Thread: Sons year 9 "Personal Best"

Originally Posted by Glenn.Visca

Hi you electronics wizards.

My son is about to start his year 9 personal best ... Effectively a long project where kids can do what ever they want ... Build rockets, make robots, design clothes, ... Pretty much anything.

My son wants to make a desktop speaker unit, with 3.5mm Jack and Bluetooth ... Like the iPod dock/remote speakers.
I can help him with the box construction ... But have no idea where to look for the electronics bits.
He tells me he wants 4 speakers ... Nominally front and rear ( top and bottom ?) And sub woofer.
Anyone have any guidance ?

Unlike , or maybe just like woodwork, just getting the bits won't help. What you need is a plan to make sure everything goes together properly. I'd definitely not recommend doing your own plan unless you really know what you are doing as it is very likely all you will end up doing is damaging components. Any plan that involves multiple speaker outputs and various inputs is likely to be quite complicated (and expensive)

I suggest starting with a simple kit of some kind from Jaycar or Altronics or Dick Smith. It will be unlikely to have all the features your son wants but he will still learn a lot from putting together several of these kits. I suggest starting with a small kit before investing in a larger kit. There's nothing more confidence destroying than starting on a kit that is too difficult. You'll see the kits are rated for level of difficulty and cost about the same as the device already made because they are meant to be a learning experience. I would go and talk to the guys in the shop as they should be able to give you some advice.,

Originally Posted by BobL

I suggest starting with a simple kit of some kind from Jaycar or Altronics or Dick Smith.

Hmmm... Does Dick Smith still do kits? (Or anything down to component level for that matter)
I don't recall seeing anything apart from consumer equipment and a bunch of toys last time I was in a store...

Here's a place that might be a help - I haven't used them, but it might be a good place to start.
http://www.kitstop.com.au/

Originally Posted by Malibu

Hmmm... Does Dick Smith still do kits? (Or anything down to component level for that matter)
I don't recall seeing anything apart from consumer equipment and a bunch of toys last time I was in a store...

I don't know - I haven't been inside one for about 15 years.
I walk past one every time I go to my nearby Altronics store which I visit a couple of times a week.

For something like your project, where ever you buy, I'd definitely talk to sales people in a shop like Altronics first.
Physical store front generally know who they are selling to and know what kits works for what ages.

Originally Posted by Malibu

Hmmm... Does Dick Smith still do kits? (Or anything down to component level for that matter)

Dick Smith (or more properly Woolworths) is nowadays just another electrical retailer. They have hardly anything in the hobbyist range and I would count myself lucky to even find a 9 volt battery holder there.

Jaycar is the place to go

+1 for jaycar

Just a few things to throw around with the project specification which he needs to pin down before he goes any further.

Inputs, 3.5mm jack for analogue audio signal input, three jack formats available for mono, stereo, or stereo headset with inbuilt mic (for mobile phone, sometimes but not always compatible with normal stereo, two connection arrangements in circulation). I assume this is to accept analogue audio from headphone sockets of portable radio, mp3 players or mobile phone. This is a low voltage analogue signal around 100mV level.

Bluetooth receiver, mono or stereo depending on what you can find. Close range digital radio link for contactless signal coupling between devices. Generally bi directional, so either device can instantaneously be the source, with the other as the receiver, or duplex where both can transmit and receive simultaneously. Doubt that you will get a bluetooth module that will offer a direct analogue output, so some form of converter would be required to handle both analogue and bluetooth inputs.

4 speakers/channels including subwoofer suggests normal stereo (Left and Right), subwoofer, and a centre channel, rather than front and back channels. The left and right signals are standard source signals available via bluetooth or 3.5 mm Jack, and can be amplified to drive those speakers. The subwoofer signal can be synthesised by combining the left and right into a mono signal, then applying a Low Pass filter, amplifying and driving a subwoofer. The mono signal could be fed to a High Pass filter and amplified to drive a centre speaker, for the fourth channel/speaker but there is little point accoustically if the unit is to be compact and portable, as the left and right speakers will be close together and not leaving an acoustic 'hole' in the middle to be filled by a centre channel.

My read on the project is that it will require a power supply, (possibly including a substantial battery backup and charger for portability), audio processing to accept analogue and digital stereo inputs and convert/synthesise to a format suitable to drive the power amplifiers, three (or four) power amplifiers and speakers plus the housing to contain the complete rig.

I think he needs to do a lot of rapid research to properly specify the project in a manner acceptable for assessment for the subject, and within the range of materials etc that can be obtained and funded. Once that is done he can start working on the project proper. If the project is to contain substantial original design input, it will be a major time and expense burner, as there are a lot of different electronic systems to be understood and integrated, plus significant acoustical design to match speakers to enclosure etc.

