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Old 5th April 2012, 08:19 PM   #1
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Location: Sheffield
Default Portable sound system (long first post - no, really...)

Been a while since I did anything DIY-audio-related, so, of course, the bug bit again.

Let me begin by telling you a bit about the weather...

The weather was rather nice recently, so I took my little battery powered radio to college (6th form, age 16-18 for those of you unfamiliar with the UK education system) which had an AUX in for iPod use. We sat out on the grass with pizza, chips, burgers etc.
Playing Bon Jovi (amongst others), this went down a treat - 6xAA batteries provided plenty of battery life for this low power device. Picture of one below.

Click the image to open in full size.

As you've probably guessed, its sound could be called functional, at best. No bass (at all), midrange colouration, and not a lot of treble extension.
Reasonable for the £10 I paid for it, but not much better. Not very loud, either.

Something had to be done.
Enter a relative who had got hold of a faulty Bose Sounddock, and gave it to me for free because its known that I'm into messing with audio stuff.

Before I continue, I know what people are thinking: "Bose?! I hope you
sliced it in half with a machete, burned the two halves, then danced around on the ashes while chanting about cryogenically treated cables."
Well, the above failed to happen.

Instead, I systematically removed the peripheral circuits: the iPod docking bit, including what appeared to be a DAC, and some other stuff.
Next, I opened up the main compartment - where the speakers are housed - and disconnected the internal amplifier, chocky-blocked the internal speakers to some wires running through the "waveguide" (seems like a long BR port of varying cross-sectional area), and hooked it up to an amplifier.

Click the image to open in full size.
, I thought. The bass sounded like it went all the way down, the actual detail through the midrange and treble was far superior to what was expected from a device of such diminutive stature. Of course, such systems retail for a rather pretty sum of money, so half-decent drivers were expected. Also went rather loud, without cone excursion becoming a problem.
There's definitely a peak before the bass rolloff, with nothing at all below 60Hz, so I shall add a high pass there later on.

Of course, such a thing fits into a rucksack quite neatly, so I started work on making it portable.

Best I found was
Mini Amplifier Board 10Wx2 Class D Amplifier DC 12V NEW | eBay
But went for a UK-based seller as the delivery time was much faster, at a small cost increase.

Day after it arrived (so I had time to test it in the evening), I took the little amplifier board, the Bose speaker, and a 7.2v R/C car battery to college, along with a screwdriver.
Sat on a textbook (Biology, to aid organic sound), it was all wired up with potential short-circuits abound.

Anyway. Hooked up my iPod etc and the sound was much-improved over the radio this had replaced.
A single 2Ah battery stood >1.5 hours of continuous teenage rock at levels where it could be heard a football pitch width away, with much improved quality compared to the previous.
Of course, people saw the little cones jiggling around, so sat the speaker on its back and there was an ongoing competition to find the best track for firing jellybabies around. Some dubstep won: SKRILLEX - Scary Monsters And Nice Sprites - YouTube

Proof of concept complete, I mounted the class D board along with some connectors to the back of the dock (see attached - actual picture later) for more permanent use. The front grille is now re-attached, as it had previously been power and signal cable running through the waveguide.

Cost so far: £15, including connectors.

If you've read this far (congratulations)...

Here's a question:
I want lots of battery life, but wish to keep the system as a whole as simple as possible.
I'd need to buy the batteries and chargers for either, so...
7.2v NiMh batteries vs 12v SLA?

I can get 2Ah 7.2v batteries for ~£15 per pop, but would need several of them for a full day (though a full day of operation would be rare).
I could get a single 12v 7Ah SLA battery for £20, but the weight is somewhat offputting.

What would you do?


PS - pictures coming soon, and I keep thinking a 5" bass unit may be in order, but that's another story.
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Old 5th April 2012, 09:07 PM   #2
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Attachment attached.

