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[Mike Sokol]

I wonder if you ran the power through a isolation transformer. or even just hung the primary of a large transformer across the line, if that would kill the buzz.

I've actually thought the same thing. Also it might be possible to add a series inductor and parallel capacitor to form a 2nd-order, 12 dB per octave low-pass filter to the output of this inverter and stop the buzz completely. But the buzz is barely audible for PA use, though it could be bothersome for a recording. And anything is better than listening to a genny whining in the background while a wedding is happening. Still, my little Fishman SA220 column is really loud for a 200 watt speaker and has a very wide dispersion pattern. I'm guessing that a pair of them could do an outside acoustic concert very easily for maybe 300 to 500 people depending on needed SPL. http://www.fishman.com/product/sa220-solo-performance-system

[Mike Sokol]

But if I had my old Altec A7 cabinets back with a modern 500 watt amplifier, I'm sure that would be over the top. Back in the 70's I had four A7 cabinets which I upgraded to Gauss 15" speakers and Atlas compression drivers on the horns. Then I added a bunch of piezo tweeters to make up for the lost highs in the Atlas drivers. Sat them on top of four SVT bass cabinets with the eight 10" woofers each. This was powered by three Dynaco 400 amplifiers via a 3-way electronic crossover of my own design with maybe 2,500 watts total. This was in the mid 70's when other bands were still using Kustom 200 PA systems, so it was a significant stepup from the normal PA of the times. We could run it off off a pair of 15 or 20-amp outlets without ever tripping a breaker, and it really rocked a mid-size room.   

I still have three raw Altec co-axial speakers in my gear closet with the multi-cellular horns in the center. I think they were only rated for 50 watts, but if they were loaded into an A7 size cabinet that would be a LOUD 50 watts. I think the key to Frank's OTG (Off The Grid) system is speaker efficiency.   

[Frank DeWitt]

The Fishman SA220 are a lot easier to lug around.  I remember trying them in our gym when you taught the coarse in Lima NY  Very impressive

but.........

http://www.ebay.com/itm/TWO-ALTEC-LANSING-A-7-VOICE-OF-THE-THEATRE-SPEAKERS-/121396628669?pt=Vintage_Electronics_R2&hash=item1c43cd8cbd

[Tim McCulloch]

I think the key to Frank's OTG (Off The Grid) system is speaker efficiency.

This. Right. Here.

[Frank DeWitt]

This. Right. Here.

http://www.reocities.com/ec1288/images/schematics/Altec825.jpg

[Stephen Swaffer]

So what is the driver behind todays inefficient speakers?

The other aspect of "off the grid" that seems wasteful to me is taking low voltage DC power from a solar array/battery.converting it with an inverter to 120 VAC, then using wall warts/switching powers supplies, etc to convert the 120 VAC to the low voltage DC actually used by most of todays electronics.  LED lighting runs off low voltage DC-I am wondering how long it will take before we start distributing DC in homes to LED lights vs AC to power supplies.  Probably a natural for the RV industry first.

[Josh Millward]

So what is the driver behind todays inefficient speakers?

Size.

Smaller loudspeakers that can take a lot more power, coupled with the fact that the power is so much cheaper than it was way back when.

I have long been a proponent of using the larger, more efficient loudspeakers and loading them with today's newer higher power drivers. The dynamics from a horn loaded system are always impressive. Unfortunately it seems that Danley is the only manufacturer interested in things like this.

The other aspect of "off the grid" that seems wasteful to me is taking low voltage DC power from a solar array/battery.converting it with an inverter to 120 VAC, then using wall warts/switching powers supplies, etc to convert the 120 VAC to the low voltage DC actually used by most of todays electronics.  LED lighting runs off low voltage DC-I am wondering how long it will take before we start distributing DC in homes to LED lights vs AC to power supplies.  Probably a natural for the RV industry first.

Yes, I expect you are on target with this. All the distribution will still be done via AC, but when it comes into your home, instead of spreading the AC throughout like we do today, we may start to see DC distribution, or at least DC subsystems like lighting. Imagine all the lighting in your home being LED's and controlled by a central controller that you can simply plug additional lights and additional control switches into. I think there is a future there.

[Tim McCulloch]

Yes, I expect you are on target with this. All the distribution will still be done via AC, but when it comes into your home, instead of spreading the AC throughout like we do today, we may start to see DC distribution, or at least DC subsystems like lighting. Imagine all the lighting in your home being LED's and controlled by a central controller that you can simply plug additional lights and additional control switches into. I think there is a future there.

400Hz AC (like the US Navy used to use, may still) with imbedded "primaries" in walls & ceilings.  Secondary coil in the device.  Rectify at will.

[Art Welter]

Sure, it was next to impossible 20 years ago, and probably stinkin' expensive 10 years ago, but what would the numbers look like now? I have a solar cell manufacturer talking to me about building an RV camper totally "green" so you don't have to listen the the generator in the woods (without the rooftop air conditioner running, of course). So how long will it be for this sort of music production can happen "in a field"? Is it now, or 5 years, or 10 years, or what?

There have been viable solar powered stages available for over a decade, Alternative Power Productions has provided staging for the Vans Warped tours for many years. They seldom have to use the back up generator, entire tours have been done without turning it on. They list $5000 for two days stage/power rental, sound and lighting is additional.

When off grid solar power got it's start, 12 volt automotive lighting and sound was primarily used. As systems have become larger, the tendency has been for increased output voltages, 24, 48, 96 and even higher voltages employed, reducing cable losses and making DC/AC conversion more efficient. As far as homes being wired with DC, not going to happen, even off grid homes are usually wired only with 120v AC now since conversion efficiency has risen to the point where low voltage DC makes no economic sense.

Art

[Mike Sokol]

I heard this little battery powered pole speaker at my niece's wedding on Saturday. The ceremony was in a woodsy location where the nearest AC power was probably 500 ft away. So having any genny there would have been banned. It's made by Podium Pro Audio and includes a USB and SSD port for playing background music. Now, this wasn't super high fidelity or power, but for walk-in music and cocktail background tunes it was perfect. The DJ who brought them told me they would easily run 4 hours on a battery charge. The battery was so well integrated into the cabinet that the only hint of it was no extension cord running to the back panel. http://www.podiumproaudio.com/pp806a.html

Just one more example of how modern battery technologies are making gear like this possible.

[ProSoundWeb Community]