32hz Portable Sub build - AVS Forum
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post #1 of 9 Old 07-31-2012, 03:25 PM - Thread Starter
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Goals/Uses

• Portability: Small enough to fit in a trunk and easy to carry, under 30lb, separate amp is allowable (battery-powered)
• Compatibility: May be used with speakers ranging from speakers with 2” drivers (max 200hz x-over?) to floorstanding speakers that need help below 80hz.
• Output: With 2-inch speakers, max req would prob be 85dB. With floorstanders, 110dB capability would be balanced, but 100dB is likely as loud as I’d ever use considering the application. These are 1m figures.
• Extension/response: After extensively checking through my music collection, response at 32hz is important. However, as long as the 32hz response is still usable (as in EQ can be used to bring up), then unaided response to 36-38 is okay.
• Idiot Resistance: I want protection in case someone happens to crank the volume to 9001 when I’m not looking. A limiter combined with a rugged pro driver and a high-pass filter would take care of this, but a compromise must be made because of the…
• Budget: I have all supplies except for a driver, connectors, and possibly another amp. No more than $50 for a driver, maybe a few more if I need connectors.

Examples of use: Friends want to hang out to watch a movie or listen to music inside their house. Subwoofer can be attached to source, e.g. iPod dock, computer, TV; Friends want to hang out outside or in another mobile situation. One friend has a stereo backpack sourced by iPod. Use y-splitter and bring subwoofer with battery amp, extend response to 32hz; At home or apt: use to supplement systems there.

Plans

• MDF enclosure with handle
• Amplifier: Unused non-portable amp at home, 150w available (75w over two voice coils if it’s DVC; if SVC, 80w), also a portable 2000w amp available (lol); lacking portable amp. Looking possibly at the Dayton AC/DC T-Amp for mobile use. Maybe a plate amp would work too, but I’d have to put it in later on.
• Driver: Looking at that 6.5” Tang Band driver in .7cuft tuned to 35hz, it seems to fit the criteria, 100dB at rated power (95dB if driven by portable T-Amp), but it’s port limited past 60w, 13inx2.5in port? I could increase the box volume a bit more, but at that point, I might as well look at a larger driver. Maybe there’s a pro driver in the price range. The Dayton PA255-8 models well (+2dB same power, +15dB full power) and would cover the rugged aspect, but then I’d lose portability at 3cuft. Any tips or suggestions…

If I go passive, then I can use more power in stationary use, but active would make the protection and portability better, except no mobile use without batteries.

Currently I’m leaning towards the passive TB. I have full processing capability in my laptop soundcard and that’d be the source most often. I could make a second sub for stereo use if this turns out well. Also, bnash mentioned something called the F20.

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post #2 of 9 Old 07-31-2012, 03:33 PM
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Use birch ply instead of MDF. Lighter and more rugged.

My Dual 18" LLT subs 120dB down to 10hz

 

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post #3 of 9 Old 07-31-2012, 04:04 PM - Thread Starter
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I'll consider it. It'd add a significant % to the build, though, forcing another month of delay. If it will be that much better, it might be worth it. My 30lb limit is a bit wimpy. I could do 40 or 50 as long as the size isn't affected. I just did a rough calc of 25lb total for the enclosure+driver, pretty light. I'm not sure if it needs to be externally rugged, seeing as its use would be in non-hostile environments. I'm just worried about someone turning everything to max and I don't know how much that TB driver can really handle. The only time it'd ever be out of my control is me away from home with 80-150w of juice (or 2000? lol) on it.

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post #4 of 9 Old 08-01-2012, 09:56 AM
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My light loud and cheap setup consists of a chunk of sonotube and this DVC 10"
Under 20lbs and efficient enough to get some bump from a 15watt t-amp.
No pro audio driver under $50 will do much under 50hz, wrong tool for the job.
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post #5 of 9 Old 08-01-2012, 10:18 AM
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First off, don't worry about excursion with the TB W6-1139SI. I've sim'ed it before, and it doesn't come close to Xmax at 2x rated power. You'll have thermal issues (melted coil) before anything hits.

+1 on the Baltic Birch for weight. I have a 3/4" MDF portable, and it's as portable as any other 30 lb. box. "Luggable" was the word we once used for early "laptop" computers that required a desk-sized workspace.

