This Check Bench characterizes a 15″ Ellipticor woofer from Scan-Communicate utilizing the corporate’s confirmed oval/elliptical design topology. The 38WE is a severely characteristic wealthy transducer, beginning with a properly configured 10-spoke cast-aluminum body and a very open space beneath the suspended spider mounting shelf for efficient cooling of the Symmetrical Drive (SD) AirCirc multi-magnet design with neodymium slugs and elliptical two-layer voice coil. This text was initially revealed in Voice Coil, July 2022.
Scan-Communicate has tried completely different strategies through the years to suppress cone modes (a supply of coloration), probably the most notable one being the Revelator sliced cone woofer collection, which incorporates the 18W/4231G00. With this idea, cone modes are suppressed by angled slices within the cone floor which are glued again collectively. This product was extraordinarily in style within the high-end two-channel market when it was launched and nonetheless is presently. Whereas the Revelator “sliced cone” method labored nicely, the corporate was on the hunt for the subsequent technology of a cone mode defeating transducer design.
Evidently, the thought of utilizing elliptical-shaped voice coils to manage cone and dome modes got here from an engineering mind storming session that urged driving the diaphragm asymmetrically would dramatically cut back concentric cone mode habits. With an oval-shaped voice coil you get an “infinite” variety of Eigen frequencies, however with much less contribution to every frequency and total decrease distortion.
Driving the diaphragm symmetrically, you get a finite variety of Eigen frequencies with a better contribution combining at sure frequencies producing cone coloration modes. Picture 1 graphically illustrates the mode variations utilizing a FEA to scanning vibrometer method to visualise the distinction between a cone pushed symmetrically with a spherical voice coil (Picture 1a) versus a cone pushed asymmetrically with an elliptical voice coil (Picture 1b). It’s my opinion that it is a subjectively very vital improvement, as confirmed by a few of my design work utilizing Ellipticor drivers within the final a number of years.
Picture 1: Scan-Communicate laser vibrometer scan of a cone pushed symmetrically by a standard spherical voice coil (a);
Scan-Communicate laser vibrometer scan of a cone pushed asymmetrically by an oval-shaped Ellipticor voice coil (b)
This month, Scan-Communicate despatched me the most recent iteration from the Ellipticor product line, the 15” 38WE8582T00 woofer (Pictures 2-4). As with the 18WE and the 21WE Ellipticor woofers, the 38WE is a severely characteristic wealthy transducer. Beginning with the body, like most of Scan-Communicate’s midwoofer/midrange frames, the 38WE body is a very properly configured 10-spoke (5 double spokes) cast-aluminum body with slender 15mm to 25mm broad spokes to attenuate reflections again into the cone. The realm beneath the suspended spider mounting shelf is sort of utterly open (Picture 4), ensuing within the very efficient cooling of the motor and voice coil.
The motor design for the Ellipticor 38WE is just like the opposite Ellipticor woofer designs and can also be a Symmetrical Drive (SD) AirCirc multi-magnet design using 12 of the 22mm excessive and 27mm diameter neodymium (neo) slugs with a black emissive coating. It’s noteworthy that the neo slugs are spaced about 5mm aside forming 12 open 27mm x 5mm vents, giving the AirCirc motor huge convection cooling functionality.
The AirCirc motor construction additionally options Scan-Communicate’s patented SD motor enhancements and as such incorporates three copper shorting rings (Faraday shields) and a T-shaped pole. FEA designed, the neo magnet motor makes use of a 84mm x 68mm elliptical 2-layer voice coil wound with spherical copper wire on a titanium former. Motor components embrace polished back and front plates for the neo magnets that features a 16mm diameter rear vent for added cooling.
For the cone meeting, Scan-Communicate selected a fairly stiff curvilinear profile black-coated paper cone with an elliptical 89mm × 70mm convex paper mud cap. Compliance for the 38WE represents a departure from most earlier Scan-Communicate drivers, and as a substitute of the standard NBR encompass, the 38WE has a pleated coated fabric encompass, related to what’s discovered within the majority of professional sound woofers. Given the motive force’s 95dB sensitivity, this alternative was possible made to decrease the Mmd to assist obtain the comparatively excessive sensitivity quantity. A typical professional sound 15” with a coated M-type pleated encompass could have a 2.83V/1m sensitivity between 95dB to 99dB, so it is a honest comparability. Remaining compliance comes from an 8.5” diameter flat coated fabric spider (damper).
As with all of the Ellipticor line-up, the 38WE has a magnetically hooked up black anodized aluminum trim ring that may clearly be customized anodized in a wide range of colours. Final, the voice coil is terminated to a pair of gold-plated spade lug bolt terminals. When it comes to bodily look, this driver is cosmetically fairly engaging.
