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.
I don't think many people measure speakers like that. There is good
software for it, like Arta from
http://www.artalabs.hr/ . Takes a
fraction of the time and gives much more info. You do need a more or
less calibrated (known characteristic) microphone. It measure both
loudspeaker impedance and phase, and als can do complete speakers,
not single speaker units. I've no relation to that company or
product, other than having used it myself.
Mat Nieuwenhoven