Port size is a variable, along with box size, that you vary to get what you want. 2.5" would be about right for a 1/2 cu ft box tuned to 40Hz or less and receiving 70W peak average power. The 40Hz port is 35cm long (~14"), gives a 1.5dB peak at 45Hz and has an F3 of 35Hz. Very nice for outdoor use, where there are no reinforcing walls. Add some walls, and you can use a 57 cm (22") long port for a flat response with an F3 of 31Hz, and more importnatly, an F10 of 25Hz.

What's really nice is to double the drivers, and double the box to 1 cu ft.. The same tunings with a 3" port now result form 10-11" ports, and 15-16" ports, but you can take 280W and get a real 110dB... with lots of port noise at this power level. Make it a 4" port and lengths are now more like 16" and 28"...
VB Response TB W6-1139SIJ_2x_28L_32Hz.gif 26k .gif file 3" x 15 to 16"
VB Response TB W6-1139SIJ_2x_28L_42Hz.gif 25k .gif file 3" x 10 to 11"

Starting to see tradeoffs? Just wait!

I also modeled the PS255-8. It's very similar, for port diameter... and that's it. First off, vented box minimum size is 2 cu ft. The "indoor" tune is now 42Hz, with a 4" port that's only 6" long. Halve that (4" port that's 3" long) and you have a nice little peak at 68Hz.
VB Response Dayton PA255-8_56L_42Hz.gif 25k .gif file 4" x 6" port
VB Response Dayton PA255-8_56L_52Hz.gif 25k .gif file 4" x 3" port

You should see a big difference in SPL, and in LF extension. Note also that the PA255 is hitting Xmax all the time... only 5mm available vs. 13mm for the little TB. One digs low, the other plays loud, and needs twice the box to do it...

Have fun,
Frank
Attached Images
File Type: gif VB Response TB W6-1139SIJ_2x_28L_32Hz.gif (26.1 KB, 4 views)
File Type: gif VB Response TB W6-1139SIJ_2x_28L_42Hz.gif (25.3 KB, 0 views)
File Type: gif VB Response Dayton PA255-8_56L_42Hz.gif (24.8 KB, 2 views)
File Type: gif VB Response Dayton PA255-8_56L_52Hz.gif (24.5 KB, 2 views)
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post #6 of 9 Old 08-04-2012, 08:03 AM - Thread Starter
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After looking at the responses and thinking about it a bit more, I may change a few details (also delaying it at least a month). By the way, during high school (not that long ago) I lugged a 50lb tuba around for hours every day and was used to carrying the case long distances in hand. I know it's not that impressive, but my point is the weight isn't a huge concern.

I'm not sure about the exact changes, but for now I don't feel I have enough experience with design to move ahead with a project. I may decide to instead build a box that allows experimentation with different alignments so I can hear them for myself. Of course, if someone knows of a way I can do this without building my own, I'm keen to it. Hey, I might even decide I want to build speakers instead rolleyes.gif

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post #7 of 9 Old 08-04-2012, 08:23 AM
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http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-030&FTR=aura%20ns6

Use a quad of aura NS-6. Perfect for powering off of T-amp, as you could use both channels @ 4ohm.
Use switch to flip to series at 8ohm total for home use.
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post #8 of 9 Old 08-04-2012, 08:45 AM - Thread Starter
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Quote:
Originally Posted by jbelljbell View Post

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-030&FTR=aura%20ns6
Use a quad of aura NS-6. Perfect for powering off of T-amp, as you could use both channels @ 4ohm.
Use switch to flip to series at 8ohm total for home use.

Hey yeah. I've been eyeing Aura for years and everything there looks perfect to me and that it will do exactly what I'm wanting to do (though I may do two boxes run in stereo). biggrin.gif

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post #9 of 9 Old 08-06-2012, 12:25 PM
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Careful what you're eyeing... these want ~1cu ft./driver to work well, ported. You'll get an F3 in the mid 30's, but from big boxes with reduced power handling:
"They can play lower but take much large(r) enclosures to do it, and max SPL suffers as a consequence" (Curt's Stentorian write-up)

Have fun,
Frank
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