Alpair 7.3 Bookshelf Bass Reflex? - Page 2 - diyAudio
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Old 2nd May 2012, 09:47 PM   #11
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Quote:
Originally Posted by chrisb View Post
I think that's definitely something not to try with any of the Alpairs
Why not?

I wouldn't do that in my living room, but nearfield the EL70 barely exceeds 1mm of travel.
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Old 2nd May 2012, 09:53 PM   #12
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When i was simming these my 1st derivative rule was broken for any box over about 9 litre (1.2 ft^3 ~ 14 litre)

dave
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Old 2nd May 2012, 09:56 PM   #13
StevenZ is offline StevenZ  United States
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And what is your 1st derivative rule? I'm not sure I follow where you were going with that statement. Are you confirming that the .5ft@50hz box sim would work, or would not work?

-Steven
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Old 2nd May 2012, 10:17 PM   #14
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The 1st derivative of the FR curve does not cross 0 more than once.

Sticking to this rule has allowed us to keep tight tuneful bass response.

dave
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Old 2nd May 2012, 10:27 PM   #15
StevenZ is offline StevenZ  United States
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Oh, I see. Thanks for the clarification. Using the box porting and size I posted earlier it doesn't cross more than once, though it comes close. It's lowest point is a 0.52db drop at 70hz and finishes off with a 0.3db drop at 50hz.
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Old 2nd May 2012, 10:46 PM   #16
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Quote:
Originally Posted by StevenZ View Post
It's lowest point is a 0.52db drop at 70hz and finishes off with a 0.3db drop at 50hz.
For that to be true the 1st derivative has to cross zero at least 2x

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Old 2nd May 2012, 10:50 PM   #17
StevenZ is offline StevenZ  United States
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I'll take your word for it as you obviously have a vast knowledge of box designing and I'm sure a more accurate way of measuring frequency response of enclosures. From what I'm seeing in WinISD is that it never crosses 0 even with those two figures I gave you. What could be the difference of results between what I'm modeling and what you're modeling? Is WinISD inadequate for designing enclosures using FR drivers?

-Steven
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Old 2nd May 2012, 10:57 PM   #18
StevenZ is offline StevenZ  United States
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I've attached a couple photos for you to take a look at. Let me know if you see any discrepancies in the parameters that I'm not seeing that may be causing it to not show the frequency response rising above zero.

Thanks,
Steven
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File Type: jpg A2.jpg (91.8 KB, 284 views)
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Old 2nd May 2012, 11:35 PM   #19
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Does winisd allow for modelling of stuff in a vented box? I know unibox does and I find (in the model and audibly) that adding stuffing to a response like you have there can mellow out the tuning peak.
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Old 2nd May 2012, 11:42 PM   #20
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by tuxedocivic View Post
Why not?

I wouldn't do that in my living room, but nearfield the EL70 barely exceeds 1mm of travel.

I'd be concerned about over stressing the much more delicate metal cone of the Alpair, but we could always ask Mark about that.
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