DYNAUDIO System 240MK2 Car Loudspeakers

Dynaudio is (arguably) the best-known highendcomponent speaker manufacturer. I fell inlove with their products during the '80s when Iworked for a catalog speaker component company(SRC Audio, for those of you who care). They wereway ahead of their time in technology and builtspeakers that sounded great.

The founder, Wilfried Ehrenholz, had a clear pathfor the company's success: From the onset wewere emphasizing quality and reinforcing the qualitymessage because we always had advanced technology. Of course, quality doesn't come cheap, and it is up to consumers to decide whether they want to pay for top-of-the-range technology or buy something cheaper that doesn't perform as well. At Dynaudio, we have always felt that there is no room for compromise, and we will not allow the company's name to be associated with any product thatdoes not deliver top quality results.

Although Dynaudio's fame centers on its drivers,the company's biggest business has been and continues to be its finished home audio loudspeaker systems. These products utilize proprietary drivers that are designed and developedspecifically for each model, and they are not sold or made available to any OEM customers or driver distribution channels. Today the company produces over 20 different models of finished loudspeakers ranging in price from $400 to $85,000. At the present, over 55 percent of Dynaudio's worldwide annual sales are attributed to its AuthenticFidelity home audio loudspeaker line.

In 1994, Dynaudio introduced a line of high-end car audio loudspeakers that have also proved to be successful. Today Dynaudio's Mobile Fidelity car audio products amount to about 25 percent of the company's yearly sales. Dynaudio also began working on a project with Volvo to develop an audio system for the new C70 coupe, which was introducedearly in 1998. All of these vehicles are equipped with 10 Dynaudio drivers specially tuned for this application. The C70 has already been lauded for having the most advanced factory-installed audio system available worldwide to date.

The System 240MKII is the heart of Dynaudio's commercial car audio line with a 7 woofer and 1.1 tweeter. It features very advanced technology for both the woofer and tweeter and includes an audiophile-quality crossover.

With my love for their products and their wellknown driver technology, I was pretty excited to get these speakers into the lab and see what they had. I really wanted to be impressed and maybe even ask tech editor Casey Thorson if I could keep the samples for my car. As you will see from the following tests, it didn't go exactly as I expected.

PARAMETER TESTING

My testing starts with Small Signal Parameters for the woofer. Some engineers, including myself, are beginning to question the validity of traditional Small Signal Parameters. This test is usually done at very small voltage levels (hence the small signal). This is so that the speaker is in its (theoretically) most linear range for the test. The coil is centered in the gap, compliance parts are at their most linear,and the coil isn't getting enough current to make it get warm and change the wire resistance. The problem with this test method is that it doesn't actuallyreflect how the speaker is used. For a small signal test on this woofer, the highest voltage that produced acceptable levels of distortion was 0.2 volts.

Of course 0.2 volts (0.01 watts) is really not howwe will be using the speaker, so is it really valid touse these measurements for performance predictions?The answer is obvious no way! This is because the physical aspects of a speaker that drive these parameters are changing over the operating range of the speaker. Two key values Bl and Cms (representing magnetic force and the speaker's compliance) change dramatically as the speakermoves. Bl drives Qes, Qts and efficiency; Cmsdrives Fo and Vas.

The chart below shows a comparison of traditionalsmall signal measurements for the MW160 7 woofer and the start of Large Signal values taken at 11 watts.

These differences are at the two extremes of performance,but it is easy to see how much the parameters vary over the working range of the speaker.

Klippel also offers another way to look at SmallSignal. Instead of a maximum distortion limit, it looks at point where the speaker is most linear over its working range. This is much closer to the average operating range of the speaker and the parameters fall between the two extremes in the chart above. For the MW160 7 woofer, these values are taken at 2.5 watts and are listed in the chart below.

SO HOW DO THESE STACK UP?

The medium Qts (0.57) and Fs of 64.4 will give a dry resonance with decent bass extension. The 86.6dB sensitivity is not very high but should be fine when used with a separate amplifier and active crossover. I can't imagine that these speakers would be used in anything other than a high-end component set system.

Ultimately, the low-frequency performance of a speaker is best judged by how linear the Bl and Cms are over the working range of the speaker. This can easily be seen in the Bl(x) and Cms(x) curves generated by Klippel. Both of these curves should be centered on the X(mm) 0 line and haveessentially the same shape on either side of this point. The dashed lines on the graphs are the mirrors of the actual test and make it easy to see if the curves match the ideal.

My testing setup has changed dramatically with the addition of the Klippel Distortion Analyzer. I still use the ACO Pacific 1/4 microphone, lab amplifier and IEC baffle; however, all of the testing is done through the Klippel now. It is the be all end all analysis tool for the loudspeakerengineer. You can test distortion in any flavor you want, non linear Thiele Small (T/S) parameters, impedance at any voltage, and of course simple frequency response (with any input signal you can imagine). The Klippel is revolutionizing loudspeaker design in virtually every application.

Check it out at www.klippel.de.

Both the Bl(x) and Cms(x) curves show less than-perfect centering and symmetry. It is interesting that both the Bl(x) and Cms(x) offsets are identical.This could mean that the suspension is shifted back in the basket from its ideal point. A quick look at the spider on the woofer looks like it is flat and not biased so it could simply be a coincidence or an asymmetrical tension between the spider and edge.

This offset will cause significant distortion at relatively low levels. It's not clear if we can hear asymmetrical distortion; however, the speaker's performance would be improved if this problem was corrected.

The Bl(x) (Graph 1) and Cms(x) (Graph 2) curves can also be used to predict the maximum excursion for the speaker (Xmax). It is defined by Klippel as the point at which the compliance or Bl nonlinearities create 10% harmonic or intermodulation distortion. For BL this happens when the Bl has dropped to 82% of its x=0 value (XBl) and Cms has dropped to 75%(Xc). For the MW160 7 woofer the XBl point is 1.9mm and the Xc point is 2.9mm. If the offset were eliminated, these values would be much closer to the 2.95 Xmax in the literature; however, it would still be short of the Linear Excursion listed there.

Another factor influencing the quality of a woofer/midbass is its non-linear inductance. Like Bl(x) and Cms(x), the inductance of a speaker changes as it moves. This can actually have as great an influence on the perceived sound quality as Bl(x) and Cms(x). This value can also be related to where it causes 10% distortion and is defined as XL or Xmax limited by inductance.

A conventional speaker may hit this limit after 1 or 2mm excursion. The MW160 7 woofer uses a motor structure that greatly reduces the inductance change. The XL value for the Dynaudio is greater than 5mm.