Parade Float - Power

[bzb]

Small update!

Sister went to Home Depot to chat with them about a potential discount - turns out they've been renting out the trailer for the float for free since it's for the local school. They're going to throw in the generator, as well!

Honda EU 2000i should be plenty, I've run a gig at a park on one of those a couple times (always able to get it about 50 feet away, though).

[byacey]

A typical amp of around 1200w output will draw a quiescent current around 500 to 750ma @120V.

I've been poking around inside a Crown K2 amp recently, and it's a very interesting output topology. It essentially shuts down until the input sees signal; it'll do 800W/channel @ 4 ohms without a cooling fan.

[bitSmasher]

Whilst this has been resolved (somewhat) - you'd be very surprised at how loud you can go with decent 12/24v dc amps - Can get 70% of the impact with 3% of the power (throwing around bs numbers since the audio world is full of them)

An efficient speaker with efficient amp gives great results - Something like Sure Electronics TK2050 or a Class D car amp, use decent processing/EQ (ie MiniDSP) to high pass relatively high and save on power... playing around with these sort of things will quickly highlight how the ***KW numbers thrown around for power handling doesn't mean that much when you can be just as noisy with a lot less effort

[byacey]

I suppose depending on how loud and clean you want the audio, a 12V amp is a possibility if you have the necessary equipment on hand. You are still looking at huge amounts of current at 12 VDC if any kind of audio power is required.

However, for a one time or even once a year use, it's simpler just to use real amps and processing powered by an AC power plant.

[Ryan A]

It all comes down to the logarithmic nature of sound and our ears.

It takes 10 times the power to have twice the perceived loudness.

By the same token, 1/10th the amplifier power is a lot louder than you may think it should be.

Most people don't watch power meters when listening to music so they don't realize the sound/power relationship.

[ncgrove]

It all comes down to the logarithmic nature of sound and our ears.

It takes 10 times the power to have twice the perceived loudness.

By the same token, 1/10th the amplifier power is a lot louder than you may think it should be.

Most people don't watch power meters when listening to music so they don't realize the sound/power relationship.

Yep. 1 Watt is a lot. 10 Watts is a whole lot.

[Grant Bunter]

I first noticed this when playing the drums, thinking:
'I can get quite a bit of sound out of this kit just letting the sticks bounce, but I have to start whacking really hard to get a substantial increase in volume!'

Hah!
My "main" kit, a Pearl Pro kit I bought in the 80's, gets stooopid loud without much effort at all.
This is good in some ways, playing with dynamics is much simpler and you don't end up as tired after a 4 hour gig.
However, my early 70's vintage kit (also Pearl) isn't as loud, ever.

It's a myth that hitting drums harder makes them louder, after a point. The law of diminishing returns applies to all acoustic drums, and you can't make them go louder than they will just because you hit them harder...

[DJPhatman]

It's a myth that hitting drums harder makes them louder, after a point. The law of diminishing returns applies to all acoustic drums, and you can't make them go louder than they will just because you hit them harder...

But you can make them sound better and keep time if you hit the drummer harder... just sayin'...

[escapemcp]

I was investigating interter gennies myself a few months back. I was trying to find out how big a genny I would need for a class D amp. I had a hell of a time trying to find any info. I was worried because the inverter gennies use a microcontroller board to control their output and because of this, they can 'overload' themselves quite easily with only a very quick peak over and above their rating.

Now due to the nature of class D amps they can draw barely any current one moment, and then LOADS the next. Although this may average out to say 1000W, at certain moments they may be pulling far in excess of this figure (see page 6 of this review of my very amp - power is quoted at 350W, yet the test recorded moments where the amp was pulling 1600W!: http://www.behringerdownload.de/_pdf/To ... _Rev.0.pdf). Watts is a function of time and all amp specs will quote the average operating wattage over a reasonably long time (RMS). They do not state (usually) what the PEAK power drain figure is. This causes a problem on our poor little inverter genny, as with these if it goes over the max figure programmed onto the microcontroller (on the inverter board), then the genny goes into 'overload' and you lose all power A normal genset's circuit breaker wouldn't have time to react to this momentary peak, so it ploughs on with maybe a small cough!

It isn't actually the class D amp that causes this, but rather the SMPS (switch mode power supply). These work differently to normal PSUs which will draw more power when the voltage differential rises and less when it is around 0V, therefore only really taking power when it available. If the SMPS has PFC (Power Factor Correcton), then it kind of emulates this a little closer, preferring to draw power then the voltage is high (and most when it is up near the PEAK of 325V (on European 230V rms) or 155V (US 110V rms)) rather than when it is on or around 0V, this helps not trip the genny so easily. I think this is down to the low power factor when the voltage is low in it's 50/60Hz cycle, but not 100% on that (or the rest of this tbh! ).

