Lost in LspCAD, help!

Discussion in 'Archived Threads 2001-2004' started by Robin Smith, May 6, 2002.

  1. Robin Smith

    Robin Smith Stunt Coordinator

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    I am trying to get the numbers for my sonosub design and am sooo lost in LspCAD. I have looked through some past posts and still can't find what I need. I have entered some different numbers to explore but can't make sense of what I see.

    How do I decide what volume is ideal?

    In LspCAD, how do I know what it is tuned to? (i.e. Which window gives me this number).

    What are the Ql and Qa numbers for?

    What about fill %age for a sonotube.

    I have the Dayton 15" DVC but am using the Tempest numbers as they are roughly the same (and it is all I've got to go on).

    It's going in a sonotube of 20.2" diameter and I'd like to use a 4" flared port (which I can buy locally).

    Basically, I am trying to work out how long my tube needs to be and how long my flared port needs to be and what the resultant tuning will be.

    I want to tune for 20Hz unless someone can explain to me why I would want to go lower.

    As an example, I entered Pat's Sunosub III numbers (since it similar to the specs of my sub other than the tube diameter) but I couldn't find anything that told me it was the 16Hz he says it is tuned to. Where is this value read?

    I know I have lots of questions but its obvious I am lost... Anyone who is willing to help me come up with the suitable numbers that would satisfy HT bass needs would get my appreciation for sure?

    Thanks in advance

    Robin Smith
     
  2. Jeff Rosz

    Jeff Rosz Second Unit

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    hello,
    ok i hope this will get you on the right track. you have to go with what you know. you know you have 50" of tube. lets say you are gonna use all 50" of that tube. this is the best place to start. since you've read Patrick Sun's website, you noticed the endcaps. you have to use at least 1 1/2" of the tube for the caps. so now we are down to 48 1/2" of tube. doing the math (pi*r^2*48.5/1728), thats 9 cu ft of volume.
    9 cu ft=255 liters (use the yankee tool). less 5 liters for the driver is 250 liters. in the box data entry window, enter this in the box volume area. you know you want 20hz tuning, so enter that in the res freq area. you know you want a 4" port so enter 10.2cm in the min dia area. the program then calculates the required length of the port for you. ~16cm
    so now you need to know the volume of the port. same formula. comes out to about 1 liter, not enough to worry about really.
    there you have it, your sub is simmed. is this optimum?
    lets see.....
    so lets add an amp to the mix. open the measurement setup box and enter 125w into 8 ohms.
    open the driver unit config box and select parallel in the double voicecoil section.
    open the driver unit parameter box. notice the xmax p-p value for the tempest...32.8mm p-p.
    now open the cone excursion graph. note the freq where the curve crosses 32.8mm...16.5hz. so unless you are gonna play some organ tunes, you should be ok. all looks pretty darn good so far....except here is something to consider...
    the airspeed in the port graph. some would say this is ok, some would not. some say 10% (35m/sec) of the speed of sound some say less, like %5. i say lower is better. either way it peaks at 16.5hz 27m/sec with 250w.
    wifey says its too big, ahem, then shorten the tube and start all over. you have to switch back and forth between the graphs and look at what effect a change you make has on the other graphs. some examples are power input, port length/dia, res freq, many others...changing one affects the other. lets take power input....increase the wattage of the amp to 1000w, then go look at the cone excursion and vent airspeed graphs. so what is optimal? not 1000 watts. or change the res freq to some weird extreme like 5 hz, then look at the graphs, and the size of the ports. its in the ears of the beholder. do some searches on alignments, maximally flat, critically damped, EBS. hope i didnt make any errors and this gets you started well. ciao
    p.s look at this thread...it should really help answer some questions you have. there is also a lspCAD message board somewhere but i cant find the link....can anyone help out here?
     
  3. Kudret

    Kudret Stunt Coordinator

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    Jeff, thank you for the quick tour of LspCAD. I used LspCAD recently but I was not aware of some of its functionality you mentioned in your post.
     
  4. Patrick Sun

    Patrick Sun Moderator
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    Robin,
    Give this website a good reading - it goes through how to use LspCAD to design a subwoofer/enclosure/tuning.
     
  5. Jeff Rosz

    Jeff Rosz Second Unit

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    good link patrick, woulda saved alot of typing, heh.

    kudret, you are welcome. i only barely scratched the surface. but i think its enough to get a handle on the workings of the program and to lessen the learning curve quite a bit. those are the basic concepts one needs to learn to get a good idea of how all this "stuff" interacts. gonna haveta buy the full version of it one of these days. woe is me. time for work, lates.
     
  6. Robin Smith

    Robin Smith Stunt Coordinator

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    Thanks for the replies, help and links guys. It is truly appreciated and is helping come up with the design

    Tonight, I played with LspCAD and tried abunch of different scenarios.

    What I discovered surprised me. It seems that a smaller enclosure will perform better. Tis would also receive a higher SAF so that is a good thing.

    I entered a 175L box with a 12" * 4" flared port and came up with a tuning of 18.7.

    The same tuning in a 250L box requires a shorter port tube but appears to have poorer numbers.

    e.g.:

    For the 250L:

    Airspeed in port peaks at 26.9 ms at 15.5 Hz

    For the 175L:

    Airspeed in port peaks at 24.5 ms at 14.7 Hz

    The 175L is better then, right?

    The cone excursion hits 30 at 15.3 Hz in the 175

    In the 250 cone excursion hits 30 at 16 Hz

    Again, the 175L is better.

    I am leaning towards this smaller config as its SAF is higher and its easier to use. I am wondering what else needs to be checked for the sub to be considered "optimum" and what would be "better" about going with a larger volume as so far it all seems to be negative.

    Thanks again

    Robin Smith
     
  7. Jeff Rosz

    Jeff Rosz Second Unit

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    really cant argue with anything you said. looks like you are on your way [​IMG] i only used the 250l box because that was the "largest" possible sub that could be built. if a smaller sub gets better results for you, then thats the sub for you [​IMG]
     

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