The chassis measurements were taken inside the Duetta cabinet. Data from a standard baffle board creates completely inaccurate results in simulation programs if the influence of the simulation program is not taken out and the influence of the baffle is not taken into account. .

Eton ER4

Manufacture:                LPG, Neu-Ulm
Sales:                          Intertechnik, Kerpen

Equipment:
Membrane:                   accordion film
Voice coil:                    vacuum metallized conductor
Magnet:                       4 neodym plates
Magnet:                       4 neodym tablets
Magnetic shielding:       no
Mounting holes:            4
Outside diameter:         110 mm
Installation opening:      84 x 94 mm
Milling depth:                3 mm
Installation depth:         13 mm

Parameters
RDC:                 3,9 Ohm
SD:                    67 cm²
Qm:                     18,4
Qe:                      30,3
Qts                      11,4
fs:                     523 Hz

Eton 7-360/37 Hex

Parameter
Fs                47. Hz
Diameter          128 mm
Re               5.3 Ohm
Rms             1.73 kg/s
Qms                2.91
Qes                 0.40
Qts                 0.36
Cms           0.67 mm/N
Mms          17.0 Grams
BL               8.14 Tm
VAS            15.5 liters
dBSPL            88.1 dB
L 1kHz           1.12 mH
L 10kHz          0.42 mH
SD               129 cm²
MMD         16.2 grams
Z Min            6.0 Ohm


Equipment
Membrane:              hexacone
Surround:                rubber
Basket:                   die cast aluminum
Pole pice hole:         yes
Centering:                air permeable spider
Magnetic shielding:   no
Voice coil:                37mm copper on aluminum base
Yoke thickness:        8 mm
Linear stroke:           7 mm
Magnet diameter:     102 mm
Mounting holes:        8
Outside diameter:     186 mm
Installation opening:  160 mm
Milling depth:            8 mm
Installation depth:      84 mm

Chassis manufacture:LPG, Neu-Ulm
Sales:                      Intertechnik, Kerpen

Eton 11-581/50 Hex

Parameter
Fs                 22 Hz
Diameter          216 mm
Re              5.2 Ohm
Rms             1.16 kg/s
Qms                7.15
Qes                 0.32
Qts                 0.31
Cms           0.88 mm/N
Mms          60.4 grams
BL               1.6 Tm
VAS            164 liters
dBSPL           89.3 dB
L 1kHz           1.53 mH
L 10kHz          0.63 mH
SD              366 cm²
MMD         56.4 grams
Z Min            5.7 Ohm


Ausstattung
Membran:                hexacone
Surround:                 rubber
Basket:                   aluminum die cast
Pole piece hole:       yes
Centering:                air-permeable spider
Magnetic shielding:  no
Voice coil:           50mm copper on an aluminum base
Yoke thickness:       8 mm
Linear stroke:          7 mm
Magnet diameter:    102 mm
Mounting holes:       6
Outside diameter:    281 mm
Installation opening: 244 mm
Milling depth:           8 mm
Installation depth:   103 mm

Chassis manufacture:LPG, Neu-Ulm
Sales:              Intertechnik, Kerpen

 Cabinet

 The structure of the cabinet evolved through multiple steps. While the whole bass section became a little more complicated, since I was also using the active SAC enclosure box as a crossover compartment, one customer’s justifiable question about the reason for the matrix in the mid-range cabinet led us to a simpler version. The many boards in the interior created stable connections for the walls; these in turn were divided into smaller segments with a lower tendency to oscillate. Still, just a couple of boards would do the trick; without any perforations, they each simply connected three plates, thereby creating areas of varying sizes and thus varying resonance frequencies in much higher ranges.

Once the upper section was finished, it was the bass cabinet’s turn. The lid was given a crossbar to keep resonances from traveling upward. The back wall was already connected to the sides through the crossover compartment, so only the reflex channel – which after all is not reinforced in the back – still needed stabilization. We provided that in the form of an upright board about 20 cm tall.

Our initial frequent switching between the active and passive versions of the Duetta eventually brought me to the realization that I liked the passive box better, since it could more easily be adapted to different listening preferences using various amplifiers. With my little “La Forza” power amplifiers, also from SAC, it sounded rounder and more harmonic, while the enclosures dissected the music a little more strongly. When I was also unable to convincingly explain the benefits of having a separate crossover, it brought the era of the crossover enclosure to an end. That reduced the depth of the lower structure by 5 cm and meant winning important points with the significant others of its future owners. Finally, I added another board to the back wall to finish off my cabinet modifications.

The structure of the cabinet is documented in its own separate photo-story (see “Building Duetta”)

Crossover

 The new cabinet structures did not have any tonal advantages or disadvantages, but now we come to the improvements resulting from crossover modifications. Finding the best components is a chapter unto itself. Almost every publication claims that the more expensive the components are, the better the sound. So boxes are built that can be equipped with “normal” or “high-end” crossovers. Does that mean one of them is good and one is bad? In that case, why even offer the bad one? By no means do I want to claim that all capacitors or inductors with the same value sound identical. However, the differences – as with amplifiers, CD players and cables – tend to be divided more according to taste than quality. Electrolytic and oiled-paper capacitors tend to whitewash the sound somewhat, which is good for some metal tweeters. Expensive MKPs give the playback a little more detail and airiness, but depending on the box it can also be a bit annoying. Air coils with thick wire are not necessarily preferable to core coils. In one, the wire length becomes a limiting factor, and in the other there are the saturation and distortions caused by the iron core. Not even the argument of lower resistance proves that one inductor or the other is “better.” For all of these parts, the interaction with the other components in the box is what makes the difference.

