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[Frank Koenig]

Loud, low, or small. In this instance I chose low and small. Over the years I've amused myself (and worried my fellow campers) with small, portable playback systems that run off tiny amounts of 12 VDC. This keeps me busy and supplies Parts Express with a steady income. The current addition to the kit might actually be of some use in very small-scale live sound or installations, so I post here.

The driver is a B&C 12BG76 12 in. woofer with fs = 44 Hz, Vas = 1.13 ft^3 and Qts = .41. B&C recommends a 1.4 ft^3 enclosure with fb = 42 Hz. After some fiddle-farting with the model I arrived at 1.5 ft^3 and 40 Hz, which, usurpingly, is pretty close. I wanted to use 4 in. ABS DWV pipe for the vent to keep the velocity reasonable and for ease of tuning. This results in a vent length of about 11 in. Making room for it on the front of the box results in the box being too shallow to accommodate the length of the vent (without bends) so I moved it to one side. As the box will be used solo with nothing beside it this should be OK.

For amplification it became a dance between peak voltage (good) and idle current (bad). I settled on a "Sure Electronics" "200 W"  single-channel amp board from, where else, Parts Express. It allows a maximum supply voltage of 36 V at which it can put an honest 50 W into 8 Ohms. Distortion measures at under .2% under normal conditions and I suspect is actually a bit better as the HF hash on the output may throw-off my antique HP distortion analyzer. The clipping behavior on this amp is a bit weird. It doesn't clip cleanly as one would like but rather grows a beard of switching hash on the part of the waveform that exceeds the amp's voltage capability. To keep an eye on clipping I added a small home-brew clip detector that lights an LED when either output gets within ~3.5 volts of ground. (The amp is single-supply in a bridge configuration and quiescent output voltage is 1/2 the supply.)

To get 36 Volts I ordered from DigiKey a 24 V, 4A output DC-DC converter made by CUI. Since its output floats it can be wired in series with the 12 V supply to achieve 36 V. (I actually trimmed-down the convertor to 22 V so as not to bust 36 V by too much when the battery is charging.) Idle current for the whole shebang at the 12 V input is ~475 mA.

I added a switch-selectable direct connection to the driver so that the speaker can be used with an external amp in louder, shore-powered situations.

The frequency response plot was taken with both speaker and mic on the ground 20 ft apart with no other boundaries within the 200 ms window. (The dB scale is relative, not SPL.) I'm very pleased with this result. An ~4 dB shelf makes it flat to < 40 Hz and so far I think it sounds fantastic, which is entirely due to the excellent, modern driver design from B&C. I would definitely use this driver again.




--Frank

[Steve-White]

^^^ Looks really good Frank.  I keep myself occupied in the shop as well.  Installed an new HT preamp in the entertainment system rack today.

Pictured are a couple of Rube Goldberg's of mine.

The other one pictured is a fueling station for the generators, ZTR mower etc.  Mounted everything on an aluminum hand truck, 14 gallon tank and hand crank pump.  Fueling up the larger generators is not easy with a 6 gallon fuel can.  The put the fill port right in the center of the fuel tank and it takes 3 hands to do it safely.  Not anymore.

[Dave Garoutte]

Do I see a rat guard on the vent?

[Steve-White]

Heater was a problem out on the patio at night for cigar in the winter.  Pulling it close enough to feel the heat was too hot, move it back and heat went straight up.  Solution was to mount a fan on top to blow the warm air across the patio.  Works great.

[Frank Koenig]

Do I see a rat guard on the vent?

Exactly right! A piece of 1/2 in. hardware cloth held on with a hose clamp. It will keep out rats but maybe not mice. I should make the experiment to see if 1/4 in. has any effect on box Q or makes bad noises at high power near fb. 1/4 in. will keep out mice, so far as I know.

Speaking of rodent problems, is there an uptick in wire insulation eating on vehicles? Two of my friends here in town have recently had major damage. Anecdotal, I know. But there could be more rats/mice, or people are driving less due to Covid, or maybe car manufacturers are using tastier insulation?

