SB 8 inch woofer sounds great on its own. - Page 2 - diyAudio
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Old 18th January 2013, 08:59 PM   #11
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Ya, don't cross at 1000hz. Here is what I do. If you want a prescription, follow this. If you don't, read and ask questions.

Buy a minidsp.
You'll need 4 channels of amplification. (if your receiver is integrated, this might be an issue)
Get the 2 way plug in (the advanced biquad plug in is better, but it's all features you won't need and will only confuse you)
Build a large ported box with the help of those here. I can try.
Build the box to include a 5 to 7L sealed enclosure inside for the alpair 7 near to the mounting hole of the SB woofer.

All that make sense so far?

Once you have the speaker built, you'll need to hook everything up. Preamp - minidsp - amplifiers - drivers.
You'll also need to program the minidsp. I can help you with that, but it's pretty easy. Just install the plug in, make the setting changes, and sync to your mini.

For starters, I'd suggest these settings.

Woofer
Level = 0db
Delay = 0ms
Low Pass = Linkwitz Riley 24db/octave at 300hz
PEQ = none needed

Full range
Level = 0
Delay = 0.6ms
High Pass = Linkwitz Riley 24db/oct at 300hz
PEQ = 6000hz, -2db, q = 3.0

Start with that and see how it goes. If it's bloated, the woofer level may need to be -1 or -2.

Last edited by tuxedocivic; 18th January 2013 at 09:02 PM.
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Old 18th January 2013, 09:25 PM   #12
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Quote:
Originally Posted by tuxedocivic View Post
Low Pass = Linkwitz Riley 24db/octave at 300hz
High Pass = Linkwitz Riley 24db/oct at 300hz
That is probably an OK start, but in the end you want to dial in the XO sucj that a simple change of woofer level can be used for BSC.

I have founf that that puts the XO in the K x 4560/(width of box in inches) K is in the range root(2)/2 > 1

dave
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Old 18th January 2013, 09:37 PM   #13
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I was thinking a 10" box is pretty likely for him. So 300hz was my first stab. I've also found with Linkwitz Riley slopes, the simple raising/lowering of the woofer achieves exactly as you say, BSC. Butterworth is to high of Q at the knee of the slope to allow for that.

There's the 6db of baffle loss, but then there's the 1 to 2db of cab diffraction right at the top of the baffle step point. I often find the diffraction to be a bigger deal than the baffle step actually. So he may need a PEQ of 650hz, -2, 1.0q.

EDIT - You may recall from the measurements I gave you on the SDX7 / LD25x speaker a wicked little diffraction peak around 650hz. You remember the baffle width of that one off hand? I couldn't take that out with a passive filter. At least not without a pricey notch.

Last edited by tuxedocivic; 18th January 2013 at 09:41 PM.
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Old 18th January 2013, 09:45 PM   #14
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Don't be such a Jessie. You haven't seen some of the XOs I occasionally crank out. You'd never complain about pricy notch filters again, I promise you that.
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Old 18th January 2013, 09:49 PM   #15
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Hehe, well, if I have a 2mH inductor on hand, then maybe I'd do it. But kills me to spend $10 on 2 db That's not a very good hifi mentality is it. Long live active dsp!
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Old 18th January 2013, 10:16 PM   #16
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Great suggestions but right now all I have is two channels of 8W each. I do, however, have plenty of foam core so I will build my test/break-in boxes and begin the learning process. Stay tuned!

John
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Old 18th January 2013, 11:53 PM   #17
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Quote:
Originally Posted by tuxedocivic View Post
EDIT - You may recall from the measurements I gave you on the SDX7 / LD25x speaker a wicked little diffraction peak around 650hz. You remember the baffle width of that one off hand? I couldn't take that out with a passive filter. At least not without a pricey notch.
About the same width as the waveguide.

Since a diffration anomaly will be very much listener axis dependent, kinda hard to EQ it.

dave
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Old 19th January 2013, 01:06 AM   #18
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Oh it's higher in frequency than I remembered.

Ya, it is a little awkward to eq diffraction. Often ok left alone.
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Old 19th January 2013, 01:17 AM   #19
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OK. Had way too much fun making 1 cu ft foam core cabinets and am now listening to my creation with a crude 1000hz

Click the image to open in full size.

first order cross over consisting of a 1.5mH inductor on the woofer and a 22uF film cap on the MA 7.3. Sounds gorgeous! The cab, if you can call it that, is 20" tall by 12" wide by 9" deep with a bit of poly fill and no vent. I have them sitting on the floor toed in a bit and Gillian Welch has never sounded better. I am new to this so I am willing to call this a starting point. Anyone want to suggest incremental changes that I can easily implement? It is minus 15 Celsius here in St.John's, Newfoundland, and it is a great way to spend a Friday evening. Thanks to all!

John
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Old 19th January 2013, 01:19 AM   #20
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That pic didn't turn out so well. Here's another.
Click the image to open in full size.
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