The measurements were conducted in conformance with Audioholics Loudspeaker Measurements Standard

A225C On-Axis Frequency Response

The on-axis frequency response of the A225C was conducted with the measurement microphone at 1 meter with a 2.83V excitation signal. The manufacturer rates this loudspeaker’s sensitivity as 89dB at 1 meter with a 2.8V input.  Audioholics measures sensitivity as the average SPL from 300 to 3kHz.  The A225C Audioholics rated sensitivity is below the manufacturers rating at 85.4dB. The manufacturer may have rated the A225C’s sensitivity in room.  The measurement technique used above involves removing all of the effects of a room.  The A225C response looks relatively linear but has a -3dB point of 102Hz with a steep 18dB/octave roll off.  Due to the slight bump at 200Hz, the speaker still sounds warm.

A225C Listening Window

The listening window response of the A225C is pretty uniform except for at 30 degrees off axis.  The huge nulls in the frequency response are due to the midrange-tweeter-midrange (M-T-M) configuration lobing error. This is one of the reasons horizontal center channels with a MTM configuration present a compromise when listening far off-axis. To confirm something else was not happening, I measured this phenomenon at several distances at 30 degrees and had the same finding with the effect reduced slightly as a function of distance.  This problem is inherent to all loudspeakers with a tweeter between two mid-woofers.  If the speaker is laid horizontally, there will be lobing error at frequencies that are dependent on the driver spacing.

A225C Polar Response

The polar response graph shows how a loudspeaker performs at various angles.  The polar response graph above is generated by measuring a loudspeaker at 7.5 degree intervals around a circle on the tweeter axis from 1 meter.  This polar response graph is indicative of a M-T-M configuration.  The majority of the energy is in the 0 to 15 degrees of axis listening angles.  If listening at extreme angles the response of the center channel will have significant notches.  This configuration may be advantageous because the room interactions and interference pattern with left and right channels are reduced due to the reduced acoustic energy off-axis.

A225C Impedance

The impedance of the A225C dips slightly below 6.4 Ohms IEC minimum rating for 8 ohm speakers between 6300Hz and 9200Hz.  This should not pose any problem for most amplifiers on the market.  The impedance graph above indicates the port tuning frequency is at approximately 65Hz.

A225C Harmonic Distortion

The harmonic distortion graph is generated using a stepped sinusoidal sweep excitation signal calibrated to reach 90db at 2 meters.  This is a loud signal for a small center channel and the harmonic distortion graph shows that the A225C disagrees with playing much below 50Hz.  The sweep indicates distortion peaks at 800Hz and at approximately 300Hz.  These were not offensive or even detectable during listening tests.

A225C Cumulative Spectral Decay

The cumulative spectral decay shows how sound at various frequencies dies out as a function of time.  It is important to note that the left most ridge is not valid and is a product of the measurement technique.

A225C Group Delay

The group delay graph shows the rate of change of the slope of a loudspeaker’s phase.  As a rule of thumb, values below 1.6ms in the mid to high frequencies will likely not effect perception of sound quality.  Increasing group delay in the low frequencies is not as objectionable as it is in the mid to high frequency ranges.  The group delay of the A225C is perfectly acceptable.

Conclusion

The Boston Acoustics A225C center channel is built using high quality parts and provides substantial sound from a small package.  With proper setup the A225C does a great job reproducing dialogue and multi-channel music alike.  Due to the relatively compact cabinet, the bass rolls off at approximately 100Hz but works well when coupled with a subwoofer. In my setup, speech intelligibility required a 3dB bump for clear dialog when compared to all other speakers in a system.  For music reproduction, the A225C sounds very smooth except when presented with recordings that are on the bright side.  All in all, I think the A225C is a great center channel with a small footprint.  This center channel blends well with the other Boston Acoustics A-series offerings such as the A360 floorstanding loudspeaker.