Axiom Home Page Forums General Discussion Home Theater QS4 or QS8 and why please

Hang on a tick. Something is not right if your surrounds cannot roar. I have one sub located in the front left of my HT room. I was watching "The Haunting" and there is definitely ROAR coming from the surrounds. It impressed me so much that I thought I had two subs right behind me. But that is not the truth. The truth is that any descent surrounds can roar if you have your sub crossed over low enough. If your crossover is set at 80 or below (80 being the top threshold of what a blind listener can tell direction on) your system will trick you every time.

Think about it. Say there is a surround effect being played on a movie track. A train passing from RR to LR. Almost certainly the sound of the train is going to be represented by many different frequencies throughout the normal range. So if your crossover is say set to 100hz you will have directional sound coming from the surrounds and the front soundstage. Whereas if you have the crossover set to 80hz or below. All the sound will appear to come from the surrounds. You will hear it all behind you even though some is actually coming from in front of you.

I used to think my sub needed to be set around 100 because it was such a good bass producer that I wanted it producing as much of the bass range as possible. But as soon as I did my testing and SPL levels and such, it was unquestionably better with the sub crossed over lower (60hz). I only wish that I could have tried 40hz but my receiver only goes down to 60hz.

There was a great article on this at Audioholics I believe. The title being something like "Turn that crossover setting down!!".
$.02

Hi ssutherland!
First of all, raise that$.02 up to at least $.09; The buck has been devalued, plus your opinion is worth more than that!

Your points are well taken! It appears you have full range speakers if you're using M22s in back. What Legairre and I were basically refering to was speakers with a lower limit of about 80hz. Babies' that small out back, in my room at least, "Hisss" when a plane flies at 'em!

Right now I'm using M3s in back with the crossover set to 60, and they aren't bad, but compared to my M50s up front, which are also crossed at 60, they seem a bit lacking in impact-they just "seem" a little smaller, not as much energy on the attack of the sound as the M50s up front.

Part of "MY" problem is my neighborhood! I have commented a few times in the past about the truce in the neighborhood keeping the dreded "Sub Wars" in check. I have to keep the frequencies that find it easy to walk thru walls to a minimum; which means the mains and surrounds have to carry more of the load than y'alls' do. So...

The thought of using a small sub(or two)in back makes a lot of sense. I can defeat the inverse square law by keeping the rear subs(s) close to the listener, plus add more to the attack, in the subs, by raising the crossover to 80 on the QS8s if I go that route-assuming the QS8s aren't described as "Hisssssers"

I certainly agree with you on turning down the crossover. When I had my(3)M3s up front, and the ability to cross only as low as 80, I used to have a problem of having a component of the male voices coming out of the sub!! Major Bummer!!! Now I have the M3 as center also crossed at 60 and I get a good full range output, with no voices thru the sub!

My new receiver crosses down to 60, but not to 40, either-I too, would like to try 40 just for fun-and fun is what it's all about!!!
Rich.

All of this conversation assumes low frequency sounds are coded for surround channels. In a DD usage, why would any sound engineer code such LF sound for surround channels when they KNOW that surround speakers do not have the capability (for consumers at home or speakers in the theatre) and when they know that subwoofers included in these systems are used for this very purpose?

The LF sound is coded to the .1 channel according to the design idea of a 5.1 system.
The hiss you hear is likely b/c there is no sound there at all.
The surrounds should play the higher audible frequencies during a LF noise to trick the ear into thinking the LF noise is actually coming from the rear or the sides, but that's about it.
Surround speakers in HT are not designed as full range channels and neither is the centre.

I forget the details, but isn't DTS different from DD in that regard ? I think I remember reading that all the DTS channels were full-range...

I did not recall but in this whitepaper it does state at one point 5 channels are full range discrete with the .1 being bandwidth limited.
In the whitepapers (pg 16) it refers to the DTS .1 channel as optional as well as main full range channels (w/o specifying) but also that the LFE channel is indepedent of all others.
However, full range does not mean that the surround channels have been encoded/mixed with full range sound. It simply states the DTS algorithm can do so.

Hi Chess;

I've noticed the effects you're talking about on a number of different DVDs, but thru experence, on other, newer DVDs, whille switching thru different rear channel speakers with different low freq responces, I've found that some "hiss" and others don't! Really!!

More cheap, smaller, more hiss!(No surprises there!)

I've also found a greater propencity to hiss on material recorded in Pro logic rather than DD, as though the rear channels were more full-range in DD.

