Missing low bass? (1 Viewer)

[ChrisBee]

Hi

A subwoofer thread on a stereo forum raised an interesting question. One that my lack of AV experience leaves unanswered. I'm strictly stereo floorstanders + SVS sub. :b

Take a standard 5.1 AV set-up with *large* speakers fed full range material.

The subwoofer is fed by the receiver's low level "sub-out" only.

Q: Where does the VLF bass go that is fed to the speakers? But which is below their in-room roll-off point.

The speakers can't reproduce it. The sub doesn't even know this deep bass exists. Does it? Not unless the sub is fed with high level connections as well as the "normal" low level)

Regards
ChrisBee

 

[Tom_L]

With my receiver (Denon 3805) if you set speakers to "Large" they get the frequencies below the low frequency crossover point, but so does the subwoofer. My Denon manual actually identifies this as a potential acoustical issue, as you could get cancellation in some areas of the room, but you could also get better distribution of low frequencies.

 

[Nathan Stohler]

Tom,

I thought most receivers only redirected bass to the sub if the mains are set to "small." I've heard of some receivers that give you the option to send low frequencies to both the mains and the sub -- is that the case with the Denon, or does it always do this?

Chris,

For the reason you brought up (lost bass), most people set their speakers to "small" in a 5.1 setup even if their speakers have good bass extension because there are very few speakers that can get as low as a good subwoofer.

I still set the speakers to "small" when listening to stereo, but there are purists who refuse to use a subwoofer when listening to stereo and obviously would run them full range.

--Nathan

 

[ChrisBee]

Forgive me for pushing the point. But some AV fans do like to set their speakers to 'large'. Otherwise there would be really no point in owning nice floorstanders. The same enthusiasts usually attach their subwoofer by low-level connection only to the 'sub-out' socket. High level connections are completely out of fashion after all! Some subs don't even have high level connections. :b

The sub-bass that the speakers cannot reproduce never reaches the subwoofer. As far as I know that only happens if the speakers are set to 'small'.

The only way to hear the sub-bass effects that are being sent to the speakers. Is by using high level connections to the subwoofer as well as low level.

So all the director's efforts to put sub-bass effects onto the speaker channels is completely wasted. The sub-bass is never reproduced.! It simply vanishes down the plug-hole. :b

Or so I am led to believe. Until told differently.

Regards
ChrisBee

 

[Rick Cohen]

Each receiver is likely different. My Sony DB 840 with the speakers set to large sends bass and subbase to the sub if the sound coding is set to auto with a two channel input. If I set it to two channel stereo the sub is not engaged and all the sound goes to the mains.

I have run sweeps and individual frequency steps with a sound pressure meter. As noted by Tom the bass can be more even set to large but cancellation can become a big issue depending on the room and mains.

My mains are JBL L-100 with 12 inch woofers and can get down to 25hz to 30hz. My sub is an SVS PB2+ with lower extension and more power down low. Your receiver may be different regarding the bass management. Hope this helps

 

[Jack Gilvey]

This is a common misconception, that somehow bookshelf speakers and floorstanders will sound the same if they're both set to "small". It's certainly worthwhile to have mains with good capabilities down to 40 Hz or so even when set to "small" as the high-pass filters in receivers are not brick walls. A speaker capable of good bass response will likely sound cleaner and more dynamic as levels get higher. Still, many owners of floorstanding speakers set them to "large", not wanting to somehow "waste" their capabilities. "Hey, I paid for big speakers and I ain't settin' them no other way!" In such a case, it's possible that much of the LF track gets thrown away, even though their owners prefer it that way.

 

[Ryan Tsang]

took the words outta my mouth. I can see the point of not wanting to "waste" a floorstander, but the fact it, if I'm watching U-571 or Finding Nemo at reasonably loud volumes, I want my sub to handle the bass, not my floorstanders (even if they're rated down to 35hz). Which would you count on to play 100+db peaks at 35Hz?

For music, you can just set the receiver/processor to "small" and set the HP X-over as low as required, providing it is adjustable.

 

[ScottCHI]

the same place it goes if you don't have a sub. you "lose" what's below your speakers' capability.

which is why they recommend that if you're going to run your speakers as LARGE, that they really be LARGE.

 

[BruceD]

I agree with Jack on this one. The point of having floorstanders as mains is so you can get a smoother transition through the crossover to the sub, because you can cross them over to a sub before their acoustic rolloff gets added to the mix.

My major problem with most AV processors is that the high-pass filter (12dB/octave slope) assumes the speakers have a 12dB/octave acoustic rolloff with an f3 of 80Hz, only THX certified speakers meet this criteria. I think this is less than an optimal solution for most main speakers. Actually I think it stinks!!!

For this reason I run my 5.1 and 2-channel combo system with:
Mains=Large
All others=Small
Sub=NO

I put a high-quality 4th order L-R electronic crossover on the L&R main preouts and split it to the mains and sub(s). This way I get all the LFE and re-directed bass to the mains and can smoothly cross it to the sub(s). This works for both 5.1 and 2-channel without adjusting the sub, and I don't lose any bass. I make sure the crossover to the sub is at least an octave above the main speaker's f3 to minimize any impact of the main speaker's acoustic rolloff.

 

[Tom_L]

Nathan:

I looked it up in the manual. The answer is, "it depends."

With the sub in LFE mode, the sub gets all LFE signals and the low frequencies below the crossover point for all speakers set to "Small". So if you have mains set to Large, the low frequencies directed to those channels will be played by the mains only.

With the sub in LFE+Main mode, the sub gets all LFE signals and the low frequencies of all speakers. Speakers set to "Large" also get the low frequencies directed to them, so you will get lows produced by both mains and sub for those signals going to the mains.

Sory for the confusion there.

 

[ChrisBee]

Tom

Is LFE+Main a common feature in most AV receivers/processors? If so, this would seem to be the answer to my original question. In other words the very deep speaker channel bass is not lost.

Provided the LFE+Main setting is used on the receiver the speakers can be set to "Large". The bass is then directed to the subwoofer as well.

ChrisBee

 

[ScottCHI]

yes, but be aware that in many cases the LFE+main setting creates some very unwanted and undesirable redundancy in the low frequencies that many are already wrestling with.

 

[Edward J M]

Scott: With speaks to Large and sub to on/yes, the only thing the sub sees is the LFE channel. Anything the L/R/C/Surround speaks can't play goes bye-bye.

Tom: You're cooking with oil now; you got it right the second time.

And Scott is correct (as usual). Large and "LFE + Mains" setting for the sub is essentially double bass and sounds terrible.

All my speaks (even the rear surrounds) have an F3 of 50 Hz or lower and I wouldn't dream of running them on large. I only wish my AVR could spec a 4th order high pass (yeah Bruce, it stinks), like some of the high end units. I know B&K's can do it.

 

[ScottCHI]

had a good teacher

 

[ChrisBee]

Thanks to everyone for their responses.
I've learned a great deal from your replies.
Not least how little I know about surround sound.:b

Regards
ChrisBee