HiFiCompass

Wavecor WF182BD03 midwoofer

What is on the test bench?

WF182BD03 is 4 Ohm (its 8 Ohm version - WF182BD04) midwoofer with a chassis size of 7", paper cone and with motor based on a ferrite magnet. All of Wavecor speakers labeled with "BD" letters belong to the "Balanced Drive" technology group, in which proprietary symmetric motor construction is implemented. The magnet field symmetry is achieved by extending of the center pole covered by a copper cap and incorporating of an aluminium ring. Thanks to such technical solutions the company managed to significantly reduce the voice coil inductance and nonlinear distortion. More information on this technology you can learn from the publication Wavecor Balanced Drive Technology Note that such measures require additional production costs and, as a rule, are used in the most top-end products. The manufacturer himself positions this model as a high-quality mid-low-frequency speaker for Hi-Fi and Hi-End systems.

Before testing we burned-in the speakers according to the manufacturer's recommendation - 10 Volts / 20 Hz / 2 hours and allowed it to cool for several hours.

You can get familiar with the Wavecor company history here.

Why do we test this?

The speakers of the Wavecor company have been long attracting our attention with its construction, innovate technologies, Danish roots and quite flattering feedback from consumers. However, for some reasons they couldn't reach us. At last, at the Munich exhibition Hi-End Show 2018 we had the opportunity to personally meet at the Wavecor stand with Allan Isaksen, the general manager of the company, and got to touch to the significant part of the Wavecor speaker model range. Allan Isaksen made us the impression of a business and punctual person and kindly agreed to provide several models for independent testing, for what we express our gratitude to him.

What did the manufacturer state?

We are opening the "passport":

The first to note is a perfectly designed document - a triffle but very pleasurably. We think, taking in account fullness of information, design and convenience of displaying graphic information (correctly selected scales of axes), the Wavecor's datasheets could be serve as a reference for other companies . As many loudspeaker designers, seeking for speaker drivers for their projects, are orienting, first of all, on the official datasheet, then they will not be disappointed here.

There is nothing to comment here, the manufacturer's words say for itself.

Of numerical parameters especially should be noted the declaring of additional parameters as Krm, Erm, Kxm and Exm for advanced TSL speaker driver model, that give an oportunity to designers to model a speaker operation much more precisely.

Despite the manufacturer didn't state clearly a maximum voice coil linear excursion, a simple calculation give us +/- 5.5 mm.

Visual inspection

The box of dense cardboard with formatted inserts made of foamed polyethylene provides very reliable transportation. The speakers having "-01" suffix in the part number are supplied each in an individual box.

The production quality is absolutely perfect - no mechanical defects, no scratches, no burrs, no glue traces, perfectly glued label, perfectly aligned foam gasket.

The cone is made of paper, is textured and painted black on the front side. There is no any coating on the back side of cone.

The die cast aluminium chassis is black powder painted. The large windows between the basket ribs provide excellent acoustical transparency and minimal resistance to air flows. The spider is lifted up over the motor front flange for enhancing of the voice coil ventilation and reducing of air compressing. The back plate is painted black (it should be noted that in all Wavecor models all metal parts are painted black), which provides an improved heat dissipation due to the radiation effect.

If you slightly press on the cone you can see through the venting holes in the voice coil former the extended center pole covered by a copper cap. The motor belongs to overhung type as you can see that part of the voice coil extends beyond the magnetic gap. The voice coil former is made of glass-fiber for reducing of dissipative losses in the moving system.

The terminals are regular and gold plated.

In general WF182BD03 demonstrates modern design in excellent execution.

The measured chassis flange diameter and thickness are turned out to be exactly the same as in the datasheet, so you can safely trust to the datasheet mechanical drawings.

The ideal quality of manufacturing testifies to a very high production culture and a serious attitude of the company to the quality of its products.

As you can see, the appearance and the construction is completely similar to the WF120BD03, differing only in larger dimensions and a vent hole in the center pole. Sure, because WF182BD03 is the older brother from the one family.

Impedance frequency response

On the diagram you can see impedance frequency responses for two samples - the curves lie each on other so way we can't see one behind the another. The speakers are sold separately but have similarity like if they were matched to a pair on a factory. Excellent consistency! The measured resonance frequencies are 35 Hz and 35.66 Hz a little bit higher than declared one (33.8 Hz). Total quality factors Qts are 0.3144 and 0.3145 higher than the datasheet says for a speaker after burn-in (0.25). The impedance curves are very smooth without any signs of parasitic resonances in the whole range and they rise linearly on the log frequency scale. When increasing impedance scale we can see a small ripples on the curves - the traces of the cone break-up modes but they are very low and unavoidable for all paper cone based speakers.

The impedance curve indicates a very well balanced moving system and a good motor with short-circuiting rings inside the magnetic system.

