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Q-pack: Light weight sound system

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Daniel Twellmann View Drop Down
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    Posted: 08 August 2014 at 9:27pm
Hello world

My Friend, Q, has asked me to build a sound system for him, which I have dubbed Q-pack.

He has borrowed my backpak sound system and wanted something similar for himself.

My system consists of:
  • 12V 7Ah SLA
  • Amp6 @ 41Hz
  • 5W chinese solar panel
  • Four ancient 8" fullranges
  • 15mm ply
  • 25*25*60cm sealed enclosure
  • USB charger
  • two shoulder straps
  • Thick padding on side facing back
  • Perforated steel sheet
  • Total weight 10kg
The whole thing was thrown together almost from scraps and extras, because why not. It has seen a lot of use and has never failed, except from a replaced battery. It has prominent peak somewhere around 200-250hz which makes synths and male voices quite powerful, but there is not a lot of bass.

The drivers are placed two on each side and the solar panel is slanted 45deg and facing away from the shoulder straps.

All in all a compact, but powerful packages. It's biggest problem is the weight, which is why I'm starting this thread Smile


My friend is an avid athlete who recently started doing marathons and triathlons, and has played badminton for almost twenty years. Because of all these activities he would like something a bit more, shall we say trimmed. Furthermore he is quite the fashionista and likes things to look clean and neat, as opposed to my system which looks like its been to Wacken and back. He also would like for it to fit on his around the bike, which has a small basket on the rear rack. The last thing he requested was that the system could also be used for sitting on, not like a chair, but more like a comfy wooden box .

So, to sum up my(his) design criteria:

  • Weight: a lot less than 10kg
  • Size: maximum 20*38*50cm
  • Bluetooth
  • Runtime: A day out cheering for the contestants, probably 10 hours
  • Easy to carry around, good integrated handles, maybe shoulde straps
  • Nice height for sitting on: ~50cm
  • Easy to charge
  • Easy to use
  • Must look nice, maybe carbon fiber vinyl and colored trims, think tri bike
  • Sound: Full and well rounded, extreme SPL not required


To fulfill these criteria I've made some preliminary design choices for the Q-pack:
  • Lithium battery instead of the ol' SLA. Since it only needs to run for a day, I think a 11.1V 3000-4000mAh battery will be sufficient. This will probably give around 10 hours at full tilt. Furthermore it is faster to get up to a full charge.
  • MaxAmp20 instead of Amp6. They cost about the same, but the MaxAmp is more efficient, doesn't require an external heatsink and has a better solution for the volume control.
  • 6-9mm birch ply. The 15mm I used on my backpack was scraps. Good bracing should make it stiff enough.
  •  Bluetooth... maybe the Sure 4.0 module, it is however expensive at $24.
  • Drivers: first I looked at the driver set for the boominator mini with SP-60/8, but all that ferrite is heavyBig smile. Instead I've been exploring some neo units like the 4FE32. The SP-60/8 is 900grams/driver and with the tweeter and crossover it will probably be close to 1kg. The 4FE32 is 270grams.
This is it for now. Please comment on anything you like, pictures and links will slowly emerge
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WesleyK View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote WesleyK Quote  Post ReplyReply Direct Link To This Post Posted: 08 August 2014 at 9:47pm
Nice! Looking forward to the results of this build :) . One little correction: the SP60 drivers are about 650gr each instead of 900gr. Still on the heavy side, ofcourse.

Edited by WesleyK - 08 August 2014 at 9:48pm
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Daniel Twellmann View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Daniel Twellmann Quote  Post ReplyReply Direct Link To This Post Posted: 08 August 2014 at 10:23pm
Originally posted by WesleyK WesleyK wrote:

Nice! Looking forward to the results of this build :) . One little correction: the SP60 drivers are about 650gr each instead of 900gr. Still on the heavy side, ofcourse.


Silly me, trusting the datasheet
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesleyK Quote  Post ReplyReply Direct Link To This Post Posted: 08 August 2014 at 10:29pm
I will put them on my scale tomorrow for you. I believe they are about 660gr each, but can't give you the exact figures yet.

