BM questions and my equipment

Carl333

I am a total newbie to the A/V world and just purchased Polk's RM6750 5.1 sat/sub speakers to integrate with my newly acquired Pioneer 7.1 THX receiver. The receiver manual suggests wiring all speakers directly to the receiver. I was sent an interesting link by Willow (http://www.polkaudio.com/education/article.php?id=19) that suggests hooking up my system using BM. Right now a have all connections of my speakers to the receiver. After reading this article, I have a number of questions. I have cut and pasted paragraphs from this article.

1-Maybe your equipment has non-standard bass management.
Q. Does my system have this?

2- Additionally, in the vast majority of receivers and processors, the subwoofer output jack is low-pass filtered. That means that there is a filter (sometimes mistakenly referred to as a crossover) that blocks sounds above a given frequency from getting out of the sub out jack. Usually that filter is in the 100Hz-150Hz, range . Why is that so bad?
Q. Is my subwoofer output jack low-pass filtered?

3- Your powered subwoofer also has a built-in low pass filter, and when the two filters combine their interaction can cause irregularities in the frequency response (see graph below). In plain English, you get lower performance.
I read the specs. On the RM6750 and this is true.

4- In the case of many systems, especially sub/sat systems (like RM Series products), the low pass filter that's built-in to a receiver or processor may be set to the wrong frequency.
Some processors and receivers have unfiltered subwoofer output jacks-so it's OK to connect the line in of your subwoofer to the sub out jack.
Q. How would I know this and how do I change to correct frequency?

Unfortunately electronics manufacturers rarely specify the filter characteristics of the sub out jack in their manuals
5-Some subwoofers (like most Polk subwoofer models) have "LFE" line inputs that bypass the subwoofer's built-in low-pass filter This feature is great for avoiding the double-filter effect when using a filtered sub out jack. Q. Does my RM6750 sub have this?
The THX Exception
(NOTE: Read this section only if you have a THX certified receiver or processor.) Receivers and processors that are THX certified are required to have a very specific set of bass management filters that are active when the processor is set to THX mode. All channels (front, center and surround) are automatically high-pass filtered at 80Hz (the bass is taken out below 80Hz), the subwoofer output jack is turned on and low pass filtered at 80Hz. For many speaker set-ups this is a good configuration. For a system of bookshelf or small floor-standing speakers with a powered sub with an unfiltered line input, this filter set is a good choice. But if your speakers are small satellites or large floor-standers with built-in sub-woofers, this filter set may result in poor performance.
To avoid the standard THX bass management filters, do not engage the THX function of your processor. The processor will revert to its standard user-configured bass management system. As THX is not a surround processing system per se, but an enhancement of Dolby surround processing, you do not need to engage the THX mode to properly decode any surround source. Q. I have a THX certified receiver.

6-The big question now is how do I correctly wire up my system with the equipment that I have, make the necessary speaker corrections ie. big or small ( I thought this setting meant big or small speakers) and what are the correct frequency settings to each speaker? I am so dumb and trying to learn.

Thanks all for taking the time with your replies and suggestions.

jwhitakr

Hi Carl -

I can't comment specifically about the receiver you have, and I won't address all of your questions, but here are my thoughts...

The RM6750 sub has an adjustable low-pass filter. When you connect your speakers using the Recommended Method from the user manual (using the line level speaker connections), you give yourself more flexibility to adjust the point at which the subwoofer filters out the higher frequencies. If you use the subwoofer out connection from your receiver (usually called the LFE), you are most likely going to be stuck with whatever frequency your receiver sets as the crossover and you are also in danger of running into problems with multiple crossover points. Again, this will depend on your receiver and I don't know the details about how your receiver works.

Once you've connected your sat / sub speakers with the recommended method, you can follow your receiver instructions to adjust the various settings (large vs. small, etc.) to match your own listening tastes.

Hope that helps, and I'm sure others will chime in with their advice as well.
- Justin