Help test my box design page...

Solid Snake · 27th January 2004, 05:35 AM

I'm not sure if the math is correct. If you guys could test the page out with subs you're familiar with and post your thoughts, it would be really helpful. As soon as I fix the sealed version, I'll start ported and bandpass versions also. It's written in PHP.

Sealed box design

roddyama · 27th January 2004, 06:30 PM

It's kind of neat.

The couple drivers I tried seemed to work out right. Do you plan on dipping into the ported designs?

Solid Snake · 27th January 2004, 06:34 PM

Yes, I plan on adding a ported and bandpass plotter also. To me it seems like the low end rolls off a bit too high, no?

GM · 27th January 2004, 09:09 PM

Well, I compared it to Lspcad Pro, BoxPlot 3.0, two different spreadsheets, one using Bill McFadden's HP calculator program and the other using the Margolis-Small HP calculator program, a proprietary program of mine, and MJK's sealed Mathcad worksheet. All plot slightly different responses for a given Vb due to how much the formulas have been simplified or values rounded off, etc., but while yours calcs the same Qtc (at least once yours is rounded off to the first three decimal places anyway), all plot a considerably lower F3/Fb than yours does.

FWIW, listing Qtc to three decimal places is sufficient and I prefer to specify Qtc and let it calc the Vb.

HTH,

GM

maylar · 27th January 2004, 09:21 PM

Low end drops off earlier than WinISD shows for the speaker I chose.

Ron E · 27th January 2004, 10:28 PM

You can find the proper equations at:
www.diysubwoofers.org

No need to campare to programs...off the top of my head:

Qtc=Qts*sqrt(Vas/Vb+1)
Fc=Fs*sqrt(Vas/Vb+1)

Fn=F/Fs
dB=20*log10(Fn^2/(Fn^2+Fn/Qtc+1))
At Fc, dB should be 20*log(Qtc)

Yours seems to be off by about 3 in magnitude, not sure how you are doing the graph, etc... perhaps your equations are right and you just have a viewing transformation - scaling issue, easy to do when making raster plots.... +/- 6dB is too tight, perhaps do +6 and -24, also go down to 10Hz. THese models certainly aren't valid above 500Hz for woofers....

Hint, Sealed box is the same as vented, you just use Fb=0 or Qp=0, depending on the model used......

...oops, forgot a parentheses....

Solid Snake · 27th January 2004, 11:50 PM

Yes, I did have the proper equation. The problem was that PHP assumes that a logarithm with no specified value has a base of e instead of 10. Once I forced the 10 base, it seemed to work properly, try it out.

Quote:

FWIW, listing Qtc to three decimal places is sufficient and I prefer to specify Qtc and let it calc the Vb.

Thanks for the feedback, I am working on adding these options. Please try the program now that it is fixed and let me know if there's anything else you'd like to see added, maybe a user defined dB range etc.

Dave Jones · 27th January 2004, 11:53 PM

Quote:

Originally posted by Solid Snake
I'm not sure if the math is correct. If you guys could test the page out with subs you're familiar with and post your thoughts, it would be really helpful. As soon as I fix the sealed version, I'll start ported and bandpass versions also. It's written in PHP.

Sealed box design

Others have pointed out that the plots don't look to be correct. Other than that, you need to go to about -15dB on the low side, for folks who will use EQ.

Solid Snake · 28th January 2004, 12:26 AM

Added:

-Colored 0dB and F3 lines
-Fixed Qtc to 3 decimal places
-Increased range: -24dB to +12dB

Working on Qtc input

Solid Snake · 28th January 2004, 01:28 AM

Qtc input is finished, let me know of anything else you guys would like to see.

27th January 2004, 05:35 AM	#1
Solid Snake diyAudio Member Join Date: Feb 2003	Help test my box design page... I'm not sure if the math is correct. If you guys could test the page out with subs you're familiar with and post your thoughts, it would be really helpful. As soon as I fix the sealed version, I'll start ported and bandpass versions also. It's written in PHP. Sealed box design

27th January 2004, 06:30 PM	#2
roddyama diyAudio Moderator Emeritus Join Date: Jan 2002 Location: Michigan	It's kind of neat. The couple drivers I tried seemed to work out right. Do you plan on dipping into the ported designs? __________________ Rodd Yamashita

27th January 2004, 09:09 PM	#4
GM diyAudio Member Join Date: Jun 2003 Location: Chamblee, Ga.	Well, I compared it to Lspcad Pro, BoxPlot 3.0, two different spreadsheets, one using Bill McFadden's HP calculator program and the other using the Margolis-Small HP calculator program, a proprietary program of mine, and MJK's sealed Mathcad worksheet. All plot slightly different responses for a given Vb due to how much the formulas have been simplified or values rounded off, etc., but while yours calcs the same Qtc (at least once yours is rounded off to the first three decimal places anyway), all plot a considerably lower F3/Fb than yours does. FWIW, listing Qtc to three decimal places is sufficient and I prefer to specify Qtc and let it calc the Vb. HTH, GM __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

27th January 2004, 09:21 PM	#5
maylar diyAudio Member Join Date: Jun 2003 Location: Connecticut	Low end drops off earlier than WinISD shows for the speaker I chose. __________________ dave

27th January 2004, 10:28 PM	#6
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	You can find the proper equations at: www.diysubwoofers.org No need to campare to programs...off the top of my head: Qtc=Qtssqrt(Vas/Vb+1) Fc=Fssqrt(Vas/Vb+1) Fn=F/Fs dB=20log10(Fn^2/(Fn^2+Fn/Qtc+1)) At Fc, dB should be 20log(Qtc) Yours seems to be off by about 3 in magnitude, not sure how you are doing the graph, etc... perhaps your equations are right and you just have a viewing transformation - scaling issue, easy to do when making raster plots.... +/- 6dB is too tight, perhaps do +6 and -24, also go down to 10Hz. THese models certainly aren't valid above 500Hz for woofers.... Hint, Sealed box is the same as vented, you just use Fb=0 or Qp=0, depending on the model used...... ...oops, forgot a parentheses.... __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan


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27th January 2004, 06:34 PM	#3
Solid Snake diyAudio Member Join Date: Feb 2003	Yes, I plan on adding a ported and bandpass plotter also. To me it seems like the low end rolls off a bit too high, no?

28th January 2004, 12:26 AM	#9
Solid Snake diyAudio Member Join Date: Feb 2003	Added: -Colored 0dB and F3 lines -Fixed Qtc to 3 decimal places -Increased range: -24dB to +12dB Working on Qtc input

28th January 2004, 01:28 AM	#10
Solid Snake diyAudio Member Join Date: Feb 2003	Qtc input is finished, let me know of anything else you guys would like to see.

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