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Old 16th December 2012, 04:26 PM   #11
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Ok, now I have a plan for when I get back home, thanks. One more thing, is the betsy run full range, or is a crossover recommended?
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Old 16th December 2012, 08:08 PM   #12
holdent is offline holdent  Canada
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If I undersand GMs dims correctly the sims for this design are worse. The Betsy is now 7 dB more sensitive than the Alpha. To clarify the dims for me, they are:

- The baffle size is 48.45"H x 15.41"W
- Betsy offset from the centreline (at 7.45") by 2.57"; so either 4.88" or 10.02"
- Betsy is placed above the Alpha - I arbitrarily set it at 42" (not exactly ear height but any lower and it won't fit wih the Alpha)
- Alpha down 40% from top or set at 29.05" from base of OB (placing it 40% up from base at 19.05" is no better)
- Note that you can't offset the Alpha because the width of the baffle is just slightly wider

You are better off simply increasing the baffle width from MJK's original size. Instead of using 38"H x 20"W, use 38" x 32" - don't be freaked out by the width, you can use a 16" wide baffle with 8" wide wings (or 20" with 6" wings etc...).
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Old 16th December 2012, 08:43 PM   #13
GM is offline GM  United States
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Quote:
Originally Posted by fameless View Post
One more thing, is the betsy run full range, or is a crossover recommended?
If it could run full range on an OB, you wouldn't need a woofer.

GM
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Old 16th December 2012, 09:06 PM   #14
GM is offline GM  United States
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Worse than what?

Not surprising if the baffle is larger since an acoustically too small baffle for the driverís specs always results in less bass, more resonances and as I previously noted, the Betsy ideally requires a very wide baffle.

Oops! A generic response on my part, Iíd already forgotten about the woofer size.

If the baffle is wider, then this may change the XO design. WRT efficiency mismatches, thatís what some form of shelving is for if either buying more woofers or more efficient ones isnít an option.

Anyway, time for me to bow out since Iím apparently too far behind the times to match wits with a computer.

GM
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Old 16th December 2012, 09:38 PM   #15
holdent is offline holdent  Canada
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Worse than the first sim of the Betsy and Alpha in the 38" x 20" baffle.

I simmed it with an active high pass at 500 Hz 2-order Bessel filter and a low pass at 200 Hz with a 2-order LR filter.

The wider baffle is an effective way of matching the Alpha to the Betsy but if you go all active you can compensate for a narrow baffle and use some bass boost.

Things become simpler if you wish to run the Betsy fullrange in the narrower 40"H x 20"W baffle. It sims well if you just use a 4.7 mH inductor with the Alpha. However if you chose to do this you're limited by the Betsy in bass.
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Old 17th December 2012, 04:10 AM   #16
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My quick hack at it (and I do mean hack). X-over parts are basically the simulated ones from the spreadsheet rounded off, I wouldn't take these as any more than proof of concept.

First order @ 250 Hz on the Alpha, 3.5 mH

Second order # 500 Hz on Betsy, 30 uf, 3 mh, invert phase of Betsy

No change to the baffle layout.

There's a bump in Betsy's response at about 800 Hz that I suspect could be smoothed out with careful driver placement / baffle sizing. I'd play with that in The Edge and transfer the placement over to the worksheet. Otherwise it looks pretty reasonable. The slopes are even kind of close to symmetrical. I might attenuate Betsy 1 - 2 dB, the worksheet doesn't allow for that.

I'm sure a decent crossover designer could do better, but it seems to me the combo can be made to work. Bi-amping and MiniDSP would make it easy!

Bill
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Old 17th December 2012, 12:56 PM   #17
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Quote:
Originally Posted by holdent View Post

Things become simpler if you wish to run the Betsy fullrange in the narrower 40"H x 20"W baffle. It sims well if you just use a 4.7 mH inductor with the Alpha. However if you chose to do this you're limited by the Betsy in bass.
I like this because it's nice and simple. I do have the subwoofer to take over for bass. If I go with this, where are the betsy and alpha located on the baffle?
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