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Old 16th April 2011, 10:54 PM   #1
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Default Smallest, lightest, sub in the world...

Here's my project:

I just bought a really cool amp to play acoustic guitar through. It's a Fishman SA 220. One of the features is that it has two channels through which to input sound. I will use one for my guitar and plug a mixer into the other. This will allow for many other input devices (mics, guitars, and perhaps a small drum kit with a kick drum). Keeping in mind that my expectations are modest as the system is pretty tiny, I want to get a signal out of the mixer (probably aux 1) and send that to a powered sub that I want to make.

I have a Bash 500W plate amp from OAudio. I have a JBL 2268HPL 18" driver. I just took them out of an enclosure that I built years ago utilizing Eminence Speaker Design software that I had some success with. It was ported and it ended up to be about 8 cu. ft.... too big these days. With these components I would like to build an enclosure that will be as small as possible. I have the T/S info. Does anyone have any suggestions on how I should proceed with this?
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Old 17th April 2011, 02:48 AM   #2
18Hurts is offline 18Hurts  United States
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Nice driver!

So just to be clear, you want to put the JBL pro sound 18" woofer in a smaller box and make it as light weight as possible? The only trick I can think of is to use Sonotube which is strong cardboard used as a form to make cement columns. Get one big enough to hold the JBL then one size slightly larger. Fill the gap between the two with foam to make it more durable and still keep it light weight.

Since the JBL requires an 8 cubic foot ported box--it makes it tougher. You could use your software and model a box tuned to say... 50 Hz? As long as you don't pump really deep bass through it you should be OK with the plate amp at lower volumes.

The other option is to cut your old box up and weigh the wood. Calculate how much wood you can deal with and run the numbers through your software. I'm afraid if you throw it in a small sealed box it will roll over way too quickly to be useful.

The final option is that sub sells for $400 and neodymium prices keep going up. Sell the mighty 18" monster and pick up a 12" sub. The Eminence Delta 12 LFA is close to the efficiency of the JBL but can run sealed or ported (or horns) They spec sealed at about 1 cubic foot and ported from 1 to 3.6 cubic feet so pick your poison.

The light weight of a 15 pound speaker with neodymium magnets is great--but throw it in an 8 cubic foot box tends to negate the weight savings. Small and light generally go against pro sound and 18 inches though.
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Old 17th April 2011, 03:31 AM   #3
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Quote:
Originally Posted by 18Hurts View Post
The only trick I can think of is to use Sonotube which is strong cardboard used as a form to make cement columns. Get one big enough to hold the JBL then one size slightly larger. Fill the gap between the two with foam to make it more durable and still keep it light weight.
When I purchased my 14 inch Sonotube I had to buy and entire tube from the local concrete supply house - I think it was like 10 or 12 ft. in length so I had plenty to play around with. Buuuuuut buying it a full length at a time can get expensive - and buying two full lengths could get steep. Maybe one of the local contractors might have some stuff left over from at a construction site - but that would require some luck to run into. I'm thinking that you might want to look into an "H" frame arrangement but doubt that will get you enough SPL for PA or club work.
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Old 17th April 2011, 04:37 AM   #4
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A cube 24" on each side will be 8 cubic feet in volume. All things considered, that's pretty small. That said, I see that your Fishmanis basically an active line array mounted on a tripod. Are you looking for something with the same stage footprint, or similar portability when "packed" up? If the former, you could just ditch the tripod and mount the Fishman on top of a 2-foot cube. If the latter you could make the enclosure a 2x4x1 foot suitcase... about the same as for a keyboard. The walls could be made of relatively thin plywood if you are will to take the time to glue in a lot of internal braces and ribs. If you want a really lightweight enclosure, then look into something called honeycomb sandwich.

:)ensen.
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Old 17th April 2011, 03:14 PM   #5
tb46 is offline tb46  United States
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Hi Peezlepop,

Maybe a sealed box w/ low frequency boost. Google for: Bag End and ELF.

Regards,
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Last edited by tb46; 17th April 2011 at 03:23 PM.
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Old 17th April 2011, 09:25 PM   #6
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Thanks to all...some good ideas there... Selling the JBL and getting a good 12" driver, and starting from there seems like the best option. I think I will however, throw a box together ASAP(as small as possible) just to see what it sounds like.

JP
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Old 17th April 2011, 10:13 PM   #7
18Hurts is offline 18Hurts  United States
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As Oliver mentioned, the ELF concept

Bag End offers subwoofers called ELF or Extreme Low Frequency. Basically, tune a sealed box really high so it rolls off at 12 dB per octave--then EQ it back in at +12dB per octave boost for flat response (down to 8 Hz).

For example, tune the sealed box for 80 Hz so the 80 Hz slider on the EQ stays at flat or 0dB. Put the 40 Hz EQ slider at +12 and you'll get flat response down to 40 Hz. It will suck power like a pig and won't be very loud but you said you do small stuff so that would not be an issue.

Say the JBL puts out 96dB at one watt at 40 Hz if using their suggested 8 cubic foot box, with the tiny box it is 84dB at one watt due to the small sealed box roll off (if tuned to 80 Hz) The BASH 500 amp puts out 300 (??) watts or so into 8 ohms or +25 dB from the amp. In theory, you'll hit max at around 109 dB at 40 Hz but 80 Hz and above will hit over 120 dB. For acoustic guitar, that should be fine for lower power needs.
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Old 17th April 2011, 11:45 PM   #8
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Eminence has a box design for their Kappalite 3012LF that's under 2 cu. ft. They have another that adds a bit of LF, but not much max SPL ~3 cu. ft. That's a 10lb 12" driver with a 9mm xmax, and a google search found it for $180.

B&C makes the 12bg100 which has an xmax of 10.5mm. I didn't notice a box design on their website, but I imagine one could come up with a pretty good one for the 45~120 passband.
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