It should be said in advance that I will be discussing errors here that occur at a very high level and that are only apparent after comparing two versions for a long period of time. I adjusted the speakers to my own personal sense of hearing over the course of many years, and I do not want to claim that we have seen the end of the small modifications. “Tempora mutantur, et nos mutamur in illis,” as we were taught in Latin class – times change, and we change with them.

The first thing that bothered me about the original Duetta was the acoustic transparency in the bass. Sometimes the tones were a little too loud and sounded washed out, which was especially noticeable at lower volumes. The thick transformer core coil was quickly identified as the guilty party. It was replaced by a much cheaper core coil made of special sinter material, which provided an additional 0.3 ohms of resistance but sounded clearer nonetheless..

The next pricey chunk of the crossover to go was the oiled-paper capacitor. While it added a great deal of calmness to the acoustic pattern, I didn’t like that it also did the same thing when a noisier sound was required. My tried and true MKP capacitors were much more neutral, so they had a home in my preferred boxes from then on. I banished the L regulator from the tweeter crossover altogether, since measurements taken in my listening room and on my own equipment showed it to be unnecessary. The soft fiberboard panels in the chamber of the ER4 were replaced by two layers of foam rubber, which make it easier to screw the tweeter on and also further smooth out the 2 to 4 kHz range.

As a final touch, the flat-coil inductor before the mid-range speaker also had to be eliminated from the phalanx of “high-end” components. I detected a slight nasal playback here, which clearly disqualified it. It was replaced by a good old air coil with round wire, and here too I was able to determine that more money didn’t necessarily mean better sound.

Since I like to use the Duetta with my modified bargain tube, I put a capacitor in the signal path of the 7-360 that also decouples it below its installed resonance. This step smoothes out the impedance below 100 Hz, which the VR-70E repays with tighter bass tones. An impedance linearization for the transition area between the mid-range speaker and the tweeter rounded out my Duetta modifications for the time being.




Measurment values

I can save my words here, since the diagrams speak clearly enough for themselves. The slight sustained decrease between 80 and 300 Hz prevents the usual mid-bass exaggeration found in many boxes, which is caused by environmental influences. The formidable 89 dBs of volume don’t need a bruiser of an amplifier – more delicate tones are called for here. With a 4-ohm minimum and nearly 5 ohms throughout above 100Hz after connected impedance correction, even a small tube amplifier should be perfect here when it comes to creating beautiful sound at home. There are not too many loudspeakers on the market with less than 3% K2 and 1% of other rattling below 100 Hz, and nowhere does the waterfall show irregularities in the onset or decay. A small hook in the angle curve at 6.5 Hz distressed me a bit at first, but I located the cause in the reflections at the microphone bracket. Once I had noticed that, I found the same peak in measurements for the other boxes in this version.

Sound

Describing the sound of my favorite box in my own words is always a tricky task – how are you supposed to avoid hiding its light under a bushel yet still sound plausible while singing its praises? That’s why I was happy to find the report by “musicculture” (real name known to the editors) in the Hi-Fi forum. I couldn’t explain any better myself what is so special about Duetta:

“Had a listening appointment with (name omitted) last Thursday, and one on Saturday with Udo Wohlgemuth. I took my system along to both meetings in the trunk of my car (Symphonic Line RG 10 Mk III; CD Sony 779, the latest Swoboda complete tuning; Swoboda Cinch with Bullett plugs; 2x 3m Jürgen Hensler cable). At home, it’s connected to an Audio Physic Virgo 2 with 8 years of listening experience. Over the years and with lots of trial and error, the system’s makeup has gotten more and more harmonic. But the boxes are too small for the space, and I can’t afford anything bigger from Audio Physic right now. (Although I like the plasticity of the sound, the whole thing could be a little more harmonic. There’s still plenty to work on here with the most important component in terms of room acoustics.) So I was thinking about building a speaker. Since I have zero experience, I dug through magazines, read reviews, etc. In the end, I combined some work errands with the abovementioned listening appointments. The comparison with the speakers I had chosen ((name omitted) and Udo’s Duetta) could not have been any more different. On the one hand, there was a seemingly professionally run company (with a very nice receptionist and very good coffee), and on the other hand I was welcomed by an ex-hippie in his tiny tinkerer’s studio. But what about the music?? While I kept putting in one CD after another at (name omitted) to pick out all of the effects (high range, drive, bass, ambiance, detachment from the speakers, etc.), since they had recently been upgraded in the “stereo,” although with a different tweeter, at Udo’s I put in one CD, we chatted animatedly, and after the 5^th piece I noticed – with complete amazement – that I was hearing the best sound show I had ever experienced. I didn’t want to change the CD, since there was no question in my mind. With just one piece, the box proved the beauty of its possibilities. The ambiance was at least as good as with the Audio Physic, but without the slightly annoying undertone (ok, since this thread is very analytical already). I really just wanted a solution that sounded more harmonic, that would put an end to my search and that I could use to listen to music for the next 10 years – that’s really the important thing, right?? There was nothing out of place, only beauty. Silky high tones; pleasant, exquisitely fine mid-tones; a deep, dry bass. Deep space, piano and cello played back like a dream; voices breathing gently, the most delicate teasing out of a slight puff on a saxophone – simply a speaker that makes you want to listen to it for hours, all night long, and I’m sure it will be my next one. And people, don’t be confused, room acoustics and speakers are definitely the most important elements in the chain – but good electronics are also essential. In the end, if you’re still feeling twitchy about it, you can think about the cables and tools, but not before. Dear Udo Wohlgemuth, thank you for the wonderful day I spent with you. I couldn’t have learned any more in such a short amount of time. My speaker problem has been solved.”

All that’s left for me to do is return the thanks for your nice explanation!