Axiom Home Page Forums General Discussion Home Theater 2 speakers as center channel? Pros and Cons

All this talk about using 2 bookshelf speakers as one virtual center channel has me thinking. Why isnt this a more discussed option in the HT community? It has the potential to:

1 - offer a more dispersed, smooth center channel signal (toe in, toe out options, one above and one below TV, etc)
2 - often cheaper than dedicated center
3 - significantly lower frequency response opportunity (in case of M3 vs VP150, at least)
4 - 4 ohm impedance (assuming wired in parallel) vs 6 ohms meaning more output (wattage), (a good thing if your receiver can handle the load)
5 - Sounds like a cool idea

There may be others as well. Would like to hear the downsides as you guys see them. I havent made a center channel purchase yet, and think this one needs to more exploring. TonyM made me start thinking about this - lets pick up from there! Thanks Guys, Jeff

Here are a couple that immediately come to mind:

1. Aesthetics - people are used to seeing a flat center channel in an HT application. The look of two vertical centers (even if they were no taller than a regular center) may strike some as weird looking.

2. Shielding concerns. While the M2 and M3 seem to be immune to this problem, it could cause a problem with lesser speakers.

3. Dead zones or null points - the center channel will aim right at the prime listening position, in a perfectly parrallel configuration. Having two speakers toes in or out may create hot zones or null spots where the signals cross. While this problem can be fixed by decreasing or increasing the amount of toe-in, the casual use may dislike having to monitor this center channel with regard to toe-in.

Keep in mind, though, that while this idea isn't discussed - another well marketed company (read the "BLOWS" cube system) has been selling a center channel cube where the top and bottom unit can be flayed left and right, respectively so as to capture a larger sweet spot in the center listening position.

The biggest downwall to this is power. Not ever HT set-up out there will be able to do a good job with a 4ohm load or simply driving 2 from one channel regardless of the way it's wired. As for the Pro's, you listed enough already. I honestly think the Pro's outway the cons but that may not be the same for everyone.

Thanks for starting this thread, Jeff. I have a somewhat related question.

Why the fixation on using the M2 as a VERTICAL center channel? I vaguely remember JohnK trying to explain why it sounded better that way, but cannot find the thread (anybody?). TonyM observed that the M2 placed horizontally sounded "funny".

Now, I understand that a single, small center is probably not as good as a double, small center due to power handling, attainable SPL, symmetrical imaging, etc. My question really relates to why it is inherently worse to use two M2's horizontally (end-to-end) rather than vertically (side-by-side or separated). Could any of those problems be overcome by rotating the tweeter 90 degrees and re-mounting it?

If this qualifies as a thread-jacking, I apologize. TIA.

TT - I think it is right inline with the intent of my post. If one is considering using 2 speakers as one virtual center, then placement becomes an important part of the consideration. I find it hard to believe that the sound would change by changing the vertical orientation, but I am willing to be convinced otherwise! jb

Hello Tomtuttle,

Hope you are well.

When I put the M2s on their sides, I also had to stick a couple of Reader's Digests under them because of the angled speaker sides to make the drivers fire forward instead of upward.

I found that the speakers on their sides lost some detail and soundstage, I think the tweeter being so close to the top of the TV was causing a problem, and that orientation also put the Vortex port very near the surface of the TV. The Vortex port is located right behind the tweeter on the M2i, so it is normally about 7.25" above the speakers base. When the speaker is on its side it is less than an 1" from the TV, I am sure that causes some kind of interference. Also, the magnetic shielding was not sufficient to shield them from the TV when on their sides, I could only achieve good shielding vertical and toed inwards.

The M2i sounds 10 times better in the vertical orientation.

Maybe if you had a stand to elevate them from the surface of the TV, then they would sound the same on their sides. Say a stand about 10 inches or so high with a shelf that is smaller than the speaker case, so that the shelf does not interfere with the sound like the TV does.

Hope this sheds some light on this discussion.

