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Title: Best gear to produce a lot of sound without "shore power"
Post by: Frank DeWitt on July 26, 2014, 11:29:52 am
Mike brought up Inverter vs conventional generators for running switching power supply powered speakers.  I thought I might learn something if we spread it out a bit.

The goal is to amplify the output of a mixer a lot so many people can hear it outdoors.  You must bring your own power.

It seems that there are three places that choices are needed.
Power source  Inverter generator,  Conventional generator,  Batteries

The amp or amps could be old school power supply. switching power supply or 12 volt DC input amp

The speakers could be popular speakers used today or some sort of high efficiency box.

For example,  Would it help to modify an amp by adding very large capacitors to the rails (In a professional manor, to a old amp that had no warranty and volunteered for the test.)

Would it be more efficient to use deep cell marine batteries and amps made for automotive use?

Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Jordan Wolf on July 26, 2014, 12:28:39 pm
Frank, I remember hearing that one of the Danley Sound Labs passive loudspeakers (Jericho?) has been driven by only an iPod.  Can't seem to find it via a web search at the moment...
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 26, 2014, 01:01:24 pm
Frank, I remember hearing that one of the Danley Sound Labs passive loudspeakers (Jericho?) has been driven by only an iPod.  Can't seem to find it via a web search at the moment...

On that note, when I was a wild child back in high school in the early 70's I had a pair of Altec Lansing Voice of the Theater cabinets for my band. Yes, these were the ones with the big 500-hz horns on top. I would leave them in the back of my van and hook them up to my Channel Master 8-track player with all of 5 watts output per channel. That small amount of power though a very efficient speaker cabinet was enough to get us kicked out of any McDonalds parking lot we wanted to terrorize. Sorry I don't have an official SPL reading, but it was loud enough to compete with the Thrush mufflers and cut-out pipes of the day.  ;D

So to design your off-the-grid sound system I think it's best to pick a really efficient speaker then work your way upstream to the power source, not the other way 'round. Once you pick the initial crowd size and SPL level, you can predict just how many speakers you need for coverage. And yes, the music style has a lot of do with this since bass takes a lot of wattage from the power source.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Frank DeWitt on July 26, 2014, 01:15:24 pm
a pair of Altec Lansing Voice of the Theater cabinet hook them up to my Channel Master 8-track player with all of 5 watts output per channel.

So you honestly think that a pr of voice of the theater cabs with 10 watts in could compete with a Behringer B207 with "150 watts"?

I do, as well.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Art Welter on July 26, 2014, 04:15:59 pm
So you honestly think that a pr of voice of the theater cabs with 10 watts in could compete with a Behringer B207 with "150 watts"?

I do, as well.
The Behringer B207 is rated at 116 dB output from 150 watts, which implies about an 84 dB one watt one meter sensitivity.
An A-7 cabinet is about 103 dB sensitivity midband, so one could produce around 110 dB from 5 watts, a pair with 10 watts would do 116 dB.
The pair of A7 would require only 1/15(6.66 %) of the power to achieve roughly the same level as the little speaker.
Large, multi- driver horn loaded speakers can further increase sensitivity by another 10 dB, either getting twice as loud, or lasting 10 times longer yet on the same power. In the low frequency range, the sensitivity of large, multiple driver horns could easily use 100 times less power than the little speaker for the same SPL.

As far as capacitor storage, they can reduce peak power demands on batteries, which reduces the Peukert's effect which is a big problem with small lead acid batteries. Peukert's effect, simply put, is when too much amperage is pulled from a battery it's voltage will drop (causing a "brown out"), the voltage then slowly returns to it's former level after the battery rests. The battery "pukes out" in use, normally not a problem in a car application where power is being provided from the alternator. Still, even with capacitor storage, the average power used remains the same, and capacitors are not cheap.

I am using  GBS-40Ah batteries from http://evolveelectrics.com/GBS.html for my electric motorcycle.

Four in series are nominally 12.8 Volts,  weigh only 12.4 pounds, cost $248.
The amazing thing is you can pull peaks of 400 amps out of the pack with hardly any sag.
You can get by with much lower rated Ah (amp-hour) LiFP04 than lead acid because they have virtually no Peukert's effect, and the same battery weight gives like 10 times the performance.

