Car Stereo Components For A Ghetto Blaster

[mikel]

Hi guys,

I have a project to build a portable stereo, and I want to use as many off the shelf car stereo parts as possible.

The unit will comprise car speakers mounted in removable boxes to get some stereo separation, and a head unit and a small sealed gel cell car battery in the main box.

My requirements are decent sound (not hifi), decent volume, reasonable portability, reasonable battery life - say 4 hours at decent volume before a recharge.

The plan is to fit an off the shelf battery charger (suitable for a sealed gel cell) inside, and run a separate linear power supply when running on 240 volts to be able to simultaneously charge the battery whilst listening to music. I'll use relays to disconnect the battery power so it charges properly while running on 240V.

Each speaker will use a car tweeter and woofer (ie 2 way). The woofer will probably be an 8" to get reasonable bass, in a sealed box of appropriate size to get a total Q of about 1 to get a little bass boost. Happy to go smaller box and higher Q.

The head unit needs to support CD (incl MP3 on disc) plus input for iPhone and USB input.

I haven't decided whether to use an active or a passive crossover between the woofer and tweeter - it will depend on what's available off the shelf.

My home stereo is a 3 way active crossover (ie tri-amped), and I'd prefer to go active crossover if achievable.

Most of my experience in stereo is home stereo. My one foray into car stereo was years ago when I built 2 active crossovers - one for the front tweeter/woofers and one for the rear woofer/sub crossover.

My questions are:

- are head units available with say 4 x 50W outputs where you can get access to the output of the pre-amp and input to the individual output amps (ie in a 2 way active crossover setup I plug the output of the pre-amp in the head unit through the active crossover and feed back into the individual (ie 4) power amp stages in the head unit?

- are 2 way active crossover units available at reasonable cost? I can build some for around $100 but there'll be more design work to get op-amps that will work with the low voltages - say +/- 5V after some voltage droop in the battery - I'd prefer to buy off the shelf.

- if I go passive, are decent passive crossovers available off the shelf for say 2nd order (12dB per octave) slopes at reasonable cost?

cheers

Mike

[NISSAN GTR]

We built a portable stereo using 40mm square tube welded as a skeleton structure 1.4 m x .5m x .5m , surrounded it with MDF , tappered at the front ,

lots of breathing holes in the bottom to allow battery gases to escape .

Put a hinged lid on it to access the components which we kept purely 12 V so we could use a deep cycle battery 140 A/H Marine battery , Kicker 12 inch in box subwoofer fitted flush into MDF box ,

2 kicker 6x9s , kicker 360w 4 channel amp and finally sony headunit which was mount at rear of box for protection ,

We have taken it to gymnastics / parkour / tricking get togethers at the beach and parks .

When we first fired it up we could not believe how loud it cranks running off an i-phone, i have been surfing out the back 300m away and could hear music still , quality is amazing battery lasts for about 7 hrs at full tilt , weight was the only enemy at 55kgs , takes two blokes to lift it or sack truck , but well worth it in the end .

Have photos if your interested . GL with yours

[Carbon 34]

all your requirements can be had with ease,

I have a active audiocontrol xover think its 18db roll off you can buy cheap if you go that route, and its tiny ? just sitting in a box now palm size unit, 1 amp of current to run it and output is around 9 volts I think on RCA's for clean signal to amp

if you buy clever and construct well you can get more bass from a good 6" then a generic sealed box 8"

battery use a 12v emergency lighting battery, small fits in the palm of your hand run a pair of those in parrellel for longer run time same voltage , off ebay I bought one for under 20 bucks new . no gas to vent either, just keep charger cool

and decent power inverter to prop up the voltage while charging and charge the battery

a battery charger can do it if you have a smart one, I found one for 30 bucks at stupid cheap clearance bin normal cost about 150

why even buy or use a deck, use the ipod for everything, you can get old 3g iphone and run the radio off the internet, and rip music and bluetooth or wireless send to the iphone. or use wi fi. then you can have video as well ??? your fidelity wont be perfect but just fine for a boom box setup.and no sand to enter the cd slot. and crust up ?? even make phone calls from it and track it if stolen too ??

buy a tiny class D 2 channel, cd cover size now. and uses less current . soundstream makes a clean one cheap, so do a lot of others companies

run the amp in bridge mono on the sub and stereo on the others, mixed mono setup , the ohm load with coils , caps will be around 2-4 ohms at all freq so the amp would be safe from toasting

why do you want 12db roll off, on crossover if passive, its over kill on a boom box just eats up the power more when your not running it in perfect location to take advantage of the roll off anyhome ?

run a coil on the sub, in bandpass box, that sits with the main unit, and splits in the satelite speakers with cap and coil 6db roll off or factory xovers

the box would be smaller then a back of groceries and get loud as hell still, clean sound and less parts that need power

custom made carbon fiber/kevlar box and its light and stong as hell easy as piss to make,, gee I have all the parts here I should do that haha

PM Me I have extensive knowledge of home audio etc. THX//Dolby theatre as well.

