Building my first boombox

[amsaarin]

Thanks, we'll go shopping tomorrow and try out the tweeters, too.

Another thing that crossed my mind today: it would be nice to have a battery level indicator on the blaster. Simplest solution could be some kind of "battery low" -indicator LED that would turn on when the battery has some predetermined capacity, which is known to last for another hour or so. And maybe another indicator when the battery is at full capacity (i.e. no need whatsover for charging).

Any ideas how this could be implemented? Would it be difficult?

[tuo]

Well, that's not very complicated, since every battery has a discharge characteristic curve that normally starts at voltage peak, then evens until at the end dives deeply before battery is empty. So measuring a this about even section and testing with some limit voltages you should be able to get nice limits for those full and empty signals.

After that you'll need accordingly biased opamps with positive feedback to drive the leds.

A second thought: opamps would normally need dual rails, so there should be a regulator for that. And the effect of the declining supply voltage also for the opamp should be handled somehow. All this makes it a bit more complicated.

[V-bro]

There are fine single rail 5V opamps for that, but why not just go simple and use a zener operated PNP transistor??



Values may be changed a bit to suit the operating voltage...

http://www.brighthub.com/engineering...les/68396.aspx

[amsaarin]

Today we heard the first sounds of SP60s combined with DT99s, and they are sounding great together! We need to do some balance tuning when we have installed them to the enclosure, but the first bites were extremely promising.

It was a beautiful sunny day, and we were doing the soldering and testing at the balcony. Awesome! Here's a few pictures of the setup

[krilli]

NNnniiiiicceeee

[V-bro]

I just love that, candy for the eyes, ears and mind!!

See how uncomplicated these drivers are, no real need for extreme filters or complicated enclosures... just build it and enjoy good sound! And with just a little more effort it can sound truely great! (speaking from experience) I have built many speakers and have used many expensive drivers and I've never quite seen quality like this offered at such a price.... Also how tough they are mechanically, I mean, have you tried to make the SP60 distort?? It's almost impossible!

[amp6erik]

Very nice to see those promising pictures as well as the text! Although I still have some questions.
Is this how I am suppose to connect all the speakers with the amp and the capacitor?
According to what I have understood after some reading, the tweeter will play louder than the woofers due to its higher ohm (?). It is any way to lower the tweeters to the same level as the woofers?

[krilli]

Which is louder does depend somewhat on the impedance - lower impedance loads will get more power out of the amp. The biggest factor however is the dB/W efficiency of the drivers. What are those figures for your speakers?

Probably the best way to lower/raise the volume of a particular driver is to have it on its own amp channel and raising/lowering the gain in that channel. Otherwise, you can "pad it down" with a power resistor. Many ways to skin this particular cat. (As drawn, you'd pad down the louder driver because both are connected to the same amp channel.)

[tuo]

Yes, that's the way to connect them. For lowering the tweeters to same level as the woofer you have two options: a series resistor or resistor L pad. Take a look here: http://www.sengpielaudio.com/calculator-Lpad.htm

Now the tweeter is 8 ohm and 3 dB louder than the woofer, so a series resistor of 3.3 ohms should do the trick. This resistor would be connected between the cap and the tweeter itself.

[amp6erik]

Thank you both for the answers! I think I do understand now. I'll probably go with the 3.3 ohms resistor, because I want to keep it simple as possible due to my lack of experience of this stuff So basically all I need for my "filter" is first a capacitor of 4.7 µF (that will cut the frequencies to the tweeter) then a series resistor of 3.3 ohms (that will lower the tweeters to the same level as the woofers) between the amp and the tweeter?
So this will make the tweeter work from 4000 - 18000hz, if I got it right?
And what about the woofer, will I have to make a filter connected to each woofers as well? If not, it will play frequencies all the way up to 8000hz. Does not that increase the sound quality when having in mind that the tweeter is playing all the way from ~4000hz or is it just like that a crossover works?

Thank you guys, I really appreciate your help!
Erik