MJK or somebody: need some math help - diyAudio
 MJK or somebody: need some math help
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 25th July 2012, 10:22 PM #1 diyAudio Member   Join Date: May 2009 Location: Seattle, WA MJK or somebody: need some math help Just for fun, I'm trying to determine how the Eminence Deltalite-II would perform in a U- or H-frame. I wanted to get an idea of the ultimate system Q for the driver in a U-frame, so I tried using the equations that MJK has given in his article. I started with the equation for Qed: Qed = (Mms + Mair)*Fd*Re*Bl^-2 When applied to the eminence alpha 15, MJK gets a result of 1.792. However when I plug the deltalite's info in... (72+22)*36[est.]*5.29*15.7^-2 I get a result of ~72.62. What am I doing wrong to get such a dramatically different result? __________________ Then again, what do I know?
 26th July 2012, 05:03 AM #2 diyAudio Member   Join Date: May 2009 Location: Seattle, WA Same thing happens when trying to solve for Qmd. According to the same paper I solved Rmd as 4.189, then when I applied that to the equation for Qmd I got 807.83. The equation given for Qmd is: Qmd = (Mmd +Mair)*Fd*Rmd^-1 or Qmd = 94*36*4.189^-1 however, if I change 94 to .94 I get a more reasonable solution of 8.07. Is that my error? __________________ Then again, what do I know?
 26th July 2012, 05:30 AM #3 diyAudio Member   Join Date: May 2009 Location: Seattle, WA Well, I might have solved the problem. I was off by a factor of what, 100? By changing a gram from 1 to 0.01 in the equation I get more reasonable results. U-frame: .94*36*4.189^-1 = 8.07 Qms .94*36*5.29*15.7^-2 = 0.72 Qes (1/0.72+1/8.07)^-1 = 0.661 Qms predicted rolloff = 55Hz H-frame 1.14*36*4.189^-1 = 9.79 1.14*36*5.29*15.7^-2 = 0.88 (1/0.88+1/9.79)^-1 = 0.807 Fd = 32 rolloff = 40hz That sounds about right to me, although of course I am fudging the numbers a bit with regard to Fs. Without measuring I can't be entirely certain what a mass of 22g (or 44) will have on a cone of 72g weight compared to the alpha 15, which has a cone weighing 59.8g. If SPL is consistent with the A15 in these configurations, then the deltalite should still be around 89-90db efficient. But I have another question now, which MJK or some other guru can answer if he or she likes. Will a U-frame of double the depth (in this case, 15" as opposed to 7.5") have the same massing effect on a speaker cone as a similarly-sized H-frame, or is the effect diminished? __________________ Then again, what do I know? Last edited by chazdrumzalot; 26th July 2012 at 05:38 AM.
 26th July 2012, 03:17 PM #4 diyAudio Member     Join Date: Jun 2007 Location: eastern PA Somebody else should check this, but IIRC, making the U frame deeper than 7.5" will result in resonance down in a region where you don't want it. Cheers, Jim __________________ A day without music is like a day without food.
 26th July 2012, 07:03 PM #5 diyAudio Member   Join Date: May 2009 Location: Seattle, WA That's what I recall too, but I wasn't sure if there was some leeway. __________________ Then again, what do I know?
 27th July 2012, 05:51 AM #6 diyAudio Member     Join Date: Jun 2003 Location: Chamblee, Ga. Not really, unless you flare the sides out to at least a 12 deg included angle to turn it into a 1/2 WL resonator with good 'slap' echo decay same as a LEDE room design. When straight back it's a 1/4 WL resonator, so even before factoring in a large end correction that will further lower it, 7.5" is already down to ~13560/4/7.5 = ~452 Hz and you want it to be well above the XO point. GM __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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