New 7.1 HT Set-Up - Bass Management Contradiction?

[Daddy Cool]

Hi there folks

Well, after searching high ‘n’ low and having read (and in many cases re-read) ALL of the articles here on AHs regarding Bass Management and Subwoofer calibration/integration, I still can’t seem to arrive at a conclusive answer to my dilemma.

But a little background to my prob first. I’m not exactly a noob and have had plenty of Home Theatre kit since the late 90’s. About 2½ years ago, I got into building media centre PC’s and HT-PC systems etc., but I’ve kinda gone full circle and ended up back where my interest in all things HT began; now integrating a high-end PC into a dedicated Home Theatre system (see sig for basic spex).

To cut a long story short, since I last bought my HT kit about 4 years ago, technology has moved on, and although I’m up-to-spec with most of it I’m getting confused regarding my sub and integrating it into the system. I’m following all the suggestions/advice applied throughout the many articles published on AHs (and many other sites) but am finding that my subs final settings are far from perfect.

The prob I’m having relates to the crossover, which I currently set at 80hz via the receiver. Having the subs crossover set at max (200hz) & connected via the Line Level input, I’m finding frequencies around 70-100hz are well overblown (tested time and again with various software & the legendary Radio Shack SPL). Further testing suggests that the sub is still outputting quite a lot of audio/SP well above the 80hz crossover point, and the only way I have so far seemed to cure this is by going against collective HT wisdom and bringing the subs crossover filter into play and setting it to just above the receivers crossover point (approx 85hz)

With both the receiver AND subs crossover in the mix, I’m obviously well confused with respects to this seemingly contradicvtory situation and have been pounding my brain for a reason why this should be happening. Therefore I’m graciously hoping that some of you HT aficionados here on AHs will be able to offer advice or even answers. Any help at all would be deeply appreciated and if you need more in-depth details from me please feel free to ask away. Please accept my sincere thanks in advance

Last but not least, congrats to AHs admin and mods in putting out a great site and forum for Home Theatre and Audiophiles alike. I’ve learnt plenty over the past few weeks and thanks to all that advice, I’ve more or less ‘calibrated’ my new HT system to a far superior level than any of my previous set-ups have ever been.

My best regards to all and thanks for reading,

DC

 

[Nick250]

Sounds like room acoustics issues to me. Subs are especially placement sensitive. IMO the receive should control bass management and the sub should not. There have been lots of threads on this topic so a search should garner a lot of hits.

Nick

 

[bpape]

What is the slope on the xover you're using for the sub? Also, do you have separate settings for the LFE xover and for the redistribution of the mains LF information to the sub? Some processors do.

Bryan

 

[Daddy Cool]

Sounds like room acoustics issues to me. Subs are especially placement sensitive. IMO the receive should control bass management and the sub should not.

Hi Nick,

Many thanx for the reply. Yeah, after digestin' the logic of only one piece of kit handling BM that's the conclusion I've also arrived at...

There have been lots of threads on this topic so a search should garner a lot of hits...

Gonna do just that if I can't get anywhere in the next few days. Thanx again m8,

Best wishes,

DC

 

[Daddy Cool]

What is the slope on the xover you're using for the sub?

Hi Bryan,

Cheers for the reply - mmm, I'll happily plead ignorance here and say that I'm not sure exactly what ya mean by 'slope' . If it ain't too much trouble could you elaborate; moreover, I assume this info should be in the manual? I only ask as I haven't seen any reference to it's slope at all

Also, do you have separate settings for the LFE xover and for the redistribution of the mains LF information to the sub? Some processors do...

Yeah, if you're referring to being able to send LFE info to either sub or both sub and mains, yeah, I have this set to sub only and the xover (seperate setting) at 80hz.

It might be worth pointin' out that I dug out a kinda old set-up disc "Ultimate DVD" (came out 'bout 5 years ago) which actually has some different 'bass' calibration tracks which I'd so far not used. Everything, generally speaking, was fine; probs only started to occur when I played a test sweep from 15hz-150hz. With the subs xover at max and the receiver controlling BM, the sub was still rumblin' upto about 110-120hz and the speaker(s) kicked in around 65-70hz. I have a feelin' this isn't quite what should be happnin'?

Anyway, I hope ya can get back to me Bryan, thankx for listening,

Best regards,

DC

 

[MDS]

The 'slope' of the xover determines how quickly it attenuates the signal. A xover is not a brickwall; ie if you set it to 80 Hz that does NOT mean that 80 Hz and below goes to the sub and 80.01 to 20 kHz goes to the other speakers.

The slope is given as 'decibels per octave' (an octave is a doubling or halving of frequency - 80 Hz is one octave above 40 Hz and one octave below 160 HZ). Each 'order' is 6 dB/octave so a first order slope is 6 dB/octave, 2nd order is 12 dB/octave, 3rd order is 18 dB/octave, and 4th order is 24 dB/octave.

The receiver will have two xovers (although you usually only get to set the 'low pass'). The low pass xover is most always 24 dB/octave and is coupled with a high pass that is most always 12 dB/octave. The two combined together make the transition between the sub and the other speakers. The low pass lets the lows pass - so it starts ABOVE the xover frequency and the high pass lets the highs pass - so it starts BELOW the xover frequency. If they work well together, the idea is that the amplitude of the signal will be flat (unchanged) directly at the xover frequency.

So, with an 80 Hz xover you will still get frequencies as high as 160 Hz (one octave above the xover) but they will be reduced by 24 dB. Likewise, you will still get some frequencies below (~40 Hz - one octave below) but they will be attenuated by 12 dB. The amplitude directly at 80 Hz should be relatively unchanged, but the xover and speakers are not perfect.

