Alpair 10P in dodecahedron cabinet - diyAudio
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Old 7th December 2014, 01:27 PM   #1
nirvana is offline nirvana  Canada
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Default Alpair 10P in dodecahedron cabinet

I would want to use an alpair 10p in a 14 cm dodecahedron aside ( 21 liters), do I have to add a port ? If yes of which size ?
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Old 7th December 2014, 04:18 PM   #2
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Quote:
would want to use an alpair 10p in a 14 cm dodecahedron aside ( 21 liters), do I have to add a port ?
No, you do not have to add a port. 21 litres, lined will have a Qtc of about 0.5 with the 10P. It doesn't matter whether it's a dodecahedron or not of course -the volume is the volume is the volume, assuming no significant eigenmodes. The question is really whether you want a critically damped sealed box or something else. Which comes neatly to

Quote:
If yes of which size ?
Which again depends on what alignment you're targeting. If you want vented, I'd probably pitch for ~42Hz for a lightly damped response assuming a voltage source amplifier; call it a 35mm diameter x 48mm long vent.
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Old 7th December 2014, 06:49 PM   #3
chrisb is offline chrisb  Canada
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Challenging build - post us along the way
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Old 7th December 2014, 11:35 PM   #4
nirvana is offline nirvana  Canada
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42 hz for vented....ok !!! For what may I hope for a closed box ?
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Old 8th December 2014, 08:23 PM   #5
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Fb = 66Hz, LF alignment as you'd expect for ~critically damped sans any step compensation.
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Old 8th December 2014, 10:09 PM   #6
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21 litres sealed will get you about 100 Hz F3. Add a vent and you'll get into what i feelare the optimum 16-20 litre vented size range and go much lower, at least an octave if not more.

dave
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Old 8th December 2014, 11:01 PM   #7
nirvana is offline nirvana  Canada
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gentlemen , thank you.
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Old 9th December 2014, 01:11 AM   #8
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We've got a few Alpair 10m/10p vented builds ranging from 15 to 28 litres. All work very well in their own way. Your cabinet volume should allow for a nice little vented jobbie! Sealed may be preferred if you will be using bass support, if not the bottom few octaves may seem a little thin.
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Old 9th December 2014, 01:21 AM   #9
AlanL is offline AlanL  United States
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@ nirvana, I'm kinda noobish myself, but the sim programs like winisd are pretty simple to play around with. Give it a try. You'll notice that with the vented it does hold the flat response lower (depending on tuning, box size). But the sealed (again depending on box size) generally has a shallower downward slope, so might actually have more response than you would think at say 30hz. It's pretty easy to build it with a vent then plug it and compare (or stuff it with straws).

One question for anyone more knowledgeable than myself (shouldn't be too hard):
I'm a little confuzled by all the F#s around here.

Lessee, Fs is the free air resonance - a TS parameter
F3 would be 3db down point.
Fb? is this the same as F3?
Mark lists Fo in his specs. Guessing this the same as Fs?

nirvana, please keep us up to date on your build, looks like fun. Maybe I'll try it after I finish remodeling my house.
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Old 9th December 2014, 01:26 AM   #10
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Quote:
Originally Posted by AlanL View Post
Fs is the free air resonance - a TS parameter
F3 would be 3db down point.
Fb? is this the same as F3?
Mark lists Fo in his specs. Guessing this the same as Fs?
Yes
Yes
Fb is where the box is tuned
Fo = Fs

dave
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