Stupid WinISD Pro questions

Discussion in 'Home Theater Projects' started by PaulDF, Mar 24, 2003.

  1. PaulDF

    PaulDF Second Unit

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    When modelling my Tempest sub with AVA 250 amp, what values do I use for the tab signal source - power and series resistance? Is it 250 and 4 ohms?

    Also, is the total cone travel of a Tempest 38 mm? Or 16.4 * 2 ?

    One more question to verify my modelling... Okay, if using 4 Ohms for resistance and the cone travel is indeed 38mm, then a 12.7 ft^3 box tuned to 15.5 hz will hit its mechanical limits with anything over 210 watts? (Assuming the frequencies being played include 26 hz).
    Is this a pretty accurate indication? Will there be any variance?

    Please feel free to correct me where I am wrong here...

    Thanks
     
  2. Pete Mazz

    Pete Mazz Supporting Actor

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    Series resistance is any resistance of the speaker wire, connectors, crossover, etc. Probably just leave it to .1 ohm is fine, unless you've got some exotic wire that measures high.

    Cone travel is 2 * Xmas = 38mm and 210W will push that alignment to max excursion.

    Pete
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    I thought I'd clarify a bit about cone excursion. First, it has nothing to do with Christmas (Xmas) unless you have a really cool wife who wraps up Tumults and puts them under the tree.

    When entering the driver information you'll notice that the Xmax box is followed by units (mm) and the word "peak". So they're asking for the one-way Xmax number - 16.4mm. I'm not sure what Xlim for the Tempest is, but I'd guess around 19-20mm. And I don't even know if WinISD Pro actually uses this information since I get the same results/graphs whether I enter a number or leave it blank.

    Now for the cone excursion graph you'll have to look at your options to determine what's what. If you select File-> Options you'll get a window that shows you the axis information for all the graphs. Check the units listed for cone excursion. Mine says "mm p-p" so 32.8 is the Xmax limit and that's what will be used in the "Maximum Power" graph. Design to the Xmax limit (32.8mm), not the Xsus limit (38mm) since the motor loses control once you surpass Xmax.
     
  4. PaulDF

    PaulDF Second Unit

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    Thanks guys, that helps a lot.

    Okay, with 230W I'm getting an excursion of 32.8 mm at 23 hz. I'm looking at the excursion graph. The max power graph seems to be close to an inverted excursion graph. I guess one determines the other..

    How do I know exactly how many watts I'm putting to the driver? One might think that with the plate amp gain set all the way up, 250-270 watts is going to the sub. It can't be that simple though. What about higher or lower input levels?
     
  5. Pete Mazz

    Pete Mazz Supporting Actor

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    Must have been before coffee. [​IMG] Xmas...Xmax...it's close. And of course 38mm was from the initial post.....it is indeed 16mm. Sorry for the confusion.

     
  6. PaulDF

    PaulDF Second Unit

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    Sorry to drag this out, but I can only get online late at night...

    Pete, it seems I don't quite understand these matters as well as I thought I did. So, if my plate gain is turned up 1/2 way, would it not compare to a plate amp rated for 130 watts with it's gain up all the way?

    Can anybody point me to some reference material on this? I don't remember ever seeing any topics on this kind of thing, or maybe I just perceived it differently.
     
  7. Pete Mazz

    Pete Mazz Supporting Actor

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    No. No matter the setting of the gain control, the amp will use it's full power rating, if needed. The gain control only affects the input signal strength to allow you to balance the sub to your main speakers. A lot of pro and consumer style amps have NO gain control. They rely on a line level pre-amp of some sort to control volume (input signal strength).

    So, if you're watching a movie and there's a quiet scene, the amp sees very little signal. The next scene may have loud explosions and now the amp sees a much higher signal level. It boosts both the low level signal and the higher level signal the same amount. Where you can run into problems is when the amp or driver is trying to reproduce those higher level signals. Say you were listening to the lower level signals at 90dB. The higher level signals are, say, 30dB higher in strength. Now the sub has to try to play those signals at 120dB! If you started at 70dB, the sub only has to attempt to output 100dB.

    Pete
     
  8. PaulDF

    PaulDF Second Unit

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    Thanks Pete, thats starting to make sense to me. But I am still confused about the WinISD excursion and max power charts.

    To put it simply... Is it possible for my sub to reach Xmax with the amp gain set halfway?
     
