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Author Topic: Limiter Wizard - voltage calculation - is this right??  (Read 323 times)

Bob Faulkner

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Limiter Wizard - voltage calculation - is this right??
« on: May 15, 2018, 07:54:13 pm »

Just want to make sure I understand the results with the Limiter Wizard spreadsheet.

Setting PEAK values for Crown MA 9000i  (3500 watts/chnl @4 ohms using 20amp service) for JBL SRX-728S (3200 watts RMS @ 4ohms)

The spreadsheet shows for 1hz to 100 hz to be ~226 volts. 

226 volts x 20amp service = 4,520 watts ( a bit more than the RMS rating of the 728)
226 volts x 15amp service = 3,390 watts (maybe more appropriate for the 728?)
Peak ms - 40ms attack with 80ms release (manually set values)

The theoretical peak limit of the 728 is ~6000 watts. 

Does the Limiter Wizard account for the potential service ampers the amplifiers (MA 9000i in this case) could draw?  It seems to be a large difference between 15 amps and 20 amps for setting limits.

Am I interpreting the voltage output correctly (in the Limiter Wizard) if thinking the Wizard is using a 20amp service rating when calculating voltages? 
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Lee Buckalew

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Re: Limiter Wizard - voltage calculation - is this right??
« Reply #1 on: May 15, 2018, 09:06:46 pm »

Just want to make sure I understand the results with the Limiter Wizard spreadsheet.

Setting PEAK values for Crown MA 9000i  (3500 watts/chnl @4 ohms using 20amp service) for JBL SRX-728S (3200 watts RMS @ 4ohms)

The spreadsheet shows for 1hz to 100 hz to be ~226 volts. 

226 volts x 20amp service = 4,520 watts ( a bit more than the RMS rating of the 728)
226 volts x 15amp service = 3,390 watts (maybe more appropriate for the 728?)
Peak ms - 40ms attack with 80ms release (manually set values)

The theoretical peak limit of the 728 is ~6000 watts. 

Does the Limiter Wizard account for the potential service ampers the amplifiers (MA 9000i in this case) could draw?  It seems to be a large difference between 15 amps and 20 amps for setting limits.

Am I interpreting the voltage output correctly (in the Limiter Wizard) if thinking the Wizard is using a 20amp service rating when calculating voltages?

Bob,
Peak values for voltage (excursion) limiting are going to be based upon instantaneous capability which would rely on the amplifiers reserves rather than directly drawing it from the wall. 
In fact all of the limiter values related to saving your drivers from damage will be related to the amplifiers output and not to what it is drawing from the wall.

If this is the same spreadsheet from Crown that I have be sure you are using the correct wattage values in the correct fields since JBL gives 3 values on many of their spec sheets (continuous, program, peak) and asks for 2 HR. and 100 HR. values when you fill in the spreadsheet.

Lee
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Dave Guilford

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Re: Limiter Wizard - voltage calculation - is this right??
« Reply #2 on: May 15, 2018, 09:41:17 pm »

And PLEASE report your finished numbers here for reference.
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Bob Faulkner

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Re: Limiter Wizard - voltage calculation - is this right??
« Reply #3 on: May 16, 2018, 07:03:50 am »

Bob,
Peak values for voltage (excursion) limiting are going to be based upon instantaneous capability which would rely on the amplifiers reserves rather than directly drawing it from the wall. 
In fact all of the limiter values related to saving your drivers from damage will be related to the amplifiers output and not to what it is drawing from the wall.

If this is the same spreadsheet from Crown that I have be sure you are using the correct wattage values in the correct fields since JBL gives 3 values on many of their spec sheets (continuous, program, peak) and asks for 2 HR. and 100 HR. values when you fill in the spreadsheet.

Lee
Thank you.  Yeah, figured the "bulk" of the power would be coming from reserves.  My thought was, using Ohms Law, the amperage parameter needed to be factored into the equation to get a "meaningful??" value in watts. 

The Limiter Wizard I'm using is the spreadsheet from Crown.  Yep, values entered into it are correct for their respective areas.  I'm probably showing my ignorance here, but the peak ms value for the attack time seems sort of long (I don't have the data in front of me at this time)... but was thinking it was around 60ms (15hz).  I referenced manually setting the peak to around 40ms (to restrict the low end to around ~25hz).  However, I do have my dbx-260 rolling off around 30hz on the "low side" of the low-pass filter, so this may be all just "words and crap" at this time.

If I do a "reverse lookup" to determine voltage, based on watts, I get a different voltage number for the SRX 3200 watt RMS rating... still, I'm needing to enter an amperage value to determine results.

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Kevin Graf

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Re: Limiter Wizard - voltage calculation - is this right??
« Reply #4 on: May 16, 2018, 08:38:07 am »

Remember that AC power circuit breakers are rated for 3 hour continuous service. Like the overhead lighting system in a store. An old fashioned incandescent light bulb draws about 10 times it's rated current when first turned on. So the AC circuit can provide way more than it's rating for musical peaks but not for long test tones.
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Speedskater
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