--Frank

[Frank Koenig]

The other one pictured is a fueling station for the generators, ZTR mower etc.

I need a fueling rig like that for the little rubber-track front-end loader I keep up in the Sierra Foothills. I've been struggling with 5 gal. plastic jugs for years now and just about everything with that arrangement is wrong. The jugs don't vent properly due to some misguided attempt by the manufacturer to comply with newer safety rules. The spout is too short and too weak to rest the weight of the jug on. And the fuel inlet is too high up on the machine. So I huff and puff and curse and dribble diesel all over while milking (alternately squeezing and releasing) the plastic jug to get the fuel out. The last 10% never comes out. Thanks for the inspiration.

--Frank

[Bob Faulkner]

Speaking of rodent problems, is there an uptick in wire insulation eating on vehicles? Two of my friends here in town have recently had major damage. Anecdotal, I know. But there could be more rats/mice, or people are driving less due to Covid, or maybe car manufacturers are using tastier insulation?

--Frank

Yes.  Some auto manufactures are putting "green" components into vehicles.  About 2 years ago, my neighbor had some squirrels chew through his Diesel fuel tank on an F350.  The fuel spill from it (all over his driveway) prompted a slight haz-mat situation, which the fire department came out to asses.  Root-cause-analysis:  the gas tank was soy based.

http://www.synlube.com/IncredibleEdibleCar1.htm

[Riley Casey]

Trying to make an F350 marginally more environmentally friendly, now that's thats some high comedy.

Yes.  Some auto manufactures are putting "green" components into vehicles.  About 2 years ago, my neighbor had some squirrels chew through his Diesel fuel tank on an F350.  The fuel spill from it (all over his driveway) prompted a slight haz-mat situation, which the fire department came out to asses.  Root-cause-analysis:  the gas tank was soy based.

http://www.synlube.com/IncredibleEdibleCar1.htm

[Steve-White]

I need a fueling rig like that for the little rubber-track front-end loader I keep up in the Sierra Foothills. I've been struggling with 5 gal. plastic jugs for years now and just about everything with that arrangement is wrong. The jugs don't vent properly due to some misguided attempt by the manufacturer to comply with newer safety rules. The spout is too short and too weak to rest the weight of the jug on. And the fuel inlet is too high up on the machine. So I huff and puff and curse and dribble diesel all over while milking (alternately squeezing and releasing) the plastic jug to get the fuel out. The last 10% never comes out. Thanks for the inspiration.

--Frank

I got so pissed off at consumer grade gas cans I put them all in the recycle bin.  Switched to VP racing fuel jugs that I saw the guys using on Street Outlaws.  They work great, hold 6 gallons and come in lots of colors.  The spouts are long and can be easily lengthened to fit need.  I use standard length.  There is a folding handle on the pump that's off of a handwheel on a milling machine, so the hand truck lays on it's back for easy filling.

https://zzdiesel.com/vp-racing-fuels-motorsport-container-round/?pid=12908&utm_source=bing&utm_medium=cpc&utm_campaign=*PDS%20All%20Products%207%2F29%2F2019&utm_term=4576717161145835&utm_content=All%20But%20GM%20and%20Cummins

[Steve-White]

I got so pissed off at consumer grade gas cans I put them all in the recycle bin.  Switched to VP racing fuel jugs that I saw the guys using on Street Outlaws.  They work great, hold 6 gallons and come in lots of colors.  The spouts are long and can be easily lengthened to fit need.  I use standard length.  There is a folding handle on the pump that's off of a handwheel on a milling machine, so the hand truck lays on it's back for easy filling.

https://zzdiesel.com/vp-racing-fuels-motorsport-container-round/?pid=12908&utm_source=bing&utm_medium=cpc&utm_campaign=*PDS%20All%20Products%207%2F29%2F2019&utm_term=4576717161145835&utm_content=All%20But%20GM%20and%20Cummins

You did a real slick job on the back plate and amp board mounting and details such as the remote power speakon are great.  It's always worth it building custom to get exactly what ya want.

Again, nice work.

[ProSoundWeb Community]