As I said above, pictures of the actual one coming soon.
Attached Images
File Type: png Bose.png (27.4 KB, 345 views)
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Old 6th April 2012, 09:22 PM   #3
NED 209 is offline NED 209  Ireland
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lipo? i bought a lipo before but then just stared at it, horrified, expecting it to explode. i never even attempted to charge it. but that was me being stupid. or cautious. i threw it away in the end.
so i bought two 12v 3200mah nimh rc battery packs from ebay.de. i bought these to power an amp32.
that was 4 years ago and theyre still going strong. love the Germans.

or, one of these,

Super CCTV DC12V Rechargeable Li-ion Battery 9800mah F9 | eBay

smaller and lighter than my nimh packs yet three times the capacity. sla is a joke compared to either nimh or li-ion.

by the way you read my mind, i was thinking of investing in a faulty sounddock and ripping out the internals. theres a vid on youtube where a guy replaced the drivers with, other drivers

Bose SoundDock speaker replacement/ Upgrade - YouTube

Last edited by NED 209; 6th April 2012 at 09:28 PM.
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Old 7th April 2012, 09:22 AM   #4
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Location: Sheffield
Thanks for the link to the CCTV battery - looks just the job. I just need to figure out if the charger will be usable over here: it appears to have the wrong pins for UK use.

As promised, here's some pictures.

Attached Images
File Type: jpg P1010173.JPG (59.1 KB, 300 views)
File Type: jpg P1010174.JPG (142.4 KB, 302 views)
File Type: jpg P1010178.JPG (68.5 KB, 133 views)
File Type: jpg P1010179.JPG (76.4 KB, 117 views)
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Old 7th April 2012, 09:33 AM   #5
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Location: The Netherlands, near the German border
Just from looking at the ebay pictures that looks like an US type power plug, so you should make sure the charger is capable of running on 240VAC in stead of the US 120VAC. Also check the peak current capability of the batterypack, and if it matches with your amp power!
Music is art - Audio is psychoacoustics & engineering
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Old 7th April 2012, 11:02 AM   #6
NED 209 is offline NED 209  Ireland
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if i were gonna be messing with battery packs id buy a second hand graupner model charger like an ultramat, or some other clever rc charger.

eBay - The UK's Online Marketplace

i have one, its German. i love it, it can charge lipo, li-ion, nimh, nicad, and sla. the readout tells you what its doing, when its doing it, and it feels very very safe.
if i had the graupner when i had the lipo battery i would have charged it.

i dont know what the peak discharge is of those batteries. worth emailing the seller. theres loads of them on ebay, just type in 12v 9800mah.
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Old 7th April 2012, 12:16 PM   #7
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Here's one that says you can have a UK plug with it...

12V Rechargeable Li-ion battery For CCTV Camera 9800mAh | eBay

Might just go for one of these - plenty enough capacity, nice and compact.

Thinking to be done.

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Old 7th April 2012, 06:53 PM   #8
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Very late edit...

This one.
12V DC Rechargeable Li-po Battery for CCTV Cam 9800mAh | eBay

Has an on/off switch, which is convenient.
Fairly sure this is the one to go for. Any objections?

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Old 14th April 2013, 01:08 PM   #9
deved is offline deved  Ireland
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which one did you go for in the end? I'm planning on making something similar and am looking for high capacity, lightweight batteries
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Old 23rd April 2013, 02:04 PM   #10
rjsaenz is offline rjsaenz  United States
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Have you seen this battery ? I use it to power a stereo backpack I built.It has a 30wpc topping amp in it. I can get about 20hours at full volume. The beauty of this battery is the different voltage outputs it has. It has a usb 5v that can keep your ipod, ipad, iphone or android phone charged. 9v-12v output and a 16v-20v output to charge a laptop. Its a little pricy but the versatility and the ability to charge just about anything makes it worth the price.

Energizer® XP18000A Portable Charger for Laptops | External Battery | Portable Charger

Here is my portable sound system. aka Stereo Backpack If you watch the whole video you'll get to hear how it sounds with different types of music.
Speaker Backpack - YouTube

Here it is in the wild (Copper Mountain Colorado). Yes I use it skiing
Perfect Spring Day at Copper Mountain April 2013 - YouTube
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