Later,

TonyM

TonyM,

Thank you for sharing your insight and experience. I was hoping that you would find this thread and contribute

I'd like to discuss the vortex porting issue a bit more also; thank you for bringing it up. Your conjecture begs another question - how much clearance do the vortex ports on the M2 need *in any direction* before the sound is compromised? It is intuitive that they would need significant clearance directly behind the port, but your observation suggests that clearance along the plane of the speaker side may also be influential. We all know that early reflections from placing a speaker directly next to a wall are bad; now we question whether those same interactions *behind* the speaker matter.

I'm also interested in your observation about the proximity of the tweeter to the TV. For me, the comparison is between a VP100 and two M2's placed horizontally. Driver compliment notwithstanding, it seems that the tweeter on the Axiom VP speakers is not farther removed from the top plane of their resting place than is the tweeter of a horizontally-oriented M2 (all are center mounted on a 7.5" width baffle). So, is it possible that getting that tweeter farther "up and away" from the top plane of the TV is beneficial? Fodder for assymetrical mounting of the VP tweeters?

For my personal situation, some of this discussion is academic. My center MUST be placed in a little hole/shelf under the TV. It's too narrow for a VP150, and too short for a vertical M2, hence my questions.

Here is a bad pic. The Center channel speaker goes below the TV in the middle of the bench.



Now, don't go trying to give me creative, non-WAF solutions. I've gone about as far as I can with HT, and anything that puts the center in a screwy place just isn't going to pass the straight-face test.

I'm basically resigned to the VP100, but Tony's experience and analysis of the crossover points really has me thinking.

Sorry for the long post. Thanks for the help and discussion.

tt - "resigned to the VP100". Let me make you feel better.

Here is my setup, which is similar to yours. I had the stand custom made before I knew anything about Axiom. The bays are each 20" wide.


Please note that a VP100 sits proudly in the middle bay, bottom. Nicely tilted up due to Ian's excellent design. Would I have gotten the VP150 if the sapce allowed? You betcha - it was "more stuff" and I'm a guy, so I needed it. However, after speaking to Joe at Axiom (in one of our 1/2 hour discussions) and exchanging emails with Alan, I was comfortable with my ordering the VP100. I have not been disappointed for a single minute with the thing.

It is terrific and the dialog is crystal clear - the point of the thing to begin with. My M60s also assist in creating a "false center" (or some such reference Alan used) and the soundstage is seamless. I tend to lean towards centers because they were designed to be just that. The M2 and M3 discussions vertical/side are interesting, but they are bookshelf speakers, that's why they aren't designated as centers. Please - no offense intended to the M2 faithful; I'm a big believer in whatever makes you happy.

I've also played with tweaking the db levels of the M60s and VP100. The difference in 1 or 2 db is surprisingly noticeable in making the pair or the center a bit more forward. When I've got something on that is mastered a bit oddly, I just tweak the settings for the duration of that piece, but it is rare occurrence. The VP100 shouldn't be viewed as a compromise. It is an excellent speaker and won't disappoint.

Whew, I got all sweaty there. Hope the input is helpful.

Hello TomTuttle,

Hope you are well.

Wow, that picture makes it look like you are very close to those M60s. Those are M60's yes?

Ideally I would think 2 feet or more of space would be plenty to let the Vortex port breathe side to side and to the back.

I am thinking the farther the better with the tweeter from any surface, those frequencies are very interactive, and will bounce around.

Unfortunately any speaker in a little alcove is going to be limited in soundstage and imaging. If you could put that VP100 on a short stand in front of the TV, I believe it would sound much better. Maybe only use the stand when you are actually using the HT, and then put it back in its proper WAF approved spot in the entertainment center when not in use.

Some companies utilize a 3 way center with a tweeter above a mid between two woofers. Supposedly to improve imaging.

Later,

TonyM

Hello Tony,

Thank you.

Yes, those are M60's. The picture is somewhat deceptive; the seating position is ~11 feet from the speakers, and I do not feel too close.

The idea of a stand in front of the TV rack is one I have considered and abandoned. It's a non-starter with my wife, and I'm inherently too lazy to move boxes around whenever I watch or listen. Life is a series of compromises.

