Report January 1995, ©Mats Andersen, Qln Acoustics AB
At QLN Acoustics we have always paid close attention to the loudspeaker crossover behaviour. Research into the complex relationship between amplifier, crossover and loudspeaker has shown it to be an area where major sonic advantages can be obtained. Today it is widely accepted that linear impedance improves any amplifier’s performance, but the Split Field technology takes us one step further.
The Split Field concept is easily recognisable by the external crossover box. When placed close to the amplifier, the concept fully optimises the relationship between amplifier, crossover and speaker units. Here are some of the major advantages.
Crossover components avoid being physically stressed by vibrations and pressure from inside the loudspeaker cabinet. All electrical components change their performance when not effectively isolated from vibrations. In a crossover this is of special interest, as the theoretic preconditions of the crossover change when the components do. The result is unwanted distortion and harshness. The Split Field crossover does not have this problem.
When test listeners compare the QLN Signature Split Field to any loudspeaker on the market, a common reaction is that they have not yet heard anything as natural, open, dynamic and clean. It is tempting to say that most people have not yet heard the real potential of their amplifier. With the QLN Split Field technology we are ready to go on.
Magnetic field influence on crossover components
Coils are not being influenced by the woofers magnetic field . In internal crossovers, and especially when the crossover is placed close to the speaker units, the coils change their characteristics when high power passes through the woofer, This is due to the fact that the magnetic field surrounding the woofer expands as the sound levels do. This interferes with the coils characteristics and ultimately changes the crossover point and other essential factors. In the external Split Field crossover the coils are totally isolated from the woofers magnetic field. The coils then maintain their characteristics regardless of the power passing through the woofer. The crossover point is then maintained at all playback levels.
The capacitor’s microphone effect
Apart from cutting off low frequencies, a capacitor also works as a microphone. In conventional internal crossovers capacitors pick up the sound from inside the cabinet (at high playback levels there can be up to 140dB!! inside a cabinet) and modulate the original signal. This blurs low-level details such as room information details, especially at high sound pressure levels. This is one of the reasons why the sound stage narrows down on many speakers at high levels. The external Split Field crossover eliminates this problem. The result is improved dynamics, clarity and detail reproduction. This alone adds metres to the size of the sound stage.
The importance of impedance matching
The difference between the speakers impedance (app. 6-30 ohms in the sonic range, the cable (app. 1 ohm) and the amplifier output impedance (< O.l ohm) is larger when the crossover is placed at the far end of the cable. This misadaptation makes the amplifier quite dependent on the characteristics of the cable, especially resistance and capacitance. When placing the crossover close to the amplifier, the cable will interfere much less on the system. Moreover, better impedance adaptation between amplifier, crossover and cable means less reflection from the loudspeaker into the feedback circuit of the amplifier and once again, better amplifier performance.
The amplifier “sees” less of the speaker cable capacitance as the crossover components are now placed between the amplifier and the cable. The result! Better amplifier performance.
All the combined advantages of the Split Field technology sets a new standard for what is technically achievable from dynamic loudspeakers. And it gives us possibilities to further improve our choice of drive units and to refine our research in cabinet technology.
Mölndal, January 1995