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Derate 300W amp for SW?

L

Louis Robson

Jan 1, 1970
0
I have a JBL BP 300 mono subwoofer amp (300W) that I would like to
feed with a continous sinewave within the spec. range of the unit
which is 10-320Hz.

What is the rule of thumb for derating the wattage where this type of
use is concerned.

I assume I then would put a suitably rated power resistor in series
with the woofer.

Regards,

Louis Robson
 
P

Phil Allison

Jan 1, 1970
0
"Louis Robson"
I have a JBL BP 300 mono subwoofer amp (300W) that I would like to
feed with a continous sinewave within the spec. range of the unit
which is 10-320Hz.

** The BP300 is a car audio product, 12 volt supply & SMPS.

What is the rule of thumb for derating the wattage where this type of
use is concerned.


** Rules of thumb are no use to you.

Only testing will show how long it can hold up at 300 watts .


I assume I then would put a suitably rated power resistor in series
with the woofer.

** Then you assume wrongly.

Woofer impedance is non simple function of frequency.


.......... Phil
 
R

Rich, Under the Affluence

Jan 1, 1970
0
I have a JBL BP 300 mono subwoofer amp (300W) that I would like to
feed with a continous sinewave within the spec. range of the unit
which is 10-320Hz.

What is the rule of thumb for derating the wattage where this type of
use is concerned.

I assume I then would put a suitably rated power resistor in series
with the woofer.

Egads! Sounds like a freakin' earthquake simulator! What is it that
you're trying to accomplish?

Thanks,
Rich
 
J

Jon Danniken

Jan 1, 1970
0
Rich said:
Egads! Sounds like a freakin' earthquake simulator! What is it that
you're trying to accomplish?

Annoy everybody who is sitting peacefully in their homes and minding their
own business in a six block radius; that's my guess.

People who operate these "thumper cars" need to be shot.

Jon
 
F

Fred Bloggs

Jan 1, 1970
0
Louis said:
I have a JBL BP 300 mono subwoofer amp (300W) that I would like to
feed with a continous sinewave within the spec. range of the unit
which is 10-320Hz.

What is the rule of thumb for derating the wattage where this type of
use is concerned.

There is no rule of thumb- that 300W rating is a "music power" rating
with underlying assumptions about what percentage of the power lies
within the 10-320Hz band, and that will be far less than 300W. Contact
the manufacturer and ask for the "continuous power" limit.
I assume I then would put a suitably rated power resistor in series
with the woofer.

That's one way to do it.
 
R

René

Jan 1, 1970
0
I have a JBL BP 300 mono subwoofer amp (300W) that I would like to
feed with a continous sinewave within the spec. range of the unit
which is 10-320Hz.

What is the rule of thumb for derating the wattage where this type of
use is concerned.

I assume I then would put a suitably rated power resistor in series
with the woofer.

Regards,

Louis Robson

Better use this:

http://www.eminent-tech.com/howitworks.htm

Or build one yourself using a RC helicopter collective pitch control
system :)
 
W

Walter Harley

Jan 1, 1970
0
Louis Robson said:
I have a JBL BP 300 mono subwoofer amp (300W) that I would like to
feed with a continous sinewave within the spec. range of the unit
which is 10-320Hz.

What is the rule of thumb for derating the wattage where this type of
use is concerned.

It's a switching amp, so the output stage is probably not going to get much
hotter at full power than at low power.

Since it is rated at 300W into 2 ohms (or 150W into 4 ohms), the supply
rails must be considerably higher than 12V; it is powered from 12V, so the
power supply itself must be a DC-DC converter, presumably also switching.

Therefore, you probably don't have to derate for continuous sinewave
operation in the same way you would a class-AB amplifier or linear power
supply. But you do need to derate for your load impedance - the higher the
load, the less power will be delivered, since the constant here is the
supply rail voltage.


I assume I then would put a suitably rated power resistor in series
with the woofer.

That assumption is incorrect unless you are trying to do something peculiar.
What is it that you are trying to accomplish?
 
P

Phil Allison

Jan 1, 1970
0
"Walter Harley"
It's a switching amp,


** How do you know ?

Seems to have a lot of heastsink area for one of them.

The JBL site says it has a SMPS.




.......... Phil
 
P

Pig Bladder

Jan 1, 1970
0
Wow, $13k. No amp, no cross-over. (I suppose some might consider this
cheap?)

****, man, if peple have that much money to spend on noisemakers, please
let them know I'll give them a bl-w j-b for only $1000.00.
 
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