ER18RNX Thiele/Small Parameters
One would naturally assume that manufacturers specifications
are accurate. When it comes to drivers, it appears
this is not often the case.
specified the ER18 Vas as 32 Liters. Measurements
with LMS indicates Vas=60.9 Liters. Needless to say,
adopting SEAS Vas would obviously lead to erroneous
Vas=60.9L, the optimum Bass Reflex tuning is a 38L
box. This is much too large for a Bookshelf. I decided
to load the ER18 in a 15L box instead. The outcome
is a higher F3 (45Hz) with a slight hump at 150Hz.
I have no qualms with this as it gives the upper bass
a very light 2dB boost.
issue with the ER18 is the pronounced rising response
above 500Hz. If left unattended, the midrange will
be overly emphasized, resulting in a rather tiring
listening experience. After some testing, I settled
on a Baffle Step Compensation of 5dB. Together with
the upper bass boost, it has the right "bounce"
in the music. The violet plot on the right is the
response of the ER18 in a 15L Bass Reflex together
with the port and Baffle Step Compensation. Frequencies
beyond 500Hz should be ignored as they are inaccurate.
Predicted Low Frequency Response
Bass Reflex (Vb=15L Fb=60Hz)
SEAS ER18 Frequency Response