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Pioneer BU20F20-51F
Comments: This speaker gets the prize for "listenable at lowest cost". It is not as efficient as a Lowther or Fostex but it has a smooth-enough character to be fairly easy on the ears. It's not as detailed but that's alright if you like Lounge music. It also can take more abuse than its more refined competition if you like to dance. Driven by a voltage source, there is a temptation to stick a tweeter on the top and indeed, an inexpensive ¾" dome with a 1uF cap just about does the trick. With a current source, you obviously get more bottom end and it does require a network to shelf down the treble to what you see here - a simple RLC in parallel will do nicely. The R0 value is 23 ohms, low enough that if you want to play with these effects without owning a current-source amplifier, you can put 25 ohms of power resistor in series with the output of a 100-watt amp and get a Thevenin equivalent of a current source loaded by the same resistance. Will it sound as good? You have my email address – let me know.
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GOLDWOOD
Comments: The Goldwood is the cheapest driver of this bunch, being slightly less than the Pioneer, but what's a couple of bucks between friends? These were my least favorite of the group – they lack the dynamics and detail that we are looking for. They'll work well enough for your bathroom and other such applications but as audiophile efforts, they aren't nearly as satisfying as the Pioneer drivers for $4 more.
Conclusion
So here you have it - a re-examination of some things that have been known for a long time but were here tested with currently available drivers. It's easy to dismiss the older ways. Somewhere in the 1960s, the speaker/amplifier interface took a left turn and headed off to high-power voltage source amplifiers and speakers designed to lean on them for performance. A small group of iconoclastic cranks has stayed interested in these fossils and in the end, we have to recognize fullrange high-efficiency speakers as offering elegance, charm and a different sort of quality.
Current sources and amplifiers with low damping offer interesting possibilities for improvement with these drivers but they require considerable work to get the enclosures, electrical networks and acoustic environment just right. Remember, you don't have to own a current-source amplifier to put this information to work. Placing R0 in series with the output of a powerful voltage-source amplifier instead of in parallel with a current source will give similar results. If R0 is 47 ohms or higher, you are going to want a big amp, say 300 watts, but in any case, be certain to use a high-power resistor of 50 watts or more. That said, it's all just entertainment and I hope it inspires some of you to have fun.
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Thanks to:
Kent English, Desmond Harrington, Jon Ver Halen, Terry Cain, Ed at the Horn Shop, Chris and Matt Williams.
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