Room acoustics come into play because even if the xovers are doing a fine job of splitting up the signal, the characteristics of the room may accentuate some of the sound so that it does not appear that the xover attenuated the frequencies above the xover point enough.

 

[Daddy Cool]

The 'slope' of the xover determines how quickly it attenuates the signal. A xover is not a brickwall; ie if you set it to 80 Hz that does NOT mean that 80 Hz and below goes to the sub and 80.01 to 20 kHz goes to the other speakers...

Many thanks MDS,

Yeah I understand 'bout the xover not being an absolute, but I deeply appreciate the rest of your explanation. I'll confess to not fully comprehending everything you mention, but yeah, I can grasp the basics of what you're saying.

But I still haven't a clue as to the slope for the sub - the manual (in fact a folded sheet/booklet) is pretty limited, nor can I find any reference to the receivers xover slope, so how do you go about finding this info out? I'll be perfectly honest and admit this is not somethin' I've ever been asked before so I really don't know where I'd start sorry!

Thanks again though m8, it's great to know that I've come to the right place for help

DC

 

[Sheep]

I had this same problem. My DPS-12 was localizable because the 90Hz Xover in my receiver, and it wasn't cutting it out fast enough. Solution: Use the Sub's xover with the reciever's Xover. I cut my sub at 70Hz with the subs Xover, and let the Receiver take over with the 90Hz one. Sounds fine now.

SheepStar

 

[Daddy Cool]

A little snippet of additional info...

It occured to me this morning that there's another thing that might be influencing my prob. The sub has a "Movie/Music" switch; am I right in thinking this is similar to the "Slam/Depth" switch on REL etc subs.

I recently read that "...the 'Slam' position will increase the SPL output between 40Hz-150Hz but at the expense of bass extension, whereas the 'Depth' mode affords maximum low frequency output and a near flat response..." and that further investigation suggests that most audiophiles choose to avoid the 'Slam' mode for the very reason(s) detailed above.

Can anyone shed any further light on this 'Movie/Music' mode, and if this might be adding to my problem, suggesting if possible, which one I ought to avoid?

Again, my sincere thanks in advance.

DC

 

[Daddy Cool]

I had this same problem...

Thanks SheepStar,

Glad I'm not the only one

My DPS-12 was localizable because the 90Hz Xover in my receiver, and it wasn't cutting it out fast enough. Solution: Use the Sub's xover with the reciever's Xover. I cut my sub at 70Hz with the subs Xover, and let the Receiver take over with the 90Hz one. Sounds fine now...

I mean, this is kinda what I've been doin' to attempt to solve my dilemma, but it goes against the grain of all the stuff I've read/been told etc., and of course, is pretty much unorthodox for calibrating one's sub into one's system But I s'pose the moral of the story is that if we're happy with it, so what?

Thanks m8 for some reassurance, this maybe the only way, I can solve this issue.

All the best,

DC

 

[Sheep]

It occured to me this morning that there's another thing that might be influencing my prob. The sub has a "Movie/Music" switch; am I right in thinking this is similar to the "Slam/Depth" switch on REL etc subs.

I recently read that "...the 'Slam' position will increase the SPL output between 40Hz-150Hz but at the expense of bass extension, whereas the 'Depth' mode affords maximum low frequency output and a near flat response..." and that further investigation suggests that most audiophiles choose to avoid the 'Slam' mode for the very reason(s) detailed above.

Can anyone shed any further light on this 'Movie/Music' mode, and if this might be adding to my problem, suggesting if possible, which one I ought to avoid?

Again, my sincere thanks in advance.

DC

My Movie/Music switch on a sub I had worked like this.

In Music mode, the subwoofer had no boosting
In Movie mode, there was a 6dB boost at 30hz.

This is how they usually work.

SheepStar

 

[bpape]

Sorry for being away so long - been buried with work.

Anyway, the manual for the receiver should tell you what the slop and optional xover points are on the receiver.

What I was referring to earlier was the ability to send the bottom end of the main signal to the sub in addition to the LFE. Also, potentially being able to send those 2 things to the sub(s) using a different cutoff frequency.

Bryan

 

[Daddy Cool]

My Movie/Music switch on a sub I had worked like this.

In Music mode, the subwoofer had no boosting
In Movie mode, there was a 6dB boost at 30hz.

This is how they usually work...

Thanks again,

This is very similar to how a few people I've asked reckoned it would work on my sub - however, to test this theory I used a relatively bass heavy stereo CD track (that would obviously bring the xover into play etc), audibly AND SPL meter testing the reaction to the different 'modes'. After about 15 minutes, it was clear that the 'music' mode sounded a bit 'boomier' and the SPL reading seems to back-up my conclusion as it was reading about 3db higher with 'music' mode as opposed to 'movie' mode.

So do you think I'd be right to conclude that contrary to your experience, the 'music' mode introduces the artificial boost on my sub and that the movie mode would offer the max low frequency/flatest output

My sincere thanks for your responses, its been a big help.

Regards to all,

DC

 

[Daddy Cool]

Sorry for being away so long - been buried with work...

Hi Bryan - no worries, I know the feeling

Anyway, the manual for the receiver should tell you what the slop and optional xover points are on the receiver...

I've pretty much read the manual from cover-to-cover and have scrutinised the tech-spex and I can't any reference to slope; as for the xover points - 40; 60; 80; 90; 100; 110; 120; 160; and 200 hz respectively.

What I was referring to earlier was the ability to send the bottom end of the main signal to the sub in addition to the LFE. Also, potentially being able to send those 2 things to the sub(s) using a different cutoff frequency...

Yes, it can send the bottom end of the main signal to the sub in addition to the LFE (receiver set to 'SUB' and all speakers set to 'SMALL'), but no, it doesn't have a variable xover for these two different things, it's just one xover for the lot.

HTH Bryan, many thx again,

DC