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Author Topic: Crest or Crown for SRX728's  (Read 19548 times)

Ivan Beaver

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Re: Crest or Crown for SRX728's
« Reply #30 on: December 09, 2011, 05:11:22 PM »

Hi !

We are a lot here using srx rig !  I am completely lost with this rms limiters. My 728's are fired with 2 x PL4.0. Am I in trouble pushing them ? how can we set a limit with a regular analog crossover such dbx234xl or similar process ?

If I understand correctly : Peak Watts : 6400W and average is 4000W
So ohm law states : V= R*I or P = V*V / R and heat losses are P = R * I * I
So :

4000w * 4 ohm =16000 and sqrt(16000) = 126.5V and 4000/126.5 = 31A  = To get Max output from an amp.

And at Peak power : 6400 * 4 ... = 160V and 160/4 = 40A.

For sure, there is cable and distance and also reactive contribution but let keep it negligeable.

My question here is : If from an outlet you can get at maximum 120V and 20A - How is it possible to reach Peak limitation under these specific conditions assuming that the impedance will remain around 4 ohms.

So if my understanding is okay, with this voltage and current limitation, how its possible to reach the drivers Watt limits ...

Please correct me if I am wrong !

Thank you,

Othmane
The simple answer is that the outlet current is rated for SINEWAVE.  We are talking about MUSIC power.  There is a much higher crest factor.dynamic range with music than there is with sine wave. If you are playing sine waves at constant levels, then you would be correct-but most people do not play sine waves for extended periods of time.  If they do-they buy a lot of recone kits.
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Yosi Melamed

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Re: Crest or Crown for SRX728's
« Reply #31 on: December 09, 2011, 05:40:48 PM »

Hi !

We are a lot here using srx rig !  I am completely lost with this rms limiters. My 728's are fired with 2 x PL4.0. Am I in trouble pushing them ? how can we set a limit with a regular analog crossover such dbx234xl or similar process ?

If I understand correctly : Peak Watts : 6400W and average is 4000W
So ohm law states : V= R*I or P = V*V / R and heat losses are P = R * I * I
So :

4000w * 4 ohm =16000 and sqrt(16000) = 126.5V and 4000/126.5 = 31A  = To get Max output from an amp.

And at Peak power : 6400 * 4 ... = 160V and 160/4 = 40A.

For sure, there is cable and distance and also reactive contribution but let keep it negligeable.

My question here is : If from an outlet you can get at maximum 120V and 20A - How is it possible to reach Peak limitation under these specific conditions assuming that the impedance will remain around 4 ohms.

So if my understanding is okay, with this voltage and current limitation, how its possible to reach the drivers Watt limits ...

Please correct me if I am wrong !

Thank you,

Othmane
Read this.
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Othmane Alaoui

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Re: Crest or Crown for SRX728's
« Reply #32 on: December 10, 2011, 07:35:10 AM »

Read this.

Hi Yosi,

Thank you ! but what is this have to do with my question ?

Crown is explaining how magnificent and brilliant they are by using two relatively old technologies...

PFC means Power factor Correction, its very normal that if you correct the power factor of a network you get extra kw. More you push the voltage up, less amp you need to achieve the same work. In the industry, 90% of power factor is a minimum to have. the lower the power factor is, higher inductive loads they are, and more capacitor you will have to use. This principle is used for the past 75 years.

The second point crown are explaining in their white paper is focusing on the SMPS, its fun to see that the amps is lighter because of magnet replacement but these smps are Harmonics injectors, the switching is not clean, so if we fluke the input of one these amps, we might have some surprises !

Othmane
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Yosi Melamed

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Re: Crest or Crown for SRX728's
« Reply #33 on: December 10, 2011, 08:02:11 AM »

Hi Yosi,

Thank you ! but what is this have to do with my question ?

Crown is explaining how magnificent and brilliant they are by using two relatively old technologies...

PFC means Power factor Correction, its very normal that if you correct the power factor of a network you get extra kw. More you push the voltage up, less amp you need to achieve the same work. In the industry, 90% of power factor is a minimum to have. the lower the power factor is, higher inductive loads they are, and more capacitor you will have to use. This principle is used for the past 75 years.

The second point crown are explaining in their white paper is focusing on the SMPS, its fun to see that the amps is lighter because of magnet replacement but these smps are Harmonics injectors, the switching is not clean, so if we fluke the input of one these amps, we might have some surprises !

