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NaO Design.....
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The NaO II Design objectives.
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The NaO II Design objectives.
the important midrange band, from 120 Hz to approximately 2k Hz, nearly ideal dipole operation is achieved. Above 2.2k Hz the
NaO II employs front and rear tweeters. While the rear tweeter helps slightly in controlling the radiation pattern above the crossover
point its primary function is to improve the spectral balance of the sound radiated to the rear of the speaker. This aids in achieving a
more even spectral balance between the direct and reflected sound.
Contrary to other open baffle designs, the NaO II uses a unique damped, U-frame woofer system which can be converted to a
monopole through the addition of a removable rear panel. With the rear of the U-frame removed the woofer approximates a cardioid
radiation pattern. There is sound reasoning behind this approach. A recent AES article by Backman[1] examined dipole, monopole
and cardioid woofer systems in the modal region with regard to room interaction and sensitivity to listening/system position. His
results indicate that in the sparsely populated modal region of the response, which is centered around 100 Hz for a typical listening
room; cardioid woofers exhibit the lowest sensitivity to changes in speaker or listening position. Backman found dipole woofers to be
the most sensitive. Additionally, below the room fundamental Backman shows that the dipole response drops off rapidly, as
expected, since a dipole source is incapable of room pressurize. The behavior of cardioid and monopole woofers is similar in nature
below the room fundamental; both can generate room pressurization effects, although the monopole woofer system benefits from
higher sensitivity. [This is a result of the 6dB/octave roll off of 1st order gradient type speakers; dipoles and cardioids]. These results
are similar to those discussed in the Music and Design articles on Room Response. Backman thus suggests that a woofer system
which operates in cardioid mode through the sparsely populated modal region and undergoes a transition to a monopole response
below the room fundamental could be optimum for low frequency reproduction. While the U-frame woofer with rear panel removed
operates in cardioid mode over its full frequency range, the required equalization is provided by the active crossover. If higher SPL is
required at low frequency the woofer system can be converted to a more efficient monopole and a switch on the active crossover
changes the woofer equalization appropriately. It should be noted that when the woofer is placed in monopole mode the radiation
pattern between the woofer and main panel is intended to undergo a transition from dipole, to cardioid and then to monopole as the
frequency decreases through the crossover region as a 4th order Linkwitz/Rile crossover is implemented. Thus, a cardioid response
is still expected to be present through the transition centered at 120 Hz.
The result is a high performance, bi-amplified speaker system which; 1) achieves nearly ideal dipole radiation throughout the critical
midrange; 2) has very uniform polar response over a wide listening window; 3) is integrated with a woofer system which provides
great flexibility is coupling the system to the room.
_____________________________________________
1) Low-frequency polar pattern control for improved in-room response. Juha Backman, Presented at the 115th Convention 2003
October 10–13
NaO II employs front and rear tweeters. While the rear tweeter helps slightly in controlling the radiation pattern above the crossover
point its primary function is to improve the spectral balance of the sound radiated to the rear of the speaker. This aids in achieving a
more even spectral balance between the direct and reflected sound.
Contrary to other open baffle designs, the NaO II uses a unique damped, U-frame woofer system which can be converted to a
monopole through the addition of a removable rear panel. With the rear of the U-frame removed the woofer approximates a cardioid
radiation pattern. There is sound reasoning behind this approach. A recent AES article by Backman[1] examined dipole, monopole
and cardioid woofer systems in the modal region with regard to room interaction and sensitivity to listening/system position. His
results indicate that in the sparsely populated modal region of the response, which is centered around 100 Hz for a typical listening
room; cardioid woofers exhibit the lowest sensitivity to changes in speaker or listening position. Backman found dipole woofers to be
the most sensitive. Additionally, below the room fundamental Backman shows that the dipole response drops off rapidly, as
expected, since a dipole source is incapable of room pressurize. The behavior of cardioid and monopole woofers is similar in nature
below the room fundamental; both can generate room pressurization effects, although the monopole woofer system benefits from
higher sensitivity. [This is a result of the 6dB/octave roll off of 1st order gradient type speakers; dipoles and cardioids]. These results
are similar to those discussed in the Music and Design articles on Room Response. Backman thus suggests that a woofer system
which operates in cardioid mode through the sparsely populated modal region and undergoes a transition to a monopole response
below the room fundamental could be optimum for low frequency reproduction. While the U-frame woofer with rear panel removed
operates in cardioid mode over its full frequency range, the required equalization is provided by the active crossover. If higher SPL is
required at low frequency the woofer system can be converted to a more efficient monopole and a switch on the active crossover
changes the woofer equalization appropriately. It should be noted that when the woofer is placed in monopole mode the radiation
pattern between the woofer and main panel is intended to undergo a transition from dipole, to cardioid and then to monopole as the
frequency decreases through the crossover region as a 4th order Linkwitz/Rile crossover is implemented. Thus, a cardioid response
is still expected to be present through the transition centered at 120 Hz.
