Multiple Pipe Resonator Loudspeaker System

Multiple Pipe Resonator (MPR)  Loudspeaker System (Released: 2011/01/24)

Approximately 30 years have passed since Tetsuo Nagaoka promoted pipe resonator loudspeaker systems. His works were single pipe resonator system using powerful fullrange drivers. Many amatuer speaker craft freaks supported his systems as high fidelity audio systems.

I propesed single pipe resonator with holes in 2004. Idea of this resonator is to add some more resonant frequencies. Some more information is in Japanese page. This application brought reasonble effect.

This time I present more epoch-making applcation named multiple-pipe-resonator (MPR). MPR was invented by Mr. Osawa in 2010. He was interested in MCAP-CR application and he actualy made his MCAP-CR application. Based on the idea of MCAP-CR, he found it would be applicable to pipe resonator application. He sent this idea and application report to a DIY group that propmtes PVC pipe loudspeaker systems.

He actualy made PVC pipe resonator application and tested with his hand-made oscilator. He made sure this MPR accurately works as he designed. Resonant frequency measure was performed using the oscilator and "hand". Human hands can detect pressure wave so that we know using "hand" sensor if the frequency is resonant or not.

Structure of MPR is shown in the following Figure 1.

Figure 1  Structure of Multiple-Pipe Resonator (MPR)

MPR consists of back pressure distributor chamber, required number of pipes (strait or folded), and throttles between pipes and back pressure distribution chamber. Throttle is just a hole but very important to let MPR work as designed.
In this example in Figure 1, there are four pipes. Number of pipes may be two or more. According to the inventor, Mr. Osawa, required number of pipes may be only two and three or more pipes may not be necessary.

Resonant frequencies are given in Table 1:

Table 1 Resonant Frequencies of MPR
Resonant Frequencies[Hz]
Pipe length = L1 c/4L1, 3c/4L1, 5c/4L1, ...
There are theoretically unlimited resonant frequencies.
Pipe length = L2 c/4L2, 3c/4L2, 5c/4L2, ... There are theoretically unlimited resonant frequencies.
Pipe length = L3 c/4L3, 3c/4L3, 5c/4L3, ... There are theoretically unlimited resonant frequencies.
Pipe length = L4 c/4L4, 3c/4L4, 5c/4L4, ... There are theoretically unlimited resonant frequencies.
Note: c represents speed of sound in air (approximately c = 346m/s at 25degreeC).

There are some more things to discuss. Followings are unknown at present:
  1. How to determine cross-sectional area of each pipe and summation of cross-sectional area
  2. How to determine area of throttle
  3. How to determine volume of back-pressure distribution chamber
MPR may acts as cavity resonator. It is uncertain at present if this cacity resonator effect may be ignored or not. This also must be discussed in the future.

MPR is thus very simple and frexible and as well easiily applicable. This system should be recognized as epoch-making finding.

I keep working with Mr. Osawa and update informatiom.

Thanks Mr. Osawa!