This SEAS Excel Midwoofer is one probably the most extremely creative and revolutionary out-of-box Hexadym Motor designs from the Norwegian firm. On this article, Vance Dickason particulars all that’s distinctive on this midwoofer design and its historic motivations, serving to to resolve the issue of reflections off the motor system and body of a woofer again into the cone. An interesting exploration with full measurements. This text was initially revealed in Voice Coil, July 2022.
Clearly the engineering staff at SEAS was keenly conscious of this situation in woofers in addition to the rear reflection downside in tweeters the place the motor has a pole piece immediately behind the dome diaphragm that causes the same reflection points. Each these issues led SEAS to develop its patented Hexadym radially charged magnetic motor construction, US Patent 6,020,805 (filed in December 1998 and granted in December 2000). Trying on the diagram from the patent proven in Determine 1, you may see that the motor construction is manufactured from a collection of rectangular neodymium (neo) magnets organized in a hexagonal six-sided sample across the voice coil of the motor.
Given the bodily structure, these neo magnet elements are charged sideways, or radially to focus flux into a spot space. Included in a tweeter motor, this implies it’s potential to make the most of a considerably hole pole piece that produces considerably much less reflection again into the dome diaphragm. SEAS at present makes use of its Hexadym expertise in 4 of its high-end Excel line tweeters: the T25CF002, which was the unique Millennium mannequin to make use of the Hexadym motor; the T29CF002 Crescendo 29mm comfortable dome tweeter: and the 2 diamond diaphragm Hexadym motor tweeters, the T29D002 and the T29D002. Eradicating the tough pole piece rear reflections beneath a tweeter diaphragm considerably will increase the subjective perceived sense of element within the higher harmonic vary.
The second necessary utility of the SEAS Hexadym motor construction was used within the topic of this Check Bench explication, the SEAS W15CH001. Whereas woofers don’t undergo from the pole piece reflection situation that’s frequent in tweeter design, they do have a mirrored image downside attributable to the body and the motor construction. By way of body reflections, it’s at present the cutting-edge to provide woofer frames with minimally broad spokes that hook up with the motor system. Taking a look at Photograph 1 and Photograph 2 of the W15CH001, it’s apparent that the body spoke width and form have been optimized to reduce reflections again into the cone (this additionally consists of the spider mounting shelf). The out-of-the-box leap made by SEAS with the W15CH001 was to include the Hexadym motor expertise to nearly fully eradicate the reflections off the motor construction that’s frequent within the majority of woofers and midrange drivers. This enhancement, just like the discount of the pole piece reflections in a tweeter, considerably reduces the “litter” attributable to motor reflections and lead to elevated perceived musical element.
Moreover the rear reflection lowering expertise included into the body design and Hexadym motor construction of the SEAS W15CH001, this driver has quite a few different necessary options. The cone meeting encompasses a excessive purity forged, machined and surface-treated magnesium cone that’s extraordinarily stiff and properly damped. Compliance is offered by NBR encompass and handled 2.5” diameter material flat spider (damper).
The Hexadym motor construction incorporates a T-shaped pole piece with twin copper shorting rings (Faraday shields), a stable copper section plug that enhances the shorting ring efficiency, a 26mm diameter voice coil wound with spherical copper wire terminated to a pair of solderable gold terminals, plus a reasonably strong (for a 5.25” driver) 200W short-term energy dealing with capability. For cooling, the body is totally open beneath the spider mounting shelf, and with no pole vent. Nevertheless, as you may see in Photograph 2, one of many advantages of the Hexadym motor structure is—as with the Scan-Communicate AirCirc motor—the substantial quantity of venting from the within of the motor construction for cooling the voice coil meeting.
Testing started with the driving force clamped to a inflexible take a look at fixture in free-air, and utilizing a LinearX LMS analyzer and Bodily Lab Imp Field produced each voltage and admittance (present) curves at 0.3V, 1V, 3V, 6V, and 10V (every sweep with the suitable 200Hz tone performed between sweeps to progressively warmth the voice coil to imitate precise working circumstances). The 10V curves had been shut to creating a helpful curve match, nonetheless I discarded them and post-processed the remaining eight 10Hz to 20kHz 550-point stepped sine wave curve pairs for every pattern. I divided the voltage curves by the present curves creating the 5 impedance curves. The impedance curves every had the LMS section calculation process utilized and, together with the voltage curve for every sweep, had been imported to the LEAP 5 Enclosure Store CAD program.
Since most Thiele-Small parameter (TSP) information offered by OEM producers is both produced using both the usual TS mannequin or the LinearX LEAP 4 TSL mannequin, I additionally embody a LEAP 4 TSL mannequin utilizing the 1V free-air curves (Determine 2). I chosen the entire curve set, the a number of voltage impedance curves for the LTD mannequin, and the 1V impedance curves for the TSL mannequin within the transducer derivation menu in LEAP 5 and created the parameters for the pc field simulations. Desk 1 compares the LEAP 5 LTD and TSL information and manufacturing facility parameters for each SEAS W15CH001 samples.
TSP outcomes for the SEAS Hexadym motor 5.25” midbass woofer had been relatively near the manufacturing facility information, with some variance within the Vas and SPL. A part of the variation is as a result of distinction in Sd calculation, a reasonably delicate parameter. The factors used for Check Bench is to calculate Sd from the diameter of the cone plus half of the encompass width on all sides of the cone meeting (the factors established in LEAP 5). That mentioned, I adopted my customary protocol and preceded to program pc enclosure simulations utilizing the LEAP LTD parameters for Pattern 1. I used LEAP 5 Enclosure store to generate enclosure volumes, which resulted in a 0.29ft3 sealed field with a Qtc=0.7 and 50% fiberglass fill materials; and an vented QB3 kind vented alignment with a 0.54ft3 quantity tuned to 37Hz with 15% fiberglass fill materials.
