Sub wolfer advice

Hey guys I need some advise on a power sub. Here is my set up. Krell FPB 400CX & Krell KCT pre-amp with BMW speakers. I have never run a power sub before. I will be running my transparent cables from the amp to the power sub. Then another set of cables out of the sub into my BMW's. The sub will be 2ft away from my right speaker. Do I need to keep both lengths of speaker wire coming out of the sub into my BMW's the same length or can I run a short speaker lead from the sub to my BMW speaker that is sitting next to the sub or am I splitting hairs?

Next question should the speaker wirer coming out of my amp going into the powered sub need to be the same quality of wire going into the speakers?

Thanks guys for all your help in advance. Hope this makes sense. Any help you can give will be greatly appreciated.

NO, As long as its is of good quality with appropriate shielding.
Wire length differences in domestic situations are irrelevant IMHO.
Why not go from the amp to your sub and from your amp to your speakers? (bi-wired) Much better than from the sub to the speakers.
+1 Zmanastronomy. don't put your subs in the path of your mains.
Thanks Zmanastronomy, I didn't know I could do that. I would much rather do that if possible. So your saying use the upper and lower speaker connections on my power amp. The upper ones going to the sub and the lower post going to the main speakers.
never use a crossover with high quality main loudspeakers,

bring the sub's crossover up acoustically to achieve the best match.
Zmanastronomy, I do not see the benefit in your recommendation. If the OP is using a powered subwoofer there is no bi-wiring involved. The subwoofer only needs a sample signal from either amplifier output while running the main speakers full range.
If you do amp to sub and amp to main speaker wiring, you don't really need anything heavier than magnet wire to the sub. The speaker ins on a sub have very high input impedance and so use little real power.
You probably don't want to really use magnet wire, but you also don't need anything approaching the size or quality you feed the mains with.
I just got off the phone with Krell and they said I could just run RCA out of my KCT Pre amp to the sub would this be better.
Here’s a different approach you can try ... your Krell KCT has a number of premium low level MAIN outputs you can put to good use

You can run a XLR balanced cable from KCT MAIN OUT (#22 in the manual) to the INPUT of 400CX amp ... then run speaker wires from the 400CX to B&W’s ... this keeps the Sub out of Premium Krell/B&W loop

As your powered Sub most likely has a low level RCA IN ... run a normal single ended RCA (#22 in the manual) from KCT MAIN OUT to the SUB INPUT RCA input on powered SUB

Now the 400CX and B&W don’t see the Subs lower quality electronics and the 400CX isn’t trying to drive the B&W’s and the SUB at the same time

Each is running exclusively of each other ... but when you turn the volume up or down on the KCT Pre amp it will turn the volume up or down equally on both the SUB and 400CX amp

You can also use the special CAST Output (#23 in the manual) to drive the CAST Inputs on the 400CX also and still use the RCA MAIN OUT to drive the SUB’s input

CAST connection requires special Krell CAST Cabling ...

Possibly you can tell us what brand and model the Sub is and how you connect the KCT to the 400CX
Get a REL, run it line level from the power amp.. Don't know what I mean? Google REL and read about the Speakon connection that is the preferred method of hooking up a REL
The sub I am looking at is a GoldenEar Forcefield-4 1200watt sub. I run XLR to my 400CX.
Right next to the XLR outs to the left is the RCA outs you can use to feed Sub ...

Unfortunately that Forcefield-4 Sub you are interested in only accepts speaker level ins and outs and has single channel LFE RCA IN

You are basically limited to using the speaker level connection ... so my suggestions for RCA/XLR hook up are mute

I guess you are back to your original query
I'd take Krell's advice and run rca out of your pre-amp to your sub. I have my rig set with the same signal routing and it works fine. Simple is better.

Good luck!
NO! NO! NO! A lot of well intentioned suggestions have been made, that in many cases would be good advice, but which evidently have been made without looking at the specifics of the equipment that is involved.

1)It appears that your power amp has balanced outputs, meaning that both the + and - terminals have signals on them (as opposed to the - terminal being grounded). If so, you cannot connect the sub's negative speaker-level input to the power amp's negative output terminal, or you risk shorting that output signal to ground (if the sub and the amp both have 3-prong power plugs, and depending on their internal grounding configuration). Instead, the negative speaker-level input of the sub should be connected to a ground point on the amp.

A chassis screw is PROBABLY such a point. You can verify that by using a multimeter to check for continuity between a chassis screw and pin 1 on one of the XLR connectors, or else by asking Krell.

2)The RCA input on the sub you are considering is designed to only work with an input signal that has already been low pass filtered and summed to mono, such as an "LFE" signal. Your preamp does not provide that kind of output, and so your only choice would be to connect that sub to the power amp outputs (the + outputs and a ground point).

Also, Magfan has made an excellent point about the fact that you don't need heavy gauge high quality speaker wire to connect the sub to the amp.

-- Al
Davehrab I would like to talk to you about this matter can you give me a call If you have the time 708 687-0829.

Thanks Dave it was nice talking to you on the phone. I want to thank all you other guys as well for your quick responses. You guys have given me a lot to think about. Little did I know there was that much to know about a sub. I guess you are never too old to learn. Time to go out tomorrow and look for a sub. I will be running the sub out of my pre-amp RCA's into the sub. Seems like this is the best way to go.
Before you follow through connecting the Krell to a subwoofer, please read page 2 (PDF reader) under "warnings", at the very beginning of the manual. This is what Almarg was referring to above. Manual link.[]
Hey guys thanks for the heads up. I just purchased a Rel R-528 sub. According to the salesmen this sub is made for two channel operation. Looks like I better call Krell to find out more about this. I've had the sub playing and I must say it's giving me the depth and detail I have been looking for. Thanks again for the heads up as I stated I will be giving Krell a call tomorrow. Any body using this sub is their another way of hooking this sub up. I am going to go through the manual and read on but you know how we are. When you get a new toy the last thing you do is read the manual.
I would call Krell or the dealer, and let them work it out. I wouldn't try anything else (especially some different connection yet IMO) without finding out first. It does have a common speaker ground wire, but shows (REL) hooking it (Neutrik Speakon) up to a one channel ground. I don't have any idea whether this is OK or not. Who knows if anything else shares a ground, like the power cord. Maybe email them the link for the manual, and let them (dealer or Krell) worry about it, and tell you. [][]
Hifihvn, thanks for providing the links.

Dancer, note that on page 6 of the manual for the sub (pdf page 7) it is specifically cautioned that if speaker-level connections are used, the ground wire from the sub should NOT be connected to the negative output terminal of a balanced amplifier. Otherwise there is a good chance that damage to the amp will occur, as I explained earlier.

The sub manual suggests that if speaker-level connections are used, the ground wire from the sub should be connected to the amp chassis. That will probably work fine, but as I indicated earlier it would be a good idea to first verify that the chassis and internal circuit grounds are common, either with a multimeter or by asking Krell.

REL generally advises that speaker-level connections are sonically preferable to line-level RCA connections, as you'll see in the manual. That is a somewhat controversial position, and there is undoubtedly no one right answer that is universally applicable. The only way to definitively tell which method is preferable in your system, to you, is to try them both.

-- Al
I finally got the sub dialed in and I must say It made my system sound so much nicer.