As an example, 72 pounds of AGM lead acid batteries dropped to a 40% charge after only 4.2 miles (the bike started limping along), while 52 pounds of LiFP04  went 39 miles. Other than expense, the problem with LiFP04 is they can be permanently damaged from too deep a discharge, and because they exhibit almost no Peukert's effect, they perform almost the same until they are dead, with a much tighter range of voltage over the entire discharge cycle.

As far as whether to use amps made for automotive use, or an inverter and high voltage amps, it would depend on the output requirements. On the smaller scale, eliminating the inverter reduces one stage of loss, while on a large scale the loss of power in the inverter may be offset by efficiencies gained from higher voltage operation. That said, with a good battery bank providing power to some good high power car audio amps in to speakers with 110 dB sensitivity, a large space could be covered at concert levels for hours.

Art
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Scott Helmke on July 29, 2014, 11:26:18 am
Frank, I remember hearing that one of the Danley Sound Labs passive loudspeakers (Jericho?) has been driven by only an iPod.  Can't seem to find it via a web search at the moment...

That first watt is always the loudest... after that it's diminishing returns.

Danley speakers are *very* efficient, though. Well worth a look if you're trying to get the most out of limited power.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 30, 2014, 06:50:56 am
That first watt is always the loudest... after that it's diminishing returns.

Danley speakers are *very* efficient, though. Well worth a look if you're trying to get the most out of limited power.

We often forget that early sound systems from the 60's and 70's had very small amplifiers, with a pair of 6L6 tubes pumping out all of 40 watts. And an Altec A7 VOT cabinet driven by a 40 watt amplifier was significantly loud. Once big amplifiers became relatively cheap (Phase Linear was one of the first IIRC), then speakers became less efficient (Bose 901s and their spawn). So comparing watts to watts on speakers is pretty useless unless you consider speaker efficiency as well.

I also built a pair of JBL double 15" scoops around that time, and drove them with a Dynaco 400 amplifier rated for 300 watts per channel at 4 ohms IIRC. That made a LOT of bass in small clubs which I needed for my Mini-Moog's low notes. Those were the days...
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 30, 2014, 08:33:40 am
The goal is to amplify the output of a mixer a lot so many people can hear it outdoors.  You must bring your own power.

I'm going to up the challenge a bit and suggest that you also need to consider stage lighting as well for your OTG (Off The Grid) system. So let's say you wanted to create a weekly "green" outside concert series that was only powered from the solar cells you use for recharging your batteries during the week. Just how many solar cells  and batteries would you need to have a decent concert on Saturday night? Limiting the musicians to low power backline gear such as Line-6 guitar and bass pedals would be a start. And certainly LED lighting for a 3-hour show wouldn't draw too much power. Efficient speaker and amplifier selection would be very important as well. Could you get a decent 100 dB SPL concert mix for a few thousand people in a "Green Shed" powered by nothing but sunlight?
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Cailen Waddell on July 30, 2014, 08:58:35 am

I'm going to up the challenge a bit and suggest that you also need to consider stage lighting as well for your OTG (Off The Grid) system. So let's say you wanted to create a weekly "green" outside concert series that was only powered from the solar cells you use for recharging your batteries during the week. Just how many solar cells  and batteries would you need to have a decent concert on Saturday night? Limiting the musicians to low power backline gear such as Line-6 guitar and bass pedals would be a start. And certainly LED lighting for a 3-hour show wouldn't draw too much power. Efficient speaker and amplifier selection would be very important as well. Could you get a decent 100 dB SPL concert mix for a few thousand people in a "Green Shed" powered by nothing but sunlight?

It would be all about the solar array and batteries then....   Give me an acre of solar panels and we are good to go .   

