building a portable stereo

Well it sounds like you know what you want. It seem to me that you could buy a boom box that does all that and more for much cheaper than what the material cost you. But, it sounds like you are bored and just want to build something.

I see some kids in my neighborhood that build their own boom boxes in the back of their 3 wheeled bikes pretty cool

You can expect about 17 watts per channel from any radio out there. 

Cooler Systems ... I could write a book.

Chapter 1:

I frequent a beach in summer where all the same crowd gathers - my 26th season this year. Hence we have large parties on the beach, buffet tables, a portable bar, etc.  So picture 20 to 40 people hanging out.  This is not a situation where 6 friends are sitting on a blanket listening to an iPod dock.  On the beach you must contend with the sound of the ocean and no walls to reflect sound back at you.  Volume drops off very quickly in open air.  Also, from car to waters edge is a half mile walk with a third mile over the sand.  Weight is an issue, a bifg issue.  Coolers are light, rigid and fairly impervious to all the beach elements.

For several years I used a Sony GFC700 (the biggest box they make) running off a 18ah SLA battery.  It perfomed adequately and was fairly loud. However, it never had quite the warmth of a good stereo with booming base at resonant freuqecies. Battery life on the SLA was good for two 12 hour days at a minimum (8 alkaline D-cells dead in a day).  The box and battery weigh in at about 30lbs. The only other box in this category is the JVC assault style boxes.  I never considered them because of the side firing woofers - all that energy wasted in the wrong direction.

This year the Sony failed due to a severe thunderstorm.  I replaced it with a Parrot Boombox (search Parrot Boombox at trustedreviews.com for an expert review).  This box has a 4" woofer at two smaller speakers for the stereo in a single box.  Very similar to the Apple Hi-Fi. It had excellent sound, and was louder than the Sony withs it 60 w-rms Class D amp.  However, the name Boombox is misleading as it only runs off AC.  Hence I powered it from the 18Ah SLA with an inverter. I was very happy until the woofer developed a bad buzz between 360Hz and 425Hz after about 8 hours the first day out (its going back for warranty repair)..  I have another one of these boxes I use with my PC when I'm playing MP3s and I never had a problem.  So was it the extended high volume in beach heat, driving it with an inverter, just a defective unit - I may never know.

I had already built a fairly massive cooler system for the larger beach parties.  The system was composed of a Power Acoustic BMF1600/4 4ch, 150 W-rms per channel amp.  A pyle EP401 preamp (to accept my mp3 player), a Kenwood KFC-3012W sub and two Pyle PLG8.3 8" triaxials.  The amp's front two channels drove the triaxials and the rear channels were bridged for the sub.

The Triaxials are mounted in cooler jugs. Notice how the speakers are protected by the jug cap for transport and storage along with built in carry handles.

The jugs make great enclosuers as they are light and rigid.  The Kenwood sub was mounted in a Igloo "cube" cooler by opening the lid and gluing an MDF board inside the cooler with the appropriate cutout for the woofer.  The sub performance was fantastic.  The sealed enclosure producing a very nice base.  The triaxial speakers were adequate but I never really got the mid base to my liking.  It may be that the jugs are a little small for the 8" speakers or I just needed to fine tune adjustements, cutoffs etc a little more.

I've used it 3 times and it sounds incredible. But, but it drained a standard car battery in 3 hours.  Given the the distance to the beach, I couldn't justify adding car batteries as the weight would require several trips.  I've already sold off the amp and equalizer and the speakers are up for sale.

I'm consdering buying a Pioneer head unit with USB so it becomes the amp, equalizer and MP3 player and running it off the SLA.  But I have reservations that its 50W peak (17w-rms, 14 W-cea) power may not drive the 8" traiaxials as I estimate their efficeincy to be about 86db (no specs from Pyle are available).

And don't forget your not getting 14.4 volts from the alternator so your not getting the rated power from any amp. Your fully charge flooded lead acid battery runs from 12.65 V down to about 11.9V before it drops off.  An SLA is slighter higher due the addition of calcium in the absobed glass mats going from 13.3 down to about 12.4 before dropping out.  You can try NiMH batterys and get a nice 14.4 from 4 cells.  However the equivalent amp hours will cost you dearly and you'll need a very smart charger to go with them.

What was it that an earlier poster wrote "sounds like you just want to build something'.  That problably applies in some part to my project as well.  In the end, I would recommend going with a good boombox that fits your taste/style,etc.  One reason I picked the Sony was its native 12V dc design.  I just wired in a power jack to the internal battery terminals to connect the SLA.  If I had it to do over, I would have bought 8 5000mah D-cell NiCds for the box.  It would have saved 12 lbs and they would have run it all day.  You can recharge with a car's 12volt system or a wall charger at home.

Having tried it all I'm going for a replacement boombox.  Light, functional, decent power and convenient.  They can be bumped around during transport pretty hard, they are compact and require no setup once your on site (the cooler system required unrolling wires with high grade phone plugs, setting up the battery connection (i used power pole connectors) and tweaking controls.  I can't see buying the big Sony again as I want warmer sound.  So now I'm kinda' stuck thinking  what I should do.

In the meantime, I wrote a friend who missed the last big party on Mon the 5th about how the "Old blue boom box came out of retirement and hit one just over the left field wall to win game 3".

Hope that helps.

Regards