Ray, thank you very much for the picture and the rhapsody. Be sure to stay hydrated. I had not seen that picture before, and you and I are in the same boat in lots of ways relative to placement and the process that got us there. I also had my cart custom built (to similar specs, apparently) because when I got the TV, there was simply nothing else available that met my needs.

I'm going to be perfectly comfortable with the VP100, I know that. I had not even had the chance to question that decision before Tony started talking about that response hole between 80-95Hz. My Denon 1804 will not allow me to set the crossover independent for each channel.

Thanks again, gentlemen.

Hello TomTuttle,

Hope you are well. You would be amazed at the change in sound between a receiver with bass management and one without. The upgrade would be well worth your while to consider over anything else.

Later,

TonyM

Hello TomTuttle,

Hope you are well. Was just thinking, does that Denon 1804 have just large and small settings for the speakers, if so do you know if it sets the crossover at 100Hz like most with only small and large settings. If that is the case then you would not even benefit from a center that has response below 100, it is all going to the sub, assuming you have the center set to small.

Later,

TonyM

The crossover is adjustable between 80, 100, and 120hz I believe. I leave my 884 on 80hz.

I have been planning my HT for about a year now and I"m convinced to give an M22 or dual M2 a try as a centre.

Here's some links I've found useful on the subject:

http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=HT&Number=2166&page=&view=&sb=&o=&fpart=all&vc=1

http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=HT&Number=32863&page=&view=&sb=&o=&fpart=all&vc=1

http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=HT&Number=10952&page=&view=&sb=&o=&vc=1

http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=HT&Number=3201&page=&view=&sb=&o=&vc=1

http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=HT&Number=1806&page=&view=&sb=&o=&vc=1

This article convinced me that a horizontal arrangement immediately introduces design challenges not encountered with a vertical speaker. After all if speakers were optimal configured horizontally why aren't all speakers made this way? [Purely for aesthetics ( which is OK if that's what you need)] For this reason I'm favoring an M22 as my centre.
http://www.futuremusic.co.uk/fm_mmusic.asp?ID=6809&PageNo=6

My only dilema is a single M22 or dual M2's... Still trying to figure that one out? Any thoughts?

cheers, Jag

Before making your decision, you might read this, Why not more discussion of 2 speakers as virtual center channel?.

I have no opinion either way, I just thought this might spur further input, particularly from the more technically knowledgeable.

Thanks Ajax - I was getting ready to point people over to my cross post... Seems there are some valid reasos to not do this, and its not like this is an afterthought....jb

Hello all,

Hope you are all well. For more information on this topic visit my very long thread in the Advice From Axiom Owners forum Here.

Alan just stopped in and added his thoughts to the discussion, a good read for anyone interested in this topic.

Later,

TonyM

...because one center channel looks so sexy



- D

Jack, as my reply to Tony in his earlier "pros and cons" thread indicates, although "comb filtering" exists, in my view it should be dismissed as being a significant concern. As Ian said about two years ago in a reply and speaker designer Dick Pierce has also stated, in a live listening room reflections create comb filtering all over the place and any small additional amount from two separated speakers playing the same sound isn't significant.

In my own multi-channel(pre-Axiom)setup, I use a vertical center speaker just slightly bigger than an M2, which is the same as the mains. One is adequate in my experience and is the logical choice for a center speaker, as in my view the horizontally aligned center is a solution in search of a (significant)problem. Two should be fine, and the center image won't move out any farther than the speaker on that side as the listener moves to one side or the other.

Thanks John. Makes me feel better.

Thanks TonyM, I missed this one, away of holidays I guess.

So as I understand it two M2's may be the way to go instead of one M22?

Can't wait till Alan gets back with comparison results.

Jag

Hello Jag,

Hope you are well. As I see it 2 M2s will give wider dispersion, one more tweeter, 1db more SPL, 100 watts more power handling, and not as tall, which gets the tweeter more on axis with the seats in my very tall setup.

Later,

TonyM