  9. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    "Is it possible for my sub to reach Xmax with the amp gain set halfway?"

    In a word - yes. It sounds like you're trying to make the subwoofer "monkey proof". This is a worthy goal if you've got kids or maybe roommates with low IQ who can't figure out that you're supposed to turn the blasted thing down when it starts making clacking noises. But if its just you and other intelligent users then the easiest solution is to just use common sense when turning the volume knob. Once you get a feel for the limits of the sub it really shouldn't be an issue.

    Here's a little example to help you understand what's going on:

    Lets say you've got the subwoofer all calibrated to a reasonable level and the gain control happens to be at 1/3 of the way up. Now you listen to some soft music on the radio for a while. The sub amp obviously doesn't have to work very hard to achieve this. Maybe it only needs 1 watt. But then a song you really like comes on and you decide to crank the volume up by 20dB. Now your sub amp has to work much harder. In fact it'll be pushing about 100 watts! You didn't change the sub gain control at all, but it sure is putting out a lot more power! Why is that?

    The power your amp puts out is dependent upon EVERY level control in the system. You've got at least 3 level controls, maybe more: Master volume level, receiver's subwoofer calibration level, plate amp gain level. My receiver also has an intellivolume level control.

    The plate amp designer knew that these amps would be used with various brands, models and styles of receivers and pre-amplifiers. They put enough range in the gain control to make up for a weak input signal in case someone's receiver had a weak subwoofer output. But that means that in most cases there's WAY more gain available than you actually need. So a plate amp is typically run with its gain set somewhere around 1/3. You could turn the plate amp gain down to "only" 1/3 but if you crank the other level controls up enough then you could still be asking for "all 250 watts" or more.
     
  10. PaulDF

    PaulDF Second Unit

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    Okay, so then what if a person has a receiver with a STRONG receiver output, and the level in the receiver is maxed out... Lets say they also have the 250 watt plate amps gain turned up all the way. Suppose its hooked up to a Tumult. It will only put the 270 watts to it?

    The amp gain will only make it more or less SPL?
     
  11. David Lorenzo

    David Lorenzo Stunt Coordinator

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    Paul: In that situation you would be asking the sub to produce huge amounts of bass and the required watts would be well above 270. The amp could not deliver the power you are asking of it and would clip the signal causing speaker destroying distortion.
     
  12. PaulDF

    PaulDF Second Unit

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    I didn't think clipping really hurt a sub driver.

    In what situation could both gains be turned all the way up?
     
  13. David Lorenzo

    David Lorenzo Stunt Coordinator

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    If you can get full power without turning both gains up, why would you want to turn them up more? It would accomplish nothing.
     
  14. Jack Gilvey

    Jack Gilvey Producer

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  15. PaulDF

    PaulDF Second Unit

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    I'm just trying to understand this, thats all.

    Thanks guys.
     
  16. Rich-Gar

    Rich-Gar Auditioning

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  17. Rob Formica

    Rob Formica Stunt Coordinator

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    Ok, this is the way i understood it, but don't be shy to point out any errors i may have made... [​IMG]

    The "power" value represents the power (Watts) you will be feeding your woofer from your amplifier and it will affect the SPL and cone excursion graphs... examples:

    1) you enter 1W... it will give you the SPL (db) you'll get with one watt (basically the efficiency often quoted (db @ 1W 1m) and notice the distance is also shown in WinISD) The excursion will be well under the woofers max

    2) you own a 1000W amp so you enter that value... you'll get a very high SPL, but if you look at the excursion graph, it's way beyond the woofers max... so basically your woofers bottoming out with the 1000W

    3) You decide to be reasonable and enter the maximum amount the woofer will take... BUT, notice that the Pe given for the woofer represents the maximum power it can deal with thermally even though you may be past it's excursion limit. Look at the maximum power graph within your design frequency range, say 18Hz to 100Hz. Your driver will be able to use up to the power at the lowest point, which will be either the thermal max (Pe) or may be the excursion limit.

    later...
    Rob
     
  18. Rich-Gar

    Rich-Gar Auditioning

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    Thanks for the info!

    Upon further experimenting with winisd pro I found that I was using different mesurement (in. instead of mm - etc..)

    now I think I am getting somewhere. Thanks again!

    I don't mean to steal the thread here, I hope I didn't offend[​IMG]
     

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