Edited by WesleyK - 08 August 2014 at 10:30pm
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Daniel Twellmann View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Daniel Twellmann Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 8:22am
Thoughts on the power source for the Q-pack:

The Amp6 and MaxAmp2 has an average current draw of about 300mA at maximum volume. I believe this is shown empirically by Saturnus for the boominator, but I'm not 100% sure. I have never really  measured/observed the power consumption on my other builds. A Bluetooth reciever uses some unknown amount, but probably not more than 100mA. So on average 400mA on full tilt with bluetooth activated.

I need a minimum of 8-10 hours of playtime, so I need a battery with around 3000-4000mAh capacity.
In order to shed some weight I'm looking into a Lithium based solution, most likely a LiPo pack similar to this: http://www.hobbyking.com/hobbyking/store/__7634__ZIPPY_Flightmax_4000mAh_3S1P_20C.html

This type of battery needs a balancing charger in order to prolong the life of the battery, and also to prevent charging accidents: http://www.hobbyking.com/hobbyking/store/__30032__HobbyKing_E4_Balance_Charger_EU_warehouse_.html



Some sort of charge indicator is also desirable: http://www.batteryspace.com/fuelgaugeforpcbof111vli-ionbatterypack1.aspx

I tried to look into LiFePO4 chemistry, but I don't know anything about them to be honest Big smile, so if any you have experience, please chime in
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 9:24am
Some people builds a halfinator (half a boominator) with the lite speakers (basslite S2010 and pht407n, you can get both from blue aran and other sources) for backpack use. That is 30x30x50cm so much closer to the original required measurements, and about 8kg including lifepo4 batteries. They then use a diver's harness to carry it which is extremely well balanced and can carry a lot of weight (and since they have to meet very rigorous safety requirements they're also pretty damn near indestructible). You can even use a solar panel on one side to make it pretty much last forever.

Regarding power consumption. The TA2020 is about 360mA just before clipping, and about 110mA at lower listening levels. The maxamp20 is about 320mA and 80mA respectively under the same conditions. However, that's into 4 ohms. In 8 ohm it's slightly over half that for the maximum volume number and about 2/3rds of the lower volume number.

I'd strongly suggest building a halfinator for this. It's pretty much a perfect fit. Though I can certainly understand that you'd like to make your own design.


Edited by Saturnus - 09 August 2014 at 9:25am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Daniel Twellmann Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 9:38am
Originally posted by Saturnus Saturnus wrote:

Some people builds a halfinator (half a boominator) with the lite speakers (basslite S2010 and pht407n, you can get both from blue aran and other sources) for backpack use. That is 30x30x50cm so much closer to the original required measurements, and about 8kg including lifepo4 batteries. They then use a diver's harness to carry it which is extremely well balanced and can carry a lot of weight (and since they have to meet very rigorous safety requirements they're also pretty damn near indestructible). You can even use a solar panel on one side to make it pretty much last forever.

Regarding power consumption. The TA2020 is about 360mA just before clipping, and about 110mA at lower listening levels. The maxamp20 is about 320mA and 80mA respectively under the same conditions. However, that's into 4 ohms. In 8 ohm it's slightly over half that for the maximum volume number and about 2/3rds of the lower volume number.

I'd strongly suggest building a halfinator for this. It's pretty much a perfect fit. Though I can certainly understand that you'd like to make your own design.

The footprint can't be more than 38x20cm, and the basslites will break the budget, otherwise it would probably be close to perfect.

How about charging the LiFePO4s? How do you accomplish that?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lutkeveld Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 9:49am
How about 2 Dayton ND105's in a 16-18 liter enclosure tuned to 50hz.

-360gr each
-F3=42hz
-Bump at 60hz
-87dbwm

To keep the weight down you can get a 4400mAh LiFe battery from Hobbyking. Only 30 euro's and it can be charged within half an hour if your charger supports such high charge rates. You can charge it with a SLA charger but you'll only utilize 80% of its capacity. With a special LiFe charger you utilize its full capacity.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 10:02am
Originally posted by lutkeveld lutkeveld wrote:

How about 2 Dayton ND105's in a 16-18 liter enclosure tuned to 50hz.

