Listed Specifications for Guitar Speaker Frequency Range
On Mon, 22 Apr 2019 10:54:35 +0100, John Williamson
wrote:
On 22/04/2019 08:03, Don Pearce wrote:
Particularly with pink noise, they have no choice but to apply a
voltage - which is what amplifiers generate. The actual amount of
power that results in is something the speaker has to negotiate with a
deity, cos it certainly isn't negotiable with any human.
When they talk about 1 watt, they are just assuming a nominal
impedance, which for any particular driver over an extended bandwidth
is a fiction.
Electrically...
True RMS current meters are cheaply available,as long as you stick to
audio frequencies. RF ones cost a bit more....
One that I use doesn't even need to be electrically connected to the
unit, as it uses a hall effect sensor to check the current in one of
the speaker wires. It works over the whole audio range.
That and a decent voltmeter along with a sweep tone generator can be
used to draw a graph of impedance against frequency, though to be
accurate, you need to use an oscilloscope t and a couple of low value
resistors in the circuit to detect any frequency dependent phase shifts
in the load, or use a hall effect sensor to generate a voltage to drive
the X plates on the 'scope. If you have a DAW, then you have a way to
generate a sine or pink tone good enough for the job, even using a free
DAW program such as Audacity.
The only reasons the makers don't do it, as far as I can tell, are that
it is time consuming, there is a lot of variation between speakers as
they come off the line, and then there is the problem of getting an
accurate enough microphone to check the physical response.
A true RMS current meter doesn't help, unfortunately. A speaker's
impedance is very reactive so multiplying RMS current and voltage
doesn't give you power. That would need some sort of measurement
system that could provide vector products. As for doing that with a
noise source, forget it. You need single frequency sine waves for that
calculation.
So no, you can't measure pink noise power into a speaker. Just supply
it a known voltage is the best you can do.
d
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