BillFitzmaurice.info

Leland provided the following formula:

You can calculate and test your amplifiers to limit them, if you don't have some kind of limiter in your PA rig. V=squareroot(W x R). To find the AC voltage for the maximum output you require from your amp, take the watts, say 400, multiply by the resistance of your speakers, say 8 ohms, then take the square root of the result.
V=sqrt(400x8). V=56volts. That would be 400watts into an 8ohm load.

I have acouple of questions I was hoping to get clarification on:

1. which watts (Peak, Program, Continuous.) referance from the speaker are using for the formula?

2. If we have two 8ohm speakers 400W in parallel turns into 4ohm, what about the watts is it now 800 for the two speakers combined?

Thank you!

1. RMS
2. Yes, but max voltage is unchanged.

Ryan A wrote:1. RMS
2. Yes, but max voltage is unchanged.

On a good amplifier 2. is true. On most, especially budget amps, the power supply can't keep up and voltage will drop when driving low impedance loads.

Please correct me if im wrong,

So if I have 400 speaker on 16ohm I i can go up to 80 volts anything below that wold be concidered "Safe" for the speaker, is that right?

why is it that most websites and stores such as guitar center do not use this method. it does not see to hard to get a grasp of.

I made these power look up tables so you don't have to do the math.

Hope you find them useful!

Or you can just go here for the calculation.

http://www.sengpielaudio.com/calculator-ohm.htm


To try and limit with a volume knob is foolish and will cost you more in speakers than a processor would cost.

TheCesar wrote: So if I have 400 speaker on 16ohm I can go up to 80 volts

Only if:
The limit as per the plans for each driver is 40V and you wire the two drivers in series.
And: to get your 16 ohms as a series load, you used 2 x 8 ohm drivers.

Regardless of parallel or series wiring, the "limit" is maximum voltage, so anything below that maximum adds further safety.

TheCesar wrote:why is it that most websites and stores such as guitar center do not use this method. it does not see to hard to get a grasp of.

Wattage is a larger value than voltage, so looks more impressive.
The watt is a power value. It can't be measured, it has to be calculated (Using a formula ie P=IV, where P is power in watts, I is current and V is volts).

When you set a voltage limit with your amplifier using a multimeter, you just have to measure voltage, not calculate watts, so it's much simpler...

Ian Westwood wrote:I made these power look up tables so you don't have to do the math.

Hope you find them useful!

That's a really nice site man!

88h88 wrote:That's a really nice site man!

Thanks!

Love the look up tables Ian!

I have a specific scenario I’ve been (theoretically) pondering, in regard to total potential number of LAB 12 T30’s I could load onto the following amp in respect of restraining the cost of amp purchases. Roughly speaking I’m thinking of a max total of 8 T30 cabs [to match with 4 tops].

http://en.synq-audio.com/product/267/DIGIT-3K6

but there is a big difference between the 8ohm and the 4ohm power rating of the amp, and it’s not obvious to me why it is so…? But it stuffs up the calc’s and substack to amp matching.

The scenario is explained in the sketch below:
2 cabs per channel seems fine (4ohm load and loads of power available for this specific amp – great!)
But at four cabs per channel, I don’t seem to be able to get less than an 8 ohm total load, and then one can’t get the power rating required (whereas at 4ohm the total power required (1250w) per channel would be well within the amps capability!)
Is there something I’m missing? Would I be unwise running 1 or 2 cabs per channel off an amp with this capability and ultimately get 2 of something smaller?
Even if you bung them all (8 cabs) on the one channel in bridge-mode then I can’t do the math to get an 8-ohm load out of 8 cabs! (where the power available at 8-ohm is 3600W). It ends up back at 4-ohm.

I would advise noone to run all their cabs of one amp or amp channel. If one of your drivers dies in a series parralel configuration you will screw up the whole line.
And if you want to run 4 ohm bridge mode you need a diffrent kind of amp.

My advise would be to get 2 smaller amps and run 2 cabs parallel per channel. With Lab 12's this would already give you a nominal 3ohm load. Or if you need max power and durability, on a budget, with the option of running 4 cabs parallel per channel look for something like http://www.thomann.de/nl/tamp_proline_3000.htm. just a little heavier than the synq

37kg is obscenely heavy

Are T-Amps rated as high quality solid bits of kit then?

88h88 wrote:37kg is obscenely heavy

That's a nice option. If one is manual handling 8 subs anyway, 37kg is not a big deal if it's in a smallish package. If one can get it in and out of the car safetly, then a truck can be used - I got one of these from Costco for under £20:
http://www.costco.com/Magna-Cart-Person ... 53765.html

Or this for a little bit more money, and only 5kg...?:

http://www.theaudioworksuk.com/index.ph ... ifier.html

88h88 wrote:37kg is obscenely heavy
Are T-Amps rated as high quality solid bits of kit then?

I think most of them are rated "good value for money". Should be plent to run 2 a channel.
But the Proline is a real monster, specs are conservative, and one of the cheapest high power amps you can get in Europe. Made in China, but high quality and with 3 year warranty.



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