Friends,
In response to Karsten’s observations, I feel compelled to offer some form of “hypothetical” explanation as to what is going on here. As we all know, the area of crossover components, wire and interconnects is a hotly debated issue in audio. I’m not pretending to offer concrete explanations – just food for thought. So please take the following for what it’s worth.
According to Karsten, the observation is that when fast rising transient signals are fed into the speakers with (supposedly) inferior crossover components, a type of high frequency “glare,” “artificialness” and irritating sound results. This is very interesting from an engineering standpoint. It would seem to imply that distortion products are being generated somewhere in the signal chain – most likely in the crossover itself.
Another interesting fact here is the observance Karsten has made with regards to the “Transporter.” This suggests that if a device is placed in the signal path that band-limits (low-pass filter function) the source signal, i.e., reduces its rise-time/slew rate (speed), then the offensive condition is reduced and/or eliminated – albeit at the expense of overall transparency and resolution. This is potentially a powerful clue as to what is going on.
In order to break things down to a manageable level, I am going to categorize what I believe to be the three major sources of potential distortion. Listed in order of significance, they are as follows:
1) Microphonic Vibrations
It is a well-known physical fact that electro-strictive and magneto-strictive forces can arise in electronic components. The analysis of these effects is rather involved so I am leaving it up to the reader to investigate further if they so desire. Suffice to say, electrical components can and usually do mechanically “vibrate” at some certain range of frequencies if sufficient voltage is applied across and/or current through their terminals. Most are familiar with the conspicuous “hum” produced by a 60Hz power transformer.
Once such a device is “excited” into mechanical vibration, the conversion of electrical energy into mechanical energy can (and does) reverse. The mechanical vibrations will in turn cause electrical signals – albeit orders of magnitude smaller in amplitude to that of the electrical stimulus – to be produced. In other words, a component that has been excited into mechanical vibration will then produce electrical signals of its own. These can be either clearly audible or scarcely detectable, depending on their magnitude. If you don’t believe me, just rap on your preamplifier or amplifier chassis while no music is playing and the volume is turned up. You’ll likely hear some analog of that action emanating from your loudspeakers – but be careful!
How does this relate to transients? A fast rising transient is akin to a drumstick striking a drum. Since the mass of the drumstick does not change, the only way to achieve a louder “snap” of the drum is to increase the velocity of the stick as it approaches the drum head. The increased velocity of the stick hitting the head is translated to greater energy being transferred from the stick to the head. This results in not only an increase in the resulting amplitude, but also an increase in the number of harmonics generated by the head. That’s why the timbre of a drum changes depending on how loudly it is played. The increased rise-time of the initial transient contains more energy and therefore stimulates the production of more over-tones.
This, I believe, is the same mechanism at work in the observed phenomena of Karsten’s observations. Any device placed between the signal source and the speaker/crossover system that “slows down” the rise-time of the source’s transient content, will be effectively the same as slowing down the drummer’s hand/drumstick in the example above. Less energy = less mechanical vibration = less harmonic excitation = less distortion. Simple enough.
Superior crossover components are constructed to more rigorous mechanical standards and are therefore more mechanically stable. Theoretically, they should suffer less from the electro and magneto – strictive effects outlined above. Both inductors and coils can suffer from these effects and there are methods that can be employed to minimize them. Inductor wire can be wound more tightly, encapsulated in varnish or epoxy or made of flat ribbon instead of round wire. The flat ribbon material was chosen for inductors used in Karsten’s latest “ultimate” crossover construction. Also, Capacitors can be wound tighter and constructed more rigidly as well. Mundorf is well known for the level of rigor they apply in the construction of all their products. Karsten also chose to build his crossovers externally from the loudspeaker enclosure and its unavoidable, low-level vibrations. I suspect this played a significant role as well.