The result is a high performance, bi-amplified speaker system which; 1) achieves nearly ideal dipole radiation throughout the critical
midrange; 2) has very uniform polar response over a wide listening window; 3) is integrated with a woofer system which provides
great flexibility is coupling the system to the room.
_____________________________________________
1) Low-frequency polar pattern control for improved in-room response. Juha Backman, Presented at the 115th Convention 2003
October 10–13
The NaO II is an open baffle design which attempts to maintain constant directivity in the form of
dipole radiation above the Schroeder frequency. The Schroeder frequency is defined as the
frequency which designates the transition between the higher frequencies where the room
reverberant effects dominate and the lower frequencies where discrete room modes dominate the
response. For design purposes a representative value in the range of 100 Hz is taken as the lower
limit for the Schroeder frequency in typical listening rooms. Below the Schroeder frequency the
NaO II panel is integrated with a unique, U-frame woofer system. The design of the NaO II follows a
hybrid approach. An active crossover is used between the woofer and main panel and a passive
crossover is used between the midrange and tweeter. The passive crossover is designed in such a
manner that its only function is to control the response of the midrange and tweeter through the
crossover region. Irregularities in the midrange response due to the open baffle design and
compensating for the gradient roll off of the woofer and midrange drivers is addressed in the active
circuit. In this manner very little amplifier headroom is wasted in the passive crossover compared to
a design where the necessary response equalization is performed in the passive circuits. The
hybrid approach results in a cost effective, bi-amplified system which has many of the benefits of a
fully active system without employing additional channels of amplification. Further discussion of the
Hybrid Design philosophy can be found in the Music and Design technical section and application
to the NaO II may be found under the NaO menu.
A narrow, flat baffle design for the NaO II midrange/tweeter panel is implemented to achieve dipole
radiation. The MTM format was chosen to allow a sufficiently narrow baffle to maintain dipole
operation of the midrange drivers frmm the panel low frequency limit to the crossover point of 2.2 k
Hz and provide sufficient radiating area for the targeted maximum SPL of the system. Thus through
dipole radiation above the Schroeder frequency. The Schroeder frequency is defined as the
frequency which designates the transition between the higher frequencies where the room
reverberant effects dominate and the lower frequencies where discrete room modes dominate the
response. For design purposes a representative value in the range of 100 Hz is taken as the lower
limit for the Schroeder frequency in typical listening rooms. Below the Schroeder frequency the
NaO II panel is integrated with a unique, U-frame woofer system. The design of the NaO II follows a
hybrid approach. An active crossover is used between the woofer and main panel and a passive
crossover is used between the midrange and tweeter. The passive crossover is designed in such a
manner that its only function is to control the response of the midrange and tweeter through the
crossover region. Irregularities in the midrange response due to the open baffle design and
compensating for the gradient roll off of the woofer and midrange drivers is addressed in the active
circuit. In this manner very little amplifier headroom is wasted in the passive crossover compared to
a design where the necessary response equalization is performed in the passive circuits. The
hybrid approach results in a cost effective, bi-amplified system which has many of the benefits of a
fully active system without employing additional channels of amplification. Further discussion of the
Hybrid Design philosophy can be found in the Music and Design technical section and application
to the NaO II may be found under the NaO menu.
A narrow, flat baffle design for the NaO II midrange/tweeter panel is implemented to achieve dipole
radiation. The MTM format was chosen to allow a sufficiently narrow baffle to maintain dipole
operation of the midrange drivers frmm the panel low frequency limit to the crossover point of 2.2 k
Hz and provide sufficient radiating area for the targeted maximum SPL of the system. Thus through
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