562 Chapter 19 Nonetheless, let us conduct a thought experiment. We know that whatever amplifier technology you use, putting two amplifiers in parallel and averaging their outputs (usually by connecting them together with 10 resistors) reduces the noise output by 3 dB; putting four in parallel reduces the noise by 6 dB, and so on. The same applies to putting two identical active crossovers in parallel, so... if we stacked up four of them we could unquestionably get a 6 dB noise reduction and meet our target. This is perhaps not very sensible, but it does prove one thing--it is physically possible to accomplish the formidable task of meeting our very demanding noise target, even if it is hardly economical to do so. 19.26 Conclusion The description of this active crossover has hopefully demonstrated the techniques and design principles described in this book. The use of elevated internal levels, plus other low- noise techniques, has allowed us to achieve a remarkable noise performance. Reference [1] D. Self, Audio Power Amplifier Handbook, fifth ed., Newnes, Boston, MA, p. 104 (power amp input noise) W ISBN: 978-0-240-52162-6.