It is often when switching on the amp that you get the highest power drain... this is called inrush current and when I switch on my iNuke3000, my regular genny coughs momentarily and then resumes. In my house on mains power the lights dim for a fraction of a second when I hit that on switch! Some amps have inrush current limiting (thinking PKN monster amps here, but there may be others) which reduces this and doesn't try charging up all the circuits in an instant. This would be good on any genny (and the mains tbh), but it can be this inrush current that could overload your inverter genny before you have even made a single dB! It is often the switch on that pulls the most current (I think) because it is charging all the empty caps.... in use, the caps are rarely drained of ALL their juice, so it never needs to pull as much as during switch on.

I am writing all this from memory as this is what I discovered when I was researching (for about a week!) buying an inverter genny. Anyway, the point is after all this research, I FINALLY found the figure that I was looking for in that it was recommended that your genny be sized 2.6x what your SMPS will need (rms(=manufacturer specs on power draw)) to avoid an overload condition. E.g. if your amp spec say it draws 1000W, you need a 2.6kW inverter genny to handle the load without any risk of the overload light going on.

I think I have got this right ... the figure of 2.6x is definitely right. I accept any corrections with humility if anyone wants to chime in, but I thought it worth sharing my research with you good folks here at BFM in the hope it will save someone else a week of their life researching this (which you can put to good use by building an Otop )

[escapemcp]

BZB - do you use class D amps? Can you test this?!!! I'd really like to know if you can overload it and with what load. An inverter genny is still on my wish list (although it has slipped a few places down now that I have a regular genset).. I'd love to know if it is still an option or not. Skills on the blag by the way... saves money so you can make more for your cause

As another sidenote, I always liked the idea of the inverter genny due to the same 'overload' condition... I knew that no sagging power would ever hit my iNuke if I used one... it's either 230V or 0V... nothing inbetween like with a normal genny (where I watch the petrol tank like a hawk to avoid any 'hunting').

[Grant Bunter]

But you can make them sound better and keep time if you hit the drummer harder... just sayin'...

Good one!
You do know that drummers are generally a fiesty lot and hit back though....

[escapemcp]

Hey, here it is... FOUND IT... point #4 (although you might as well read the lot if you have made it through my meanderings!)

http://www.samlexamerica.com/support/faqs/faq15.aspx

Shit... wish I found that before I typed all of my post... pretty well says what I did in far less words. There's even a mention of our old friend 'crest factor'

That took me an hour to write... I could have had panel 2 on by now... better get back in the garage, it's definitely being attached tonight!

[Grant Bunter]

escapemcp,
interesting be your calculations and research.

I ballparked, and bought a 7Kva (5600W) non inverter genny for my rig.
While you do get some sag from inrush current, as exhibited in your amp, it's nothing like what's required to turn over a compressor that first turn. My old 2Kva genny wouldn't run the compressor or a welder.

Still, I think 2Kva for a Lepai amp, or even a pair (one for subs, one for tops) should be plenty...

[byacey]

A typical amp of around 1200w output will draw a quiescent current around 500 to 750ma @120V.

So that's AT LEAST 60 watts, even reproducing background levels? Most 'stand and event' music can be done with the amp out of a pair of PC speakers.

Nope; Quiescent means idling, no signal. Depending how it's biased, it may even draw around 1 amp. That's 60 to 120 watts of heat dissipation before you start putting any signal to the inputs.

I don't know what a "stand and event music" is, so I can't offer much comment. I would question the power amp ratings provided by the manufacturer for PC speakers. Many of the cheapo units powered by a 12VDC wall wart probably max out around 8 watts per channel.

[Jerry Caldwell]

If your playing pre-recorded audio, why not use a automobile type amp? You may be able to borrow one from some of the people involved or hit eBay... 1KW is not a real big deal in automotive audio- lots of mono block class D amps available for a couple hundred and less- I've been shopping recently. I'd search a few out and read the reviews and run with it. You could use a battery in the back of the truck or on the trailer and then route power to the amp from there. You can pick up a decent 8 guage "audio install kit" for a reasonable cost to provide constant moderate current to the remote battery and then use the 4 guage to go from the remote "buffer" battery to the amp. Only major consideration that I can think of that would be commonly overlooked is a sure ground connection between the frame of the trailer and the truck- bada$$ jumper cables zip tie-secured in a pinch... There are other considerations too, but this may end up being a viable and time / cost / PITA reducing solution. Find someone who has a sub amp with a defeatable crossover, ask them if you can hook you rig up behind their trunk and see if it does what you require.

eBay the amp when done or load up four AT's and loose some serious hearing...

Go easy guys, don't flame me too much.