-360gr each
-F3=42hz
-Bump at 60hz
-87dbwm

The 87db/w/m is wrong. Datasheet says 83 for the 8 ohm version and 82 for the 4 ohm version. Both are a little optimistic as well. They're about 1 db below that really.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lutkeveld Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 10:10am
WinISD showed combined sensitivity, so -3db for one unit. Around 83db average indeed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 10:58am
Originally posted by Daniel Twellmann Daniel Twellmann wrote:

I need a minimum of 8-10 hours of playtime, so I need a battery with around 3000-4000mAh capacity.
In order to shed some weight I'm looking into a Lithium based solution, most likely a LiPo pack similar to this: http://www.hobbyking.com/hobbyking/store/__7634__ZIPPY_Flightmax_4000mAh_3S1P_20C.html

This type of battery needs a balancing charger in order to prolong the life of the battery, and also to prevent charging accidents: http://www.hobbyking.com/hobbyking/store/__30032__HobbyKing_E4_Balance_Charger_EU_warehouse_.html



Some sort of charge indicator is also desirable: http://www.batteryspace.com/fuelgaugeforpcbof111vli-ionbatterypack1.aspx

I tried to look into LiFePO4 chemistry, but I don't know anything about them to be honest Big smile, so if any you have experience, please chime in


Well - if its any help - I'm successfully using a Zippy branded 5000mAH 6S Lipo pack to drive a Sure STA508 amplifier ..... LipO pack and Turnigy Accucell 6 balancing charger bought from Hobbyking.
I was going to go LiFePo4, but there were some bad reviews of the Hobbyking-supplied packs.

Watch out a bit for Hobbyking - they're a bit slippery .... I thought I was getting delivery from a EU warehouse, but it actually shipped from HK (took nearly 3 weeks to reach) .... high shipping charges buried deep until last phase of checkout ...... and they're pretty hardcore with the "marketing" email.

I'm quite pleased with the performance of the LiPo pack though ..... I have reason to think the real-world capacity is close to spec.
The STA508 gets powered by the 5000mAH LiPo pack for portability mode, and by 2 x 7Ah SLA in static mode. The LiPo pack weighs about 750g - so much lighter (and smaller)  than 2 x 7Ah SLA.
The connections are a bit awkward - you need those 4mm HXT connectors/adapters and the JST-XH connectors for balancing ..... would be a PITA if mounting battery inside your box .....
I like flexibility wrt power, so I always have batteries external anyway.

The Accucell charger works well - caters for Pb, NiMH, Li-ION, LiPo and LiFePo4.


REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Daniel Twellmann View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Daniel Twellmann Quote  Post ReplyReply Direct Link To This Post Posted: 09 August 2014 at 11:55am
Originally posted by slaz slaz wrote:


Watch out a bit for Hobbyking - they're a bit slippery .... I thought I was getting delivery from a EU warehouse, but it actually shipped from HK (took nearly 3 weeks to reach) .... high shipping charges buried deep until last phase of checkout ...... and they're pretty hardcore with the "marketing" email.

I'm quite pleased with the performance of the LiPo pack though ..... I have reason to think the real-world capacity is close to spec.
The STA508 gets powered by the 5000mAH LiPo pack for portability mode, and by 2 x 7Ah SLA in static mode. The LiPo pack weighs about 750g - so much lighter (and smaller)  than 2 x 7Ah SLA.
The connections are a bit awkward - you need those 4mm HXT connectors/adapters and the JST-XH connectors for balancing ..... would be a PITA if mounting battery inside your box .....
I like flexibility wrt power, so I always have batteries external anyway.

The Accucell charger works well - caters for Pb, NiMH, Li-ION, LiPo and LiFePo4.

Is there a way to make sure it is from the EU warehouse?

I've been thinking about the charger connection as well. I was considering rewiring the connection to a multipole plug, maybe 5 pin XLR or something. 


Edited by Daniel Twellmann - 09 August 2014 at 3:25pm
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