Edited February 10, 2012 by Carbon 34

[mikel]

cheers guys,

great call Troy on not needing a head unit - hadn't thought of that, just use iPhone straight into digital amps using the analog out of the iPhone.

Food for thought on simple 1st order passive crossovers - a decent poly cap in series with the tweeter and a coil in series with the woofer (or resistor in series and cap in parallel to avoid the coil).

I don't plan on running a sub - how can you get more bass from a 6" unless ported? - I'd prefer to stay with an 8" in a custom box - ports are a bigger slot to get sand in, and will unload at high volume and pole the driver.

Carbon/Kevlar boxes would be great but beyond my manufacturing expertise - pity you're not in Brisbane. I'll likely go marine grade formply, heavy but waterproof.

cheers,

Mike

[Carbon 34]

cheers guys,

great call Troy on not needing a head unit - hadn't thought of that, just use iPhone straight into digital amps using the analog out of the iPhone.

Food for thought on simple 1st order passive crossovers - a decent poly cap in series with the tweeter and a coil in series with the woofer (or resistor in series and cap in parallel to avoid the coil).

I don't plan on running a sub - how can you get more bass from a 6" unless ported? - I'd prefer to stay with an 8" in a custom box - ports are a bigger slot to get sand in, and will unload at high volume and pole the driver.

Carbon/Kevlar boxes would be great but beyond my manufacturing expertise - pity you're not in Brisbane. I'll likely go marine grade formply, heavy but waterproof.

cheers,

Mike

Iphone cables are pretty cheap, they can output video, rca left and right, and charger in one

class D amps arent real digital, only the transistor switching is, not the input from RCA. , saves size, heat, and sounds fine for your application

a cap on the tweeter to x over around 6khz -8khz depending on the tweeter, some can go lower to 4.5khz on the 4" vifa soft dome or titanium models

a cap on the mid to block the bass around 120 -300hz depending on mid size, let it roll off naturally , f3 db is about 4khz -7khz on a mid ,

keeps it simple, cheaper and more dependable use poly caps only and iron core coil for woofer to keep it sounding clean

and a poly cone single 4ohm VC woofer with coil xover around 80-100hz, 8 inch is fine , or even reverse isobaric 6" in a double reflex box for even more DB and bass control

you can get fancy and build a zobel network but not required the ohm load wont drop below 2 ohms in most cases running mixed mono on the amp. stereo to the fronts 4-8ohm , and bridged to 4ohm woofer

ohm load at each freq wont drop lower then 2 ohms so just about any 2 channel 2 ohm stable amp can do it. just buy a small form factor, class D if you can to save power and size/heat

mount the amp in the port tunnel to keep the air moving over it , just take that into account when building it to protect it . the main box could be boot box size ? and front stereo speakers the size of a small stack of DVD's depending on how crazy you want to fabricate something

you can build the front boxes in a horn config front so the throw is further and the DB is louder ? better for outdoor or big rooms use ?

the sub port build it slotted not tube shape so crap can be poured out if it gets in it ?

you could mount the amp in the port side so the air moves over it ? just account for it when building the specs. and mount with silicone rubber feet so the vibration doesnt end its life early , it would be cool and protected from the elements pretty well , unless you had a kid dump sand or water in the box ?

plus the bandpass box is the best of both worlds, the driver back is sealed= nice smoothe/tight/fast bass and protection

the other side slot ported for added 3-6db @1watt and a natural bass filter , you can run no coil in a bandpass box but I would to stop all voices from coming out of the port

dont forget sand on the tweeters will be perm stuck on the cones. the neo magnets are much stronger and will capture the iron in the sand , a titanuim dome or poly would be best outside. a kevlar , silk, soft dome sounds nice but not practical outdoors

even with marine ply I would still epoxy coat the system ? you can mix colour in the epoxy so it cant scratch thru to see wood. like paint would and could be polished with car wax to a show finish ?, I wouldnt use ply anyway its too heavy, can sound bad if your not careful, cost to much, you could do cheaper hi density MDF epoxy coated it sounds nice, or even a natural wood solid, besides pine . maple , birch, gum with a tight grain no blemish wood if you want it pretty ?

fiberglass or exotic kelvar even better , wilder shapes and stronger . carbon fiber is 7 times stronger then steel , but can resonate ring if your not careful with the internal construction, allows for exact fit of parts to make the package smaller

my old r34 test box is carbon a few layers of it and you can hit it with a big ball peen hammer full force, without any damage at all. ? I love hadning the hammer to people to try to break it , wont even shatter the epoxy on the face of it

and look here for goodies

parts express

Edited February 11, 2012 by Carbon 34

[mikel]

cheers Carbon34,

great tips...though using an iron core in a coil ? - unthinkable where I come from (home diy hifi) - any core increases inductance but then includes significant distortion as the core saturates.

