my stereo amp has R and L pre outs (no dedicated sub out). My active sub has a single line level in ( in addition to speaker level inputs which i don't want to use). Should I connect either the R or L pre out on amp to line level in on sub (and in this case am i losing info from other channel) or combine both the R and L pre out with a RCA y-splitter to feed both of them to the single line in on sub. thanks in advance.
The sub is mono. Just run one RCA cable out to the sub. Doesn't matter which one (R/L). If you're obsessive like me, you can run the Y splitter out of the L/R, then one line to the sub.
Thank you Nuck,Leo and David for the comments. I guess i will just connect the L pre out to the mono input on sub. My question is still: do we lose low frequency info from the R amp pre out? is it worth getting a stereo sub?
There are advantages to having two subs but there isn't a "stereo sub" (in most cases and at most reasonable pricing), just an active (powered) subwoofer with L/R inputs where the inputs of the subwoofer plate amplifier do the summing of the two channels in the circuitry of the plate amp. This is far preferable to using a "Y" connector for the reasons Nuck suggested.
You can split an output but you should never combine an input. Let the circuitry do that job.
Bass is generically mixed into mono by all record producers to provide a simpler task for the amplifier(s) and the recording studio mastering labs. It's unlikely you will loose any bass with a single connection unless you listen to some very, very off beat recordings and even that would be a minimal loss.
As Leo suggests determine which output from your receiver is the Mono mix output. The information should either be on the reciever or in your owner's manual. This guarantees no loss of bass information even if you are listening to Albanian Phart Music (APM). If it doesn't mark one output as mono, then don't worry.
You'll have some advantages to running two separate subs in one room if you can space them on separate walls and do a proper set up. Just plunking a sub where it fits won't gain you anything with one, two or a dozen subs. Put "subwoofer placement" into a search engine and do some reading before you go a plunkin'.
If the system is a low to mid fi system, then you would do much better for yourself than spending money on another sub at this point. So, rack/bookshelf/entry level receiver systems, don't bother. Separate components and high dollar everything with high dollar set up, consider it down the road.
Otherwise, find that mono output from your receiver.
If the receiver looses it's main amplifier input and produces no sound when you plug into the "pre out", then you can use a "Y" splitter to run one side of the "pre out" to the subwoofer and one side back to the "main in" on your reciever. If there are straps or a "U" style connector between your reciever's "pre out" to a "main in", replace those with some better quality interconnect cables and you'll likely hear a bit better sound overall.
Thank you Jan. Your comments are always very enlightening. My amp is a denon PMA 2000 ivr. It has R and L pre outs without any designation for which is a mono. For some reason people always suggest the L to use for mono. I will do that. I just purchased a martinLogan Vantage (goes down supposedly to 35 Htz. I am not sure what the sub will add ( i listen exclusively to classical music, orchestral, chamber and solo), Just thought to try if the sub would integrate well with the system.