RM6900 Bass Management

thosmos

Okay, I'm new here, and new to surround, but at least have read the bass management article here on the site. Very interesting. So, with the current set up that I have HK AVR340 and the Polk RM6900 -- the best bass management option that I have available are ...

#1. Speaker level mains out from amp, into sub, out from sub to front L & R Large speaker settings, no sub set in amp. (Any crossover suggestions ? for front then ?)


#2. Pre amp mains out RCA to in RCA on sub, Sub out speaker level to L & R fronts, still no sub selected in amp.

I have it set up now as the recommended setting -- #1.

I noticed in the article that option #2 could result in a better sound. Maybe they word this lightly, in case some have an amp without preamp outs ?

My question is : Does the Sub for this system power the L & R fronts anyway -- in either configuration ? Speaker level in or nine level in ?

Or, to make it a simpler question:

Is the power of the amp not effecting the L & R fronts when they go through the subs bass management system ?:rolleyes:

John K.

Tom, welcome. First, keep in mind that there's also a third option, although Polk strongly suggests not using it, especially for the RM speakers which have built-in high-pass filters. This is to set all speakers "small" in the receiver with a suitable crossover frequency(possibly 120Hz for the RM6900 speakers)and feeding it into the unfiltered LFE input on the sub with a single coaxial cable from the single sub output on the receiver. This is used by some and you might experiment to see if you prefer it.

As to option #1, no suggestion for a crossover to the fronts is relevant, since when they're set "large" they're fed a full-range signal from the receiver and it's only the high-pass filter in the RMs which rolls off the low frequencies.

Option #2 isn't stated correctly; when line level inputs are used into the sub there's no speaker level output from it. Speaker wires are connected directly from the receiver to the speakers.

As to what powers the speakers, it's always the amps in the receiver, even if the wiring passes through the sub, as in option #1. It's simply a straight passthrough and doesn't go through the sub's crossover or use any receiver power for the sub(just the audio signal is fed into the sub amp). The sub amp powers only the sub itself.

thosmos

I think the HK 340 only has line out left and right for the sub, no LFE -- but there are crossover settings for the line out -- and by setting these high, I believe it would be the same as bypassing the filtering that would be present.

Or maybe there is no LFE out -- and just the input to LFE on the sub bypasses any filtering from the amp signal ?

Also, you were saying that by using the line level out for the sub, it would disable to powered speaker level output ? Is that right ?

Thanks for all of the info though -- and with these further options, I have more to work with.

thosmos

keep in mind that there's also a third option, although Polk strongly suggests not using it, especially for the RM speakers which have built-in high-pass filters.

But why would I even bother trying this -- if not recommended ?? This is a Polk site, message board, etc. Do most here think Polk is **** with their recommendations ?

Just curious.

You said Polk "Strongly suggests not using it". That means, "sure, fry your speakers, but it sounds great for five minutes", to me.

What is the mystery in that phrasing ?

Is this what those "in the know" use for their hook ups ?

John K.

No, in the section of pre-outs on the 340 there's one specifically for the subwoofer; it doesn't have to be termed "LFE". That's the one that you would use if you want to try option #3.

No, it's the opposite; the LFE input on the sub bypasses the sub's internal crossover filter so that only the filtering by the receiver takes place(if you try option #3).

If you feed only a line level signal into the sub with a coaxial cable(instead of speaker level power with speaker wires into the speaker level inputs) there's no speaker level power from the receiver that comes in, so of course there's nothing that can go out of the speaker level outputs.

As to why Polk suggests not using the receiver filtering, especially with their RM speakers, it's because they suggest that interference between the high-pass filter in the RMs and the receiver filter will cause uneven response in the frequency area where both are operating. There's no danger of the receiver or speakers being damaged. Again, some prefer and use the receiver filtering; try it if you'd like to check, otherwise stay with option #1.

thosmos

So, this third possible set up is just the standard front L R powered speaker connection to the Front L R -- and the sub using sub out (LFE input to sub) -- set front speakers to small and bass management in the 340 to LFE on sub only.

I was wondering -- what is going to be better ? letting the HK send the sub signals, or let the Polk filter the sub freqency -- and telling the HK that there isn't a sub present.

Has anyone compared to two ?

Anyone here use the RM6900's ?

I hear most on here using some pretty high end stuff, but if anyone has tried, please, let me know.

Thanks all -- for the help.

I have them set to option one now, and love the sound, but curriosity may have me try the option three at some point.

MLZ

I have tried both methods of hookup.

I have RM6800's fed by an Onkyo 603. I found that the Polk method (Receiver -> Sub -> Fronts) was best for music.

Since I use this system 75% movies, I switched back to the "Option 3" setup where my receiver's LFE outputs to the Sub, I set fronts to small and the Onkyo's crossover to 120 (Actually set by the receivers auto setup). This gives my sub the "rumble" in movies I like.

RM6800's are similar to your RM6900's, so do a search on RM6800.

thosmos

So, with your experience, the bass signal is stronger using the sub out, rather than letting the Polk do the processing ?

I guess you get no sub with music in this case, if a 2 channel CD.

nebborjk

The Polk method will always give you LFE no matter what the playback.
Most receivers have a Subwoofer Remix option. Basically this will redirect the lower frequencies to your sub even if your operating in 2-channel mode.

thosmos

Okay, I finally did get to set up option 3 and do like the sound.

I have set up the fronts now as small -- set all xovers to 120 -- but then let easy set up do it -- it set it almost the same, and I left it there.

I did notice in set up that there is sub lfe settings for

L&R (What it's on now)
Center
Surround
Surround Back (if you have surround back hooked up - I don't)

Using the Sub out (pre amp, of course) on the 340, to LFE in on the 6900 sub -- now from what I understand, the filtering for the LFE is being done on the 340 at this point. Because the LFE input on the sub bypasses it's own filtering.

Does that sound right ?

Also, there was mention of Subwoofer Remix option, that would send LFE info to the sub in two channel mode. I don't see this as an option in the receiver. Is this just in surround settings ?

John K.

The LFE setting that you mention is of little significance, but for your information, it sets a low pass filter which rolls off the LFE channel above the frequency set for the speaker group selected(a rather indirect way of doing things, but that's what the 340 does). The LFE channel isn't the low bass content from speakers set "small", it's the Low Frequency Effects(explosions, etc.) sometimes present during movies on DVDs and theoretically extends as high as 120Hz, although in practice there's rarely anything of significance above about 80Hz. So, using the L&R main speakers(set at 120Hz)to determine this results in a 120Hz rolloff, which happens to also be the theoretical upper limit of the LFE channel, and can't lose any LFE.

Yes, that's right; using the LFE input on the sub bypasses its internal filtering and uses only that done by the receiver.

When your 340 has all speakers set "small", the sub output automatically contains the low frequency sounds(including two channel CDs) which then go into the LFE input on the sub; no special setting is needed. Note again that this low frequency CD material for the main speakers isn't "LFE" as such (which is only present in DVD movies), but still goes into the LFE input on the sub to be played.