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Author Topic: Limiters and HP filter on XTI...  (Read 2189 times)

Yosi Melamed

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Limiters and HP filter on XTI...
« on: December 09, 2011, 08:03:55 am »

I'm trying to set the limiters on my amp (Crown XTI 4002).
I'm calculating the values for the setting on the amp and something doesn't add up...

My speakers are 225W continuous, 8 ohms,
My amps voltage gain is 34.2db.

Using this formula 20*log(sqrt(P*Z/0.6))-G, I get 0.57dBu... So far so good.

Now I want to enter the numbers into the amp, but the amp takes db units, which I guess is in relation to its maximum output voltage no matter the load, or it is in relation to power output and then the calculation takes the load into effect.

Generally speaking if my amp has 650W @8 ohms and my speakers only take 225W, I think it should be in the neighborhood of -4 to -5 db but I don't know how to calculate it exactly, help...

One more, I'd like to set a high pass filter to try and prevent physical damage, what would you suggest I put in the frequency, slope and crossover type to accomplish that?

The Frequency Response of my speakers is:
55 Hz - 20 kHz ( 3 dB)

This is the frequency response chart if it helps



« Last Edit: December 11, 2011, 12:12:20 pm by Yosi Melamed »
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Jonathan Betts

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Re: Limiters on XTI and HP filter...
« Reply #1 on: December 09, 2011, 11:07:03 am »

Are you using these speakers with a subwoofer?
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Yosi Melamed

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Re: Limiters on XTI and HP filter...
« Reply #2 on: December 09, 2011, 11:52:41 am »

Are you using these speakers with a subwoofer?
Fullrange.
I forgot :-)
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Chris Van Duker

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Re: Limiters on XTI and HP filter...
« Reply #3 on: December 09, 2011, 12:47:54 pm »

I've got one XTI 1002, and I control it using System Architect, rather than twiddling with the front panel. I don't know if it's available from the front panel, but in SA, you can set the limit as an actual voltage, which should be much easier to figure out. (Though I don't know if they're doing the fiddly stuff Ivan Beaver was mentioning on the Itechs here as well)
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Ivan Beaver

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Re: Limiters on XTI and HP filter...
« Reply #4 on: December 09, 2011, 12:49:43 pm »

I'm trying to set the limiters on my amp (Crown XTI 4002).
I'm calculating the values for the setting on the amp and something doesn't add up...

My speakers are 250W continuous, 8 ohms,
My amps voltage gain is 34.2db.

Using this formula 20*log(sqrt(P*Z/0.6))-G, I get 1.02dBu... So far so good.

Now I want to enter the numbers into the amp, but the amp takes db units, which I guess is in relation to its maximum output voltage no matter the load, or it is in relation to power output and then the calculation takes the load into effect.

Generally speaking if my amp has 650W @8 ohms and my speakers only take 250W, I think it should be in the neighborhood of -4 to -5 db but I don't know how to calculate it exactly, help...

One more, I'd like to set a high pass filter to try and prevent physical damage, what would you suggest I put in the frequency, slope and crossover type to accomplish that?

The Frequency Response of my speakers is:
55 Hz - 20 kHz ( 3 dB)

This is the frequency response chart if it helps


Is that the ACTUAL response of the loudspeaker-or a response with procssing applied?

It makes a difference.

Maybe the make/model number of the loudspeaker would help
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Ivan Beaver
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Ivan Beaver

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Re: Limiters on XTI and HP filter...
« Reply #5 on: December 09, 2011, 12:56:51 pm »

I've got one XTI 1002, and I control it using System Architect, rather than twiddling with the front panel. I don't know if it's available from the front panel, but in SA, you can set the limit as an actual voltage, which should be much easier to figure out. (Though I don't know if they're doing the fiddly stuff Ivan Beaver was mentioning on the Itechs here as well)
Just for the record-I have been playing around with the Itechs and the limiters some more.  The usable numbers I enter to get the required output voltage, at the point of limiting that I want, are nowhere near the numbers that you would come up with by calculating using the wattage and the impedance of the loudspeaker.

In a couple of systems with the calculated voltages, the system would not get loud enough.  But when the MEASURED voltages are used (actual input numbers are ignored-and adjusted to get the proper output voltages), the system get a good bit louder.  One system gained 8dB.  That is nothing to sneeze at.

This has happened on several large projects with the same result.

I don't know what it is, but I am sticking by my measured results and ignoring the calculated voltages.

To me the funny thing is when you pull up a JBL preset for a particular model (I only did this on a couple of models-so cannot speak for all of them), the amps limit the output well below (typically 6dBish) the continuous rating of the loudspeaker-this would be 12dB below the peak rating.
« Last Edit: December 09, 2011, 01:04:15 pm by Ivan Beaver »
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Yosi Melamed

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Re: Limiters on XTI and HP filter...
« Reply #6 on: December 09, 2011, 01:31:16 pm »

Is that the ACTUAL response of the loudspeaker-or a response with procssing applied?

It makes a difference.

Maybe the make/model number of the loudspeaker would help
this is a link to my speakers

The frequency responce chart is there too and I have no idea if it's with processing or not.
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Ivan Beaver

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Re: Limiters on XTI and HP filter...
« Reply #7 on: December 09, 2011, 01:48:04 pm »

this is a link to my speakers

The frequency responce chart is there too and I have no idea if it's with processing or not.
Part of the reason I ask, is that the stated response (-3dB) is 55Hz, while on the response chart the -3dB point is below 40Hz.

Why would they cheat themselves on a spec like that?  Maybe either the graph or the spec is wrong.  It happens.
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Yosi Melamed

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Re: Limiters on XTI and HP filter...
« Reply #8 on: December 09, 2011, 02:52:49 pm »

Part of the reason I ask, is that the stated response (-3dB) is 55Hz, while on the response chart the -3dB point is below 40Hz.

Why would they cheat themselves on a spec like that?  Maybe either the graph or the spec is wrong.  It happens.
Assuming the worst is the safest way to go so lets do that.

Is there a quick way to measure it directly from the speakers?
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Yosi Melamed

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Re: Limiters on XTI and HP filter...
« Reply #9 on: December 10, 2011, 06:39:46 am »

OK, I got it... I saw on another thread in another forum that the XTI takes dBfs units and not dB, this explains why I was confused about the units and what data to give the amp.

So the maximum power output 650W equals 0 dBfs, from here it's just a plain dB ratio formula from here and I get:
10 X Log(P1/P2)=10XLog(225/650)= -4.61 dBfs

Any suggestions on the HP filter for my speakers?
« Last Edit: December 10, 2011, 11:27:53 am by Yosi Melamed »
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