Seriously though - would you give thought to a grid tied system to eliminate the batteries?   With appropriate solar cells, you could potentially make the concerts free with the electricity offset....
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Chris Hindle on July 30, 2014, 09:05:08 am
I'm going to up the challenge a bit and suggest that you also need to consider stage lighting as well for your OTG (Off The Grid) system. So let's say you wanted to create a weekly "green" outside concert series that was only powered from the solar cells you use for recharging your batteries during the week. Just how many solar cells  and batteries would you need to have a decent concert on Saturday night? Limiting the musicians to low power backline gear such as Line-6 guitar and bass pedals would be a start. And certainly LED lighting for a 3-hour show wouldn't draw too much power. Efficient speaker and amplifier selection would be very important as well. Could you get a decent 100 dB SPL concert mix for a few thousand people in a "Green Shed" powered by nothing but sunlight?
Sure. What's the battery budget.... Hope you have deep pockets....
I participated in an experiment a few years back. Before LED lighting really took hold.
There's gonna be some big-ass solar cells to get those babies charged up. Around here, I would count on 3-1/2 to 4 days of full sun per week. Just means more cells, and more batteries.
"Green" and "Off the Grid" all sounds fine and nice on paper. Then the realities sink in..... Nothing beats a 25KW sitting behind the charger shed, just in case...
SunSparky estimated our loads, and figured we'd be good for 4-5 hours. (sorry, don't remenber the VA he came up with)
After an hour's worth of showtime, squints went to Jenny. After the next band changeout, so did audio.
SunSparky was, ahh, "puzzled" to say the least.
I'm guessing he calculated based on a steady state draw. A live show is anything but.
The sun/battery rig was "retired" from R&R and did sponsered dinner party / background canned music type stuff, where it worked very well.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Frank DeWitt on July 30, 2014, 09:42:53 am
Green venues bring people from far and wide so you will be limited on the size of the solar array because of the size of the parking lot you will need.  Figure extra spaces for the Hybrid only parking.  Parking spaces for vehicles like the Chevrolet Tahoe Hybrid need to be large.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 30, 2014, 10:51:58 am
Sure. What's the battery budget.... Hope you have deep pockets....
I participated in an experiment a few years back. Before LED lighting really took hold.

My point is that as newer low-energy products such as LED lighting and switched power supply amps get more common, solar panels become more affordable, and battery technology improves, how close are we to doing something like this without breaking the bank. 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? I did a little play over the winter with a bunch of LED lighting fixtures (maybe 16 total) powered by a single 15-amp outlet. That was pretty impressive since I didn't have to run feeder cable from a genny in the parking lot due to the fact that the electrical system in the building was really old and limited.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Tim McCulloch on July 30, 2014, 11:16:03 am
It depends on artist requirements and audience expectations.  I think we could do Traveling Shakespeare In the Park on a 20 amp circuit for both sound and lights (LED lighting).  We used to do it with 3 circuits with lighting on all 3 and sound on the least-loaded circuit; the lighting was pretty dismal.

I don't think we'd get away with that for the Husker Du reunion... Oh, wait, Bob Mould said that would require lawyers on stage... never mind.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Guy Holt, Gaffer on July 30, 2014, 02:42:30 pm
… choices are needed. Power source  Inverter generator,  Conventional generator,  Batteries …

The primary factors limiting the use of non-linear loads on portable generators are their inefficient use of power and the harmonic currents they generate. Because of their radically different designs, inverter generators, like the EU6500is, and conventional AVR generators, like the ES6500, react very differently to these factors. The harmonic currents generated by non-linear loads, in fact, have less of an adverse effect on inverter generators than they do on conventional AVR generators and so do not require de-rating as conventional AVR generators do.

Harmonic currents cause two major problems in conventional AVR generators: heat and voltage waveform distortion.  The first problem is that harmonic currents generate heat in the windings, core, and in the electromagnets of the rotor of conventional AVR generators. Since generator ratings are limited by allowable temperature rise, harmonics act as derating factors. In derating, the magnitude of the current is of obvious importance, because losses are proportional to the square of the current. Increased frequency causes increased core losses and increased copper loss from skin effect. 5th and 7th harmonics are the offenders here because they are in the 600 Hz range.

The second difficulty caused by harmonic currents is voltage waveform distortion. According to Ohm’s law, as each harmonic current encounters the impedance of the power distribution system, it will cause a voltage drop at the same harmonic voltage. Because, the capacitors of switch mode power supplies only draw current at the peak of the voltage waveform, this voltage drop occurs only at the peak of the voltage - leading to a flat topping of the voltage waveform.

