Originally Posted by pjp
If you've compared the real-world sound of speaker-level connection to line-level, I'm very interested in your experiences..
Since I agree with Velodyne
and every other sub maker on the planet [exception: REL, a company which spouts audio mythology] I'm at a loss why you'd think I'd even attempt to listen to the inferior method if the superior method is available?
The added hum, hiss, frequency response skewing, and distortion is thankfully usually fairly innocuous, I admit, however for critical listeners using high end gear it can theoretically be noticeable in direct, rapid fire A/B comparisons with the right material. Even if we pretend for a moment the amp itself is "perfect", the voltage divider or "line out converter", LOC, which knocks the speaker level signal back down to line level, where the signal then gets re-amplified by the powered sub's own amp, is not always innocuous. A high end one made with high quality Jensen transformers costing hundreds of dollars might be close, but the cheap ones we get thrown in for free when we buy consumer subs often isn't.
The companies which make these passive devices as outboard products, often used on factory car head units since they usually lack preamp level outs, often lie and claim their frequency response is dead flat, at least from 20-20kHz that is, but in truth when they get measured they often come up short. Some people who are forced to use them buy several and then measure them to see which is the least problematic, like this guy
"Better Than I Expected
By S. Scott on Jan 19, 2014
I needed a LOC for an automotive subwoofer installation and did not want to pay a fortune for an active unit. I decided to take a chance on this one. Many of these cheaper units use inferior transformers with limited low frequency response (normally about 80Hz). I tested this after temporarily installing it to see if it would be suitable, and was surprised to find the -3dB point to be between 40 and 60Hz, which is very good for a device in this price range. It found a permanent home in the car and works very well for me."
Here is his measured response of the LOC from his car's head unit's speaker level out:
Most companies don't post their frequency response graphs for their LOCs because they are often inferior to this one and even this one doesn't cut it in my book (for home use).
Even the high end passive ones
aren't technically perfect.