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Old 19th April 2011, 01:04 AM   #1
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Default Speakernoob trying to build a small sub

Alright, I have a pair of AV30 monitors I use for my TV in my dorm, but they are slightly lacking in bass for movies. This is an unusual for me as I am not a basshead by any stretch of the imagination (my favorite headphones are grado's and the sub going in my car is an 8" ), but for movies I'd like a little more from my dorm setup. Heres the kicker: I'm on a budget, and I have a very tight space constriction. (Specifically 10.5" high and 11.5" deep for the external dimensions of the box, with as much width as necessary to match the internal volume)I was considering between these two speakers:http://www.parts-express.com/pe/show...=295-480Should I just go with a sealed enclosure? how much power will it take to get decent volume out of it? Will a 25w amp be enough or will I need to step up to a 70w? Or should I go with some sort of a bandpass? Sorry about all the dumb questions. I hate being "that guy" but I'm knew at this stuff.
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Old 19th April 2011, 01:58 AM   #2
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So your looking at a sealed box thats about .75cuft. You should beable to do that with that 10" woofer you picked. Ported is for bigger boxes, not smaller.

Id also stick with the SA70 70Watt model, its worth the extra 20 bucks for 3x the power.
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Old 19th April 2011, 02:41 AM   #3
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Just shy of 3/4 of a cubic foot.I get .9 cubic foot, stuffed with Dacron for a Qtc of .707 Yes indeed I would opt for the 70 Watt version also.

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Old 19th April 2011, 09:42 PM   #4
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This sounds deceptively simple. A few more (fairly simple)

Like dacron batting adhered to all the surfaces of the box interior, or some sort of shredded dacron foam?

Is it necessary to subtract the volume of the sub and housing from the .9cuft of the box?

Is there a good single-source I shold consider reading for info on all the technical stuff? I'm a physics student, so for some dumb reason I find all of the Q values and such very interesting.
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Old 20th April 2011, 12:36 AM   #5
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Alright, I've been doing some reading, and some fiddlin', so I now know just enough to be vagrently stupid and dangerous, haha. I just ran the WinISD program for both the drivers listed, and I've got two setups "designed".

8.68x6.97x10.41 (with .25" boards) for the 8" driver. Granted, with an EBP of 66.1, I'm not sure a sealed enclosure would actually be best here, suggestions? (vb = 8.7L to get a Qtc of .71)

26.57x16x10.3 (with .25" boards) for the 10" driver. (vb = 63.1L to get a Qtc of .71 (which seems very high...), EBP = 52.4)

Now, compared to the 10", the 8" in a sealed enclosure is -3d at 30hz (~-10 as opposed to ~-7)

About how much of a difference is that going to be in a small room?
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Old 20th April 2011, 11:19 AM   #6
bjorno is offline bjorno  Sweden
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FYI: Crude comparison:

b

Last edited by bjorno; 20th April 2011 at 11:48 AM.
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Old 20th April 2011, 11:55 AM   #7
bjorno is offline bjorno  Sweden
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Picture:

b
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File Type: gif SD270A-88_versus_SD215-88.GIF (58.4 KB, 75 views)
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Old 20th April 2011, 01:12 PM   #8
DrDyna is online now DrDyna  United States
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I would definitely go with the 70w plate amp at least. It also more than likely has equalization in it, which may end up helping the 10" get a little lower.

Internal volume is calculated using the inner dimensions of the enclosure, from which you should definitely factor in the woofer's volume, as well as the plate amp's volume, as it's most likely 3 or 4 inches thick recessed inside the box. If you end up using a ported design, the volume of the port should also be subtracted.

Personally, I tend to find that my ported designs end up being more pleasing (read: more efficient and tunable) in the end, and as such I haven't built a sealed sub cabinet in about 10 years or so. It gives you the ability to tune the enclosure and if done properly (experiment with WinISD) you can tune that box and get that woofer down a little lower.
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Old 20th April 2011, 04:09 PM   #9
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bjorno: Many thanks for the sheet comparison. Now that I see all the numbers and formulas it makes more sense.

DrDyna: I would consider a ported enclosure, but the more I play with volumes, the more I realize I don't have the volume for a proper ported enclosure, as this is going in a dorm room (specifically on isolating mounts on the bottom shelf of a bookshelf). Maybe someday I'll have the room for a proper ported system, but by then I hopefully won't be using a pair of av30's as theater speakers, haha.
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