Sub design perimeters

[KennyG]

I'm going to build a Isobarik-push/pull design. Using 2 tempest drivers. The applicable specs off Adire's web page are as follows: Qtc .38, Fs 19hz, Vas 317L = 11.2 cu.ft.
Thomas you had mentioned a Qtc of .5 as a good starting place for high quality bass, so that's where I started, then after doing some calculations (assuming Fc = 25) I came up with an F3 of 27.8hz, and a Vb of 15.3 cu.ft.
The F3 is alittle high for a pure sub...I do want it to pack a punch down low, so I tried a Qtc of .707
Assuming Fc = 35.4, my new F3 is 17.7hz...does this seem right? and my Vb drops to 4.6 cu.ft.??? NO way I must be doing something wrong...the only thing I can figure is my Vas conversion is wrong. I'm assuming I was supposed to convert Liters to cubic feet?
The only other reasoning I can come up with is that .707 is a "universal code"...think about it .707 is also the RMS point of a sign wave! :B and it seems that number has come up in other math related items that I've studied, but none come to mind right now...maybe not.
Anyway assuring my F3 calc's are right, is .707 a good option for tight-well defined bass down to approx 20hz?

AND...is that Vb right???

[ThomasW]

Kenny

What design program are you using? It's important that the program be able to model an isobaric design and that the parameters be entered correctally.

Remember the Vas drops by 50% when using as isobaric design. So for the software program the Vas, you need to enter 159L or approx 5.6 cu ft not 10.12

Also you are making some assumptions that don't work for a sealed system. They roll off at a fixed rate, 12db/octave, so you have little control over the the F3

Also Fc is the resonant frequency of a sealed system. Normally this isn't used as a variable when calculating a design.

A "Q" of 0.5 is considered critically damped for a sealed system.

Now I haven't updated the T/S parameters to the newer ones on the Adire site. My program still is using the the prototype ones. So there will be a small difference in the plots.

BassBox Pro models the following isobaric for two Tempests (prototype Tempest parameters)
Qtc 0.5, Vb 2.575 cu ft, F3 46.57Hz




theAudioWorx (http://www.theAudioWorx.com)
Klone-Audio (http://www.klone-audio.com)

[Lexman]

Kenny, I am impressed! So much so, we might just require all the moderators to do this, hehe.

Goodluck on your ambitious project!

Lex

[ThomasW]

Kenny

Later today when I get some spare time, I'll update the Tempest T/S parameters in my program. Then I'll run the special "optimize" function in BB PRo and see what it recommends for the best performance.




theAudioWorx (http://www.theAudioWorx.com)
Klone-Audio (http://www.klone-audio.com)

[Andrew Pratt]

I agree Lex all moderators should be required to own a Sonosub:) ...or at least a DIY sub:)




http://www.htguide.com/CFBoards/images/signatures/andrew_sig.jpg (http://www.mts.net/~glendap)

[KennyG]

Thomas, I'm not using a program, I'm trying to do this by hand using "the loudspeaker design cookbook", your right I forgot to cut my Vas in half. This book says that Fc is a design perimeter, and Fc changes with each different Qtc. (Qtc x Fs)divided by Qts = Fc
Damn, 46.75hz is awfully high for F3...don't you think? At 25hz how much of a roll-off would I be looking at, 10 to 12db? Man that's alot!
Will a Qtc of .707 bring this down? (it is the magic universal code you know :W )

Thomas, if "a"= (Qtc divided by Qts)squared -1...exactly what is "a"(alpha)??? is this total system dampening?

P.S. Lex your easily impressed. :W at this point I can't even get my math right. :?

[Lexman]

Kenny, if you were going to carry 120 pounds cross country, would you:

A. Carry it on your back.
B. Make your wife carry it, if your married. (Neighbor's wife works equally well)
C. If no one helps get a Mule.

I think pick C. get a mule. (Software design tool)

How's that for an analogy? Ok, enough, I am off to the golf course.

Lex

[ThomasW]

Kenny

Let's get up to date. You'll go nuts, and you'll drive me nuts trying to do this by "hand". So put away that slide rule :) And download WinISD from here.
http://www.linearteam.org/

It's free, it's not a demo, and it's pretty accurate.

Alpha, that's what comes before beta :B




theAudioWorx (http://www.theAudioWorx.com)
Klone-Audio (http://www.klone-audio.com)

[KennyG]

Lex, sometimes it's good to get that exercise yourself!!! It's good for the brain, and easy to do...once you understand it all...that's my problem, I don't understand it. Doing the math manually helps me see how all the "parts" fit together.
Plus Thomas is always here to help when we falter. :W
I gotta go watch my crappy football team, and do math!

[ThomasW]

Kenny

"Drop that slide rule buddy, and hands against the wall." http://smilecwm.tripod.com/ut1/mgwhore.gif

I really don't remember the "math" I've been using software design tools since 1984!!! That's why I bought a computer.

Get the program, and use it against the "formula's". To start, you'll need to make a driver base and add the Tempest T/S data.

The Dickason book is overly complicated and not all that accurate with regard to some of his design assumptions. You can ask Dan Wiggins and the boys at Adire, if you don't believe me about Vance!




theAudioWorx (http://www.theAudioWorx.com)
Klone-Audio (http://www.klone-audio.com)

[KennyG]

Thomas, O.K. you win, I Put the Calculator away!
Thanks for the site above, I'll try it again tomorrow, for some reason I can't get past the home page, everything just seems to be locked up.

[ThomasW]

Kenny

You've got mail, and it's a pretty big file :B




theAudioWorx (http://www.theAudioWorx.com)
Klone-Audio (http://www.klone-audio.com)

[KennyG]

Maybe all these troubles I'm having are on my end, I just checked my mail but nothing has come in.
This has been a frustrating day all the way around. :( Gee's never mind I just checked my mail again and there it was! Thanks alot Thomas

[KennyG]

Thomas is PE the same as Pmax???

[ThomasW]

Pe is the maximum electrical power that a driver can handle before it is damaged, meaning the VC burns out. I'm not familiar with Pmax, but yes it's probably means the same thing. Again this isn't necessary for cabinet design




theAudioWorx (http://www.theAudioWorx.com)
Klone-Audio (http://www.klone-audio.com)

[KennyG]

Very nice program! but alas, to get the type of response I want I must join the masses and build a vented sub. :( :) but I can still build it Isobarik-push/pull...it looks to me like something in the 185 liter Vb, tuned to about 19.5hz is the way to go. It's basically flat to 21hz with an F3 at 18.2hz
What do you guys think? Seem about right?

One last gasp for the sealed enclosure, it there an electronic EQing system I can buy to flatten out the response???