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Old 2nd June 2010, 01:37 PM   #1
c3conv is offline c3conv  Philippines
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Default 8" and smaller fullrange vs 12" and up fullrange in OB

What could be the differences between 8" and smaller fullrange driver as compared to 12" and up full range drivers in OB? Any pros and cons of it?
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Old 2nd June 2010, 01:59 PM   #2
borispm is offline borispm  Hong Kong
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It depends on the motor structure and the construction as well... It's hard to say, but larger full range drivers generally have higher efficiency and you'll have more room for adding passive correction circuits, although you may not want to do so as it will add coloration to the pure "full range" idea...
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Old 2nd June 2010, 03:32 PM   #3
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A smaller driver will have smaller gaps in the basket, so the reflections from the back will be different.

Large drivers will also beam, so you'll have to sit very very still, but the magic of true full-range will mean you'll sit there for hours.
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Old 3rd June 2010, 01:56 PM   #4
smbrown is offline smbrown  United States
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FWIW, I've used Electro Voice SP-12Bs in OB (12") and been very pleased with them. I'd guess effiency to be in the 98 to 99db range. Beaming? Maybe a bit, but not all that noticable to me. The baffle is about 18" wide and 40" high, SP-12b's mounted center toward top, bottom is a 15" parts express IB woofer. The woofer is driven by seperate amp, low passed at about 30hz.
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Old 3rd June 2010, 10:44 PM   #5
brookbh is offline brookbh  United States
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I would be interested on the details of how that Dayton IB driver is crossed, and the amount of power needed to keep up with the EV?

I've always wanted a pair of the 12 trxb... Btw
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Old 3rd June 2010, 11:03 PM   #6
smbrown is offline smbrown  United States
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It's an interesting idea that a friend introduce me to. If you imagine how the curve runs for the IB, which is it rolls off at a frequency close to where the SP12 runs out of steam, then consider the bass rolloff of the open baffle to start with, what we do by crossing at 30 or so is to create a fairly flat curve behind that from, say 30 up to 200hz - better yet, in reality it extends the sub to more like 20 flat to 200 or so. So just like the Sp12 runs out down low, the IB runs out up high. I have used a 200w SS amp on the IB with no lack of power. Both the amp for the SP12 and the one for the IB need seperate volume controls, and once set, the volume control on the preamp controls both at the same time. The low pass to the IB is simple first order using an R and C at the input to the bass amp.
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Old 4th June 2010, 12:31 AM   #7
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Ditto on EVSP12B. Pure magic. I am using a Alpha 15a in an H frame driven by a plate amp for the low end. I am also using a Fostex T90A up high to fill out the top end. Design is based on MJK's OB with Jordan full range project.

I just need to stop listening and finish them up

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Old 4th June 2010, 07:06 PM   #8
brookbh is offline brookbh  United States
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smbrown,

you are using the low pass on the IB via a low pass x-over, and are using the size of the baffle to control the natural roll off of the sp12?
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Old 5th June 2010, 09:57 PM   #9
smbrown is offline smbrown  United States
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Quote:
Originally Posted by brookbh View Post
smbrown,

you are using the low pass on the IB via a low pass x-over, and are using the size of the baffle to control the natural roll off of the sp12?
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Old 5th June 2010, 10:02 PM   #10
smbrown is offline smbrown  United States
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Brookbh, yes, exactly. The crossover is a simple first order line level crossover and then I take that into a SS amp that has a volume pot. Very simple - something that can be knocked together in a few minutes to try. For example, a series 4.7k resistor and a parallel 1.7uf cap (call it 2uf) will give 20hz rolloff. Important for this to be first order, not steeper. What I did was make a simple 3 position switch all with a 1.5uf cap and 3 different R to give me about 20hz, 50hz and 100hz so I could try different settings.
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