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  • Solar/battery powered speaker system

    Hey everyone,

    I got this crazy idea to build a small portable speaker system for outdoor use that would run off a 12V sealed lead-acid battery with a small amp and want to hook up a solar panel to keep the battery charged. The solar part of it should be pretty easy, there are a lot of 12V charging solar panel kits available that I'd just hook up directly to the batteries (assuming the charge controller has a diode to prevent current flow from going into the panel). I can pick up a 15W solar panel for around $80 with a 12V charge controller that would take care of keeping the batteries charge. I have access to some 5.8Ah 12V sealed lead acid batteries and would probably use two of them in parallel for a longer runtime.

    As far as the speakers, I have four 6.5" car speakers that are OEM 'premium sound' two-ways, 40W max input, 4 ohm that I would like to reuse if possible - sound quality is just fine and I'm trying to keep the cost down on this project for now, with the knowledge that I can upgrade the speakers later if I want. I would be open to some of the closeout/sale speakers here instead if it solves my problem below. I would want the total speaker cost to be <$50 though and not sure I can get anything better than what I have for that.

    For the amp, I was looking at several options, but not sure what I want to do... I do want the capability to integrate a 12V power supply with a DPDT switch so I can switch to AC power if I want (batteries on one side, power supply on the other...) I was thinking the Lepai 2x20W amp, but I would like to drive four speakers (two per input channel) and since my speakers are 4 ohm I'd have to wire them in series, which would bring the output down to somewhere around 10W per channel (doesn't that mean only 5W per speaker?). Is that enough juice to do anything? The other option would be either a 2 channel amp that is 2 ohm stable and wire the speakers in parallel, or a 4 channel amp... hmmmmmm... or of course just running two speakers (but I feel that I would get better sound dispersion with four speakers rather than two).

    Any thoughts or suggestions? This will mostly be for recreational use like playing frisbee in the park or hanging out at the river.

    Thanks for the input!

    Aaron
    Last edited by fastenova; 08-19-2011, 02:28 AM.

  • #2
    Re: Solar/battery powered speaker system

    I would also would love any opinions on the idea of using one larger speaker instead of the two smaller on the second set of channels (assuming I use a 4-channel amp) for lower frequencies... Can I drive a relatively sensitive 8" woofer with not a lot of power and get any real bass response? Since I'm going off batteries should I forget the idea of a dedicated woofer altogether and just focus on giving more power to the smaller speakers to increase the bass response?

    All of my past experience has led me down the path of a dedicated subwoofer (home theater and car audio) so I don't know what's possible with low amounts of power, say 20-40W and the right speaker.

    Thanks!

    Comment


    • #3
      Re: Solar/battery powered speaker system

      I know you wanted to use the speakers you already have, but if you would consider buying two of these:...

      http://www.parts-express.com/pe/show...number=292-430

      ...you could get away with the cheap 2 channel Lepai amp and nothing else. They are 91 db efficient at 1 meter with 1 watt and would make the most of any power you gave it.

      MikeV from Parts Express gave these three options for boxes (each) on the Q&A section:

      1) Ported bookshelf: 17-3/4" H x 11" W x 9" D. Use a 2-1/2" diameter port that is 8-1/2" long. That will tune the box to 45 Hz and give you an F3 of 64 Hz.

      2) Ported tower: 36" H x 10" W x 10" D. Use a 3-3/4" diameter port that is 7-5/8" long. That will tune the box to 44 Hz and give you an F3 of 46 Hz.

      3) Sealed bookshelf: 17-3/4" H x 11" W x 9" D. The F3 would be 78 Hz and the Qtc would be 0.737.

      I'd probably pick option #1 or #2 and be happy. It's hard to reproduce low bass in an open environment like the great outdoors with a box-type scenario, so I'd suggest not trying to go too low with extension. Pick a realistic bottom end cut-off of 60-70 Hz and things will be much easier.

