Advanced Loudspeaker Application Development Project

Multiple-Degree of Freedom Cavity Resonator System

Project MCAP-CR

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QNDR(Quasi-Non-Dimensional Radiator) with MCAP-CR
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NDR was proposed by a Japanese engineer about thirty years ago. His name was Mr. Kono. He passed away already.

My friend Mr. Matsu foud NDR very interesting and frequently visited Mr. Kono .

Mr. Matsu thought that NDR would take effect with MCAP-CR enclosure, and he did it.

I heard his work and found NDR will be good for sound field presence.
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 QNDR is more sinple than NDR. I tried just to simplify NDR and to get similar effect as NDR. It was the QNDR.
 As a result, QNDR brought very different, but remarkable effect!!!
Let us review NDR's features:

NDR, per channel, is equipped with drivers in three surfaces as seen in Fig.1.

Fig.1 Concept of NDR

 Front driver undertakes direct radiation of sound, and rear drivers undertake indirect radiation. Indirect radiation will be reflected by walls or any other objects in the listening room and reaches the listener. Some part of direct radiation, as well, will be reflected by walls and reaches the listner, but direct effect is larger. According to Mr. Matsu, indirect radiators were sometimes, tweeter and direct radiator was combination of woofer and tweeter. Thus NDR did not employ same drivers as direct and indirect radiaters.
 When I heard demonstration of Mr. Matsu's NDA work, sound field was very wide and clear. I felt that arrangement of each musical instrument had been clearly seen.

 I agree to that NDR is wonderful system. On the other hand, NDR has following disadvantages:
  1. Enclosure is not easy to build, because cross-section is not square.
  2. Drivers cost much.
  3. Level adjustment of indirect radiator is required.
  4. Network circuit is necessary.
  5. Number of tuning parameters is too many.
 QNDR was designed to avoid above disadvantages of NDR.
 Fig.2 shows idea of QNDR.


Fig.2 Concept of QNDR

 Hire are the advantages of QNDR compared with NDR.
  1. QNDR has squared cross section as seen in Fig.2. This lets builders to assemble the enclosure easily.
  2. QNDR employs cheap small full-range drivers. Lower frequency is compensated by MCAP-CR.
  3. There is no level adjustment for indirect radiators.
  4. There is no network circuit. Four drivers are connected jus serial-parallel.
  5. There is no tuning parameters.
  Sound pressure level of each driver of QNDR is same, so that efect of two drivers in the front is conbined so that they behave a little bit intensive. Inner front drivers take direct effect, while outer front drivers take indirect and direct effects.
 In case listner shifts to right or left, then one outer front driver takes direct radiation effect.

 QNDR is thus simple, but interesting. Actual performance of QNDR is:

Advantages:
  1. Sound field effect is not lost if listner moves anywhere in the room. It means that listners can enjoy music wherever they are.
  2. Sound field is larger, and listening room is filled with indirect sound.
  3. Power imput capacity becomes four times than single driver system. It is effect of serial-parallel connection.
  4. Low frequency level is enough, though small full-range drivers are used. It is effect of MCAP-CR with four drivers.
Disadvantages:
  1. Sound field is not as clear as NDR or single driver system.
  2. Level of higher frequency drops. This is effect of using four drivers: each driver interfers and high frequency drops.
 Actually building QNDR, I became very sure advantage is much bigger than disadvantage. Especially, 1st advantage is outstanding for users who enjoy music in living room or other spacious room. Not being specified listening point is unexpected effect!

 Here is drawing of a QNDR model (model# DU050x4).




Below is assembly process. Two sets were made simultaneously.

Material plate (pre-cut)
Paper ducts were inserted to flanges
Outside paper is laminated to adjust diameter to flange



Internal ducts are just glued
Ducts are smoothed and coated

Flanged ducts are fixed with glue and screws
Internal structure


Triangular log is glued to corner

Trianguler log is glued and fixed to corner

Exterior is painted
Now complete

Used drivers for DU050x4
Used drivers for 2 systems:

Left:   FF57BK (Foster) x 8 units (for 1 pair)
Right: W2-802SE (Tangband) x 8 units (for 1 pair)

Other 2" drivers may suffice.
Drivers with rigid frame are recommended.

There is another 3" model (DU080x4) . You may request drawing of 3" models.

mail to: mcapspeakers@gmail.com


  MCAP-CR is patented by Japan Patent Office (patent# 5083703).
  It is not for commercial use without contract.
  Try one of applications and make sure that MCAP-CR is good for highest-end applications, if you are interested in commercial use.

  This is personal small laboratory. Any kind of financial assistance is appreciated.
 
  Contact me at: mcapspeakers@gmail.com .

  Author: Shigeru Suzuki