Two-Sided Baffles - Table of Contents.
The Listening Room Measurements.
June 28, 1997, July 5, 1997 and July 11, 1997.
The following is a comparison of two BG RD-75 drivers for closeness of match.
A basic thin board, rectangular baffle was used for the comparisons.
Additionally, chifon material was used as acoustic damping on the front of
the drivers, and was shown to be beneficial in improving frequency response
linearity. The chifon 'grill cloth' was used in all further tests. The
driver BG54 (with chifon) was selected as the one for use in all further
tests.
The comparison of the baffles BG54C, BASIC and ROUNDS is one of the primary
foundations of the study and demonstrates two things about baffle
diffraction effects. 1. The baffle must be the same thickness as the driver
for improved frequency response linearity, and; 2. Rounded edges on the
baffle further improve frequency response linearity.
The '3&SQ' baffle was duplicated with a left-side slope. There are small
differences in the frequency response of the two baffles, each using the
same driver. Room effects and/or environmental changes might explain the
differences.
One of the explanations for the large increase in low frequency output
below 1000Hz seen in all the baffles is the 'floor mirroring effect' as
postulated by Newman and others. To test this, different thicknesses of
foam were placed between the baffle and microphone to try and damp the
'mirror'. The low-frequency performance is not much affected; but
dramatic smoothing in the 1000Hz range is seen as the thickness of the foam
on the floor is increased.
The increase in low frequency output below 1000Hz seen in the two-sided
baffles has been shown to not be a floor mirror related effect. In the
'Auditorium' measurements section conclusive data is presented to
demonstrate this fact [JRW February 1999].
The full potential of the the RD-75 baffle is obtained with use of a
parametric equalizer in addition to the highpass active filter. There are
distortion reduction implications in the shelved response below 1000Hz.
The passive notch filter supplied with the RD-75 driver does not completely
eliminate the cavity resonance of the driver. The RD-75 and all other
similarly constructed planar drivers are affected by such cavity resonances.
Shown is the portion of the resonance not removed by the passive notch
filter, which can be eliminated with parametric equalization.
AT THE LISTENING POSITION AND
FREQUENCY RESPONSES WITH REFLECTIONS
After the measurement chamber was converted back into a listening room,
the '3&SQ'
baffles were moved into their playing positions. Rudi Blondia provided an
independent measurement of their response at the listening postion.
Additionally, a frequency response from the study, with all room reflections
included, of the equalized '3&SQ' baffle is shown for comparison.
The Comparisions Compendium menu has many additional overlayed plots of
comparsions between the Two-Sided baffles. It provides for scrolling
analysis of related comparisons.
The Listening Room Measurements - Test Setup, 2m.
The Listening Room Measurements - Test Setup, 1,2,3 & 3.5m.
The Listening Room Measurements - Table of Contents.
Acoustic Line Source Research - Table of Contents.