      2 speakers = $26.50
      1 amp = $22.80
      Total: $49.30

      TomZ
      *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
      *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

      *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

      Comment


      • #4
        Re: Solar/battery powered speaker system

        This is similar to the system concerns of those who have solar panels powering their homes ( I know several who do ).
        Universally they use deep cycle batteries because of the charge discharge pattern.
        Also speaker sensitivity is paramount. Get the most SPL out, per watt in as possible.
        The downside of going for maximum efficiency of power usage is speaker cabs have to be large.
        Before large wattage amplifiers sound systems were horn loaded.
        "Not a Speaker Designer - Not even on the Internet"
        “Pride is your greatest enemy, humility is your greatest friend.”
        "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

        Comment


        • #5
          Re: Solar/battery powered speaker system

          I remember pe was running a special on a pyle marine amp. It was a 2ch amp 70wpc rms, 120wpc pk. It was on sale for $30! I picked one up for a future boombox build. Should some nice cheap power. Not to mention it has a small footprint and can be easily hidden.

          Comment


          • #6
            Re: Solar/battery powered speaker system

            Originally posted by fastenova View Post
            Hey everyone,

            I got this crazy idea to build a small portable speaker system for outdoor use that would run off a 12V sealed lead-acid battery with a small amp ...
            Not so crazy in my book, especially if you add an FM radio to your goals. Here are a few specific comments.
            http://techtalk.parts-express.com/sh...d.php?t=225559

            Solar chargers are not power supplies. 15W is at the solar cell in direct sun on a bright day, not at the charger output. For $80, you get a good maintenance charger for things that sit out in the sun all day, like RV's.

            Your car speakers are likely ideal, especially for the price. Remember, you're re-purposing things you already have to save cost. My driver choice was based more on the Singularities thread using the PS220, and the knowledge that sensitivity makes up for a lot of things. Unfortunately, the PS180 driver I used is getting priced out of the market.

            As to amps, the FM section is not as common, but it's the input I use most; I highly recommend it unless you have an MP3 player on your person at the moment. I planned 2 6-ohm speakers so 2x18w amp was fine; with 4 4-ohm speakers, you'll want a 4-channel amps, just don't believe the power ratings.

            There's a lot written about these small amps and their power ratings. To my mind, it's simple Ohm's Law - at 12v, my 6-ohm speakers can only draw 24W, so I chose a unit rated in that RMS power range. In practice, I get no clipping at full volume, so it's a good match regardless it's peak power rating. Here's a link to LePai products at my vendor:
            http://www.hifidiyshop.com/Wholesale...amplifier_c889
            and one that looks like a good fit (4x 40WRMS @ 4 ohm... and 14.1V)
            http://www.hifidiyshop.com/4ch-4x100...b-sd_p321.html

            I will note this place is in China. Payment is by PayPal, and shipping through Singapore. It takes a while, but I'm 3-for-3 in China-direct purchases. You can always Google a specific model to see who else sells it if this doesn't feel right.

            There remain a bunch of design specifics that you start discussing on in the second post. I would note that bass is power hungry, and absolutely voracious outside. (Conversely, there are amps with bass channel outputs if you want an integrated sub.) I was happy with a high-80's tune on mine, but I was also assuming a specific application - on the ground, widely separated, as at a drive-in theater (nobody sits in their car on a nice summer night), or on the patio at a picnic. Stereo imaging was high on my list, so I was thinking 2-piece from the start.

            If you want a sound source near a tree while you play in a field, you'll want a modern boom-box - single integrated box with speakers facing out. That begs to have everything on the inside with sockets and interface connectors on the outside, more like Podzuma
            http://www.parts-express.com/project...roject=Podzuma

            Finally, be aware of weight. Mine started as a subwoofer, and with a 7Ah battery, tips the scales at 35lb. It's clearly in the same class as the early laptop PCs and cell phones - lugable at best. Hopefully, YMMV.

            HAve fun,
            Frank

            Comment


            • #7
              Re: Solar/battery powered speaker system

              Originally posted by tomzarbo View Post
              I know you wanted to use the speakers you already have, but if you would consider buying two of these:...

              http://www.parts-express.com/pe/show...number=292-430

              ...you could get away with the cheap 2 channel Lepai amp and nothing else...

