To Doug Schneider,
I love reading your reviews, very well done. But I have a quick question. Which type of tweeter do you prefer, a ribbon or a beryllium dome, and why? I hope you’ll find the time to reply.
Thanks and cheers,
I do not necessarily have favorites because the type of tweeter technology and the material used in its construction are things that cannot be thought of in isolation; instead, they have to be thought of as pieces of systems.
For example, beryllium is all the rage because it is stiff and light, which is good for a tweeter diaphragm. Furthermore, certain properties of the material can allow designers to push its natural resonant frequency farther past the audioband than most other metals allow. The thing is, how high they can push the resonance doesn’t only have to do with the material, but also the shape of the dome itself. With beryllium, pushing the main resonance beyond 40kHz is possible, which is very far above the audioband. But it only happens with the right dome shape. I’ve seen measurements where beryllium-based domes were ringing at 25kHz, which is surprisingly low, and is no better than aluminum. In addition, the designers at KEF and Vivid Audio have pushed the resonances of their aluminum-dome tweeters past 40kHz by working carefully with the shape; in other words, they are matching what beryllium can do. Therefore, the material alone isn’t all there is to it -- one has to look at the dome profile, as well as the entire tweeter design.
Likewise, the drivers themselves can't be thought of individually -- they are part of an entire loudspeaker system that involves other drivers. Ribbon tweeters can have some excellent characteristics, including being able to reproduce very high frequencies. However, at lower frequencies (below, say, 3500Hz), I’ve found that the distortion from ribbon tweeters rises dramatically and can be easily heard. So, if the ribbon driver is required to reproduce those lower frequencies, which is common in many speaker designs (particularly two-ways, since the midrange-woofer can be used only so high in frequency until it has to hand off to a tweeter), then that onset of distortion from the ribbon tweeter can become detrimental and will likely overshadow its strengths. Ribbons are also more directional than dome-type tweeters, vertically and horizontally, so that will affect how well it blends with the other drivers it has to interact with, which the designer has to take into account. All told, it is not a matter of if a ribbon tweeter sounds good or not -- how it is implemented into the design of the rest of the speaker governs the end result. Implemented well, it could sound very good; implemented poorly, it could sound awful.
I hope these examples help to illustrate that how a tweeter performs is not as simple as what technology has been used and what material it is made of. Remember, never think of these things in isolation -- they are part of a bigger picture when it comes to loudspeaker design. . . . Doug Schneider