While the center channel may not be designed as full range, in my house, at least on TV shows, espically, a big chunk of the lower sounds of male voices found their way to my sub, and wow! that was annoying! Crossing the center to 60 got rid of that nastiness. And while it may be "wishfull thinking" the center(M3) "seems" to be just a bit fuller as well, without disrupting dialog. Again, this effect is more pronounced on TV shows.

But yeah, on some material, when I had my old HTIB speakers with an 8" main driver, capable of fairly low frequencies(they would actually "rumble!" when used years ago as mains up front in those old pre-Axiom, pre sub, days, using an Aiwa HTIB with, Wow! Bass Boost!!) But using those old dears in back-though too large for the walls-produced a satisfying surround experience, and would actually "roar" when a plane flew over! So, at least on some material, there's gotta be something there!

But yup, there are tons of folks out there who have some very high powered and sophisticated systems that subscribe to the "Nothing below 80hz" concept. (No, guys, Not just Bose!) THX systems, of course!!

Is this hobby fun, or what!?
Rich.

Just spotted the other posts: Cool
Rich

Ok guys I've been pretty absent from this so I'll try to explain why I use surround subs. First of all the DD and DTS spec does say that all five channels can carry a full range signal. Of course whether they do or not depends on the person mixing the sound.

About four years ago there was an article in Widescreen Review magazine that talked about bass in general, but it also talked about how there's bass "below" 50hz recorded into the surrounds that we're all sending to our LFE sub(s), by setting our surrounds to small. So I decided to get a couple of subs for the surrounds and see if this is true. In order for this to work properly you need to run a speaker wire from the amp or receiver to L/R input on the sub and then run a separate wire from sub L/R output to the surround speaker. Then set the surround speaker to large in your receiver or pre-amp. By sendig a full range signal to the sub you'll be able to use the subs crossover to control what stays in the sub and what goes to the surround speaker. Esentially what you're doing is turning a small surround speaker that only goes down to 75hz(like mine) into a full range speaker by adding the sub.

Movies like U571 for instance take on a whole new feeling. There's scenes with thunder while they are taking over the German sub and with surround subs the roar of the thunder comes from either the left or right side of the room and it's impressive. Without the surrounds subs it's barealy heard when redirecting the bass to the LFE subs by setting the surrounds to small. Having the surrounds subs makes a noticable difference.

Here's some links to six pages of movies that have bass below 50hz mixed into the surrounds. I have the rest of the article from Widescreen Review if anyone is interested. The article is from 2001 so there must be a LOT more movies by now with bass below 50hz mixed into the surrounds.

http://pages.cthome.net/lradden/ht/surroundbass1.jpg
http://pages.cthome.net/lradden/ht/surroundbass2.jpg
http://pages.cthome.net/lradden/ht/surroundbass3.jpg
http://pages.cthome.net/lradden/ht/surroundbass4.jpg
http://pages.cthome.net/lradden/ht/surroundbass5.jpg
http://pages.cthome.net/lradden/ht/surroundbass6.jpg

Just scroll over and check out the right most column of each page.

To enlarge the images just hover over the image and click the "sizing" block in the lower right corner.


Hey guys thanks for the nice comments on the room.
Legairre

Legairre, the most logical reason for this effect you hear is simply b/c they are MORE speakers in the room.
You've added subs so yes, the LFE will sound more prominent. I've had 2 subs play in the front and also hooked one up to the rear, but in keeping with a single subwoofer config, there is no change in sound. Adding the second sub did add more "prominence" to certain movie scenes. Of that observation i agree, but again for an obvious reason.

As for directionality, well, that's how the surround sounds work to trick ones ear as to LFE location. You need a range of sound, even for explosions, that go well above the 80Hz point.
If you get the chance to hook up nothing but subs in your room, unhook everything else and then try to ascertain their positions during a low 40Hz note (this has to be an equivalent note to all channels though, not just playback of a movie with some encoded material in this range as the SPL may vary for each individual channel). Unless something is rattling close to a wall, it is unlikely your ears will be able to triangulate the noise. The wavelengths are simply too long.

Chess, I've always valued your help so I'll try what you suggested. The only thing is the surrounds subs don't carry any LFE because they are not hooked up to the .1 LFE channel. They are hooked up in-line so they are carrying the bass that is mixed in to that surround channel. So the extra bass or sound I'm hearing is not from the LFE at all. By adding the surround subs I've only extented the range of the surrounds by letting the subs pick up where the surrounds leave off. It's really no different than having a speaker that goes down to, say 25zh as a surround and setting it to large.

But if your speakers are set to small (and on some receivers if they're set to large) anything under your crossover is sent to the sub. So your sub isn't just playing the LFE channel.