              TomZ
              Tom, thanks for the suggestion. With these being 8-ohm speakers, this would reduce the amp's output to half of rated, correct? So approx 10WPC?

              Now please excuse me for my lack of knowledge here, but with 8-ohm speakers the amp would be putting out about 20W at full volume, which means it would be pulling about 1.6A @12VDC (not taking into account amplifier efficiency losses). Now with 4-ohm speakers the same amp would be delivering closer to 40W at full volume, which translates to 3.3A @ 12VDC. Is this correct? This would mean with all things being equal (sensitivity and power handling, for instance) between a 4-ohm and a 8-ohm speaker, the 4-ohm speaker will be somewhere between 1.5x and 2x louder but have roughly half the runtime on a given battery source.

              Also, I know these are "full-range speakers" but with a driver this size, and not having any sort of tweeter in there makes me think that the highs will not be very crisp. Then again, I don't really know anything about whizzer cones. Thoughts?

              Thanks for the input.

              Comment


              • #8
                Re: Solar/battery powered speaker system

                Originally posted by Sydney View Post
                This is similar to the system concerns of those who have solar panels powering their homes ( I know several who do ).
                Universally they use deep cycle batteries because of the charge discharge pattern.
                Also speaker sensitivity is paramount. Get the most SPL out, per watt in as possible.
                The downside of going for maximum efficiency of power usage is speaker cabs have to be large.
                Before large wattage amplifiers sound systems were horn loaded.
                Sydney,

                I am not sure what to do about these batteries, as I know I don't want to deep discharge them... Maybe have a low voltage shutoff so as long as they're over 12.5V or so it's on, otherwise it won't power the amp on? Thankfully the batteries are free and I have continual access to them as they're rotated out of equipment (my friend works in a data center for a large company and they rotate their UPS batteries out ahead of schedule to ensure reliability).

                In terms of the enclosures, I was really hoping for either an open baffle design or building the enclosure out or a light material to make it easily transportable. If I decide to do an enclosure I was thinking 1/2" or 5/8" painted plywood front and sides and a thin (probably 3/16") masonite back with limited bracing to keep it from flexing too much. Open baffle would make me happy but I know bass response will suffer if I go that route...

                Comment


                • #9
                  Re: Solar/battery powered speaker system

                  Originally posted by fastenova View Post
                  which translates to 3.3A @ 12VDC. Is this correct? This would mean with all things being equal (sensitivity and power handling, for instance) between a 4-ohm and a 8-ohm speaker, the 4-ohm speaker will be somewhere between 1.5x and 2x louder but have roughly half the runtime on a given battery source.
                  You are correct in that the power delivered is 1.5 - 2X greater - because of a load that has less impedance ( current goes up proportionally ).
                  Unfortunately that does not translate proportionally to loudness which is a human perception.

                  Also, I know these are "full-range speakers" but with a driver this size, and not having any sort of tweeter in there makes me think that the highs will not be very crisp. Then again, I don't really know anything about whizzer cones. Thoughts?
                  I've yet to hear a whizzer that was as good as a dedicated tweeter.
                  ( still listening for one however )
                  "Not a Speaker Designer - Not even on the Internet"
                  “Pride is your greatest enemy, humility is your greatest friend.”
                  "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                  Comment


                  • #10
                    Re: Solar/battery powered speaker system

                    Originally posted by Sydney View Post
                    I've yet to hear a whizzer that was as good as a dedicated tweeter.
                    ( still listening for one however )
                    I was going to recommend to him the Pioneer 2-way coaxials I have used and liked a lot, but I guess they're no longer available. Possibly a cheap piezo could be used to 'fill in' the upper end without the need for a complex/costly crossover (relatively speaking)

                    Side note, I'm very happy with my Lepai amp I just picked up yesterday. It's running my Nano Neo's louder than needed while staying cool; and as opposed to Dayton's T-amp, this unit actually lets all the bass through!