The more harmonic content in the current, the more voltage distortion occurs throughout the distribution system. This includes the output terminals of the generator where the generator’s source impedance (particularly the subtransient reactance or “Xd”) will create the greatest voltage drops. If the flat topping distortion at the generator’s output terminals is severe, it can cause voltage regulator sensing problems (Self-Excitation or SE) and inaccurate instrument readings.

The effect that harmonic currents have on the generators is factored into the rating limits given them. How rating limits are affected by load can be illustrated in a “Limit Characteristic” graph that plots kVA and kW versus Power Factor. The fluctuations in the kVA line in the illustration below represent the generator’s operating limits depending on whether its load has a leading or lagging Power Factor. It is important to note that a generator’s Limit Characteristic graph will vary by the type of generator. The illustration below (courtesy of Caterpillar) is for a conventional AVR generator. Since the power quality of an AVR generator is intractably linked to its' engine - the effect of harmonics on the engine's governing system is the primary limiting factor. How the engine and its' governing systems are affected by lagging and leading power factor loads is illustrated by the engine kW limit line below.

(http://www.screenlightandgrip.com/images/generators/R_Gen_Rating_Limits.jpg)
A Limit Characteristic graph for a generator illustrates the effect of leading
or lagging Power Factor on the generator's output.
 

What this generator’s Limit Characteristic graph tells us is that, operating a capacitive non-linear load (the leading power factor quadrant right of the Unity Power Factor center line), this AVR generator first reaches a thermal limit as a consequence of heat generation in the generator's rotor from harmonic currents. And since, conventional AVR generators regulate voltage by means of a power feedback loop from the generator Stator (via the Sensor Coil), through the Exciter (Voltage Regulator), to electromagnets in the Rotor, Armature flux generated by harmonic currents in the Stator leads to erroneous Self-Excitation (SE) and therefore voltage. Put simply, lower power factor loads cause instability of the generator’s voltage output. Finally, since there comes a point as the Power Factor of the load decreases, when harmonics inhibit the successful operation of the generator’s Automatic Voltage Regulator all together, and hence the generator’s capacity to generate any power at all, the kW output eventually drops to zero. Since the voltage instability in conventional AVR generators is a function of the non-linear loads they power, the conventional wisdom is to limit the amount of non-linear loads it can power by roughly half of the generators capacity.

(http://www.screenlightandgrip.com/images/generators/EU_Gen_Rating_Limits.jpg)
The Limit Characteristic graph for an Inverter generator.
Note the negligible effect that leading Power Factor loads have on the generator's power capacity.
 

As the Limit Characteristic graph for an inverter generator above illustrates, it is a completely different situation with inverter generators. Because the speed of the motor is always changing, inverter generators cannot maintain voltage output by the conventional means of regulating the excitation current in Rotor electromagnets. Instead, inverter generators use permanent magnets in place of electromagnets. 
A permanent Magnet is an object made from a material that is naturally magnetized (Neodymium in this case) and hence creates its own persistent magnetic field. Since permanent magnets do not require an excitation circuit, armature flux created by harmonic currents will not cause voltage instability as it does in conventional AVR generators.

(http://www.screenlightandgrip.com/images/generators/waveform_elec_ballast_AVR-I.jpg)
Left: Conventional AVR Generator w/1200W non-pfc electronic ballast. Right: Inverter Generator w/1200W non-pfc electronic ballast.

And since the generator’s inverter completely processes the raw power generated by the permanent magnet (converting it to DC before converting it back to AC by means of a micro-processor), the AC power it generates is completely independent of the engine. By switching IGBTs according to Pulse Width Modulation control logic, an inverter generator is much better able to sustain output voltage against transient loads and, therefore, it has a much lower internal reactance compared to conventional AVR machines. Finally, since the Impedance encountered by harmonic currents that causes voltage waveform distortion is a function of the internal reactance of the generator’s engine to changes in load, a second benefit to using permanent magnets in place of electromagnets in the generator’s Rotor is that as is evident in the oscilloscope shots above, inverter generators consequently are much less susceptible to voltage waveform distortion.

 
(http://www.screenlightandgrip.com/images/generators/Inverter_Gen_Comp_Chart.jpeg)
TABLE COURTESY OF KIRK KLEINSCHMIDT.