Any coils will be air cored or I'll go active.

Your idea of dumping the head unit means less current draw to allow a 2 way 24dB/octave active crossover into a 4 channel (or 2 stereo channels or whatever) D class amp/s.

I like your thinking on running the amps inside a port - very clever, but I'll probably just run a sealed woofer and accept less bass (shock horror).

I'll seek out a low Fs high Qts bass driver that will work ok in a sealed box and not have to worry about the driver unloading below the box resonant freq, larger box size required for ported alignments, and the design specs changing as the driver ages.

Your ideas on isobaric bass boxes are again worth considering - but I have no idea what a "reverse isobaric in a double reflex box" is.

Reverse Isobaric implies to me the drivers are in phase (I'm probably wrong) - which means you need to double the size of the box - and if they were facing the same direction you'd get major suckout (ie no bass)....If reverse isobaric is the drivers mounted back to back (or front to front) then that's just normal isobaric to me, and if the double reflex ports are the ports not venting the common space between the drivers I understand.

A normal rear firing Isobaric will just annoy other people in the campsite - assume anyone listining to music is in front of the stereo.

I want to avoid vented enclosures, as there's too many problems (as mentioned above, plus the extras you've mentioned - sand/water etc) - being an active enthusiest, if I thought the bass drivers could handle it I'd add a linkwitz transform to get more bass rather than ports.

Assume I only want to go 2 way (tweeter + 8" woofer and no sub/mid etc), 2 way active,

Can you recommend any brands of:

- active crossovers,

- digital amps

- drivers (tweeter or woofers)

greatly appreciate your input so far - I've chnaged direction based on it already, plus got me thinking

cheers

Mike

You're right on marine ply being heavy, and I'll probably go with MDF and just seal it with epoxy etc - sealed boxes are easy in that regard.

Again good call on the tweeters

[Carbon 34]

You use iron core coils on subs to keep the ohm load from exceeding limitations and cost /size of the core of copper , even hand wound can get huge and wire size needs to big large $$

Air on mids to reduce distortion on speaker you can hear?

A 24 db crossover on a mp3 based system is a waste of money , the cost to build or buysome built exceeds practical i thought you wanted this portable ?

Those crossovers would be larger and rot in the sea air copper !! And outdoors at the beach you wont know you have a 6db or 24 db xover !! Phase group delay would vary so why bother outside unless your at a concert

in a house yes

Plus your wasting lots of power to run them ?

6db is fine

Or go active , if you do a 4 channel amp most have 2 or 3 way xover options built in so you wont need more crap

External xover audiocontrol is best for your money and lasts forever 60 bucks you can have mine ? Just sitting in a box 18db xover and preamp

Sealed box is fine , your looking too deep into this its not a home stereo setup at the beach or park or shed you want

Simple, good sound, depenable, cost effective, and must take a beating being moved all the time right ?

You want the best sound, semi weather proof , cost effective and unique , not audiophile monster that needs a motorized esky to move it !!!

The isobaric i speak of both ports are on the same side

Your brain washed to sealed so why bother dropping exotic better options ? You need the port to increase db outside !!!! Trust me on that one !!! a well built ported box wont unload unless you drive it like a tard 12db bass boost and amp clipping at low voltage limit , but whatever keep reading the loudspeaker cookbook which is out of date by 20 years in speaker box building and drivers Still good lite reading lol

You loose db transfer function boost outside !!! So you need more power off the amp which requires more battery power and heat reduction of some type ?

Amps you wont like since your hung up on SQ digital 4 channel amps arent a perfect choice for SQ due to switching noise and amplitude cut off compared to a class a/b model , there are a few other hybrid amps as well

I would say soundstream, rockford, alpine, for mid range price point

Speakers i would use vifa, morel , dynaaudio for mids and tweeters and a JL sub or kicker solobaric for sealed small sub , cheaper or a neosub for more money and for SQ

The sub needs rubber surround and plastic alloy or carbon cone or weathet proof ? And small box parameters with lots of excursion and spl at 1 watt should be at least 86db more is better

You need windfarm, solar, hydrogen , and wave power to run some of your options lol

The battery would never keep up for long

You need to rethink the use , portable or not ?