                    TomZ
                    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                    Comment


                    • #11
                      Re: Solar/battery powered speaker system

                      Originally posted by fbov View Post
                      Solar chargers are not power supplies. 15W is at the solar cell in direct sun on a bright day, not at the charger output. For $80, you get a good maintenance charger for things that sit out in the sun all day, like RV's.

                      Your car speakers are likely ideal, especially for the price. Remember, you're re-purposing things you already have to save cost.

                      ...

                      As to amps, the FM section is not as common, but it's the input I use most; I highly recommend it unless you have an MP3 player on your person at the moment. I planned 2 6-ohm speakers so 2x18w amp was fine; with 4 4-ohm speakers, you'll want a 4-channel amps, just don't believe the power ratings.

                      ...

                      There remain a bunch of design specifics that you start discussing on in the second post. I would note that bass is power hungry, and absolutely voracious outside. (Conversely, there are amps with bass channel outputs if you want an integrated sub.) I was happy with a high-80's tune on mine, but I was also assuming a specific application - on the ground, widely separated, as at a drive-in theater (nobody sits in their car on a nice summer night), or on the patio at a picnic. Stereo imaging was high on my list, so I was thinking 2-piece from the start.

                      ...

                      Finally, be aware of weight. Mine started as a subwoofer, and with a 7Ah battery, tips the scales at 35lb. It's clearly in the same class as the early laptop PCs and cell phones - lugable at best. Hopefully, YMMV.

                      HAve fun,
                      Frank
                      Frank - you have a lot of great points. Originally my idea was a completely solar-powered setup but I quickly realized that wasn't realistic unless I wanted to carry around a huge solar panel and have the SPL drop when a cloud was overhead. The solar idea is mostly so I can keep the battery charged while not in use as well as slow the drain a little bit if it's in use and sunny.

                      As far as the amp, the more I think about it the more I think a 4-channel amp would give me a lot of flexibility (especially if I wanted to replace two of the four speakers later with a larger woofer of some sort) but on the flipside I am not meaning for this to be a power sucker or enormous, I have nice PAs with 15" drivers that I can lug around where there's power available. I have no intention of driving a subwoofer and two speakers off <30W of total power - I was just thinking of using a larger woofer (8" as opposed to the 6.5" speakers I have) to get a little more kick... If I won't be able to effectively do this with the limited amount of power I'll have, I am happy to ditch the idea and just stick with my 6.5" coaxial two-ways.

                      Finally, for the cabinet design I was hoping for the speakers to be mounted at a 90 degree angle from each other, mounted vertically with two speakers on either face. I plan to either make it triangular or square, with the amp mounted on the top and the wiring and everything tucked inside in a small compartment.

                      Comment


                      • #12
                        Re: Solar/battery powered speaker system

                        By the way, this project started with an old JBL 4 channel car amp I had sitting around and a 20W 12VDC wall wart and a couple of spare speakers. I quickly realized I needed something more efficient than the power-hungry car amp and that I also needed more power on tap than 1.2A.

                        Also, that car amp is heavy and huge and totally unnecessary!

                        Comment


                        • #13
                          Re: Solar/battery powered speaker system

                          Here's a more electronics-related scenario, it makes sense in my head but I want to make sure I am not forgetting anything or overcomplicating it...

                          My thoughts for power switching using a DPDT on-off-on switch are as follows:

                          position 1: battery/solar power - The amp would be connected to the (2) 12V batteries (wired in parallel). There would be a quick connect wired in parallel to allow me to easily plug in the solar panel or a battery tender, both of which would output 12V and will safely charge a lead acid battery. The solar panel would be used to slow battery drain while the speakers are active. I wouldn't use the battery tender while the system is in use because I'd just use AC power instead.

                          position2: off/charge - The battery tender or solar panel could be plugged in while the amp is off to bring the battery up to a full charge.

                          position 3: AC power - the amp would be connected to the 12V 2A power supply it comes with to allow it to be powered directly from available AC power. This would be separate from the battery circuit since the power supply is not meant to safely charge, then float a battery without any sort of controller or supervision. This is basically using the amp just as it comes from PE.

                          Does that all sound reasonable?

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