The end result is that leading power factor loads do not cause voltage regulation errors in inverter generators as they do in conventional AVR generators. Inverter generators are able to hold their voltage stable within ±1% of the mean voltage, as opposed to the ±3% of conventional generators using analogue AVRs and are much less susceptible to voltage drop and AC Frequency (Hz) as a function of load (see table above.) 

The rock solid power and low sub-transient impedance of inverter generators enable you to operate larger non-linear loads on them than can be operated on conventional AVR generators. For instance, we have struck 6kw HMI Pars on a modified Honda EU6500is inverter generator without problem.

These power quality issues have been vexing film electricians for years, to learn more about how we have learned to remediate the adverse effects of harmonics read a white I have written on the use of portable generators in motion picture production available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.

Guy Holt, Gaffer
ScreenLight & Grip
Lighting Rental and Sales in Boston
Cell 617-224-85634
rentals@screenlightandgrip.com
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Art Welter on July 30, 2014, 04:22:42 pm
I'm going to up the challenge a bit and suggest that you also need to consider stage lighting as well for your OTG (Off The Grid) system. So let's say you wanted to create a weekly "green" outside concert series that was only powered from the solar cells you use for recharging your batteries during the week. Just how many solar cells  and batteries would you need to have a decent concert on Saturday night? Limiting the musicians to low power backline gear such as Line-6 guitar and bass pedals would be a start. And certainly LED lighting for a 3-hour show wouldn't draw too much power. Efficient speaker and amplifier selection would be very important as well. Could you get a decent 100 dB SPL concert mix for a few thousand people in a "Green Shed" powered by nothing but sunlight?
The intensity level of lighting, SPL desired and efficiency of both lighting and sound are primary considerations.
If lighting were done at a "moderate" level, say using thirty 25 watt RGB LED lights, only about 1050 watts would be required, assuming it takes 35 watts per 25 watt unit (which is what the RGB LED lights I use draw).
Sound and stage power could be run using less than 2000 watts average with an efficient sound system and moderate stage gear and achieve over 100 dBC for a few thousand people. I found out that for fact when a miswired guitar amp tripped a breaker, the single breaker served four separate quad receptacles which I had assumed (duh) were on separate breakers, killing the sound system as well as the stage power  :o.

In a high insolation area as we have in the summer here in the Santa Fe and Albuquerque New Mexico, allowing for loss in the inverters and battery storage, a system with around thirty 100 watt panels, about 235 square feet (only a fraction of the area of a 30' x 40' stage roof) could provide continuous daylight operation of both sound and light systems.

Depending on insolation and battery storage size, between one to several days of charge could provide all the power needs for a "Green" show. For shows using tons of video screens, incandescent lighting, a stage full of tube amps, and low efficiency main speakers the power demands would be several orders of magnitude greater.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 30, 2014, 05:03:08 pm
Depending on insolation and battery storage size, between one to several days of charge could provide all the power needs for a "Green" show.

So just as a WAG for battery size, if we assume 4KW average use during a 3 hour show (your 2KW for FOH speakers, 1 KW for lighting, and maybe 1KW for losses, backline power and monitors) that could be 40 amps total (rounding up) at 120 volts, which would become 400 amps at 12 volts (yeah, there will be additional losses, but this is a WAG). So that's 1,200 amp/hours worth of 12-volt batteries at 100% discharge. I think the general rule of thumb is not to exceed 50% of battery amp/hour capacity, so that will require 2,400 amp/hours worth of 12-volt deep-cycle batteries.

Trojan makes a L16RE-A 325 AH Deep Cycle Battery at 6 volts, so that's 8 x 2 batteries needed (gotta series stack the 6 volt batteries) for a total of maybe 16 batteries at $300 each (total maybe $5K) to power a 3-hour show you described. Or you could just get one big fork truck battery and do the entire show. Your backup power could be a single EU6500 generator or maybe a pair of EU2000s which is certainly doable.

Also, I think at least some LED stage lights have a 12-volt DC option, so that could eliminate some of the inverter losses for lights, but maybe that would increase the line losses due to voltage drop. Argh...

