25-Apr-2015: This is a summary in German language about analog audio interfaces. Based on excellent and essential papers of Bill Whitlock and Bruno Putzeys it explains why and how single-ended in- and outputs are a very fragile construct with obvious sonic deficiencies.
The paper was put together for the German speaking DIY-community and I keep updating it as I find new details worthwhile mentioning.

21-Nov-2014: Be part of the Philips Golden Ears challenge.
Here is a nice and at times challenging listening training and test.
It is recommended to sign up, which allows to save the progress.
Most of the decisions are a question of milliseconds. But MP3 compression nowadays is not really easy to hear beyond 128kbps, and virtually only if there is polyphone ringing.
I found that some of the differences are easier to hear with closed headphones compared to an open headphone like the Sennheiser HD 650, which I prefer otherwise for listening (I just don't like the coconut shell type of sound of a Beyerdynamic DT 7xx long term).

03-Aug-2012: Douglas Self presents extracts from his well done book about active cross-overs at the Burning Amp Festival 2011.
An anecdote about the book:
I was reading it around October 2011 partly during vacation on a scuba diving safari. One of the instructors was asking what thick a book I would read and I said that it had to do with loudspeakers, which was my hobby etc. And the guy was like...what, you can write a book about loudspeakers ?!? And I said: Weeellll, you is actually only about cross-overs for loudspeakers. And he was like...WHAT ?!? you can write a book only about cross-overs for loudspeakers ?!?
In the end I did not tell him that the book was actually only mainly about analogue active cross-overs for loudspeakers...J

Updated 01-Jun-2012 to add some better explanations and due to some interesting findings with Demokrit (originally posted 23-Nov-2011):
This is an interesting article by Alvin Foster, member of the Boston Audio Society (BAS). It was originally published in May 1999 in the BAS Speaker (BASS), which is the newsletter of the society (Volume 22, Number 2). The link embedded in the document was recently posted in a discussion at I have created the pdf with my comments and markups.
Over the time I have obviously come to many equal conclusions as the author.

22-Jun-2011: Initially, I did not want to link this because it is available from other places. But I am still so pleased about it as matches my personal experience so well. Increased directivity and less excitation of room modes etc. cannot be the only reasons why dipole bass sounds like it does compared to monopole subs. And I still wonder how cardioids and multi mono sub arrays would compare.

12-Nov-2010: Photo show about the Seas factory.

15-Oct-2010: Video about the Scan-Speak factory.

Last updated 27-Mar-2017