求翻译：Last，The horns we proposed have a fundamental frequency of 75 Hz, horns should not have a sweeping frequency this tends to indicate excessive air usage. Thinking about instrument horns an instrument like a trumpet has a fixed frequency usually b flat this can then be changed by pushing a valve and altering the tube length to a second fixed recency, the only musical horn with a sweeping frequency is the trombone which can have this as it is possible to infinitely alter the tube length. The kockum horn has a fixed length and therefore if the wave generator is correctly acoustically coupled should have a fixed frequency.是什么意思？

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