Post by TTSNIP<
In an in-depth discussion I had with Philip Vafiadas a while
ago he actually produced graphs that showed me that speaker
cones do run in. >SNIP< > Regards TT
I think the following 'snip' from a couple of years ago is what you are
referring to....
Just a note, almost all of the drivers that VAF use are proprietary,
but the one below we modify 'in house', and in it's basic form as
tested, it is freely available and of undeniably high quality....
anyone interested should easily be able to verify the data below.
Best regards
Philip Vafiadis
Founder, VAF Research Pty Ltd
www.vaf.com.au
Results of detailed running in.
Driver: Excel W21EX001
Manufacturer: SEAS Fabrikker AS Norway
Serial #: 2/00-50 and 2/00-48
Manufactured: February 2000
Overview.
Tests were conducted to qualify the existence of, and/or quantify the
magnitude of, changes in electroacoustic parameters of a loudspeaker
driver over time. The aim of the test described herein was to measure
the parameters of a new driver, by impedance measurement and
analysis, and compare them with the same parameters measured after
specified periods of 'running in' with a suitable test signal. The
results were then examined for evidence of time related changes.
No attempt was made in this test to examine the parametric behaviour
over long time scales. This will be done in another series of tests
to accurately establish the existence or otherwise of such long term
changes.
No attempt was made to examine the relative effects of different
'running in' waveforms.
Test Conditions.
Tests were conducted in VAF Research anechoic chamber, solely for the
purpose of noise isolation. No acoustic measurements were taken. The
Drivers were suspended asymmetrically in free air at least 600mm from
the nearest (heavily absorptive) surface.
Temperature was controlled at 21degrees C +/- 2degrees as dictated by
the thermostat hysteresis of the air-conditioning system.
Test signals.
The 'running in' signal was generated using proprietary VAF signal
generating software. The signal comprised a swept sine wave from
10Hz-100Hz with a sweep time of 1 second. This was applied to the
drivers at a level of 4 Volts p-p (2 Volts peak, 1.414 Volts RMS,
approx 0.25 Watts). This level was selected arbitrarily because it
results in significant excursion of the driver cone (approx +/- 2mm)
at the lowest frequencies but does not approach the maximum linear
excursion of the driver (specified by SEAS as +/- 6mm).
The impedance measurement waveform was generated by a proprietary MLS
Measurement System and constituted a low frequency MLS signal sampled
at 1.9kHz. This was applied at a level of 4 Volts p-p. Impedance
measurement bandwidth was 10Hz - 200Hz. No smoothing or windowing was
applied.
The resonant frequency Fs was taken to be the frequency at which the
impedance phase angle passed through 0 degrees.
This method has been verified to our satisfaction in comparison with
manual swept sine wave tests and commercial MLS impedance
measurements. It has the advantage of exposing the driver to very low
average power and hence minimises thermal effects.
Method.
The impedance of the driver was tested by application and analysis of
the MLS impulse. The driver was then subjected to the running in
signal for a fixed period as shown in the results below. The
parameters were again measured immediately to allow for
quantification of driver thermal effects. The driver was then allowed
to cool by natural convection for ten minutes. The parameters were
then measured again and the cycle repeated.
Additionally, a control driver was measured once at the commencement
of the test and again at its completion. No 'running in' was applied
to this control driver. results are included below for comparison.
Results.
Sample 2/00-50
Conditions Total RunIn Fs Qts
---------------------------------------------
Initial Test 0 min 35.47 0.49
Run in for 1 minute
Cool down 10 minutes 1 min 34.7 0.42
Run in for 1 minute
Cool down 10 minutes 2 min 34.64 0.43
Run in for 1 minute
Cool down 10 minutes 3 min 34.63 0.44
Run in for 1 minute 4 min 34.34 0.43
Cool down 10 minutes 4 min 34.54 0.44
Run in for 1 minute 5 min 34.41 0.41
Cool down 10 minutes 5 min 34.65 0.43
Run in for 5 minute 10 min 34.33 0.43
Cool down 30 minutes 10 min 34.68 0.43
Run in for 10 minute 20 min 33.35 0.42
Cool down 30 minutes 20 min 33.65 0.43
Run in for 20 minute 30 min 32.14 0.42
Cool down 30 minutes 30 min 32.80 0.42
Run in for 30 minute 60 min 32.03 0.41
Cool down 60 minutes 60 min 32.06 0.42
Run in for 60 minute 120 min 31.23 0.41
Cool down 60 minutes 120 min 31.62 0.41
SEAS Specification FS: 31Hz Qts: 0.41
Sample 2/00-50 Initial Fs: 35.38 Qts: 0.48
Final Fs: 35.37 Qts: 0.48
Conclusion.
It has been demonstrated that the Fs and Qts of a high quality bass
driver change from their initial values with use. The rate of change
appears to decrease as the final value (in this case very close to
the values specified by the manufacturer) is approached. This would
support the theory that this driver will settle down to parameters
somewhat different from those tested when the driver was new. The
difference in Fs in particular is approximately 11%.