I connected my computer's 1/8" audio jack to my Yamaha HS8's 1/4" input. Songs sound very weak and compressed compared to my old Logitech Z4 speaker system and Mackie CR4s. Sometimes vocals are nearly silent or the bass will disappear completely.

What's so puzzling is that I tried sweeping a sine wave across the frequency spectrum and it sounded just fine - no sudden drops/rises in volume. What could cause this behavior? Does this have anything to do with balanced/unbalanced input?

None of these made a difference:

* 2 different 1/8" cables and 1/8" to 1/4" adapters
* Daisy chaining the HS8 off of the Z4's remote volume control
* Plugging my phone into the monitor
* Upgrading my computer's audio driver

I had some Mackie CR4s a few days ago and those sounded great. I'm starting to wonder if the monitor I received is defective.