I started evaluation of the 38WE/8582T00 utilizing the LinearX LMS analyzer and Bodily Labs Imp Field (equivalent in operate to the LinearX VIBox) to create each voltage and admittance (present) curves with the motive force clamped to a inflexible take a look at fixture in free-air at 0.3V, 1V, 3V, 6V, 10V, 15V, 20V, and 30V. As with nearly all 15” diameter woofers, the motive force stayed sufficiently linear out to 30V for LEAP to get an affordable curve match.
As has turn into the protocol for Check Bench testing, I now not use a single added mass measurement to find out Vas. As an alternative, I take advantage of the precise measured cone meeting mass (Mmd) equipped by the motive force’s producer, which was 71.9 grams for the Scan-Communicate 15” woofer. Subsequent, I post-processed the 16 550-point stepped sine wave sweeps for every Ellipticor 38WE pattern and divided the voltage curves by the present curves (admittance) to derive impedance curves, part added by the LMS calculation technique. I imported them together with the accompanying voltage curves to the LEAP 5 Enclosure Store software program.
Since most Thiele-Small (T-S) information offered by the vast majority of OEM producers is generated utilizing both the usual mannequin or the LEAP 4 TSL mannequin, I moreover created a LEAP 4 TSL parameter set utilizing the 1V free-air curves. I chosen the whole information set, the a number of voltage impedance curves for the LTD mannequin, and the 1V impedance curve for the TSL mannequin (Determine 1) within the transducer derivation menu in LEAP 5. Then, I created the parameters for the pc field simulations. Desk 1 compares the LEAP 5 LTD, TSL, and manufacturing unit revealed parameters for each of Scan-Communicate 38WE samples.
Please be aware the LinearX LTD mannequin is a extra advanced transducer mannequin (23 extra variables than the TSL mannequin). This additional complexity is why the simulations obtain a considerably extra correct prediction of most tour at excessive voltage ranges. So if you’re not accustomed to it and questioning why I’m utilizing it, the LTD mannequin, although considerably dated, remains to be probably the most superior transducer mannequin accessible to the loudspeaker trade.
LEAP parameter calculation outcomes for the Ellipticor 38WE had been sufficiently near the revealed manufacturing unit information, with the one vital variation being sensitivity. The sensitivity quantity I publish is a calculated midband SPL that outcomes from T-S parameter routine, whereas Scan-Communicate is utilizing a 2.83V/1m response measurement common.
As typical, I adopted my regular protocol and arrange laptop enclosure simulations utilizing the LEAP LTD parameters for Pattern 1. Two laptop field simulations had been programmed into LEAP 5—one a Qtc=0.7 Butterworth sealed field with a 1.5 ft3 quantity with 50% fiberglass damping materials; and the second was a vented QB3 enclosure with a 1.9ft3 quantity tuned to 46Hz with 15% fiberglass fill materials.
Determine 2 shows the outcomes for the Ellipticor 38WE8582 within the vented and sealed enclosures at 2.83V and at a voltage degree sufficiently excessive sufficient to extend cone tour to Xmax+15% (11.8mm for the 38WE). This produced a F3 frequency of 78Hz (F6=63Hz) with a Qtc=0.68 for the sealed enclosure and –3dB=70Hz (F6=58Hz) for the vented field. Rising the voltage enter to the simulations till the utmost linear cone tour was reached resulted in 127dB at 150V for the sealed enclosure simulation and 128dB for a similar 150V enter degree for the vented enclosure. Determine 3 reveals the two.83V group delay curves. Determine 4 reveals the 150V tour curves. I restricted the voltage on the vented simulation as a result of the motive force began to over excurse beneath 35Hz, and like most all vented methods, must be band-limited with a high-pass filter.
The SPL at most tour quantity are very excessive, however that is depending on the ability dealing with ranking enter into the LinearX software program. I believe that this driver can be thermal restricted earlier than it will get to that prime an SPL, however the 38WE additionally has spectacular convection cooling options in its AirCirc motor, so I’d guess that its efficiency in larger-than-average acoustic areas can be spectacular for a house audio product. I’d additionally be aware that the 38W shouldn’t be a subwoofer, however a extremely correct sounding midbass driver that may work nicely with a big devoted subwoofer system, although the motive force may be made to play to a lot decrease frequencies in a bigger vented field, I believe that is likely to be lacking the purpose.
This month, Klippel evaluation for the Scan-Communicate 15” woofer was carried out by Jason Cochrane at Warkwyn, the US distributor for all Klippel merchandise. His evaluation on the Klippel KA3 analyzer produced the Bl(X), Kms(X), and Bl and Kms Symmetry Vary plots given in Figures 5-8. This information is extraordinarily invaluable for transducer engineering, so if you happen to don’t personal a Klippel analyzer and wish to have evaluation accomplished on a selected undertaking, Redrock Acoustics can present Klippel evaluation of virtually any driver for a nominal payment. (Go to www.redrockacoustics.com for extra info.)
