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Other-audio-port NX Tspeakers

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I was working on getting a small mp3 player rig that has good sound beyond most small speakers able to fill a 300 sq foot room. Well, actually just the amp and speakers as I already have a nokia n900. The n900 is a great little machine about 1.5x the width and thickness of an itouch but has a larger screen and slide out keyboard and since it runs on linux it's OPEN !! Meaning I don't have to deal with iToad or what ever it's called.

Anyways, this search had me try the typical $50 computer 2.1 set up .. while good, not great, no clarity with a fair amount of distortion. So I took it back to fry's electronics and started to look on the web for what others have done.

If I was going to get something I wanted something better, clearer for about the same price ... or better value if I was spending more.

I found a dayton dta-1 class T digital amp with decent specs: manual is here

  • 15wrms x 2 channels for 30wrms .. same or better than the desktop sound boxes.
  • lowish distortion: 10 watts RMS into 4 ohms @ 0.1% THD .. yeah 15wrms shows 10%, so I won't crank it up.
  • 3 hour battery run time with average use. stated 88% efficiency.
  • comes with a 12v dc wall wart or runs on (8) AA size batteries.

This was now getting interesting ... hadn't thought about portable, but interesting. Hmmm ... something I could move around the house / yard / forest / football pre game parking lot bbq / etc /. Yeah right, really probably nothing more than sitting in my shop, but you got to plan ahead ...

With a possible amp selection, I now needed speakers ... 2.1 is nice .. but I started looking at what others had done for their mp3's.

So I looked at rolling my own speakers and came across a thread started by 'zygadr' on audiocircle.com

that lead me down the path of a 2.0 system powered by this 30wrms tclass amp that runs on 12vdc, 8xAA batteries.



ended up ordering the following:

  • $45 - dayton dta-1 class T digital amp 12v 8x AA battery powered.
  • $10 - 2 pair of these surface transducer / exciter.
  • $0 - 5way banana plugs.(didn't use).
  • $5 - super glue gel for mounting exciters.
  • $30 - 2 sheets of poster foam core black, 32 x 40 x 0.125(1/8)inch ... kind of 'sheet foam' sandwiched by paper; also called poster board.
  • $5 - clear exterior 'lacquer' spray paint to coat the foam core. The thought is to try to give it some moisture resistance.
  • $0 - short 3 foot, 3.5mm male to 3.5mm male stereo phono jack to connect the mp3 player to the new amp.(comes with t-amp).


speaker configuration and impedance matching with multiple speakers.

wire size6 ohm8 ohm
22 guage9 feet12 feet
20 guage15 feet20 feet
18 guage24 feet32 feet
16 guage36 feet48 feet
14 guage60 feet80 feet
12 guage90 feet120 feet
10 guage150 feet200 feet

nice page on speaker wire sizes.
... basically says for 8ohm speaker if we're ok with less than 5% line loss you can run a 22 guage wire up to 12 feet.
for the table to the right, half the max distance of 8 ohm for 4 ohm speakers or halve the 6 ohm if you need 3 ohm; ie the table is linear.
NOTE: .. it doesn't matter if the wire is strand or solid, expensive or cheap, clear jacket or not at the audio frequency we work at it truly doesn't matter.

good pricing for large diameter speaker wire at monoprice

interesting thread for using the exciters on gatorboard or foam board.
gatorboard can be had for $65 for a 4x8' sheet. Also called gatorfoam board.

smokenJoe used 12" square foam board taped to the front of an .030" aluminum sheet.

nxt quidelines and here
picture of podium loudspeakers showing frame, spine, floor feet spike.

basic nxt from audiocircle thread:

  • 2.5'x6' gatorboard(wood clad foam core).
  • 7 exciters @ $16/pair.
  • exciters removed from their plastic cases.
  • remove resister and cap off cheap $5/pair version.
  • use permanent tape to attach exciters, 3m F9473PC.
  • center exciters in the 2.5' side to side direction, ie 1.25' from the long edge.
  • evenly spaced up the 6' panel with larger space on both ends.
  • no exciter in dead center of panel.
  • use stiff wire 20 or 22 guage so the wire doesn't touch the gatorboard or exciters.
  • suspend gatorboard via fishing line or wire.
  • or if frame mounting, try sponge rubber foam insulation in the corners ?
  • the exciters like 100 hours of break in.

based on above, I'll try

  • foam core from the art supply house.
  • spray one of them front,back,sides with exterior clear for moisture resistance.
  • tape to board for placement and comparison to non painted.
  • after working try spine of 1"x1" oak for exciter syncing, push back and mounting to floor/wall and speaker pins.
  • maybe look at 'micro speaker stands or wall mounts' if using spine ?

tried:

  • using 15x20x0.125 inch foam core and they s*cked.
  • very 'tinny' sounding.
  • I used 1 exciter per foamcore board.

this is what I ended up with and they rock <grin>

  • 32 x 40 x 0.125 inch foam core, used 2.
  • sprayed foamcore with lacquer.
  • notice one of the foamcore curved while drying ... curve is 3inches or so off flat. used it anyway.
  • 1 pair in series of the $5 exciters per foam core. ie 8ohms.
  • left exciter pair pre wired with high pass cap and resister installed as received from PExpr.
  • super glued exciters to foamcore; one drop for each of it's 4 feet plus covered the plastic speaker core lip(1 inch ring).
  • placed exciters 16 inches from 40 inch side(ie half the 32 inch direction) and equal distance from 20 inch center on 40inch direction, ie as far apart as pre wired would allow.
  • used t-amp at 15watts per channel.
  • hung from rafters with 18 guage stainless steel wire by simply pushing wire through foamcore 1.5inches from top corners.

results:

  • these things rock.
  • spl is as loud or louder than live instruments.
  • clarity is amazing.
  • non beaming sound.
  • very good 'sound stage' image.
  • bass tight and present, although I suspect below 100hz is non existent, it still sounds great.
  • highs transparent and non beaming.
  • I really like these speakers.
  • next I need to figure how to use these cheap exciters to replace my baby magnepan's, these things are that good.


youtube video of nxt style exciters using 12" square aluminum plate.
Smokin Joe !!! from Cleveland, Ohio

I bought two of these little guys with minimal expectation. I was somewhat suprised at how small they were. After opening the box, I spent the rest of the day holding them to about a million different materials. As a final setup, I used two .030"thk. x 12x12" pieces of aluminum sheet and also two 12x12" x 1/4" pieces of paper foam paper sandwich board from a craft shop. I stuck the transducer in the center of the aluminum, and used scotch tape (two pieces per corner) to attach the foam board to the other side of the aluminum like a sandwich. I also bought a pair of little 500ohm. tweeters from an electronic surplus store here, for $2 and super glued them to the foam board at the 12oclock position and hooked them in parallel with the transducers. I mounted these guys to a set of micro speaker stands and used them as satelites, with a 12" passive sub. I was in awe when I heard the finished assemblys. The realism of sound is breath taking, highs to the moon, mids to die for, and the sub carries the lows to combine into freakin unbelieveable sound stage. This setup is being powered by a KT88 Music Angel amp. The combo has become a huge conversation piece at my house. People think I am fooling them and start looking for hidden speakers immediately. I am definately ordering more of these, you should do the same!!! I am planning on putting a video of them on youtube soon, check my page to see them in action! Cut and paste smokinjoeh2750 in the search window to see my videos.

Smokin Joe !!!

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Page last modified on December 09, 2009

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