Determine 3 depicts the outcomes for the SEAS W15CH001 within the two enclosures at 2.83V and at a voltage degree sufficiently excessive sufficient to extend cone tour to Xmax+15% (4.6mm for the W15CH001). This simulation resulted in a F3 frequency of 65Hz (F6=52Hz) with Qtc=0.7 for the 0.29ft3 sealed enclosure and –3dB=44Hz (F6=37Hz) for the 0.54t3 QB3 vented field simulation. Growing the voltage enter to each simulations till the utmost linear cone tour was reached resulted in 97dB at 11V for the closed enclosure and 98.5dB at 12V enter degree for the bigger vented field. Determine 4 exhibits the two.83V group delay curves. Determine 5 exhibits the 11V/12V tour curves.
Klippel evaluation for the SEAS W15CH001 produced the Bl(X), Kms(X) and Bl and Kms Symmetry Vary plots given in Figures 6-9. This information was produced by Jason Cochrane, of Warkwyn, with the KA3 Klippel analyzer.
The Bl(X) curve for W15CH001 woofer (Determine 6) is flat, very broad and symmetrical, particularly for a 5.25” woofer, and with small quantity of tilt and coil-in (rearward) offset. Trying on the Bl Symmetry plot (Determine 7), by the point we get to a degree of cheap certainty at 4mm bodily Xmax of this driver, the coil-in offset is a negligible 0.39mm.
Determine 8 and Determine 9 give the Kms(X) and Kms Symmetry Vary curves for the 5.25” midbass driver. The Kms(X) curve does exhibit a level of asymmetry, with a small quantity of each coil-out offset. Trying on the Kms Symmetry Vary curve proven in Determine 9, there’s 1.6mm coil-out offset at 4mm bodily Xmax tour level.
Displacement limiting numbers calculated by the Klippel analyzer for the SEAS W15CH001 had been XBl @ 82% Bl=4.82mm and for XC @ 75%, Cms minimal was 5.1mm, which implies that for the W15CH001, the Bl was the limiting issue for the ten% distortion standards, however each quantity had been past the 4mm bodily Xmax of the driving force, so positively good efficiency right here.
Determine 10 offers the inductance curves L(X) for the W15CH001 5.25” midbass driver. Inductance will usually improve within the rear route from the zero relaxation place because the voice coil covers extra pole space, which is what we see with the radially charged Hexadym motor. From Xmax out to Xmax in, the inductance vary (“swing”) solely varies by 0.08mH, which is great inductive efficiency.
Subsequent I fired up the Hear, Inc. SoundCheck analyzer utilizing SoundCheck 18 software program and the AudioConnect interface together with the 1/4” SCM measurement microphone and set it up for distortion measurements (offered courtesy of Hear, Inc.). The SPL at 1m for the 5.25” SEAS woofer mounted in a free-air was set to 94dB (my customary for house audio gadgets). This required 8.36V. With the microphone positioned at 10cm from the mud cap, the W15CH001 produced the distortion curves proven in Determine 11.
Following the distortion measurements, I mounted the 5.25” SEAS W15 midbass driver in an enclosure with a 12” × 8” baffle and made a 2.83V impulse measurement. This was imported into Hear’s SoundMap software program, windowed to take away the room reflections. Determine 12 exhibits the cumulative spectral decay (CSD) waterfall plot. Determine 13 exhibits the Wigner-Ville plot.
For the remaining collection of SPL measurements, utilizing the identical enclosure as with the impulse response testing, I then measured the driving force frequency response utilizing the Loudsoft FINE R+D analyzer and the GRAS 46BE microphone (courtesy of Loudsoft and GRAS Sound & Vibration) each on- and off-axis from 300Hz to 20kHz with a 1/6 octave smoothing (to simulate the 100-point LMS decision used for years on this column) at 2.83V/1m utilizing the cosine windowed FFT methodology. Determine 14 depicts the W15CH001 on-axis response, yielding a comparatively easy rising response from 300Hz to 4kHz, adopted by the magnesium break-up mode peak centered on 8.2kHz.
Determine 15 illustrates the on- and off-axis frequency response at 0°, 15°, 30°, and 45°. The -3dB at 30° with respect to the on-axis curve happens at 2.6 kHz, which recommend a possible crossover level of two.5kHz to 3kHz could be acceptable for the W15CH001. Determine 16 offers the normalized model of Determine 15.
Determine 17 exhibits the CLIO Pocket (courtesy of Audiomatica SRL) generated horizontal aircraft polar plot (in 10° increments with 1/3 Octave smoothing utilized). And final, Determine 18 offers the two-sample SPL comparisons for the SEAS W15CH001 Hexadym motor driver, displaying each samples very carefully matched inside ±0.25 all through the working vary of the driving force.
As I might anticipate, the SEAS W15CH001 Excel driver displays wonderful construct high quality together with well-thought out design engineering. Nevertheless, the compact Hexadym motor and the ensuing diminished reflections of the small footprint are a major proprietary accomplishment and an impressive contribution to the present paradigm of loudspeaker engineering.
I ought to moreover point out that SEAS additionally provides a Nextel-coated paper cone midrange driver, the M15CH002, which additionally incorporates the Hexadym motor construction. Its response vary is from about 100Hz to 10kHz, with a attribute sensitivity of 88.5dB. For extra details about these drivers, go to the SEAS web site at www.seas.no. VC
This text was initially revealed in Voice Coil, July 2022