Conversion for limiter dB to Watts

Pscribby

In my system, one of my monitor banks has an amp output which exceeds the max power rating of the monitors in that bank by 65 watts. I want to use the limiter to prevent speaker damage. I have done a little Googling and there are formulas out there for this, but usually additional parameters are needed (ie: dB referenced to what? millivolts, etc?).

My driverack PA2 is feeding a Crown XLS1500. (there's much more in the PA, but the bank in question is just the driverack, then amp, then monitors).

My desire to limit is not to prevent clipping (I've already got a well balance gain structure set up - DR limits about same time occasional clip lights up on amp, per procedure in the manual)... my desire is to limit max power to amp to protect monitors (which aren't mine).

I get how to use the limiter, but I don't know how to translate a limit threshold of, say, -XdB to equivalent Watts reduction at amp ouput.

I am thinking that limit threshold of 0dB means no limiting... so, in my set up, max amp output is 265 in my configuration (2 - 8 ohm cabinets on channel 1 of XLS1500). So, if I want to target 200 max amp out, then I can convert that to a ratio (200/265) so I want to limit to roughly 75% of unlimited output. It's been years since college and I don't use the algebra for log scale stuff anymore, but I seem to remember that 6dB was a doubling/halving of signal.... so is -3dB the number I'm looking for? Also, I know that power is actually volts^2 X amps... so would it actually be sqrt(3)? (I think so). If my assumptions and math are correct, then I would want to limit to -1.7 dB... however, that's not the same thing as the limit THRESHOLD, is it?

I think I'm in the ballpark with my understanding above, but I want to be sure, so am asking for any help from someone who is sure...

Thanks for any assistance!

Dra

What are the Con/Prg/Peak rating for the monitors? Where do you have them high passed?

DRA

Pscribby

Dra wrote:

What are the Con/Prg/Peak rating for the monitors? Where do you have them high passed?

DRA

These are old Peavey PV115TI monitors... they only state "Max Power: 200W". The are running full range from DriveRack. (internal passive crossover between horn and woofer, of course)...

Dra

Is this it?
http://assets.peavey.com/literature/man ... 301940.pdf

If that is it, then you can assume 100/200/400. I would not be concerned over 65w... especially if you add a HPF between 800 and 100hz. If it is a vocal / guitar monitor then 100hz would be plenty low enough. Some folks will go as high as 120hz. Cleaner and louder on the stuff you need, without the added stress (and heat / power) of reproducing the lower content.

Threashhold should only be considered as it relates to actual output.
If you truly want to limit at 200w, then you need to actually measure the equivalent in volts coming out of the amp.
400w @ 4 ohms = 40v
200w @ 8 ohms = 40v

So, 40 volts is your goal.
(You need to be aware that if you ride the limiter, the peaks only are stopped, but the continuous power push right up to the limit...causing overheating.)

DRA

Pscribby

Dra wrote:

Is this it?
http://assets.peavey.com/literature/man ... 301940.pdf

If that is it, then you can assume 100/200/400. I would not be concerned over 65w... especially if you add a HPF between 800 and 100hz. If it is a vocal / guitar monitor then 100hz would be plenty low enough. Some folks will go as high as 120hz. Cleaner and louder on the stuff you need, without the added stress (and heat / power) of reproducing the lower content.

Threashhold should only be considered as it relates to actual output.
If you truly want to limit at 200w, then you need to actually measure the equivalent in volts coming out of the amp.
400w @ 4 ohms = 40v
200w @ 8 ohms = 40v

So, 40 volts is your goal.
(You need to be aware that if you ride the limiter, the peaks only are stopped, but the continuous power push right up to the limit...causing overheating.)

DRA

Thanks Dra, I was figuring it would end up there (have to measure volts out at amp)...
That is the speaker cabinet - I could not find the one for the TI version for some reason.. what's weird is that the plate on the unit clearly states "Max: 200W" then right below the 200W is 100W (not labeled continuous or anything like that)... I've read that rule of thumb is usually 50% over program rating for max peak rating... which would be 300 so I would be ok...

I too was concerned about "riding the limiter"... I was planning to roll off around 100 Hz and use the compressor a bit and maybe limiter set at -2dB to -4dB... but didn't want to do it all seat of the pants... hence the request for advice...

Dra

FYI, 3db is 2x (or 1/2x) power. Not 6db.
Rating vs power is also dependent on use. Live sound - usually all the way to Peak for the amp. DJ - some argue Continuous only, other say Program is OK.

DRA

Pscribby

Dra wrote:

FYI, 3db is 2x (or 1/2x) power. Not 6db.
Rating vs power is also dependent on use. Live sound - usually all the way to Peak for the amp. DJ - some argue Continuous only, other say Program is OK.

DRA

I thought 3dB is 2x-1/2x when talking power but when talking volts (as in signal) it's 6dB...