The Bl(X) curve for the 38WE (Determine 5) is generally symmetrical with a level of tilt and coil-in offset, nevertheless that is pretty broad Bl curve. Trying on the Bl Symmetry plot (Determine 6), from an space of affordable certainty (the gray overlay) at practically 0.0mm the coil-in offset is much less that 2mm steadily reducing coil-in offset to the motive force Xmax of 10.25mm.
Determine 7 and Determine 8 present the Kms(X) and Kms Symmetry Vary curves for the Ellipticor driver, respectively. The Kms(X) curve is unquestionably symmetrical in each instructions with a small diploma of coil-out that’s solely 0.68mm on the 5mm tour level and stays comparatively fixed out to the ten.25mm Xmax level and remains to be lower than 1mm (0.95mm).
Displacement limiting numbers calculated by the Klippel analyzer for the Scan-Communicate 38WE had been XBl @ 82% Bl=7.4mm and for XC @ 75% Cms minimal was 6.1mm, which signifies that for this Ellipticor, the compliance is probably the most limiting issue for prescribed distortion degree of 10%. If we use a much less conservative 20% distortion standards, which is extra applicable for a big diameter driver like this, with Bl falling to 70% of its most worth and compliance falling to 50% of its most worth, the numbers can be XBl=10.4mm and XC=9.8mm, each numbers about the identical as bodily Xmax of the motive force.
Determine 9 offers the inductance curves Le(X) for the 38WE/8582T00. Inductance will usually improve within the rear route from the zero relaxation place because the voice coil covers extra pole space, which is what you see right here. Nonetheless, due to the efficient use of copper shorting rings (Faraday shields) within the Scan-Communicate SD AirCirc motor, the inductive swing from Xmax in to Xmax out is a really small 0.13mH, which is excellent inductive efficiency.
With the Klippel testing accomplished, I mounted the Ellipticor 38WE woofer in an enclosure, which had a 18” × 16” baffle (equipped by David Nelson of Portland Audio Labs), and was stuffed with damping materials (foam). The gadget beneath take a look at (DUT) was then measured on- and off-axis from 300Hz to 20kHz frequency response at 2.00V/0.5m, normalized to 2.83V/1m utilizing the Loudsoft FINE R+D FFT analyzer and the GRAS 46BE 1/4” microphone (each the analyzer and the mic had been offered to Voice Coil by the producers).
Determine 10 offers the 38WE’s on-axis response, indicating a easily rising response to about 1.2kHz adopted by a broad 5dB peak heart on about 1.7kHz the place it begins is low-pass roll-off. Determine 11 shows the on- and off-axis frequency response at 0°, 15°, 30°, and 45°. The -3dB frequency at 30° off-axis relative to the on-axis SPL is about 1kHz, suggesting a crossover between 1kHz must be potential, however I’d extra possible selected a cross level beneath 400Hz to maximise the system DI curve. The normalized model of Determine 11 is proven in Determine 12, with the CLIO polar plot (accomplished in 10° increments) displayed in Determine 13. And eventually, Determine 14 offers the two-sample SPL comparisons for the 15” Ellipticor driver, exhibiting an in depth match (lower than 0.5dB variation) all through the working vary.
For the remaining collection of checks, I arrange the Hear, Inc. SoundCheck 18 software program, AudioConnext analyzer, and 1/4” SCM microphone (courtesy of Hear, Inc.) to measure distortion and generate time-frequency plots. For the distortion measurement, I mounted the 15” woofer rigidly in free-air, and set the SPL to 94dB at 1m (2.21V), utilizing the pink noise generator and SLM constructed into the SoundCheck 18 software program. I then measured the distortion with the Hear microphone positioned 10cm from the mud cap. This produced the distortion curves proven in Determine 15. Scan-Communicate claims very low distortion for the 38WE, and as may be seen, that is certainly the case with third-order harmonic distortion extraordinarily low.
For the final take a look at, I used SoundCheck 18 to get a 2.83V/1m 38WE impulse response and imported that information into Hear’s SoundMap Time/Frequency software program. Determine 16 reveals the ensuing CSD waterfall plot. Determine 17 reveals the Wigner-Ville plot (chosen for its higher low-frequency efficiency).
The take a look at outcomes for this distinctive oval-shaped voice coil 15” transducer point out excellent efficiency. Whereas I’ve as but no expertise designing the 38WE right into a system, I’ve managed to design a product utilizing each the Ellipticor 18WE and the D3404, and in my humble opinion, the outcomes had been extraordinarily musical sounding. For extra details about these and different high-end Scan-Communicate transducers, go to www.scan-speak.dk. VC
This text was initially revealed in Voice Coil, July 2022
