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Author Topic: LAB12 driver high power performance  (Read 3034 times)

Phil Pope

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LAB12 driver high power performance
« on: June 02, 2004, 09:53:48 am »

I am trying to do some high power modelling and wondered if anyone knows

i) when the driver is driven at the max rated power (400W RMS) for a long period, what temperature does the voice coil reach?  (I am guessing at about 220C)

ii) at the same power, what temperature does the magnet assembly reach?

If no one here has any idea, who should I speak to at Eminence?

thanks
Phil
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Phillip_Graham

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Re: LAB12 driver high power performance
« Reply #1 on: June 02, 2004, 10:34:33 am »

snowflake wrote on Wed, 02 June 2004 09:53

I am trying to do some high power modelling and wondered if anyone knows

i) when the driver is driven at the max rated power (400W RMS) for a long period, what temperature does the voice coil reach?  (I am guessing at about 220C)

ii) at the same power, what temperature does the magnet assembly reach?

If no one here has any idea, who should I speak to at Eminence?

thanks
Phil


The answer to this question is non-trivial.  It depends on the frequency content (low frequencies move more air through the structure), duty cycle, box volume, etc.

Easiest way to get an idea for your application is to put the signal of interest through it for the desired period, and then quickly measure Rdc, and compare that to the cold Rdc.  The change in resisitivity of the voice coil metal is well defined.

This won't be completely accurate for total power compression loss, though, as the heat also reduces the strength of the magnet structure.
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Phil Pope

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Re: LAB12 driver high power performance
« Reply #2 on: June 02, 2004, 11:51:59 am »

>Easiest way to get an idea for your application is to put the >signal of interest through it for the desired period,

I don't have the equipment to do this.

>This won't be completely accurate for total power compression >loss, though, as the heat also reduces the strength of the >magnet structure.

yes, the coefficient for ferrite magnets is -0.002 per deg C so

BL(H)=BL*(1-0.002*(t-20))

Phil
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Phillip_Graham

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Re: LAB12 driver high power performance
« Reply #3 on: June 02, 2004, 01:50:47 pm »

snowflake wrote on Wed, 02 June 2004 11:51

>Easiest way to get an idea for your application is to put the >signal of interest through it for the desired period,

I don't have the equipment to do this.

>This won't be completely accurate for total power compression >loss, though, as the heat also reduces the strength of the >magnet structure.

yes, the coefficient for ferrite magnets is -0.002 per deg C so

BL(H)=BL*(1-0.002*(t-20))

Phil


Don't have the equipment?  All it requires is an amplifier, tone generator (e.g. your computer) a multimeter, and the driver and/or labsub box.

I am a little suspect of your formula, do you know the source?
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Phil Pope

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Re: LAB12 driver high power performance
« Reply #4 on: June 04, 2004, 04:55:12 am »

>I am a little suspect of your formula, do you know the source?

I found the value for the coefficient at:

http://www.magnetsales.com/Ferrite/ferrprops.htm#magnetic
http://www.hitachi-metals.co.jp/e/prod/prod03/p03_05.html

my understanding is that a quoted value for B is at 20C.  As you increase temperature the strength of the magnet will fall linearly (at the rate determined by the coefficient) until the Curie temperature is reached at which point the magnet has become demagnetised (in the case of ferrite magnets about 450C).  This process is fully reversible.

>Don't have the equipment? All it requires is an amplifier, >tone generator (e.g. your computer) a multimeter, and the >driver and/or labsub box.

how do I work out how much power I have been putting into the speaker?  I can measure the DC Re and the voltage but will V^2/R work here? Re is not the actual load across the amplifier, is it?

Phil
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Phillip_Graham

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Re: LAB12 driver high power performance
« Reply #5 on: June 07, 2004, 05:05:51 pm »

Quote:

As you increase temperature the strength of the magnet will fall linearly (at the rate determined by the coefficient) until the Curie temperature is reached at which point the magnet has become demagnetised (in the case of ferrite magnets about 450C).  This process is fully reversible.


This sounds right, but I can't remember if it's a linear slope when plotted on log paper.  I will check my magnetics textbook.

Quote:


>Don't have the equipment? All it requires is an amplifier, >tone generator (e.g. your computer) a multimeter, and the >driver and/or labsub box.

how do I work out how much power I have been putting into the speaker?  I can measure the DC Re and the voltage but will V^2/R work here? Re is not the actual load across the amplifier, is it?

Phil


Ahh, I see what you are trying to do.  You want to measure true power, and then integrate that over time to calculate total energy input.  Your are right that this is a more difficult proposition.  What is your ultimate goal in this process?
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