Othmane
I thought you asked how is it possible to feed the 728s with up to 6400W during the peaks using 20A breaker (X120=2400W), I was referring to this part of the document:
"massive amounts of energy reserve into I-Tech’s switchmode power supply, With plenty of energy available to reproduce transient program material"
So when you get the transient peaks, the PSU relays on energy stored in on board capacitors instead of grid power alone.

Please correct me if I'm wrong.
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Othmane Alaoui

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Re: Crest or Crown for SRX728's
« Reply #34 on: December 10, 2011, 08:16:12 AM »

I thought you asked how is it possible to feed the 728s with up to 6400W during the peaks using 20A breaker (X120=2400W), I was referring to this part of the document:
"massive amounts of energy reserve into I-Tech’s switchmode power supply, With plenty of energy available to reproduce transient program material"
So when you get the transient peaks, the PSU relays on energy stored in on board capacitors instead of grid power alone.

Please correct me if I'm wrong.

Hi Yosi,

My question was toward how its possible to blow a driver that can take 6400w peak with 20A outlet using a 4000W rated breaker.

For your question, the capacitor bank inside the amplifier is simply used to raise the voltage. I cannot state they are use like super capacitors because it is not needed to correct PF. I am also wondering what could the be the power factor of such Itech6000 or 8000

Othmane
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Tim McCulloch

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Re: Crest or Crown for SRX728's
« Reply #35 on: December 10, 2011, 10:57:40 AM »

Hi Yosi,

My question was toward how its possible to blow a driver that can take 6400w peak with 20A outlet using a 4000W rated breaker.

For your question, the capacitor bank inside the amplifier is simply used to raise the voltage. I cannot state they are use like super capacitors because it is not needed to correct PF. I am also wondering what could the be the power factor of such Itech6000 or 8000

Othmane

In the "old days" before Class D amps were common, amp power supplies had large filter capacitors that stored energy for peaks as well as filtration.  That, combined with a reasonably robust output section gave amps "dynamic headroom" that could approach 3dB above rated output (without excess line draw).

Today with switching power supplies, we can "steal" a bit more current over part of the AC wave form, and do it so long as we don't average above "x" amount of current (trip breakers, etc).  IIRC, the Crown white paper *does* explain some of this as well as why using PFC allows more peak current draw than might be otherwise possible.

Go back and re-read Ivan's post, he outlines why the above will work.

Tim Mc
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Othmane Alaoui

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Re: Crest or Crown for SRX728's
« Reply #36 on: December 10, 2011, 02:41:07 PM »

In the "old days" before Class D amps were common, amp power supplies had large filter capacitors that stored energy for peaks as well as filtration.  That, combined with a reasonably robust output section gave amps "dynamic headroom" that could approach 3dB above rated output (without excess line draw).

Today with switching power supplies, we can "steal" a bit more current over part of the AC wave form, and do it so long as we don't average above "x" amount of current (trip breakers, etc).  IIRC, the Crown white paper *does* explain some of this as well as why using PFC allows more peak current draw than might be otherwise possible.

Go back and re-read Ivan's post, he outlines why the above will work.

Tim Mc

Good Tim , Yosi and Ivan ! So we are using caps as super caps, it doe's make sens to me like in electrical cars, we use super caps to store energy from Regen and we take this energy for acceleration !

I have read the paper several times and I do understand I-Tech fundamentals, Thank you :) Its a very interesting subject because it touch Power Qiuality witch is more and more important in our day to day gigs.
What about using other type of amps ? Doe's a bridge PL4.0 will act same as an Itech ?
Because the topic is in regards to amps, one of my costumers have 2 x 728 and 2 amps : 1xPL4.0 and 1xPLX3602. he is asking me if we can bridge each amp for each sub. My answer was yes as long as you keep your gain equal. Am I right ?

Othmane


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Jonathan Betts

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Re: Crest or Crown for SRX728's
« Reply #37 on: December 10, 2011, 02:58:29 PM »

Why would you want to bridge those amps? In stereo they are a good match for the 728. This way you could add another set of 728's if you need more low end and not have to purchase another amp.
« Last Edit: December 10, 2011, 03:05:24 PM by Jonathan Betts »
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Re: Crest or Crown for SRX728's
« Reply #37 on: December 10, 2011, 02:58:29 PM »


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