What happened

Shares of digital audio processor specialist Cirrus Logic (NASDAQ:CRUS) fell 26.1% in the first half of 2018, according to data from S&P Global Market Intelligence. The company was exposed to weak Apple (NASDAQ:AAPL) iPhone sales, and the Cupertino account represents about 80% of Cirrus' quarterly sales.

So what

The close relationship with Apple is hugely positive for Cirrus and its shareholders when times are good for its largest customer. But when Apple says that it will build fewer iPhones in 2018 than previously expected, Cirrus Logic investors suffer. That's what happened in February, driving Cirrus shares 10.6% lower.

A worker with hardhat and toolbelt shrugs helplessly as a red charting arrow crashes downward through the concrete platform under his feet.

Image source: Getty Images.

The stock continued to fall through March and April, with no company-specific news to explain the drops. Over this span, independent market researchers continued to report softening demand for smartphones, which could translate into even weaker Apple results -- and as you know, that's bad news for Cirrus Logic.

Now what

Cirrus Logic is showing its volatile side these days. The stock is currently trading 40% below its 52-week highs and just 16% above its yearly lows. It has seen three sharp price increases and seven single-day drops of at least 5% each in 2018 alone. The company is working hard to find a foothold in the larger Android market, but Apple is Cirrus' lifeblood until further notice. You can treat this stock as a more volatile way to invest in Apple itself.