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Boston Acoustics A360 Measurements and Analysis

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The measurements were conducted in conformance with Audioholics Loudspeaker Measurements Standard

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Boston Acoustics A360 On-Axis Frequency Response

The on-axis frequency response of the A360 was conducted with the measurement microphone at 2 meters with a 2.83V excitation signal.  The results are scaled to 1 meter mathematically.  The manufacturer rates this loudspeaker’s sensitivity as 89dB at 1 meter with a 2.8V input.  Audioholics measures sensitivity as the average sound pressure level (SPL) from 300 to 3kHz.  The A360 Audioholics rated sensitivity is abysmally low at 82.7dB because there is a significant dip in frequency response from 300Hz to 3kHz for the A360.  Compared to an average loudspeaker with a sensitivity rating in the 87-89dB efficiency range, the Boston Acoustics require four times as much power to reach the same average sound pressure level from 300Hz to 3kHz.  Listening tests clearly confirm that the output of the A360 using quasi-anechoic sensitivity measurement techniques is not close to the manufacturer’s rating.  The manufacturer may have rated the A360 sensitivity in room. The frequency response dip centered around 3kHz contributes to the laid back response described in the listening impressions section.  The measurement technique used above involves removing all of the effects of a room.  The in-room bass response with the A360s placed 1.5’ to 2’ from the rear wall is subjectively the loudspeaker’s strong point.

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Boston Acoustics A360 Listening Window

The listening window response for the A360 is conducted with a 2.83V input signal at 2 meters from 7 locations.  The measurement provides a picture of how the loudspeaker performs from seating locations that are not directly on axis with the speaker.  The top curve is the average of the other positions and provides an average of how the speaker performs throughout the listening area.  Subjectively, the off-axis response within the listening window area is pretty uniform.

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Boston Acoustics A360 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 2 meters.  The A360 has relatively uniform directivity from 0-30 degrees.  As a listener approaches 60 degrees severe aberrations in the frequency response become increasingly apparent at high frequencies. 

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Boston Acoustics A360 Impedance

The impedance of the A360 remains above the IEC 8 ohm minimum threshold of 6.4 Ohms throughout the entire audio band.  At approximately 1kHz, the loudspeaker reaches a minimum impedance of approximately 6.5 Ohms.  The impedance graph above indicates the port tuning frequency is at approximately 35Hz.

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Boston Acoustics A360 Harmonic Distortion

The harmonic distortion graph was generated using a 90dB stepped sinusoid sweep measured at 2 meters.  The above harmonic distortion graph and cumulative spectral decay graph shown below indicate some sort of resonance at approximately 1.5kHz.  Maybe this is what that interesting circular disc is meant to tame!  Although this is present, it is not something to obsess over. 

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Boston Acoustics A360 Cumulative Spectral Decay

Cumulative spectral decay is derived from the impulse response measurement made with a 90dB excitation signal at 2 meters.  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. 

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Boston Acoustics A360 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. 

 

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Recent Forum Posts:

DCmoe posts on June 13, 2013 07:01
gtpsuper24, post: 972123
Like Klipsch who uses the tweeters sensitivty to falsely jack up the SPL.

Same thing for BIC speakers.
gtpsuper24 posts on June 12, 2013 13:49
Pablo Albino, post: 972120
82,7 dB? That really disappointed me a lot! Couldn't be a defective sample?
I was planning to purchase an little integrated amp (75 W) to feed that towers. However, that measurements has made me reconsider my original plan.

Or it could be accurate given how so many manufacturers falsely inflate their specs. Like Klipsch who uses the tweeters sensitivty to falsely jack up the SPL. When actually they are probably closer to 91-92 as a system.
gene posts on June 12, 2013 13:49
Pablo Albino, post: 972120
82,7 dB? That really disappointed me a lot! Couldn't be a defective sample?
I was planning to purchase an little integrated amp (75 W) to feed that towers. However, that measurements has made me reconsider my original plan.

you're gonna find that most manufacturers fudge sensitivity ratings on speakers. We measure sensitivity from 300Hz to 3kHz which is the IEC standard way of doing so. Most manufacturers simply do a fullrange test to give the illusion of higher sensitivity. We've measured Klipsch speakers to be a whopping 8dB less efficient than their published spec. Bryston's new tower speaker was measured by the NRC to be 4.5dB less sensitive than published spec.

You will probably be ok with the amp you want to use if you power these speakers in a small to medium sized room. Otherwise, you may want to get a bigger amp or go with a more sensitive speaker.
Pablo Albino posts on June 12, 2013 13:42
Sensitivity

82,7 dB? That really disappointed me a lot! Couldn't be a defective sample?
I was planning to purchase an little integrated amp (75 W) to feed that towers. However, that measurements has made me reconsider my original plan.
internetmin posts on May 15, 2013 10:22
Boston Acoustics

Ah, I had a pair of Boston Acoustics HD-series monitors back 20+ years ago. Those speakers got me into the high-fi hobby. I haven't listened to any of the recent speakers but I've always had a special sentimental affinity for BA.
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