AES meeting January Loudspeaker Design: Tradition versus Science [London]

[dragonser]

Hi,
the next Aes meeting in London has a talk about Loudspeaker design.
Title: Loudspeaker Design: Tradition versus Science [London]
Location: Royal College of Pathologists, 2 Carlton House Terrace, London. SW1Y 5AF
Description: Lecture by John Watkinson
Start Time: 18.30 for 19:00
Date: Tuesday 10th January 2012

more detail available via their web site.
http://www.aes-uk.org/

just thought I would mention it in case anyone is interested.

regards Peter B

[revtonynewnham]

Sadly, there's no way I can get there.  Should be interesting though.

Every Blessing

Tony

[dragonser]

Hi,
it was an interesting meeting, and one of the most well attended that I have managed to get to.
John Watkinson gave the talk and also demoed some new speakers.
to my ears they sounded very nice,  and he used some Organ Music to demonstrate the good bass response......
a link to a pdf by John Watkinson.
http://www.audiophilerecordingstrust.org.uk/articles/speaker_science.pdf
He also mentioned that he writes for resolution magazine, which I hadn't heard of before.
http://www.resolutionmag.com/content/slaying-dragons

regards Peter B

[revtonynewnham]

Hi Peter

Thanks for this - I've bookmarked the Watkinson link to read later.  Resolution is the successor to the late, lamented "Studio Sound" - anyone in pro audio can get a free subscription (see their web site - just search for "Resolution Magazine").  IMHO it's not as good as Studio Sound, but still makes an interesting read.

Every Blessing

Tony

[David Pinnegar]

Dear Peter

Thanks so much for your report on this and for giving the links.

Associated with the links:
http://www.resolutionmag.com/pdfs/DRAGONS/SPEAKE~1.PDF is interesting, dealing with the issue that member Contrabombarde raised a few weeks back.

Of the main link the following is of interest:

Using a codec to measure the bit rate of a speaker gives a direct assessment of its figure of merit.
The use of this technique has had some further interesting consequences. Traditional
loudspeakers use ferrite magnets for economy. However, ferrite is an insulator and so there is
nothing to stop the magnetic field moving within the magnet due to the Newtonian reaction to the
coil drive force. In magnetic materials the magnetic field can only move by the motion of domain
walls and this is a non-linear process. The result in a conductive magnet is flux modulation and
Barkhausen noise. The flux modulation and noise make the transfer function of the transducer
non-linear and result in intermodulation.
The author did not initially believe the results of mathematical estimates of the magnitude of the
problem, which showed that ferrite magnets cannot reach the 16-bit resolution of CD.
Consequently two designs of tweeter were built, identical except for the magnet. The one with the
neodymium magnet has higher resolution, approaching that of an electrostatic transducer.

I have been fitting conductive pole pieces to speaker magnets recently to useful success noticeably reducing bass harmonic distortion and giving more control to the cone but the percieved advantage of neodimium magnets over ferrite mentioned here is interesting. One speaker company of which I am aware makes units with AlNiCo, Ferrite and Neodimium but comparisons are not on a level playing field as the geometry of the speech coils and connexions with the cone differs between the Ferrite and the other models.

However, an American company selling speakers originating from Chinese factories uses copper pole pieces as standard and markets the same cones fitted with the differing magnets. The latest neodimium unit does indeed have a better defined high treble response.

Best wishes

David P

[KB7DQH]

Unfortunately reflections with delays of the order of 700 microseconds are exactly what are
provided by the legacy rectangular loudspeaker with sharp corners. These reflections are due to
acoustic impedance changes and if we could see sound we would double up with mirth at how
ineptly the sound is being radiated. Effectively the spatial information in the audio signals is being
convolved with the spatial footprint of the speaker. This has the effect of defocusing the image.

I guess my next question is which surface of the speaker enclosure needs to be made "non-rectangular" to reduce or eliminate this "defocusing" ??? ??? ???

I ask this as I have constructed two pairs of speaker enclosures to place some automotive speakers I have had lying about that apart from the defects common to these "commodity" devices-- appear to function unexpectedly well and compare favorably to and actually "sound better" than high-quality commercially produced devices.  And the enclosures are NOT rectangular except for the speaker mounting surface and two other side panels of equal dimension ;)   

Eric
KB7DQH