That source is sound itself.

那一根源就是声音本身。

youdao

The house needs attention but the roof is sound.

房子需要修葺，不过屋顶还完好无损。

《牛津词典》

Check that joints are secure and the wood is sound.

检查接头是否牢固，木头是否完好。

《柯林斯英汉双解大词典》

That is sound recorded with equipment placed underwater near the busy shipping lanes off Vancouver Island in Canada.

VOA: special.2011.06.29

But the beauty in this calculation is it shows that this concept of electron sharing in an unequal manner is sound and it gets you into the right ballpark.

但在这个计算过程中,真正漂亮的是对电子,非平均共价的考虑很完全,从而指引我们向一个正确的方向思考。

麻省理工公开课 - 固态化学导论课程节选

So although I don't like, I don't believe the argument is sound-- Premise one doesn't happen to be the premise I myself would want to reject.

尽管我不喜欢,或是我不认为这条论证可靠,但前提一恰是我想要反驳的,它作为前提并非偶然

耶鲁公开课 - 死亡课程节选

What if there is sound evidence that you are alive after being declared brain dead?

WSJ: What You Lose When You Sign That Organ-Donor Card

This logic is sound, but there is little evidence, for now, to support it.

ECONOMIST: America's economy

Deloitte's "methodology is sound, " says Mike Belko, chief underwriter at USAA Life Insurance Co.

WSJ: Insurers Test Data Profiles to Identify Risky Clients