to flat at 20hz would require that 4X the power applied to the vented EBS allignment be applied to the overdamped one. In the 40-60hz range both allignments would have the same power requirements.
     
  15. ling_w

    ling_w Second Unit

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    A overdamped system will have a higher f3 point, therefore requiring equalization, but with its gentler rolloff, it will have a equal f6 and higher f9 point than the critically damped system.

    Also, due to its higher midband efficiency, and its gradual rolloff, efficiency becomes roughly on par with the critically damped sub at some lowband freq, roughly in the 20-25hz range.
     

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