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Old 19th March 2009, 11:33 PM   #11
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Quote:
Originally posted by Scottmoose
Ha! That coincides almost exactly what I've been predicting for the past year or so, with a ruddy great peak at Fb. I don't have the exact dimensions for the 2.8 box, but this is what MathCAD predicts, with the dimensions fudged from the site, a 6in vent, & the claimed driver specs...

Welcome to the house of fun.
Here is what we measured today....

dave
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Old 20th March 2009, 09:11 AM   #12
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Thanks Dave.

Hmm. Well, that's just resoundingly confirmed my dark suspicions about the manufacturer's claimed driver parameters.

FWIW, again, fudging the cabinet dimensions (they'll be close enough), 3 FR plots for a 6in diameter vent: top = 0.75in long, middle 6in long, lower 10.25in long. The 6in diameter vent is a bit OTT IMO; certainly at anything less than a 6in length. Ferret owners best exercise extreme caution...
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Old 20th March 2009, 05:15 PM   #13
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Scott-
Those modelled curves don't look much like the ones I saw on Dave's screen yesterday. The problems with the shorter vent tubes were more dramatic in Dave's models.
It looks like different software can make a big difference, so best to leave the final judgment to real ears!
BTW, my drivers had 100+ hours on them, so that may account for some of the differences from the published numbers at commonsenseaudio.

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Old 20th March 2009, 05:33 PM   #14
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could you explain why a port can give benefit? isn`t the 2.8 a quarter wave design and not a bass reflex cabinet?

really the 2.8 would only go that low? i`m going to build them for the super 8 when i got the time, but then from my actual really unbalanced spiral-horn design i heard some good 35hz tone... and it`s completly a wrong design, since it was for the 206, as scott helped me figure out on another thread...

dave why don`t you give a try to a spiral-horn with a little fostex unit? so we can have a trustworthy comparison of the design purpose?
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Old 20th March 2009, 06:02 PM   #15
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Quote:
Originally posted by VictoriaGuy
Those modelled curves don't look much like the ones I saw on Dave's screen yesterday. The problems with the shorter vent tubes were more dramatic in Dave's models.
The last curve is very close to what i generated. My 3/4" curve looked to have a bigger bump, i'll have to do an overlay to see if it is just a graph scale artifact.

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Old 20th March 2009, 06:16 PM   #16
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Edit -you beat me to it Dave. Had a bit of a problem, halfway through writing my post, with a lump of Aberdeen Angus steak getting caught in my throat. Not recommended, I assure you.

Quote:
Originally posted by VictoriaGuy
Scott-
Those modelled curves don't look much like the ones I saw on Dave's screen yesterday. The problems with the shorter vent tubes were more dramatic in Dave's models.


I dunno -the short-vent graph[s] I did above are pretty similar to the one Dave posted above, with a ~ +5 - 6db lift at Fb. I was feeling charitable & damped the box quite heavily, plus, as I mentioned, I don't know the exact dimensions of the cab itself, so I fudged it slightly. ~close enough to give a good idea of the general trend though.

Quote:
BTW, my drivers had 100+ hours on them, so that may account for some of the differences from the published numbers at commonsenseaudio.
No chance. I'm not sure which units you have, the Super, or Cast Frame models, but it doesn't really matter; 100 hours of use isn't going to dramatically reduce the total damping / motor power and Vas, or add ~ 20Hz to their respective resonant frequencies. The Super 12 measurements also corrolate quite well with some others I've seen, so my conclusion is that Audio Nirvana's published specs are as ficticious as those from most other FR driver manufacturers.
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Old 20th March 2009, 06:27 PM   #17
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Quote:
Originally posted by human.bin
could you explain why a port can give benefit? isn`t the 2.8 a quarter wave design and not a bass reflex cabinet?

really the 2.8 would only go that low? i`m going to build them for the super 8 when i got the time, but then from my actual really unbalanced spiral-horn design i heard some good 35hz tone... and it`s completly a wrong design, since it was for the 206, as scott helped me figure out on another thread...

dave why don`t you give a try to a spiral-horn with a little fostex unit? so we can have a trustworthy comparison of the design purpose?
It's a bit of both. Most supposed bass reflex cabinets are in fact hybrids. Technically, a BR requires an even air-particle density within the enclosure and no standing waves at all, and very few cabinets meet that criteria. In this case it's a badly designed BR / MLTL.

Anyway, yes, the 2.8 with the short vent & AN10 really will only go that low -it's just basic physics / box tuning, so expect a cut-off around 50Hz.
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Old 20th March 2009, 07:07 PM   #18
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Default To the OP's point

If you're going to assume stereo subs, I'd go with a small sealed box. You'll lose something in transient response near box cut-off, but if you tune it to where you want to bring the subs in, you can save yourself the HPF, and even potentially mitigate baffle step with the sealed box bump.
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Old 20th March 2009, 08:29 PM   #19
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That's certainly one way, although I'd be looking at stereo woofers, rather than subs per se. Most sub drivers can't get up high enough, & don't sound as good. Ouch. Controvertial perhaps, but I know I'm not alone in thinking that. YMMV as ever of course.
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Old 21st March 2009, 02:13 AM   #20
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Quote:
Originally posted by Scottmoose
That's certainly one way, although I'd be looking at stereo woofers, rather than subs per se. Most sub drivers can't get up high enough, & don't sound as good. Ouch. Controvertial perhaps, but I know I'm not alone in thinking that. YMMV as ever of course.

In my limited experience with FR, it seems the last thing one wants is a sub that goes boom. Dayton has the reference series subs that are musical, but I would consider going with something as small as a 10 inch woofer. Dayton has a continuum of woofers to subs, with some models clearly borderline.
I find it's a bit tricky with dayton woofers to determine the highest xover that's going to be smooth and musical.
I'm hoping we get more extended range designs, rather than FR. But perhaps I'm wrong in assuming there's an musical advantage in designing extended range instead of FR.
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