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Old 18th October 2012, 06:15 AM   #1
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Default Completed micro-boombox with TA2020

Hi All, this is my first post here on DIYaudio. Have red a lot though!

Objective: To build a really small sound system for indoor and outdoor use. Should be easy to pack when travelling by air and loud enough for normal indoor listening in small apartments or hotel rooms (I travel quite a lot), or background music to BBQ etc.
Then the bass extension should be as good as possible given the two first criteria. Hoffman's Iron Laws I guess.
There seem to be a few ready-made solutions like this out there, but I felt like having a project and put some personal touch on it.

Drivers:
3'' Aurasound NS3-193-8A1
5/8'' Dayton Audio ND16FA-6

Passive crossover 6dB at 4500 Hz,
the tweeter attenuated with 3,5 Ohm serial and 2,7 Ohm parallel resistors
294uF GHP serial cap on the woofers to lower the QTC that otherwise should have
been high due to undersized enclosure.

Amp: AMP6 from 41Hz.com (TA2020 Tripath)
Battery is a 3300 mAh LiFePO4 battery from Batteryspace

Box is 5 mm birch plywood, each channel has roughly 1 liter sealed each, lightly stuffed with polyfill. There is a separate electric compartment on the back, since I did not want to seal in all the small bits and pieces.
There is bracing in between the tweeter and woofer in both enclosures.

The NS3's models nicely in very small enclosures, but with the punishment of crappy sensitivity. I was worried that it would not be loud enough so I
made a prototype to check that. It was just ok loud, but I found out that even though the NS3's are full-range, the high frequency dispersion is quite bad and certainly not good enough for a boombox where the listeners are almost never directly in front of the speakers. So I added tweeters and crossovers. The Dayton tweeters seem to have really good dispersion and I feel that the dedicated tweeters give something extra "zing" to crashing cymbals comparing to the NS3 even on-axis.
One note though, if I would have chosen dedicated tweeters from the start I would have one with the 4-ohm version of the woofer to get some more output from the amp.

The sound is quite clear and nice, and the bass fills nicely down to 100 Hz something then drops slowly.
There seems to be some peak around perhaps 135 Hz when listening to a tone generator, but nothing that really bothers me when listening to music. Maybe the bass is a little mushy when cranking the volume, but I guess that is due to the 10 mm xmax of the NS3's. Better with a little slow bass than none at all!
Overall I'm happy anyway!

Obviously the paint job is remaining. However, the girlfriend approval factor is high enough already, it is currently playing mostly her music and is stationed on the dining table!
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Old 18th October 2012, 07:44 AM   #2
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Nice job
Some observations . The two Auras, being very near each other, could also share the same volume , so each would 'see' a bigger volume, and maybe the series cap wouldn
't be needed . Also , the value of the coil : How big is it ? For a 6dB slope @ 4K5 Hz
maybe it's too big and so the efficiency lowers , since it's a fullrange speaker and it's optimized for it .
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Old 18th October 2012, 04:02 PM   #3
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Hi, thanks!
Regarding sharing the same space; really? I thought having two speakers in the same volume just required the volume to be double to have the same QTC. Or is that an idealized model?
The coils are Jantzen 0.80 mH, 20 AWG.
Thanks for your comments!
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Old 18th October 2012, 06:46 PM   #4
H3x0S is offline H3x0S  Croatia
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You could've gotten better speakers. Also, isn't that amplifier inefficient in terms of cost/quality ratio?
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Old 18th October 2012, 07:58 PM   #5
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Quote:
Originally Posted by H3x0S View Post
You could've gotten better speakers. Also, isn't that amplifier inefficient in terms of cost/quality ratio?
OK any suggestions for alternative speakers? There might always be a v2... Mind the requirements, small enclosure (and reasonable light, these are neodynium) and as good bass as possible with max SPL.
I have thought of doing something even smaller in the future.

I don't know about the amp, it was a little cheaper when I bought it a while ago and I was living in Sweden then, so that weighted in. Don't have any personal experience of other amps, but at least the really cheap ones have somewhat mixed reviews.
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Old 20th October 2012, 07:27 AM   #6
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I was to say some obvious things like : make the boxes separate, put
the tweeter axially on the woofer,try some classic B class amp...
but those things are useless since the source - I guess- is a phone or an Mp3
player . That's why I think you made a good job, because you nearly touched
the limit of portable equipment with a low quality source
V2 will be the transition to the ultimate v3
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Old 20th October 2012, 07:17 PM   #7
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Quote:
Originally Posted by picowallspeaker View Post
I was to say some obvious things like : make the boxes separate, put
the tweeter axially on the woofer,try some classic B class amp...
but those things are useless since the source - I guess- is a phone or an Mp3
player . That's why I think you made a good job, because you nearly touched
the limit of portable equipment with a low quality source

I put the tweeters horizontally as far from each other since they contribute the most to the stereo imaging. Of course separate boxes would have been better, but that would have struck against portability and complexity.
Yes the source is most likely a phone or a laptop, so not exactly hi-end!

Quote:
Originally Posted by picowallspeaker View Post
V2 will be the transition to the ultimate v3
It will never stop, will it?
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Old 20th October 2012, 07:27 PM   #8
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.....

Mhhhh

...forget it !

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