I can recommend the
by Dick Olsher and all its
after building all kinds of speakers for the last 20 years. You can even
improve this idea by activating it like I did and use high Qt drivers.
Right now I´m using different kinds of 8
inch German vintage widerange drivers without crossover in my open-cabinets.
A Saba Greencone 1672
with its special Saba cone-tweeter as you see
above and a Loewe-Opta from 1953 without
additional tweeter . These drivers are from
the fifties and were used in console tube-radios. They have two advantages
compared to modern fullranges. They have a high Qt which makes them more
suiteable for open-baffle application and I can therefore cross them with the
sub between 100 and 200hz with 24db. Furthermore they have no interfering
whizzer-tweeter, which beams a lot and makes voices sound harsh in my opinion.
The disadvantage is the additional tweeter. But I cross it with
1µF beyond 8khz. As
a woofer I use 15 inch JBL E-145 speakers in 125
liter bass-reflex cabinets.
The System is
driven by a 6c33c-b DIY SET tube amplifier and tube preamp with double outputs(2x2
ECC82) built by a friend; the woofers by a HiAmp100
DIY ic-amp(dual-mono TDA7293v). There is no
crossover in front of the Saba Greencones or Loewe-Optas; the
acoustic short-circuit of the open-baffle is the
high-pass acoustic crossover. The woofers are separated by a digital crossover,
tuned Behringer DCX-2496. I also use the DSP to eliminate the resonance of the
room at about 60 hz. The system is fed by a Sony SACD-player SCD-XE670.
I had been
using the Fostex FE208 Sigma recommended by Dick in
an open baffle with the LCR-correction of the Jericho
horn, but I dropped it due to its low Qt, which forced me to cross in the
woofer too high in the range of deep voices. Other reasons were the whizzer and
the strong beaming. To my taste these factors make voices sound harsh. It had
the typical Fostex-sound. You have to like it. In my opinion high Qt horn
drivers, like Lowthers and Fostexes, should not be mounted on open baffles,
because their amplitude begins to fall at about 400hz towards the low end. No
matter how large the open-baffle is designed.
Advantages for the
sound of this (activated) system:
reflections on the back of the cone from the cabinet.
2. Single point source between 100hz and 8 to 10khz.
3. High dynamics without horn sound. All horns I know
have to be separated in the frequency of the voice. It is very difficult to
achieve a good sounding crossing in this area. I tried it for some time with
JBL 2446j drivers and 2380a horns combined with JBL K130
15 inch woofers. I have also listened to a commercial 50.000,- $ high-end
4-way system in my neighbourhood. Voices were not much better. Just too many
sources. Dynamics is not everything!
sensitivity for feeble SET-amps (2A3, 300B) or small but fine solid state
class-A amps (Nelson Pass and André Buscher).
5. Strong and cheap Mosfet- or Chipamps, like Gainclones or
subwoofer-amps, can be used to drive the woofer. The quality does not have to
be high-end, because they only work up to about 100hz.
6. Full control on the woofer with Mosfet-amp without passive
7. Affordable woofers with lower
efficiency can be adapted to high efficiency drivers. It allows me to combine
all kinds of drivers, for example a fullrange Vifa
10BGS 119/8, without any correction, in a 4 litre sphere made of clay,
hanging from the ceiling with the JBL´s or two Klipsch horns and a
crossing at 50 hz. Beautiful pinpoint sound with little dynamics.
8. Easy adjustment to the room resonance and the amount of
bass you prefer according to the recording. There are no standards.
9. The cabinets are easy to build compared to horns.
1. Placement away from the
wall behind for at least 5 feet.
Vintage drivers are hard to find, but
ebay and DIY can help! Use a cheap subwoofer-amp with built-in active crossover
to include in the cabinet of the woofer. Short cables!
3. Bad recordings become unbearable to listen to. Lots of
cd´s for Christmas for others!
Two more flavors of the system
1. Another speaker is a
Fostex FF85K 4 liter sphere made of clay
without crossover. It has the best Bl to Mms acceleration factor (BL 4,33 /
0,0018kg = 2405) of any fullrange driver I know. No other Fostex, Tangband,
Lowther or Jordan can beat it!
With kind permission
from Udo Spieker and Markus Redemann:
An Excel-file with the TSP of 7 different Coral Beta 8
calculating an average : Coralbeta8.xls Data of the Flat-fullrange-series
Flatallg.jpg and an overview of the high-power
studio drivers Coralka.jpg.
were taken with digital cameras kindly provided by Jörg Birkemeyer and