In an etching method, an etching amount is controlled on the basis of the number of times an etching process is performed under the condition that an etching amount is determined independently of an etching time. The audio housing includes a first housing body and a second housing body defining a mounting slot for a shaft of the outdoor umbrella fitting therewithin. The step board in combination with the pair of the first supports can be used for performing the push-ups and step aerobics. A detector head is fixed to the inner surface of the annular support. A baffle assembly is coupled to an inner wall of the exhaust conduit.