The NaO Note Design objectives.
PLEASE NOTE: These pages are now for historical purposes. Music and Design is no longer offering these products for sale.
The NaO Note also departs from the use front and rear dome tweeters. The Note uses a single B&G Neo 3 PDR
tweeter without the rear cup. The tweeter is mounted in a simple wave guide which helps control the axial
response of the tweeter. The use of a single, opened backed tweeter also helps reduce the cost of the system.
As with the NaO II, the NaO Note panel is integrated with a dual driver, damped, U-frame woofer system. While
similar in size and principle to the NaO II U-frame, the woofer system has been completely redesigned. The low
frequency response follows a 3rd order Bessel alignment with -3dB point at 30 Hz and -6dB point at 22 Hz. This
provides greater low frequency extension than that of the NaO II while improving protection from over excursion
at sub-sonic frequencies. The U-frame, quai-cardioid format system was chosen based on research by Backman
. Backman examined dipole, monopole and cardioid woofer systems in the modal region with regard to room
interaction and sensitivity to listener and system position. His results indicated 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 listener position. Backman found dipole woofers to be the
most sensitive. Additionally, below the room fundamental Backman showed 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. These results are similar to those discussed in the Music and Design articles on Room Response. Thus,
the damped U-frame which achieves a quasi-cardioid response seems to be the optimal woofer format.
While the U-frame woofer system is the woofer of choice at Music and Design, it is realized that individual
preferences and specific applications may make other low frequency solutions desirable. In that regard, the NaO
Note plan set includes fully design and tested dipole and ported box, monopole woofer system options, and a
sealed box option is available on request. This is possible because like all NaO dipole speaker systems, the NaO
Note has been designed as a two component system in which the main panel and woofer system are carefully
integrated. Thus regardless of which woofer system is chosen the integration between main panel and woofer is
seamless. The dipole woofer design is provided for those who insist on full range dipole response. However, it
comes at a cost of approximately 6dB low sensitivity and maximum SPL than the U-frame format. The monopole
option provides an economical solution since it requires only a single driver per channel. Additionally, the
integration of a monopole woofer with the dipole main panel using a 4th order Linkwitz/Riley acoustic crossover
provides a smooth transition from dipole to monopole with an intermediate cardioid polar response through the
The design of the NaO Note continues to follow a hybrid approach. An active crossover is used between the
woofer and main panel and a passive crossover is used to control the panel driver set. The passive crossover is
designed in such a manner that its only function is to control the response of the panel drivers through the
crossover regions. Irregularities in the 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 the
previous application to the NaO II may be found under the NaO menu.
That the NaO Note accomplishes the design objectives set for it can be see by examining the comparison in the
polar response data between the NaO Note and the NaO II.
1) Low-frequency polar pattern control for improved in-room response. Juha Backman, Presented at the 115th
Convention 2003 October 10–13
The NaO Note has been superseded by the Note II RS. Information here is
presented only for historic reference. The objectives of the NaO Note are similar to
those of the NaO II but they are addressed from a different design approach. The design
differences are directed at maintaining constant directivity, above the sparsely populated
room mode frequency range, in the form of more uniform horizontal polar response in the
front hemisphere, and retention of the dipole pattern to significantly higher frequency than
currently seen in other dipole designs. The picture to the right shows the NaO Note panel
mounted on a redesigned NaO U-frame woofer system. The driver complement for the Note
panel consists of two Seas ER18RNX reed cone mid woofers, a Scan Speak Discovery
10F4424G upper midrange and a B&G Neo 3 PDR tweeter without rear cup. The panel is
effectively a 3.5 way design with the lower ER18 being used only boost the output below 300
Hz. The woofer system uses the Peerless XXLS 835016 subwoofer. Details may be viewed
here and to oder plans please see the Options and Pricing page. A complete driver set for
the Note is available from Meniscus Audio.
Many dipole speaker systems employ a baffle of constant width and the midrange driver(s)
are crossed over directly to either a single front or front and rear dome tweeters. Such
designs typically depart from the dipole radiation pattern above the crossover point where
the radiation pattern broadens or blooms significantly. The NaO Note addresses this
departure from the dipole response buy employing a contoured baffle with a small
mid/tweeter coupler driver, the 10F44424G. The contoured baffle in conjunction with the
directional characteristics of the 10F provide significantly improved polar response.