So Frank's original idea isn't out of the question even after I added LED lights and backline power, and could be feasible as a promotion of battery, solar cell and inverter technology. Hey, we could even throw a wind turbine up on the roof to make the wind generator guys happy as well.  8)

Now I'm not seriously proposing this project. Just musing over how high efficiency sound and lighting technology could make such a thing possible.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Josh Millward on July 30, 2014, 06:24:12 pm
Frank, I remember hearing that one of the Danley Sound Labs passive loudspeakers (Jericho?) has been driven by only an iPod.  Can't seem to find it via a web search at the moment...
That was at InfoComm2013.

The loudspeaker was Caleb. Ten feet tall, four feet wide, and five feet deep I think... it may have been five feet wide and six feet deep... No details on the website about Caleb.

Anyway, yes, they took the mini-plug output from an iPhone, hardwired it into all the circuits on an NL-8 connector, and played music through the thing with no crossover filters or anything. It was an amazing exercise in efficiency.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Barry Singleton on July 31, 2014, 12:25:51 am
  I think about this often since Craig Leerman brought it up in a post a while ago.

  I have several Middle Atlantic 2200VA two rack space UPS units that can be connected to external 48V battery packs to add capacity/run time to the internal batteries. I want to series four Optima's and see how long one of the smaller sound rigs would run on just that.

  I haven't done any measurement or math yet but plan on trying it when the weather breaks.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 31, 2014, 08:22:24 am
  I think about this often since Craig Leerman brought it up in a post a while ago.

  I have several Middle Atlantic 2200VA two rack space UPS units that can be connected to external 48V battery packs to add capacity/run time to the internal batteries. I want to series four Optima's and see how long one of the smaller sound rigs would run on just that.

  I haven't done any measurement or math yet but plan on trying it when the weather breaks.

Something like that would be very interesting. Of course, you could also stack eight of the 6-volt Trojan batteries for 48 volts. I often get requests for battery powered systems to do gigs like outside weddings in a park or a ground breaking ceremony. I have a Diehard 600-watt battery/inverter pack that does a reasonable job of powering a Fishman Line Array speaker for up to 2 hours, but there's a little buzz in the speaker from the inverter harmonics. That's works fine for what it is, but your setup might be able to power a small band in a remote area for an hour or two without a genny running.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Frank DeWitt on July 31, 2014, 10:01:52 am
there's a little buzz in the speaker from the inverter harmonics.

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.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 31, 2014, 10:49:00 am
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 (http://www.fishman.com/product/sa220-solo-performance-system)
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on July 31, 2014, 11:12:51 am
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.   
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Frank DeWitt on July 31, 2014, 11:50:18 am
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
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Tim McCulloch on July 31, 2014, 11:51:12 am
I think the key to Frank's OTG (Off The Grid) system is speaker efficiency.

This. Right. Here.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Frank DeWitt on July 31, 2014, 12:02:14 pm
This. Right. Here.

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

(http://www.reocities.com/ec1288/images/schematics/Altec825.jpg)
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Stephen Swaffer on July 31, 2014, 01:40:56 pm
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.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Josh Millward on July 31, 2014, 02:16:25 pm
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.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Tim McCulloch on July 31, 2014, 03:16:40 pm
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.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Art Welter on July 31, 2014, 03:43:44 pm
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
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on August 04, 2014, 09:30:54 am
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 (http://www.podiumproaudio.com/pp806a.html)

Just one more example of how modern battery technologies are making gear like this possible.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Stephen Swaffer on August 04, 2014, 11:40:49 pm
I was looking really hard at a similar unit by MiPro last spring-it even has built in wireless mic receivers.  Just need the money-but looks like it would serve our need for a very portable PA for BGM music and an MC mic quite well.
Title: Re: Best gear to produce a lot of sound without "shore power"
Post by: Mike Sokol on August 05, 2014, 07:13:30 am
I was looking really hard at a similar unit by MiPro last spring-it even has built in wireless mic receivers.  Just need the money-but looks like it would serve our need for a very portable PA for BGM music and an MC mic quite well.
Yeah, the MiPro stuff does look pretty interesting for this sort of gig. A pair of them with the wireless mic option would be really useful for outside weddings needing walk-in music and PA. http://www.mipro.com.tw/p4_en.html?gid=274 (http://www.mipro.com.tw/p4_en.html?gid=274)