Thiel Drivers, Cumulus Horn 2

Cumulus Horn 2 as in Hobby HiFi 2/2009 - with pure three-dimensionality

Technical data:
- impedance: 4 Ohm
- rated SPL (2.83V/1m): 89 dB
- size (HxWxD): 105 x 22 x 43.5 cm
- frequency range (-3dB): 50-40 000 Hz
- crossover frequencies: 1600 Hz
- speaker type: exponential horn

In addition to the projects Cumulus and Cumulus Horn a new variant, the Cumulus Horn 2 with Thiel SCS4, is now available.

Like the Thiel SCS3 the SCS4 is a coincidentally mounted driver (coincident source array) where tweeter and bass drivers are mounted on the same vertical and horizontal axis, resulting in time and phase coherence regarding low and high frequencies.

Bernd Timmermanns, the editor in chief of Hobby HiFi, describes in issue 2/2009, how to design a bass horn using this driver, resulting in a speaker that not only shows correct timing but also ample bass.

With more than 20 components the 6 dB crossover looks quite complicated. 6 dB are realised by two components, a coil in the path to the bass driver and capacitor in the path to the tweeter. The remaining components are smoothing exaggerations by the tweeter from 20 to 30 kHz, or exaggerations by the bass driver (wave trap) or flowing into the pull circuitry carrying out minute corrections in parallel to the tweeter and bass driver.

To those who wish to use a valve amp we recommend 6 additional components to correct the impedance.

To build the cabinet some woodworking experience is required. The cabinet consists of many boards, some with mitre cuts.

Excerpt from the review in Hobby HiFi 2/2009:

... "From the beginning these slim horn speakers showed an enthusiastic liveliness and simultaneously great authority. The Hilton Ruiz Ensemble's "Home Cooking" (Something Grand) was reproduced with sheer unbelievable verve. The extensive drumming on this recording seemed to trigger one explosion after the other. All instruments were within reach and portrayed with a three-dimensionality we rarely had the opportunity to experience. Afterwards, Nils Lofgren demonstrated with his unplugged live version of "Keith Don't Go" how diverse his acoustic guitar playing is. The explosive dynamics of this recording flabbergast time and again, but this time the performance reproduced with a Marantz CD player and a Stax power amp was even more direct and transparent. Every picking of the string had its own unique character. That can only be done by a speaker with outstanding attention to detail and the Cumulus Horn 2 is one of these rare breeds." .....

Verdict in Hobby HiFi:

"The Cumulus Horn 2 is simply magnificent. Those who don't require high volumes will discover clarity and truthfulness, as well as tonal perfection combined with exceptional three-dimensionality. The loudspeaker vanishes, just music fills the room."

Our kit contains:

- Thiel SCS4 coincidentally mounted driver
- 2 x gold plated brass binding posts
- 1 mat Bondum 800
- 1 Pack Polyester Dämmstoff
- 0.5 x foam sealing tape
- 6 x Allen screws 4x16 mm

- 3 m cable 2x2.5 mm²
- the crossover components
(for standard and high-end version, see below)

- building instruction

with standard crossover:
- 2 x PCB's RA 160
- 1.5 mH backed varnish air core coil 1.4 mm
- 4.7 mH i-core coil (backed varnish wire)
- 2.2 mH backed varnish air core coil, 0.7 mm
- 0.68 mH backed varnish air core coil, 0.7 mm
- 0.01 mH backed varnish air core coil, 0.7 mm
- 2.2 mH backed varnish air core coil, 0.7 mm
- 100 uF ELCO, non-etched
- 33 uF ELCO, non-etched
- 15 uF MKP capacitor
- 3.3 uF MKP capacitor
- 0.82 uF MKP capacitor

- 1.5 uF MKP capacitor
- 6.8 uF Mundorf MCAP Supreme
- 3.9 uF MKP capacitor
- 22 uF ELCO, non-etched
- 10 Ohm resistor MOX10 (brown-black-black)
- 3.9 Ohm resistor MOX4 (orange-white-gold)
- 6.8 Ohm resistor MOX4 (blue-grey-gold)
- 4.7 Ohm resistor MOX4 (yellow-purple-gold)

with high-end crossover:
- 3 x PCB's RA 160
- 1.5 mH cfc10 Mundorf foil coil
- 4.7 mH cft12 foil transformer core coil
- 2.2 mH cfc14 air core coil, 0.7 mm
- 0.68 mH cfc14 air core coil, 0.7 mm
- 0.01 mH cfc14 air core coil, 0.7 mm
- 2.2 mH cfc14 air core coil, 0.7 mm
- 100 uF MKP capacitor
- 2 x 22 uF MCAP RXF
- 6.8 uF MCAP Supreme Silver Oil
- 3.3 uF MCAP Supreme Silver Oil
- 0.82 uF MCAP Supreme Silver Oil
(0.47 uF in parallel to 0.33 uF)
- 1.5 uF MCAP Supreme Silver Oil
- 6.8 uF MCAP Supreme Silver / Gold Oil
- 3.9 uF MCAP Supreme Silver Oil
- 22 uF MCAP RXF
- 10 Ohm resistor M-Resist Supreme 20W
- 4.7 Ohm resistor M-Resist Supreme 20W
- 6.8 Ohm resistor M-Resist Supreme 20W
- 5.6 Ohm resistor M-Resist Supreme 20W

Both crossover kits comprise Mundorf components: the Mundorf MCAP 400V capacitor, Mundorf backed varnish and i-core coils resp. foil coils (high-end version) and foil transformer core coils (high-end version. In the signal path to the Thiel tweeter (high-end version) a Mundorf Supreme Silver Gold Oil is being used (in accordance with Hobby HiFi).

Price for Cumulus Horn 2 kit, with high quality crossover, without impedance correction:
without cabinet per unit: EUR 867,00

Price for Cumulus Horn 2 kit, with high-end crossover, without impedance correction:
without cabinet per unit: EUR 1433,00

Impedance correction

If you prefer to use a valve amp we recommend mounting the following components on the additionally supplied PC board (RA 160):
- 1x 4.7 mH backed varnish air core coil, 0.7 mm
- 1x 0.22 mH backed varnish air core coil, 0.7 mm
- 1x 22 uF ELCO, non-etched
- 3 x 680 uF ELCO, etched (in parallel)
- 6.8 Ohm resistor MOX10 (blue-grey-black)
- 4.7 Ohm resistor MOX10 (yellow-purple-black)

These components are sufficient for both, the standard and the high-end version. However, upon request we also supply higher quality components (cfc coils, ELCO non-etched, MCAP RXF …).

Price for den impedance correction for one speaker: EUR 44,65

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