http://sound.westhost.com/bi-amp.htm
Die wichtigsten Punkte:
1.16 - Adding up the Plusses
* Effectively (up to) twice the 'real' power of the amplifiers themselves
* Reduced intermodulation distortion
* Elimination of the low frequency passive crossover, its inherent losses, potentially poor linearity and crossover point inaccuracy
* Reduction of the difficulty of the load presented to the power amplifier
* No padding is required to align the driver sensitivities, so we are not simply wasting power
* The damping factor is greatly improved for both the low and midrange loudspeakers
* Complete freedom from any interaction between the loudspeaker driver (and its environment) and the crossover network
* Cost savings, since complex passive crossover networks are not needed
* Bi-wiring is included free!
* The flexibility to choose amplifiers which are at their best within a defined frequency range
* Ability to match amplifier power to the exact requirements of the drivers for maximum overall efficiency
Für sehr wichtig halte ich den folgenden Hinweis hieraus:
http://sound.westhost.com/bi-amp2.htm
4.0 - .....
In many cases, different amplifiers will be used, often with differing power ratings as well. This is where some measurements are needed, since both amps must have the same gain...
.4.3 - The Effect of Amplitude Inaccuracies
To see what happens when the gain is not correct, we need to look at the crossover curves again. Refer to Figure 7 - the red and green traces. This is the optimal frequency response of the crossover/amplifier/speaker combination, with the resulting output being virtually flat (there is a slight rise at the crossover frequency which can be corrected using Linkwitz Riley alignment, where the crossover point is 6dB down - see Project 09)
Have a look at what happens when the amplitude of one filter is different from what it should be. This is also shown in Figure 7, and it is clear that the effective crossover frequency is shifted. What is not so clear is the final frequency response, and in the case of any crossover filter that is not phase-coherent, the adverse effects of the relative phase relationships. These are extremely difficult to quantify, but may be apparent in listening tests. The problem is that if you are unaware of the problems that can be created by modifying gain indiscriminately, it will be very hard indeed to determine why the system just doesn't sound right.
Fig 7
Figure 7 - The Effect of Changing Gain on Crossover Frequency
It is very obvious that the effective crossover frequency has changed. At normal gain, the crossover is 295Hz, but if the gain is increased as shown, the crossover frequency shifts up to 500Hz. If the gain is reduced, the effective crossover frequency is now about 150Hz. Naturally, the same thing happens if we change the mid+high gain. Note that the filter cutoff frequencies are not changed, only the level with respect to the adjacent filter.
This is not just the output of the filter we are looking at, but rather the final output from the speakers - as shown above, it will often be necessary to change the gain of amplifiers to match the efficiency of the loudspeaker drivers used. This does not alter the crossover frequency as you might expect, but brings it back into proper alignment. In fact, if the gain is not changed, then you will get a result similar to that shown, by effectively amplifying one frequency band more than it should be for the correct tonal balance.
Somewhat remarkably, it is actually fairly easy to get the balance very close to optimum purely by ear. If you have a pair of good headphones, this provides an excellent reference, and any appreciable response deviation in the loudspeaker system can be corrected quite accurately. It is even possible (although not recommended) to use the crossover level controls as a "tone control" - this can even help make some recordings listenable. Some speakers using passive crossovers provide level controls for mid and high frequencies, and the same can be done with an active system (but with no power loss).
4.4 - What Does All This Really Mean?
The crossover / amp / speaker combination has to have the correct gain structure if a flat response is desired, and any variations can be quite audible. The audibility varies with the type of music, and depends a lot on your hearing. In some cases, a slight unbalance can sound better than a perfectly flat system, and can be used to compensate for room influences or personal preference. Some passively crossed loudspeakers have a L-Pad level control for the tweeter, although these are a lot less common that they once were. If available, this does the same thing as changing the amp gain in an active system.
Ich fasse das mal zusammen: Verwendet man unterschiedliche Verstärker (zB. ein Subwoofer-Modul und einen Stereo-Verstärker) und haben diese unterschiedliche Verstärkungsfaktoren, verschieben sich die Trennfrequenzen erheblich. Das gilt auch für Verstärker mit einstellbarem "gain"! Im rot markierten Text: Soll ist 295 Hz, je nach Verstärker kann sonst die Übergangsfrequenz zwischen 150 und 500 liegen. Wie das klingt, stelle ich mir lieber nicht vor! Daher muss der Verstärkungsfaktor bestimmt werden. Oder man macht es so wie ich bei der teilaktiven Concorde, auch wenn es teurer ist.
Wir haben sogar ein Apartment mit Blick auf den Fuji (11. Etage)...
Da muss man dann durch.
; für den abend haben sie aber raffinierte suppen.
), aber als ich den Preis des fertigen Teils gesehen hatte, naja.
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