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Old 20th June 2004, 07:26 PM   #21
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Originally posted by GM
nothing ventured, nothing gained.

GM
I did put an equation into the worksheet to re-calculate Qts, but I got a different number, so I'll check my formula.

[Added a few minutes later] Actually, I just copied the formula from a worksheet on Martin's web page. The worksheet is for the Fostex fe206e. (Of course I changed the original Q to the one for the fe107e.)
Here is the formula:

Qed' := Qed*(Re)*(Re-Rs)**-1

Is that right?

I'm probably already reaching the limit of what those little drivers can do, even in a small room. For a given SPL, cone excursion quadruples every octave, right? And the xmax on those is tiny. Still, I'll play around some more.

Dave

"Nothing vented nothing gained."
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Old 20th June 2004, 08:22 PM   #22
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I think I have the Qes figured right now, and I put in the numbers exactly as you said. Here's the function, assuming a total added resistance of 5 Ohms:
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File Type: png spl.png (3.9 KB, 517 views)
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Old 20th June 2004, 09:00 PM   #23
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>For a given SPL, cone excursion quadruples every octave, right?
====
Correct.
====
>And the xmax on those is tiny. Still, I'll play around some more.
====
Yeah, and I don't know how much excursion it has before either popping out of the gap and hanging, or bottoming out. For sure I wouldn't drive it past 1/8" until you find out what Xsus/Xmech is.
====
>I think I have the Qes figured right now, and I put in the numbers exactly as you said. Here's the function, assuming a total added resistance of 5 Ohms:
====
Hmm, don't know what you're doing, but you're not getting the right response. Notice that the IB response hasn't flattened out so it's not plotting the higher Qts response, ergo the higher Q vented response.

GM
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Old 20th June 2004, 10:20 PM   #24
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Quote:
Originally posted by GM
Hmm, don't know what you're doing, but you're not getting the right response. Notice that the IB response hasn't flattened out so it's not plotting the higher Qts response, ergo the higher Q vented response.

GM
It actually is flattened out a little bit, but very little. I'm probably not calculating the new Qes correctly. See the attachment.
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Old 20th June 2004, 10:28 PM   #25
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Originally posted by Dave Jones


It actually is flattened out a little bit, but very little. I'm probably not calculating the new Qes correctly. See the attachment.
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File Type: png gm added res.png (10.1 KB, 533 views)
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Old 20th June 2004, 11:36 PM   #26
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Okay, it's better now.

Sometimes MathCad 2000 starts refusing to update the graphs for me. If I save the file and re-load it, everything is cool again.

Does this chart look better?
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Old 21st June 2004, 12:02 AM   #27
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Yep, now it looks like mine. I have the same problem with Mathcad too, but I just assumed it was my machine since it's so outdated 'n slow.

GM
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Old 21st June 2004, 12:16 AM   #28
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Yep, now it looks like mine. I have the same problem with Mathcad too, but I just assumed it was my machine since it's so outdated 'n slow.

GM
MathCad does not impress me. But Martin's worksheets do.
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Old 21st June 2004, 12:23 AM   #29
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BTW, why didn't you parallel the bypass cap around all the resistance?
GM
I tried it both ways. I liked it better across only the 4 Ohm. ... a little less treble boost than BSC boost. There's not a big difference of course.
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Old 21st June 2004, 12:55 AM   #30
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Fair enough. Not having heard this driver, I was just curious. Yeah, they impress me too. I've been designing tower speakers (now ML-TL) since the late '60s, but no formula I could ever find would accurately predict vent length, and not having the math skills to wade through all the gas law formulas I never could come up with any calc or even rule-of-thumb to figure it. And of course stuffing was trial n' error.

GM
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