Hope he can achieve his objectives with it.

Tell him to have a search on instructables.com. There have been loads of Bluetooth speakers on there, and he's bound to get dome good ideas.

So son and I did some research over the weekend ... after a fair bit of time attempting to capture exactly what he wanted to achieve.

Turns out ... he didn't want 4.1 channels ... he only wanted 2.1 channels ... but wanted component speakers rather than general 2 ways.

Approximate set up is as follows:

Belkin BT receiver
Lepai 2.1 channel mini amp

What we both like about this setup (well ... me more than he I expect) is there is little requirement to cannibalise components, as BT receiver to amp is achieved via 3.5mm to RCA adaptor (supplied with BT unit). Amp has RCA inputs. All good.

We have started to research the speaker impedance and power requirements.

AMP can be powered by a 240vAC/12vDC transformer. BT receiver comes with its own 240v transformer .. just not sure what voltage/current it makes should we attempt to consolidate everything into a single power supply. I am pretty sure I have some old PC power supplies tucked away somewhere too (possibly cracking a nut with a sledge hammer ... but ...)

We are now researching speaker box design (ideal dimensions, resonance, internal baffles etc.) ...

And in case you are wondering ... all of this research needs to get captured and put in a portfolio that is delivered with the project.

Thanks all for your help - and comments are always welcomed.

Keep us posted Glen, pics too if possible.

An update ...

We have purchased the following components:

Lepai 2.1 amp
Belkin BT receiver
Clarion SRQ1622S component drivers
8" Sub from Jaycar

Much research into enclosure dimensions using thiele / small parameters, sealed versus bass reflex enclosures, WinISD modelling software, TrueRTA.

I haven't done this much arithmetic since form 5 .. and I have been in IT for near 30 years !

Anyways, we hope to assemble a couple of test enclosures this weekend to validate theory against practical.

I should state now that I don't think the Clarion drivers are suited to a desktop enclosure .. well .. more correctly . are more suited to car rear parcel shelf.

But never mind . We have purchased them now, and that in itself is part of the learning.

Are their any audiophiles out there who might be willing to check our maths ?

What a great father/son project!
Looking fwd to hearing about the progress!

From what I remember about projects like this at school, a lot of the marks come from documenting the whole process and plans. The final project was only part of the marks.....I struggled with that bit...I suffered from that as I just wanted to make things work!

What is looking at as far as the enclosure?
Some of the ones I liked have been old school technology fitted out with new, but I'm sure he has a look that he is after.
You don't often hear about kids tackling projects like this anymore. I think it's an awesome project!
Just throwing up some ideas but you can get pretty tiny tablet PCs now. A small touch screen jukebox would be a fun addition if their is space. Even an old touch screen iPod built in maybe?

A long long time ago I did work experience for a week at a company called 'speaker box' they did a lot of work with sound equipment including building new high end speaker boxes.

They had a bit of software that would allow you to input many different parameters about a speaker and box dimensions including material types as well as how the speaker was to be used. The softwares job was to design the perfect box for the speaker!

From memory they would start the program running at the end of the end of the work day as it would take hours to do all the calculations....
I'm sure modern computers would churn it out in seconds now but it was well past my Yr 10 brain to get around..
Hahaha even now I would be seeing the job like a carpenter... Just make it strong, fit the space and make it look right...

People can get pretty into the perfect sound... Like expensive wine, it would be wasted on me.
I did a rewire job a long time ago for a music buff. He requested 16mm cable from the meter board to his stereo! I'm sure he could appreciate the difference and as always, if that's what they want they can have it (as long as it's above board).

Mind you, I'm always wanting a bigger workshop and more tools. Most people don't understand that!

Been a few months since last post. The kids weren't allowed to start until the beginning of 4th semester. Throw in Melbourne cup weekend, and I am glad we started the research when we did.

Sam has learnt a lot throughout the process, including the use of sketchup as a 3D design tool. He has used circular saws, sliding compound Mitre saw, jig saw, drill press with twist drills and forstner bits, jig saw, table saw (which he doesn't like using), bradding gun, power drill, cordless drill, squares, gauges, and the list goes on.

He has done well. Although his choice of enclosure covering (bleuch !!) does absolutely nothing for me.

On a positive note, he did choose to play Born To Run as the test piece of music when we tested it out tonight.

RIP Clarence.

Hahahaha! Yep the covering is a bit out there but maybe he is onto something!?

It's nice to see a young fella working on a project and taking it seriously!

I'm looking forward to doing the same thing with my little man...I have a long wait though. He is only 15 months old.

I'm thinking water rockets will be a good first project!