The Proteus - To D' Appolito or not to D' Appolito, that is the question
By Tony Gee
27 Feb 2001
To D' Appolito or not to D' Appolito? That is the question.
Version nr. 1 - The D' Appolito version.
It sounds smooth and sweet with a nice wide sound stage but the sweet spot is a little narrow. The sound stage is more forward than deep. Bass is tight and deep considering the modest size of the speakers. A surprising thing is that the bass is tighter than with the 2-and-a-half-way system. If you listen a lot to jazz trio's and classical quartets you will be amazed by the amount of detail, but if you like Top 40 pop and rock you will probably find this filter a bit on the bright side. It is not at all harsh just very revealing. Efficiency is high at about 92,5dB's for 2,83V/m, so it won't need much power to get loud. The impedance varies around 4 ohms.
Version nr. 2 - The non-D' Appolito version.
This version has a very 3-dimentional sound, not only very wide but also with more depth than the other version; very enveloping. The sound is very open and warm, bass is full and deep. Basically it is an all-round speaker with no preferences for any type of music. The tonal balance seems more neutral than the D' Appolito version partly because of the extra warmth and forwardness in the midrange. Maybe the ideal phase characteristics contribute to this. Efficiency is about 91,5dB's for 2,83V/m and the impedance a very smooth 5 ohms.
Of course there is nothing to stop you building both filters and trying out which one you prefer. Or to have both so that you can switch filters depending on what kind of music you are playing.
Measurements.
For both versions I have made three measurements.
The relative output level.
The horizontal scale is 5dB's. Both have a relatively flat response with version nr.1 +/-2,5dB over the whole range with a gradual roll-off towards the top end. This is measured with a 1-ohm resistor in series with the tweeter. The peak at about 2500 and 3800Hz is due to cone break-up of the CB17RCY/P. Fig. 13. Image 13
Version nr.2 is even smoother with +/-1,5dB over the whole range and completely flat right up to the top end. I must modestly say that I was positively surprised when I first saw these readings. This is measured with a 1,5 ohm resistor in series with the tweeter. Fig. 14. Image 14
The step response.
Here you can clearly see the differences in phase. Version nr.1 spikes up and down at the beginning showing that the signal from the tweeter arrives first and then about 0,2ms later in opposite polarity the signal from the two woofers. It then continues with fluctuations of about 0,05 Volts. Fig. 15. Image 15 But don't worry, it all looks more serious than it is, many commercial loudspeakers spike up and down for several milliseconds before starting on the decent.
But how about version nr.2 Wow! Fig. 16. Image 16 The rise time is practically vertical with no up and downs. It then continues with nearly no fluctuations at all. This shows that the 30mm thick additions on the baffle are doing their work.
The waterfall response.
The waterfall spectra show some interesting results. The tighter sounding bass with the D' Appolito version can been seen in a shorter decay in the bass and low midrange up to about 1000Hz the only difference here is the filter. Fig. 17. Image 17 The cone break-up at 3800Hz can easily be seen being less prominent in version nr.2 because only one of the woofers is active in this region. Fig. 18. Image 18
Programme material.
I thought it might be interesting to make a list of some of the music I listen to when tuning my loudspeakers. I listen to many CD's and also a lot of radio. The human voice is still one of the best instruments for tweaking speakers.
1. Mathew Locke - Consort in Fower Parts performed by Hesperion XX on the Astree Auvidis label.
2. Johann Sebastian Bach - Weihnachts Oratorium BWV 248 performed by Collegium Vocale Gent, conducted by Phillipe Herreweghe on the Virgin Veritas label.
3. Wolfgang Amadeus Mozart - Quartets for pianoforte, violin, alto and cello K478 and K493 performed by Paul Badura-Skoda on the Arcana label.
4. Giovanni Antonio Grossi - Saints and Sinners performed by Capella Figuralis, conducted by Jos van Veldhoven on the Channel Classics label.
5. Buena Vista Social Club - Buena Vista Social Club on the World Circuit label.
6. John Scofield - A Go Go on the Verve label.
7. Chick Corea & Origin - Change on the Stretch Records label.
8. Tony Overwater - OP on the Turtle Records label.
9. Bassdrumbone - Hence the Reason on the Enja Records label.
Please and thank you's.
I would be very pleased if anybody who is going to build a pair of these speakers could send me a photo of the finished result. Some of the images for this article were made by an audiophile friend who also built a pair (thanks Jan). His speakers can be found at:
http://members1.chello.nl/~j.deckers05/tonycuben.htm
NOTE: This design is strictly for the home DIY enthusiast and not to be used professionally without my permission!
Tony Gee
The Netherlands
geenius@usa.net
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