Cost wise your exceeding the sane price for a boom box

You could do it for undet 500 if you had nothing to start with ?

You could easy dump 500 in xover parts at 24 db alone !!!

I think you need to narrow your focus on what you truely want and how much it might cost ? Imo

My 2 cents worth

[mikel]

cheers Carbon 34,

valid points - I wouldn't think of going 24dB passive - way too power hungry and way too hard.

If I went 24dB it would have to be active - otherwise I'll go 6dB and use iron core inductors as you suggest.

Happy to consider a ported box for the woofers - especially since I'm not planning to run a sub, just stereo 2 way.

lol I haven't pulled out the loudspeaker cookbook in years, but it is a good read. If you can suggest any sites on ported box design that may be more appropriate with modern drivers that's simple to build, and don't make the boxes too big that would be great.

I'm not so hung up on SQ that digital amps aren't suitable, basically they're essential whichever way I go (active or passive) for battery life.

I just love the sound of an active setup, but the simplicity of a 6dB passive has huge merit for a portable system.

If there's design options for small ported boxes (ie not much larger than a sealed box for the same driver) it would be the go for the extra dB as you suggest.

I'm happy to go for a more esoteric cabinet (ie isobaric etc), but as you say - I don't want to need a crane to carry this thing around.

So

Active - twice the amps, more electronics, higher cost (?), better sound

Passive - fewer amps, simple

Sealed box for woofers - simpler box, smaller boxes (? based on 20 year old thinking), not as much bass, more weatherproof

Ported box for woofers - harder to design, larger boxes (? based on 20 year old thinking), more bass, easier ingress for sand etc

Leaning towards passive and ported.

Thoughts?

Mike

all the reasons you mention (ie more dB

[Carbon 34]

I think you need to answer these questions first

How much do i want to spend ? You can buy a boom box cheaper then you can build one but sound wise a home built would sound great !

Can i fabricate myself or pay someone to do it? Could get expensive ?

How big can it be ? To big to drag around or uses to much power to be worth it

Is it for the shed or portable to beach etc? Big difference in sound and parts you can use

Another option is just buy some splits for a boat / marine speakers and marine amp ? Most car audio companies have a line for boats now ???

If not then two ways , you could spend 50 a pair or 5k a pair , if i was building some and didnt have a box full of speakers alteady , i would try some car audio on sale splits 6.5 or even 8 in if you can find some cheap then they have crossovers already , might meed some tweeking but you have the parts boards covers etc

Or some audax titanium tweeters , tiny as hell and cheap too ,, and some 4in mids gold-sound brand my mate designs them in usa , sealed front channel speakers and a 8 in sub built into main enclosure slot loaded single reflex box in mdf for you but i would go exotic kevlar carbon for weight and destruction proof box and not a box shape but something crazy cool

And iphone 4 or 3 or ipod

Iphone charge cable and rca out interface

Digital class amp . Prob soundstream or rockford since in usa there cheap and dollar is high

2or 3 emergency light batteries run parrallel to stay 12 volt but current available shoots up , a built in Fold out mutiple panel Solar cell with transistor / diode swtch to supplement charge at beach , as well as mini hydrogen cell , which i have already brand new lol and a super cheap smart charger for mains top up Over night

Hard wired in

Run amp mixed mono class d 2 channel amp bridged / stereo same time

Stereo to splits passive and 6.4 mh iron core to sub @ 4 ohms if memory serves me right on inductance xover point been a while since not just going active lol

Active is always better but not always possible

Size wise it would be about the size of a two boot boxes maybe give or take ? Weight about 10 kilos , more for mdf

you could do a pair of marine speakers Splits 6.5 inch

Ipod

Batteries

Charger

Conversion rca charger cable

Two channel class d amp , cd cover size

Charger

And box , even smaller since no sub , 1 boot box size maybe slightly bigger would be enough for 6.5 in speakers , they would be sealed box but front face of cabinet horn flaired for extra throw and tiny db increase , not worth porting splits unless you can get parameters to calculate the port right ?

Take a look at that link i sent you they sell heaps of speakers , amp kits you can use and if your handy with solder iron you could use amp kits etc Just watch usa shipping costs they can eat up the benefit of dollar being so high now

Anyway i have access to the rta and a half dozen box programs if you get stuck and want a box design

Best of luck , maybe I'll recycle some old gear for one when i get time but all my dust collecting amps are too big for the boom box but have everything else already

[mikel]

cheers Carbon34

I'll keep the forum updated on progress.

great idea for the charger output to charge the iPhone.

Thanks for all your input/links etc.

Carbon would be sooo good, but beyond my manufacturing abilities.

thanks

Mike