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Between 20-40 there is one octave like between 10,000 - 20,000 Hz - nothing new for the specialist. But few consumers know that the scale from the low C to high C fits into this 20 Hz range like it fits only one time only into 10,000 Hz range between 10,000 - 20,000 Hz. Therefore the high frequency range is overestimated - the deep bass underestimated. No music enthusiast buys a speaker limited to 10,000 Hz but most speakers decrease below 40 Hz or loose sound pressure capacity. Electronic generated tones and effects especially in movies request for much stronger deep bass. Good subwoofers can reproduce it but with increasing distortions. The hardest test for deep bass impulse is a natural bass drum with its short beats driving the speaker to the limit. If you compare "live" versus the speaker performance you will be mostly disappointed: instead of a very deep and short punch you hear a muddy "boom". Why?
| 1. | The drum diapghragm is much larger but lightweight compared to the speaker cone. Consequently it accelerates faster and stops sooner. And with just 1 mm excursion it pushes 3-5 times stronger air waves into the listening room as a 10-15" speaker at same excursion. The speaker must compensate with much longer cone excursion but slow reaction. After the bass drum has stopped the speaker cone still moves. At fast multiple bass beats the cone still flutters from the last beat when the next is just there. |
| 2. | Pushing up weak bass performance with bass reflex, bandpass and other "dirty tricks" comes at the price of even worse impulse performance compared to a closed box. But closed boxes are not loud enough deep down there. |
| 3. | The most expensive long throw woofers need extremely high power to force it very heavy cones to live sound. But the reaction speed is even lower now compared to the bass drum. Additional electronic feedback controls can reduce distortions but cannot elliminate the high moving mass problem. |
The horn concept
During the valve amp age with output power of hardly 50 watts high speaker efficiency was essential. Today the "side effects" are more important: unbeatable precision plus dynamic. The large horns seem to be exotic regarding todays cheap availbale high amplifier power. This allows good deep bass from compact size closed / bass reflex / transmissionline / compound / etc. boxes - but not very good plus very high sound pressure. With volumes of 20-80 liters the 10-15° drivers must have high moving mass and long cone excursion. That decreases the efficiency dramatically and can be hardly compensated with 1000 watts and electronic corrections. The heavy cone with long excursion delays the impulse answer much behind the signal. Even the best such closed or bass reflex boxes produce much higher distortions than good bass horns.
Conclusion: Well designed and built bass horns even before 1960 driven with 30 watt amplifiers are better regarding distortions, impulse response and dynamic range than the above described "modern" boxes.
The corner horn
Free standing horns for 20 Hz would need a length of more then 8 meters and a mouth opening of over 20 m². Even folded such monster is too big and ugly for the living room. Already in the 1940s ingenious inventors built corner horns that use the walls as horn extension.
Cylinder enclousure
A very high sound pressure will extremely press on the housing walls. High pressure containers therefore have shapes as spheres or cylinders which are much stronger compared to square flat wall boxes even with reinforcing inner parts. A speaker enclousure must even withstand steadily changing in/out pressure at different frequencies. Every flutter of the enclousure walls decreases the sound quality and the sound pressure. The RECKHORN cylinder enclousure avoids these problems. Starting from the pressure load volume the expotential extention presses the sound to the bottom and further into the room (patent application).
technical data:
RECKHORN H-80
| concept | front loaded coner horn with cylinder enclousure and bottom side sound output |
| design | cylinder covered with black microfibre textile and top side natural marble plate |
| driver | 13" woofer W-330D4 with dual voice coil |
| impedance | variable 2 x 4 ohms or 1 x 8 ohms or 1 x 2 ohms |
| efficiency | 95 dB 1 watt / 1 meter in 50 m² living rooms |
| frequency range | 20 - 500 Hz |
| recommended range | 20 - 80 Hz |
| power handling | 2 x 100 watts rms |
| impulse power | 2 x 200 watts / 2 seconds |
| dimensions | height 75 cm + foot 8 cm, diameter 39 cm |
| weight | 16 kg |
| recommended cable | 4 mm² up to 10 meters, 6 mm² up to 20 meters |
Driver W-330D4
| aluminium casting frame | diameter 330 x 365 mm, mounting hole 305, mounting depth 150 mm, 6-hole mounting diameter 335, large ventilation behind spider |
| magnet system | double ferrite rings with superior force, 3-point screw fixing yoke directly on the frame, ventilation holes for pole piece and air gap |
| voice coil | 2" glassfiber bobbin with 2 x 2 layer copper wire of 250 C° class,winding height 28 mm, ventilation holes above the wire |
| damper | 180 mm heat and long term stabilized NOMEX with integrated braid wire |
| cone | 600 cm² effective diaphragm from air dried non-pressed mix with carbon fiber, 6 corrugations for center cone reinforcement, 2-time chemically hardened, 30 mm wide and high excursion foam edge |
| dust cap | same material as cone with bullit shape |
| weight | 4 kg |
W-330D4 13" precision subwoofer driver
Unfortunately speaker construction is compromising. There is hardly one good feature without any disadvantage, examples:
very stabil diaphragm - high weight
high efficiency - lightweight weak cone
very long cone excursion - low efficiency
Fundamental know how and high quality parts are the conditions for an optimized driver. Even expensive bandpass and horn drivers have weak cones which cannot withstand the high air load resistance of front loaded horns. If you press from the back side into the middle of the diaphragm you can make it into a curve. The W-330D4 cone has an unmatched stability-weight relation - the most important condition für precision sound.
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B: The double magnet from enriched strontium ferrite has 30% higher force as standard magnets.
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D: diaphragm made from non pressed pulp mixture with carbon fiber, waterproof and chemical hardener. The unusual horizontal strength is a result of the 6 corrugations with very little extra weight.
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G: The double voice coil consists of 2 x 2 layer round copper of the 250° C class regarding enammel and adhesive. The voice coil former from glassfiber has an additional glassfiber collar above the wire for increased stability. 5 ventilation holes in this area increase the cooling of this hot spot between magnet pole and dust cap.
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