"reduced the volume" is a correct and usable phrase in written English.
You can use it whenever you want to describe a decrease in the loudness of something, usually sound. For example, "He reduced the volume on the television so the neighbors wouldn't hear it."
We reduced the volume of people who could speak and read Russian.
The abolition of regional spatial strategies has reduced the volume of planned new development.
The trade deficit shrank to $27.89 billion as oil prices fell and the manufacturing slowdown reduced the volume of petroleum imported.
The Postal Service said the anthrax scare had reduced the volume of mail by about 10percentt, for a revenue loss of at least $500 million.
Part-privatisation is needed, argues the business secretary, because "email, texting and other forms of social networking have sharply reduced the volume of mail sent in the UK".
At the same time, the company had reduced the volume of new books it was buying, to adjust for the sluggish market.
And while e-substitution has reduced the volume of letters between domestic customers, the delivery of items ordered through new media has grown exponentially and represents a profitable new market.
But she said that since his arrival, the company had reduced the volume of its financial positions by more than 25percentt, starting with the "complex and difficult-to-manage positions".
The authors acknowledged that "the sample size did not permit us to examine whether the legislation reduced the volume of cigarettes smoked".
The Conservatives have reduced the volume about the referendum because they know that the fears of leaving the EU are real and that business, while it has no love for EU regulation and Brussels, will not take kindly to Britain leaving a market of 500 million consumers.
He therefore suggested a lower levy on letters, since high taxes reduced the volume of mail and thus diminished the revenue derived therefrom; a uniform postage rate irrespective of distance, since excessive numbers of rates for letters traveling different distances greatly increased accounting expenses; and that all mail should be prepaid.
