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March 21, 2010 / consort3

Pioneer Powerbass

This was used in a mini music centre.

We bought the music centre (XR-P270C) for my daughter as the speakers looked deep enough to have a long port but mainly because it sounded good. The edge of the woofer cone intrigued me as there appeared to be no surround!

The mystery was solved by Forr off the Diyaudio forum I saw his  ‘cabinet de curiosities ‘ on the Audax forum and there were pictures of a stripped down speaker The picture shows that the roll surround is attached some way down and behind the cone. The other interesting feature was the stuffing seemed to be pieces of torn paper! The question is whether the ‘waveguide is cosmetic or does it have some function?

🆕Genelec appear to have borrowed this idea for their latest active monitor:

Update: Waiting for Bodot

Surfed the Audax forum and found  Jean-Claude (aka JCB) who uses some ideas on negative impedance output amplifiers which I used on my Consort design. Ian Hegglun pointed out in an article in Wireless World that it was a form of motional feedback. The Sony SA-W2500 appears to use the technique and makes the motional feedback claim. Interesting Diyaudio thread on this:

Jean Claude has spent 40 years developing the idea. See this in french for a project:

My project based on the idea can be found here:

There is a link on there to the original ETI article. As well as negative resistance that project used 10dB of boost in a sixth order alignment. I found that 6dB of boost was about right and if it was at the port tuning frequency the excursion,  being a minimum there would not be too compromised. Then lo and behold  I found Don Keele’s paper describing exactly that:

Here is the original paper from Werner in 1958 on the negative resistance technique:

Interesting analysis of the Negative technique on pages 72 and 73 of this Phd thesis:

Is negative resistance a form of Motional feedback? That is the question. For fans of the Philips MFB version there is a Dutch website:

I use Imtranslator to translate the above site

Another sensor for the motional feedback concept that I was unaware of until now

Some papers on the Negative resistance idea:

These guys did not get a fair crack of the whip when their book Current driving of loudspeakers came out

Thread here. Would have commented but did not find thread as title inappropriate! Also mean time in window (MTIW) of typical Diyaudio threads is 3 hours so you can easily miss interesting topics

The forum discussions on these topics have degenerated into arguments mainly about semantics which is a pity as the negative resistance concept is simple and easily implemented.

A while ago I found out about Bose’s automotive woofers which have the magnet and voice coil inside the cone

The Gego Orthophase speaker had such a woofer back in the fifties! Test of Bose here:

Discussion on the concept here:

Bose have an interesting Bluetooth speaker

Another solution to the slim speaker problem, the dome woofer:

More on the MFB system

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