Axiom Home Page Forums General Discussion Technical Questions Sub Out vs. Line Level

Hey Guys and Gals,

Been a while since my last post but I have been a frequent visiter on a near daily basis. This is one of the best places to get info with from some of the nicest folks on the web.

This has probably been asked before but I have not been able find a thread on the subject, ok too lazy to look. Anyway, what offers better lfe/bass output from a sub - the sub-out from the receiver or connecting the lft/rt speaker out to the sub?

Here is a follow up. I have battled a ground loop problem since introducing the EP500 to my system. Tried everything short of calling out an electrician. I currently have it under control using a Jensen product in-line to the sub. If I run my sub off of the lft/rt speakers, might that resolve the ground loop or will it find a different path to my sub?

Thanks eveyone. Can't wait to read the responses.

I have never seen a real comparison between the two inputs but I would expect that the line-level "sub out" signal would be higher quality since it doesn't have to go through the power amplifier.

If you had a tube amp with a transformer-coupled output it's possible that using speaker outputs for the sub would help with ground loop problems (since the transformer output can float relative to ground) but AFAIK all modern solid-state amps use ground for one of the speaker outputs.

That last point is not true when the amplifier is bridged but I don't *think* a bridged amp would help since both of the outputs are still "relative to ground". Not sure though...

I assume you tried all the normal things like "remove that little screw Axiom included to float something in the amplifier" ? Ground loops on the EPxxx subs often seem to be related to the cable TV and/or satellite TV inputs to the receiver -- it's worth disconnecting them if only to find out which one (if any) is the culprit so you can eventually yell at the cable/satellite vendor enough to get the root cause fixed. Until then, those Jensen transformer widgets do seem to really help...

John, as far as the speaker-level vs line-level connection, there shouldn't be a noticeable difference in the basic quality of the signal, but the line-level connection has the advantage of using the bass management of the receiver. The speaker-level connection would rely on the often inaccurate internal sub crossover for the bass management to the sub and there wouldn't be any to the mains unless there was a fixed high-pass filter on the sub's speaker- level outputs. So, in general, use line-level.

If you mean that the isolation transformer has solved the problem, be happy. It wouldn't appear that using speaker wire rather than coaxial cable would in itself get rid of the second path to ground.

JohnK and Bridgeman:

Thanks for the responses. I have tried to isolate the ground loop issue and have determined that the cable is part of the problem but not entirely the culprit. By that I mean that when the cable is connected, the hum is very noticeable. When it's disconnected, the hum goes away for a short while then returns, although not as pronounced. I purchased an isolator for the cable connection, which solved the hum, but when I switch inputs or when the dvd player tray loads, a "thump" eminates from the sub. That's when I went with the in-line isolator for the sub. That took care of all noises. My only concern with that is I am afraid that I am robbing the sub of signal. I've since recalibrated the system and all seem to be performing fantastically. But you know how it is, there is always that nagging question "can it be better?".

After reading your replys, I think I have the best possible setup.

Thanks again!

I can't help you with the problem, but I like your equipment list.

>>The speaker-level connection would rely on the often inaccurate internal sub crossover for the bass management to the sub and there wouldn't be any to the mains unless there was a fixed high-pass filter on the sub's speaker- level outputs.

D'oh !!

I forgot about that. Whatever would I do without JohnK ?

No question; we'd all be babes in the woods!

There's babes in the woods? Where???

Bad Peter! *whacks with rolled up newspaper* No!