On-axis frequency response

As in the case with impedance curves, on-axis magnitude frequency responses lie one on another just perfectly. The measured axial FR almost repeats the datasheets one. The measured average sensitivity is around 90 dB and it is 1dB lower than the datasheet value (91 dB). In general, on-axis frequency response is very flat and the total unevennes in the range of 200 Hz- 2.5 kHz doesn't exceed 2 dB (!) which is excellent for a paper cone speaker.

Frequency range of 800 Hz - 1.5 kHz is a potential problem area for all of 7" soft cone midwoofers due to a surround-cone resonance. In that range a slight smooth rise up to 2 dB is observed for the WF182BD03 unlike a dip which can be seen in many other speakers. Such a small hump is very easy to fight with in a crossover, in contrast with a dip, which is almost impossible to overcome and it remains to rely on the fact that the audibility of a narrow dip is negligible.

Off-axis frequency responses

The off-axis frequency response behavior demonstrates uniform and smooth decrease with increasing of frequency and angle, it has a good agreement with the curves from datasheet. The frequency response decreasing at 2.4 kHz/60 grad doesn't exceed 6 dB.

Harmonic distortion (315 mm)

We have shown nonlinear distortion for SPL about 93 dB and 102 dB at 1 meter. The second order harmonics dominate over the whole frequency range and this is the most favorable case for human listening because second order distortions are the least annoying.

Even at SPL level of 102 dB the paper cone of WF182BD03 still save its stiffness and the THD frequency profile in the range 200-3000 Hz remains the same, only going higher up. Considering the size of the membrane, its material (for soft membranes the second order harmonics as usually higher than for the hard ones) and volume of our statistical data, we can characterize the nonlinear distortions in frequency range >200 Hz as "low".

Harmonic distortion (5mm - 20 mm)

Due to the features of our measurement setup, for analizing nonlinear distortion in frequency range lower than 200 Hz it is much more correctly to use the data coollected from near field (distance is around of 5 - 20 mm from a cone) measurements. The diagram above demonstrates harmonic distortions at voltage level 5.6 Volt. Even with a such insignificant level there is a decent level of distortion below 60 Hz. It is hardly possible to get the clean and deep bass from WF182BD03. Do not take it as a defect or that "it just happened". This model is an example of a design approach to speaker design, where the emphasis is on high-quality performance in the upper bass and mid-range bands to the detriment of deep bass.The same features we can see, for an example, in Peerless (NE series) and SB Acoustics midwoofers. There is no a free breakfast in the loudspeaker drivers world and each manufacturer chooses his own set of compromises.

Step response

The step response demonstrates an excellent slew rate and a rapid decay. Return to the resting state is quite fast. The teeth on the falling part of the step response are the echoes of the 5.5 kHz membrane resonance, so you have to filter it out well.

Waterfall

The waterfall demonstrates the same effects as the step response, in addition revealing hidden resonances that are difficult to discern on other types of measurements. In this case, the waterfall demonstrates the good rapid decay of the transient process, exposing a long main tail at a frequency of 5.5 kHz and a very small one at 9.5 kHz, which, by the way, can't be easy seen on the magnitude frequency response.

Listening impressions

We can tell about our listening impressions only after testing the midwoofer in real loudspeakers. Since we have not yet reached this point, we will leave this report for later.

This section will be updated after a real test in loudspeakers.

"How to use" recomendations

Below are the results of the evaluation of the mid-woofer WF182BD03 behavior in a vented type loudspeaker. It was assumed that loudspeaker radiated in a 2-pi half-space, the Thiele&Small (T-S) parameters were taken from the manufacturer datasheet and were slightly corrected taking in account theirs little modification by the active resistance of the connecting wires and the crossover inductors (0.35 Ω in this estimation).

As you can see, even in the vented design, the speaker driver does not allow to obtain a low frequency limit F(-3dB) below 60 Hz (for QB3 approximation). This value is in good agreement with the low frequency limit dictated by the allowable level of nonlinear distortion and it is the confirmation that the midwoofer parameters were chosen by the manufacturer consciously to ensure high-quality operation in the range above 60 Hz. We recommend to use this speaker driver in the same way.

The simulation offers an enclosure volume slightly above 8 liters - quite a bit and there is the problem of integrating into such a small volume a rather long port tube, about 410 mm, to provide the minimum required diameter 61 mm. The task is not easy and we have to compromise, understating its length and diameter to 246 mm and 45 mm respectively.

You can use the WF182BD03 as a midwoofer driver in two-way loudspeakers and as an high quality midrange driver in a large-scale three-way loudspeakers up to 2.5 kHz.

What is price and where to purchase?

The average retail price of WF182BD03 in the Europe internet shops is around 129 EURO (VAT not included).

Summary

It can be summarized that the testing confirmed the very close correspondence of all measured parameters with the claimed ones. We liked this midwoofer, the characteristics at the level of the best models of world manufacturers for this class of paper cone based speakers and definitely worthy of application in the most serious loudspeakers. So, what we have: